I hope everybody is fit & well in these difficult times.
After bolting down the barrel in my rebuild I turned the crank but when the pistons were reaching the bottom it became very stiff until they started on there way up again, It appears that I have done something wrong but Im completely baffled at what the problem is.
I would be grateful if someone could give me a clue.
Many thanks Robert
you don't give any details about what you have replaced, but my first thought is that the pistons may be wrong for the crankshaft and are touching the flywheels at the bottom of the stroke. 500 cranks are full circle flywheels 600 ,650 and 750 all have flat areas to allow clearance for the bottom of the pistons skirts.
Was it free before the barrels went on?
Maybe one of the faces (crank or barrel) is not flat. Do the case halves match?
If you remove the barrel, maybe try a dial gauge on the flywheel to check it it is running true.
If you had the conrods off and fitted new shells,did you check the rods were free to turn over a complete revolution? ,or just rocked them?. Its not unknown for old rods to go a little oval and the act of fitting new shells to make a tight spot. Also check the cam followers are all free .Cylinders not parallel? I hope not!
Sometimes when fitting new main bearings the cranks can appear stiff especially if the cases haven't quite gone back to their seated position. I don't know your age Robert but here's a little trick if you're strong enough. Place a thick piece of hardwood on a hard surface (concrete or paving flagstone is ideal) lift the engine above the wood such that the drive-side end of the crankshaft is about 9 inches above the wood - then carefully release your grip a little and let gravity do its work. You can retain enough grip to stop it falling once it hits the wood. A couple of hard shocks usually lets everything slot back together. It is usually the timing-side crankcase half that hasn't quite settled. The engine nuts will need a tweak afterwards. Good luck, Howard
It is a 650 & I had it re bored so purchased Gandini pistons reference NORTON 69 6822/100S.
I have just looked at some old pistons & they do have a scooped out portion to clear flywheel, I do not remember if the new pistons were square or scooped out.
I did replace the mains using superblend ref ss08 d3 064118c3 on drive side, they were tight.
I think I get your remedy in that the shock put onto crank drifts the bearing casing as far as it will go, thank you once I have determined that the new pistons are correct I will give it a go.
In my wisdom ? I didn't do that, the crank was re ground, new shells but using existing conrods.
Another mistake, if I had rotated the crank after joining the 2 matching halves I would have known that the new pistons cleared the flywheel.
I would put poorly ground crankpins top of my list with distorted rod eyes or caps as a close second. Alternatively the corners of the crankpins may have the wrong size radius and be snagging the sides of the big-end shells.
I would also be looking very closely at the rebores. Norton twin often had barrels manufactured with cylinders that were not parallel. Generally this shows up after a rebore when you find one side of the barrel has more metal thickness than the other. I don't think it is the pistons touching the flywheel. They either foul big-time or not at all if decent pistons are fitted..
The first time I fitted new pistons to my 650SS, they jammed on the flywheel. I had to take them off and relieve the piston skirts to get clearance. I'm not sure if 600 pistons, although the same bore, have longer skirts. Maybe that's the root of the problem?
If the pistons were for a 99 then the skirts would be too long for a 650. But it would just go CLUNK and stop I think. When I rebuilt the 99 with new shells on a well used crank I had to re-fit the rods a few times to get free movement.Did the pins pass freely through the small ends? .
hello for a start of the barrels do taper out to the bottom of the barrels if the rebore as not allowed for it that where the pistons are fouling and the bore will need correcting I had this sometime back When I then owned And Wartburg Tourist 353 mk1 and I had the block rebored the machinist did not tapper out at the bottom of the stroke And could not even get the pistons in So I took it back to the engineering workshop in Selby and explained to them the problem So they rigged a machine up to do the tapper and then I could fit the pistons OK So you may find your self going back to the engineering shop to sort this out, Yours Anna J
Don't ask questions ,you'll only become more confused, because it's obvious to me that some of the answers aren't relevant to the question. Do something positive , very carefully remove the barrel and start from there , otherwise you're just going to be guessing.
