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Dommie cylinder lubrication

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I've had my Dommie, originally an 88, now with 99 barrel and crank since 1972 and it has always had a tendency to seize the left hand piston, whether with Hepolite or GPM pistons in the 500 barrel or, as it is at the moment, Heplex pistons in the 600.

I've just honed the cylinders and cleaned up the pistons from the latest tightening up. The left piston had scuff marks in four places fore and aft of the gudgeon pin holes (see attached pic.)

I wondered if there might be a clearance issue, so following a suggestion I heated the barrel and pistons to 150?C and found the pistons would slide down the bores under their own weight, supposedly indicating that there is sufficient piston - bore clearance.

I believe some engines had oil holes in the conrods and big end shells to squirt oil onto the bores, but my 1963 engine doesn't have these, and as far as I know it has the original rods.

Is it desirable to have this extra lubrication, and if so how exactly would I go about making the holes in the correct place? Is there anyone who has done this?

Attachments copy-of-imgp1710-jpg
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Previously rob_bradley wrote:

I believe some engines had oil holes in the conrods and big end shells to squirt oil onto the bores, but my 1963 engine doesn't have these, and as far as I know it has the original rods.

Is it desirable to have this extra lubrication, and if so how exactly would I go about making the holes in the correct place? Is there anyone who has done this?

Dear Rob,

during the restoration of my 1959 Norton 99 we made a few changes to the oil system, one was to put oil holes in the conrods and the big end shells. The conrods are still the original ones, but had been polished.

We also changed the drive gear of the oil pump for one of the later âfasterâ ones, so the pump is building up more pressure now. And of course we opened up the âoil-gapâ at the tappets a bit, to let the oil flow down easier from the head to prevent over oiling.

These arrangement is now working pretty well for over 40.000km. No over oiling, no smoking, especially no over heating or seized pistons. Even in very hot conditions with luggage and on motorways. (The funny thing is that my 99 stands hot weather much better than my old Italian bike and my former old Japanese bike... For anybody who does not know â Japan is a very hot country!!)

In preparing for the International Rally this year I had to change the head gasket and discovered that the pistons and the barrels had hardly any wear after all that time. So in my opinion these âspit holesâ are a good idea.

Unfortunately I can not give you any advice how to set the holes correctly, because I did not do these kind of work by my self. It was done by one of the Norton experts over here in Germany, but there must be people in the UK who could do that for you or give some advice how to do it.

I wish you the best in sorting out your problems because the 88 and 99 are such fantastic useful little bikes!

Best regards from a hot northern Germany

Bernd LienstÃ?dt

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Of course the left hand piston is furthest away from the oil pump so less likely to receive copious lubricant. Back in the days of my youth and merciless thrashing of Norton and BSA twins by the gang, it was accepted that the LH piston was more likely to sieze. However,these days I would think that merciless thrashing is less common. How long is it since the crank was stripped and the sludge trap cleaned out? It's just possible that the oilway is narrowed or blocked.

You really shouldn't need to put a six start gear on the oil pump with a 99, though it shouldn't really do any harm. Is the existing oil pump OK? Have the barrels been heavily powder coated? That can inhibit heat loss. And finally are your mixture and ignition timing correct. I would certainly knock the timing back a couple of degrees from the book value (32 to 30 degrees) to cope with current low-octane petrol. And make absolutely sure your ignition timing is correct on both cylinders - probaly the biggest culprit in these cases.Gordon.

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I have found this problem on my Nortons too,always the drive side,my 99 now runs with 41/2 thou clearance, six start pump gears, it also has the orriginal well worn crank which is probably passing more oil than usual . It has not had any problems.I have suspicions that oil can escape from the built up crank as it flexis leading to less oil at the drive side.I don't think we can blame Joe Lucas as if there is a difference in the timing it will always be wrong at the timing side. After all we fit the disc and view the points at the drive side ,don't we??.I don't think the six start gears are the answer either ,but help my motor with its worn crank and poor rocker supply.

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It has been found that at high revs the oil pressure on some nortons would drop to zero,possibly due to centrifugal action ,or maybe leaking due to flexing, Not enough left for the drive side?,I will not be working the old 99 hard enough to worry me,If i do get the crank serviced i will go back to the 3 start gears with the Jubilee restrictor,

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Lateral Thinking Thoughts........................Back in 1962/63 Norton managed to export a number of Atlas models, to the rest of the world, which had poorly drilled crankshaft oilways. The problem was that the horizontal drilling, though the Timing Side journal, did not always fully connectwith the drilling through the crank web shoulder. Usually they did meet but only with a very small passage hole between them, which let just enough oil through to the Timing side journal. ie right side big-end andpiston. Centrifugal force worked wonders here in feeding all the important bits on this side of the engine but at the same time deprived both the left hand journal and piston. The restricted oil ways then caused a minor 'domino' effect, in that it led to excess pump pressure, which in turn triggered the pressure release valve in the Timing cover. This surplus oil then ran down to the sump, via an oilway and main bearing; both on the Timing side of the engine. Where it was picked up again by the pump or thrown around the right hand side of the engine. So not much got to the left piston (& big end) most of the time.

I wonder if any other models also suffered from this problem? It might explain the left side piston problems we are hearing about. Whenever I rebuild a crankshaft I always check these oil passageways. The attachment shows the suspect area.

Attachments Crankshaft.JPG
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Previously rob_bradley wrote:

I've had my Dommie, originally an 88, now with 99 barrel and crank since 1972 and it has always had a tendency to seize the left hand piston, whether with Hepolite or GPM pistons in the 500 barrel or, as it is at the moment, Heplex pistons in the 600.

I've just honed the cylinders and cleaned up the pistons from the latest tightening up. The left piston had scuff marks in four places fore and aft of the gudgeon pin holes (see attached pic.)

I wondered if there might be a clearance issue, so following a suggestion I heated the barrel and pistons to 150?C and found the pistons would slide down the bores under their own weight, supposedly indicating that there is sufficient piston - bore clearance.

I believe some engines had oil holes in the conrods and big end shells to squirt oil onto the bores, but my 1963 engine doesn't have these, and as far as I know it has the original rods.

Is it desirable to have this extra lubrication, and if so how exactly would I go about making the holes in the correct place? Is there anyone who has done this?

Hello well My thoughts Are Something Not right here , and You have not said weather you have fitted a tap or some other anti- drain valve, as the Cylinder bores are SLASH Feed from the downward motion of the underside of the piston And Having any device to stop oil draining in the Sump area is a bad thing as on Start up there is no oil for some 30secons or more this means no lubrication for that mount of time is wearing the engine parts ,and doing damage, and I think something out of line, as the score marks are on one side the left so there more pressure on that side of the piston or the Cross hatch Honing as Not been carried out right, so you have to check out the elineament and the barrel its self, or the other thing is a drive side bearing is not fitted correctly and is not seating in its housing , and putting pressure on the crank this then put the rods out of line you do not need very much too put the rods out of line, so check every thing first to try this out , do a dry fit and put engineers blue on the piston and you see were its proud but do not fit the rings this is just to find out what out of line and were, engineer blue washes for with white spirit , so its a Check -ing job

good luck with it your anna j

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Something not right. Yes, that's what I thought when it seized...

There is no tap or anti-drain valve.

If you read my post, I said the piston had scuff marks in four places, i.e. both sides. I just showed one side because the other side looks the same.

A close-fitting steel bar will pass through both little ends at once, so if the crank's out of line as you describe wouldn't both pistons be similarly affected?

It's done this with two different crank and piston set-ups, 500 and 600 (same crankcase and rods).

Phil's oilway theory is interesting. I'll have to look at the 500 crank which is currently out of the engine. I don't want to do a strip down to get at the 600 crank that's in at the moment, maybe in the winter.

I'm still interested in the conrod oil holes. There must have been a reason why some models had them (anybody know which?). Was their disappearance to do with the introduction of the 6-start pump and high pressure head lubrication? (Which my engine doesn't have).

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As far as I know, the con rod bleed holes came in with the bigger big ends on the 89mm crankshaft (BSA did the same with their big bearing A10 cranks). On BSAs, the bleed hole is on the drive side big end only - perhaps a hint that the factory was aware of a lubrication problem.

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Previously rob_bradley wrote:

Something not right. Yes, that's what I thought when it seized...

There is no tap or anti-drain valve.

If you read my post, I said the piston had scuff marks in four places, i.e. both sides. I just showed one side because the other side looks the same.

A close-fitting steel bar will pass through both little ends at once, so if the crank's out of line as you describe wouldn't both pistons be similarly affected?

It's done this with two different crank and piston set-ups, 500 and 600 (same crankcase and rods).

Phil's oilway theory is interesting. I'll have to look at the 500 crank which is currently out of the engine. I don't want to do a strip down to get at the 600 crank that's in at the moment, maybe in the winter.

I'm still interested in the conrod oil holes. There must have been a reason why some models had them (anybody know which?). Was their disappearance to do with the introduction of the 6-start pump and high pressure head lubrication? (Which my engine doesn't have).

Well your model did not have the Six start gears fitted As they did not start fitting these gears until 1964 season and the 99 stopped being built in 1962/3 after bracebridge street closed and every thing moved to plumstead . and upper cylinder lubrication as Nothing too do with oil ways as the cylinder lubrication is solely down too Slash feed

Yet again I have said this over And Over And some of you do not realize that the Biggest Part Of Lubrication On All British Machines And some from Europe And the USA Are Slash Feed . The Parts that Are Under Pressure from the Oil pump Are The Crankshafts Big end Journals And Low return pressure feed to Rock Shafts the oil from the rocker shaft then runs down the push rod tunnels and lubricates the cam Followers in there guides and then makes its way too the sump were its then pick up on the return scavenging side of the oil pump then past on to the oil tank and round back again but also in the cylinder head there are oil ways for returning oil via a small oil way on the right hand side of the cylinder head the barrel in to the timing chest this some time gets blocked so returning oil then as to find other ways of getting back too the sump This oil way is there to drain the let valve side of the cylinder head . so then please take note of this, for a piston to make contact with the side walls of the cylinder bore and seize up in its bore , there are a number of reasons for this too happen as heat transferrer is lost the piston and the bore gets hot and expands then the oil film brakes up and loses viscosity and then things get even hotter and result in a Seizure . the main reason is one weak fuel mixture and the timing advanced these two give you heat and heat is what causes a seizure ,

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Previously phil_hannam wrote:

Lateral Thinking Thoughts........................Back in 1962/63 Norton managed to export a number of Atlas models, to the rest of the world, which had poorly drilled crankshaft oilways. The problem was that the horizontal drilling, though the Timing Side journal, did not always fully connectwith the drilling through the crank web shoulder. Usually they did meet but only with a very small passage hole between them, which let just enough oil through to the Timing side journal. ie right side big-end andpiston. Centrifugal force worked wonders here in feeding all the important bits on this side of the engine but at the same time deprived both the left hand journal and piston. The restricted oil ways then caused a minor 'domino' effect, in that it led to excess pump pressure, which in turn triggered the pressure release valve in the Timing cover. This surplus oil then ran down to the sump, via an oilway and main bearing; both on the Timing side of the engine. Where it was picked up again by the pump or thrown around the right hand side of the engine. So not much got to the left piston (& big end) most of the time.

I wonder if any other models also suffered from this problem? It might explain the left side piston problems we are hearing about. Whenever I rebuild a crankshaft I always check these oil passageways. The attachment shows the suspect area.

Roy Bacon in Norton Twin Restoration says "do not try to remove the plug in the timing side crank of the big twin as it won't come out."

How do you check, let alone enlarge, these passageways without taking the plug out?

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You can check these oilpassageways by squirting an oil-based fluid through them before trying to remove the plug.

If you stand the crankshaft half on its end and squirt in WD40 or similar it will help clear any sludge at the same time. A small amount of something like paraffin poured in will quickly tell you if there is any blockage. Try threading an old carb cable through the passageway. This does not always work due to the position of the plug.

Generally, the oilway plug will come out if given some heat and strong arm persuasion. Though I have had to drill out a few. There is plenty of metal in this area so there is room for a next size up re-thread. Of interest here....I once came across a crankshaft where the plug was screwed in too far and was thecause the blockage.

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Previously phil_hannam wrote:

You can check these oilpassageways by squirting an oil-based fluid through them before trying to remove the plug.

If you stand the crankshaft half on its end and squirt in WD40 or similar it will help clear any sludge at the same time. A small amount of something like paraffin poured in will quickly tell you if there is any blockage. Try threading an old carb cable through the passageway. This does not always work due to the position of the plug.

Generally, the oilway plug will come out if given some heat and strong arm persuasion. Though I have had to drill out a few. There is plenty of metal in this area so there is room for a next size up re-thread. Of interest here....I once came across a crankshaft where the plug was screwed in too far and was thecause the blockage.

Hello I am in a quondery Hear Whats The feed holes in the Crankshaft

too do with upper Cylinder lubrication !!!!! Yours Anna J

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The oil gets pumped along the crakshaft to the big ends and from there it sprays out and gets flung around the crankcases and the cylinder walls not to mention the underside of the pistons wot it cools. Simple enough?

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hello, anna does have apoint about ignition causing one cylinder to overheat. some magneto cam rings wear or were never machined perfectly and used to cause this indirectly as the engine is usually timed on one cylinder. what ignition does rob have?

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In my first post I did mention the need to have the ignition set accurately on both cylinders. I had one cam ring which was so bad when I set up the timing on one side at 32 btdc, the other was 57 btdc. Not good.

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Previously Gordon Johnston wrote:

The oil gets pumped along the crankshaft to the big ends and from there it sprays out and gets flung around the crankcases and the cylinder walls not to mention the underside of the pistons wot it cools. Simple enough?

Hello Well Gordon I think in technical College When I was 15 years of age , I think we learn this one, So then Lets all start again , and take a fresh look at the problem , and start ruling out things as we go, For one its Not the oil pump and Not the oil-ways In the crankshaft ether , Because if it was the first thing to size would be the large end journals as they will not take a lot of Heat, So then its Not oil starvation , And its Not weak fuel mixture as well as the right hand side piston is ok so this leave us with two possibility one the over advanced ignition on one side only or the other is the bore on the left hand side is under sized . is one or the other, this is that I think from the information given , yours anna j

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To time the pre-Commando motors you worked from the drive side,as that is where the disc was attached and the side you accessed the points on Mag or dissy,so its most likely that any discrepancy would be on the other (unchecked )side. Logic would say that siezes due to timing discpepancy would be most likely to be on the pump side of the motor.That is not my experience.Its well known that centrifugal effect can suck the oil out of the crank as fast as the pump can supply, This would leave the furthest big end (drive side ) with a lower supply. A stressed overheated motor is going to fail at its weak point,so we get siezed big end ,broken rod and piston failure at this point. All things i have seen most on the drive side.Not had any problem since speeding up the pump ,although i think this is not ideal .

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I can't agree with Anna about the crankshaft oil ways. This crankshaft has thesmaller journals and at moderate running-in speeds would probably cope with a piddle sized flow. Conditions would be very different at sustained higher revs, with hot, thin oil and next to zerooil pressure.

I don't ever remember a steam train with pressure fed big ends. All the ones worked on used drip or wick lubrication.

The cranks on Norton twins used white metal big end shells which are designed to provide a form of self-lubrication when oil is scarce. Especialy when a motor is first started.

I know where my bet is still going.

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The seize marks are adjacent to gudeon pin, not thrust face of piston

This has been happening for a long time, suggests misalignment as opposed to oiling problem

Laurence

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Previously phil_hannam wrote:

I can't agree with Anna about the crankshaft oil ways. This crankshaft has thesmaller journals and at moderate running-in speeds would probably cope with a piddle sized flow. Conditions would be very different at sustained higher revs, with hot, thin oil and next to zerooil pressure.

I don't ever remember a steam train with pressure fed big ends. All the ones worked on used drip or wick lubrication.

The cranks on Norton twins used white metal big end shells which are designed to provide a form of self-lubrication when oil is scarce. Especialy when a motor is first started.

I know where my bet is still going.

Hello Well Steam locomotive have ether Timkin roll bearing are Bronze plan bearings with side shims , I am a Steam Locomotive enthusiast too, and The Norton Model 88&99 are No steam locomotive , white metal bearing will go for so long with very little oil pressure but when they get hot they then give up and fail and with the amount of scoring on the piston is a wounder they have not, failed ,

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That type of piston damage was common, it would interesting if we could get some accurate bore measurements in the upper part of the bore with the head on and fully tightened down, perhaps a torque plate should be used when re-boring.

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Damage around the gudgeon pin sides would possibly suggest that either the bores are not parallel or possiblythe crankshaft is a bit bent.

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Laurence..........this 'piston seizure' article is an excellent find and possibly the answer to many questions. Some of the explanations are heavy reading and not all relevant to Norton enginesbut several photos are exactly what I have seen when pulling apart a dead motor.

I have attached the two pages which appears to match best with Rob's piston problem.

Attachments Piston%20Damage%202.bmp piston-damage-jpg
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Previously phil_hannam wrote:

Laurence..........this 'piston seizure' article is an excellent find and possibly the answer to many questions. Some of the explanations are heavy reading and not all relevant to Norton enginesbut several photos are exactly what I have seen when pulling apart a dead motor.

I have attached the two pages which appears to match best with Rob's piston problem.

Well Its very obvious what happen to this piston And I have been trying to say this all along but no one is taking any notes ,I have been around Norton motorcycles for well over 40years and I was A marine engineer and this is Child's play to me , So Sort It out your selfs Yours Anna J

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Well Anna, so you have over 40 years experience of Nortons. Rob has had his bike since 1972 (and it was not new then), this predates your "experience" by some years.

So, as you keep telling us, you were a marine engineer, what relevance has that to motorcycles? I was once an aircraft fitter (before you were born) so what? Did you take a Norton to sea?

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So we are back to insuficient lubrication / overheating/too tight!!,As this is most common on the drive side ,this is not a timing issue,but can be prevented by allowing a bit more clearance and ensuring good oiling./cooling.

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Very useful information provided by Laurence. It mentions a very important point re plateau honing and running in. Plateau honing is essential otherwise the rings have to wear away the peaks (running in) left by the normal honing process. This wears the rings too, shortening their life and results in increased oil consumption. Properly honed, running in is not necessary. Before handing over your barrels to be rebored ask what tolerance of bore ovality does the machine shop work to - should be within 0.0002", 360 deg. and full length of bore, checked with a proper bore gauge. Also ask if they plateau hone the bores and with what grit and what included angle of the cross-hatch pattern. Piston to bore clearance should be as recommended by the piston manufacturer. Ring manufacturers specifications should also be used including grit size for honing. Re-using rings is false economy, buy top quality from a reputable source. There is alot more that goes into a rebore than just bore to piston clearance.

Also the article mentions an engine running rich (excess fuel) will wash away oil from the cylinders resulting in accelerated wear.

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Going back to Rob's original post, this looks like a classic case of a piston running out of clearance when hot and seizing. So not a lubrication problem. So was it just a lack of clearance or getting too hot for some reason? One possibility is mixture bias - one side running leaner than the other. BSA used to list a wedge-shaped spacer for their single carb A10s to correct mixture bias. A good reason for supporting Simon's preference for twin carbs. Mind you, I have never yet come across a case of mixture bias in A7s, A10s, 88, 99 and Atlas on single carbs so I will stick with the just the one. Gordon.

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Wow, there's been a lot going on in here since I last strolled by.

Ignoring the various tetchy disputes, let me try to narrow things down with some more information.

My money's on overheating, possibly combined with lack of clearance. I don't have an internal micrometer, but I can get 0.0045" of feeler gauge between the bottom of the piston skirt and the bore, on both cylinders, which I believe ought to be enough if lubrication is adequate. I suspect left cylinder lubrication is marginal at the best of times so it wouldn't take much to break it down.

Ignition is wasted-spark by twin-output Emgo coil through the usual 18D2 distributor minus rotor, so there's still the possibility of a timing mismatch between the two cylinders. However, I spent some time levering the distributor shaft against the points plate with a screwdriver to get the same points gap on both cam lobes (I don't claim to be an engineer!), so it's within a degree or two. I strobed it to 30? BTDC at full advance on the left cylinder using marks I made on the alternator stator with reference to a degree disc when I had the head off. I believe it's advisable to retard from the standard 32? by a couple of degrees for modern (what passes for) petrol.

Single 1 1/16" 376 Monobloc, 250 main, 20 pilot, 3 cutaway, .106 needle jet, 5-groove needle in middle groove, paper air filter.

BUT, because it has been burning oil, particularly on the left, and the plugs were black I tried changing from BP7ES to hotter BP6ES, which were both coming out white, so I'm sure overheating has had a part to play. Not affecting the right piston though, so there's clearly at least one other factor at work.

I have in the past dismantled both these crankshafts (500 and 600) and cleaned out the sludge traps, then squirted through the oilways, so I don't think they suffer from Phil's drilling fault. I also stripped and rubbed down the oil pump body to take out the sloppiness so I should have as good pressure as I can get with a 3-start pump drive.

I considered misalignment, but I can get a close-fitting bar through both small ends at once so the rods appear to be straight. And it's done this seizing on at least three different left pistons with two different crankshafts and two different barrels, so if there is misalignment it must be in the crankcase.

I honed the marks out of the cylinders quite easily with a 220-grit 3-legged glaze breaker. Talk of plateau honing and correct cross-hatch angles, counsel of perfection as it is, is likely to paralyse me with indecision. The senior VMCC types I've talked to are of the opinion that it's not that critical and I should just get on with it. I considered finishing off with 400-grit but was told that was too fine for bedding in cast iron rings. Piston and ring manufacturers' specifications are not easy to come by with second hand pistons and unknown rings, but what information I've gathered suggests 0.0045" skirt clearance and 0.010" ring gaps should be about right. And I have checked ring radial and side clearances.

Finally, and I hesitate to open this can of worms, I run it on 20w-50. I've tried straight 50, but it was too hard to turn over on cold days. The first time I tried straight 40 it seized, though I realize now that probably wasn't the cause. I've run my Commando on 20w-50 for 30 years and have never had the bottom end apart, and I can't see any major differences between the two engines apart from the oil pump and head feed, though does the Commando have the conrod oil squirter holes?

Thanks for all the responses (well, most), and apologies for the long post.

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Previously rob_bradley wrote:

Wow, there's been a lot going on in here since I last strolled by.

Ignoring the various tetchy disputes, let me try to narrow things down with some more information.

My money's on overheating, possibly combined with lack of clearance. I don't have an internal micrometer, but I can get 0.0045" of feeler gauge between the bottom of the piston skirt and the bore, on both cylinders, which I believe ought to be enough if lubrication is adequate. I suspect left cylinder lubrication is marginal at the best of times so it wouldn't take much to break it down.

Ignition is wasted-spark by twin-output Emgo coil through the usual 18D2 distributor minus rotor, so there's still the possibility of a timing mismatch between the two cylinders. However, I spent some time levering the distributor shaft against the points plate with a screwdriver to get the same points gap on both cam lobes (I don't claim to be an engineer!), so it's within a degree or two. I strobed it to 30? BTDC at full advance on the left cylinder using marks I made on the alternator stator with reference to a degree disc when I had the head off. I believe it's advisable to retard from the standard 32? by a couple of degrees for modern (what passes for) petrol.

Single 1 1/16" 376 Monobloc, 250 main, 20 pilot, 3 cutaway, .106 needle jet, 5-groove needle in middle groove, paper air filter.

BUT, because it has been burning oil, particularly on the left, and the plugs were black I tried changing from BP7ES to hotter BP6ES, which were both coming out white, so I'm sure overheating has had a part to play. Not affecting the right piston though, so there's clearly at least one other factor at work.

I have in the past dismantled both these crankshafts (500 and 600) and cleaned out the sludge traps, then squirted through the oilways, so I don't think they suffer from Phil's drilling fault. I also stripped and rubbed down the oil pump body to take out the sloppiness so I should have as good pressure as I can get with a 3-start pump drive.

I considered misalignment, but I can get a close-fitting bar through both small ends at once so the rods appear to be straight. And it's done this seizing on at least three different left pistons with two different crankshafts and two different barrels, so if there is misalignment it must be in the crankcase.

I honed the marks out of the cylinders quite easily with a 220-grit 3-legged glaze breaker. Talk of plateau honing and correct cross-hatch angles, counsel of perfection as it is, is likely to paralyse me with indecision. The senior VMCC types I've talked to are of the opinion that it's not that critical and I should just get on with it. I considered finishing off with 400-grit but was told that was too fine for bedding in cast iron rings. Piston and ring manufacturers' specifications are not easy to come by with second hand pistons and unknown rings, but what information I've gathered suggests 0.0045" skirt clearance and 0.010" ring gaps should be about right. And I have checked ring radial and side clearances.

Finally, and I hesitate to open this can of worms, I run it on 20w-50. I've tried straight 50, but it was too hard to turn over on cold days. The first time I tried straight 40 it seized, though I realize now that probably wasn't the cause. I've run my Commando on 20w-50 for 30 years and have never had the bottom end apart, and I can't see any major differences between the two engines apart from the oil pump and head feed, though does the Commando have the conrod oil squirter holes?

Thanks for all the responses (well, most), and apologies for the long post.

Hello So let start with the Bore Is not straight it tapered at the bottom end of the bore to let the piston rings in , And to measure the bore in three places from top to bottom and take your readings and add them up to get a over all measurement , you pilot should be 25 size pilot and your spark plugs are wrong the a extended nose, you be better with W7DTC Bosch or Champion N5 From Green Spark plug ,Co he is on line, you have No oiling problems if you have black sooty plugs it down to flooding of the carburettor float bowl , If you have black oily plug its is down to a oiling problem or oil getting by the rings , you piston to bore clearance should be 0.003 with out piston rings fitted .fit the piston in upside down to take readings and about half inch from top dead ,

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Previously John Shorter wrote:

Well Anna, so you have over 40 years experience of Nortons. Rob has had his bike since 1972 (and it was not new then), this predates your "experience" by some years.

So, as you keep telling us, you were a marine engineer, what relevance has that to motorcycles? I was once an aircraft fitter (before you were born) so what? Did you take a Norton to sea?

Hello Well Marine Diesels Come in two types Four stroke diesel or two stroke diesel or uni-flow diesels I have even had diesel engine with spark plugs fitted to start the engine a petrol/diesel , then there's the Hot bulb start engine , and air start engine , but there all internal combustion engines just like Your Norton , But a lot bigger like up too 80 feet bigger and a lot of Marine Diesels are Dry Sump design just like a big Norton engine And don't your Norton to sea you get barnacles on it , Yours Anna J

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I don't think anybody's mentioned the pressure relief valve. If it's opening too soon you'll get low oil pressure and possibly not enough oil spraying out of the drive side big end to lubricate the piston. You need something like 50lb/insq with a hot engine, if not you need to add shims and/or service/replace the oil pump. The VMCC types who reckon bore ovality and proper honing aren't that critical obviously don't mind high oil consumption. 20/50 oil should cause no problems whatsoever. Why fit unknown rings? Do the engine a favour and spend about £40 on a decent set - after you've had the barrel checked for ovality and honed to suit the rings. Peoples opinions are one thing, but there is no substitution for accurate measurements when trying to eliminate possible causes (in my opinion), hope you get it sorted,

Simon.

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Previously simon_ratcliff wrote:

Why fit unknown rings? Do the engine a favour and spend about £40 on a decent set - after you've had the barrel checked for ovality and honed to suit the rings. Peoples opinions are one thing, but there is no substitution for accurate measurements when trying to eliminate possible causes (in my opinion), hope you get it sorted,

Simon.

Unknown rings in the sense that I don't know the manufacturer. +0.030" are hard to find so I've had to get what I can, from Cox & Turner.

What counts as excessively oval? Is 0.002" OK, front-back vs side-side?

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CP pistons state no more than 0.0002", so I would rebore if you have 0.002" ovality, I can't see how the rings can make an effective seal with this difference.

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My 88 appeared to have a mixture bias.I fiited twin carbs and increased the clearance as advised by JH . I would not use 3 thou .

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Hi - just another thought to further confuse the issue- have you checked the inlet manifold to confirm that the joints/faces are true and that the left (drive side) in particular, where it connects to the head is not distorted? it may be sucking in extra air causing a weak mixture particularly at higher revs.

good luck - terry

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I always take advice from the component manufacturers rather than journalists. What do you think would be best for cylinder sealing - a 0.005" (5 thou') or 0.0002" (2 tenths of 1 thou') ring to bore gap? The workshop manual suggests a difference between the worn part and unworn part of the bore of 0.005" to be max. acceptable wear. However, this was written approx. 38 years ago. Why not have a rebore to current recommended tolerances? Rebuild the top end with 0.002" cylinder ovality/wear if you like, but don't be surprised if you have high oil consumption, piston ring blow-by, excessive crankcase pressure, loss of power, oil contamination of valves/combustion chamber/spark plugs and smokey exhausts. It's also false economy as you'll have to strip the top end sooner and have the required work done anyhow. I suppose it depends what your priority is - money, or doing it properly.

See www.cp-carrillo.com for relevant info.

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I take your point, of course.

However, when I last rebuilt the engine, with cylinders I bought newly rebored to the pistons supplied, the results were exactly as you describe for oval cylinders. Maybe the rebore wasn't done right, but the parts were supplied by an expert member of the NOC who insists all was correct. I wonder if poor ring sealing could just as well have been caused by my not running it in correctly.

As things stand at the moment all I have to lose by going ahead with the rebuild is finding no improvement and having to take it apart again for a rebore. But that's not a big job.

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Rob's carb jetting......

Single 1 1/16" 376 Monobloc, 250 main, 20 pilot, 3 cutaway, .106 needle jet, 5-groove needle in middle groove, paper air filter.

With the paper air filter in place this engine is probably going to be runninga little rich throughout most of the range to start with. The manual suggests just a 25 pilot jet. A 20 jet is used by bigger engines with generally bigger carbs.

Plus, unless all the bits are newish, the needle jet will probably also be worn, causing richness in mid-range running. This could be why the original plugs were sooty.

Plus...Plus....Plu... apparently the Ethanol, that has been addedto our petrol, affectsits overall specific gravity and causes original floats to sink a little. Thus causing the carb to be constantly flooding. Just wondering if this and a rich mix anyway, is washing/dilutingthe oil getting to the pistons. Thoughthis surely would affect both pistons.

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Previously simon_ratcliff wrote:

Rob,

I'm beginning to see why you've had the problem since 1972.

There's no need for that. As I said, I take your point.

I've had rebores in the past, just as you suggest, and still the problem recurs from time to time. Probably none of the people who did the work were as good engineers as you, but I'm stuck with who I can get to do it. It's not necessarily all down to my lack of perfection.

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Previously phil_hannam wrote:

Rob's carb jetting......

Single 1 1/16" 376 Monobloc, 250 main, 20 pilot, 3 cutaway, .106 needle jet, 5-groove needle in middle groove, paper air filter.

With the paper air filter in place this engine is probably going to be runninga little rich throughout most of the range to start with. The manual suggests just a 25 pilot jet. A 20 jet is used by bigger engines with generally bigger carbs.

Plus, unless all the bits are newish, the needle jet will probably also be worn, causing richness in mid-range running. This could be why the original plugs were sooty.

Plus...Plus....Plu... apparently the Ethanol, that has been addedto our petrol, affectsits overall specific gravity and causes original floats to sink a little. Thus causing the carb to be constantly flooding. Just wondering if this and a rich mix anyway, is washing/dilutingthe oil getting to the pistons. Thoughthis surely would affect both pistons.

Thanks for your continued helpful thoughts Phil.

I'm confused by your pilot jet thinking though. Isn't a 25 bigger than a 20, i.e. richer? If so, by your reasoning I should be heading in the right direction by going down to a 20. I selected it on the basis of turns of the air screw with the aid of a Colortune. With a 25 the air screw was almost falling out. It does seem very sensitive to pilot settings over a surprisingly wide range of throttle. It often needs full throttle to start, either to give it enough air because it's rich or enough petrol because it's weak, I don't know.

I renewed the needle and jet not long ago so they shouldn't be too worn. At the same time I replaced the brass float with the latest "stay-up" plastic type.

It's definitely been using oil and smoking. The plugs were oily black rather than dry and sooty.

Interesting point about ethanol. I didn't know its SG was lower than straight petrol. Before I went back to a Premium Concentric on the Commando I occasionally had problems with petrol flooding out of the back of the Mikuni. I try to use super unleaded on the grounds that it's maybe less likely to contain ethanol, though I know that varies between brands and which refinery it comes from, but sometimes you have to use what's available at the time. I wonder if that explains why it only happened occasionally? But now I'm rambling off the point of this thread.

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Of course the valve guides could be to blame for an oily combustion chamber.My 1952 Land Rover would lay down a good smokescreen which was cured by replacing the valve guide seals. Of course pre Commandos don't have guide seals, but the guides themselves could be a loose fit in the head or simply just worn.

Fuel can do nasty things. Years ago Shell produced some horrible petrol which hadVauxhall ifI remember giving them the bill for a spate of engine seizures. I filled up my BSA with some out of necessity and it too seized - 12,000 miles after a rebore.

As a matter of course,if I have an engine reboredI go for the lowest available compression ratio pistons. It runs cooler, it's easier on the rest of the engine and it adds a bit of future-proofing. There's nothing like detonation for destroying engines. Gordon.

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Rob,

I don't do rebores. I was pointing out that without measuring accurately and establishing dimensions you don't know, you are just guessing. Ditto oil pressure. The way you're going about the problem, it may be another 41 years before it's resolved. If ethanol was to blame then every reciprocating internal combustion engine in the uk would be seizing. As you have a single carb then I would have thought you can eliminate carburation, especially as you mention it's been running rich. If you get your barrels checked and also check your oil pressure, then at least you can rule them out as the cause. I'll leave you to go about it in your own way.

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Previously rob_bradley wrote:

Previously simon_ratcliff wrote:

Why fit unknown rings? Do the engine a favour and spend about £40 on a decent set - after you've had the barrel checked for ovality and honed to suit the rings. Peoples opinions are one thing, but there is no substitution for accurate measurements when trying to eliminate possible causes (in my opinion), hope you get it sorted,

Simon.

Unknown rings in the sense that I don't know the manufacturer. +0.030" are hard to find so I've had to get what I can, from Cox & Turner.

What counts as excessively oval? Is 0.002" OK, front-back vs side-side?

Hello Well 0.030 oversize pistons and ring are the Norton motors bracebridge street works recommendations for there over size were plus 10 +20 +30 , the other sizes that are now available are after market over sizes pistons from +20 +40+60 these are the pistons that have been found to be giving Norton Owners some problems And Fred Swift found that Norton piston tolerances too be too tight in the bore and he had his racing 88 and 650s bore to 0.005 , my Norton Manxman is on standard pistons made by BHB and Honed to 0.003 and these work nice with no smoke or oil loss , to me 0.002 is tight in the bore and 3thou sound be good enough as long as the end gaps are right on the piston rings and do not forget to measure the lands gap as well .I have a document on Piston and Rings and there measurements , I will send a copy to MW for the roadholder and then you can keep this copy in your files for the future uses , yours anna j Dixon

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Wassell stocks the "Hepolite" rings which are made in the USA by Hastings (see: http://www.hastingsmfg.com/ )& are of an excent quality & are offered in .010 incriments from stock to .060 oversize. If you cant find a dealer in the UK, PM me & as a Wassell dealer myself, I can get them for you also (I am in the USA).

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Previously eugene_brolund wrote:

Wassell stocks the "Hepolite" rings

Interesting, I'll remember that. There's a Wassell dealer locally.

Incidentally, are Hepolite oil control rings one-piece or three-piece?

 

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