That's exactly what reluctantly I have to do Ian take the pot off in my usual 1 step forward 2 back .Lol.
I am so grateful for everybody taking the time to try to be helpful, thank you all.
Ive taken barrel off & found that the pistons have ground into rear of crankcase, the left hand which appears to have scuffed most has left the gudgeon pin free but the right hand gudgeon pin is seized. Can someone make sense of why the pistons have touched like this .
I have enclosed a couple of pics to hopefully show.
That's really odd. The piston skirts should not get near the case . I'm wondering if you have mixture of parts. What are the case numbers. The pistons do not look too damaged in the important areas as long as no cracks.Some photos of the engine may help. A wild guess, 650 /750crank in 88/99 cases and 99 pistons?. A conumdrum.
History is, casing I am using is 18SS/112765/P from original engine that had split barrel combined with camshaft that had destroyed the key, camshaft was unusable also because end of camshaft was bent, crankshaft was also knackered.
I have used the 18SS/112765/P casing & conrods. Used reground crankshaft, camshaft & barrel from an earlier engine 100207 18
And of course the Gandini pistons ref Norton 69 6822/100S.
The issue seems to be the piston skirts, have they been marked by the rods on the inside of skirts?. Marks on the rods indicate that the rods may have been pushing the pistons against the cases. Supplier should change these as wrong for the motor. If no luck there I would alter the skirts to match the old pistons.
There is nothing to suggest that has happened Robert but I haven't withdrawn the gudgeon pins yet.
I can see horizontal marking on the rod faces. Could be the pointer.
Very interesting thread so far. Robert you say that you had the crank reground and new big-end shells presumably ? Did you take the crankshaft apart or did the workshop, doing the regrind, do that ? Sometimes the three segments can be buggers to fit back together properly. My thoughts are that the two pistons are incorrectly aligned with the bores in the barrel causing the pistons to scue against the cases at the bottom of the stroke. Another question please Robert - I presume you fitted new main bearings when you rebuilt the bottom half ? Did you use the original lipped roller on the drive-side (MRJA30) and a rigid ball bearing on the timing-side? When you tightened the worm nut to pull the crank against the t/s bearing you did remember to fit the triangular washer and the tin bearing cover. If you have fitted Commando roller bearings both sides there may be an issue with the end-float. Cheers for now, Howard
I took the crankshaft apart & rebuilt. The new mains I fitted were ball bearings on timing side & superblend for pre 200000 reference SS08 D3-064118C3 for drive side. I have not got as far as assembling the timing gear, this would have been my next step.
You had the right answer in your 2nd post . Piston skirts too long for the longer stroke of this engine, At some part of the stroke maybe the rods are coming into contact with the inside edge of the skirt and rocking the piston by just enough to catch the .case ,or they are long enough to catch anyway. At one time Mix and match was done to the 88/99 motors with interesting results .Not seen your problem before though. Very entertaining!.
Thanks Robert, but I compared the new pistons with old & there wasn't any difference in size the old pistons were more oversize than the new + 10, I'm wondering if I have brought the crank cheeks onto the flywheel up properly, I torqued them up correctly but maybe they haven't butted up as they should, if they are not that would push the pistons out enough to touch casing. I have to split everything anyway because there was a few alloy bits which could be anywhere. I am rather hoping it is this then the mystery is solved.
I have some 99 pistons ,I will compare them to your photos. My 99 runs with 650 SS pistons So I have been aware of the differences.I think your original pistons were wrong too but had been made to fit. Now an extra +10 is making a problem.
Here are the pistons Robert, the 1 on left is from what was the going engine from 1000207 18, the 1 in the middle is the new +10 & the 1 on the right is from the 18SS/112765/P engine.
The scrape on the new piston goes up to the bottom of gudgeon pin
It sounds as if your cases had a interesting time when the cam shaft was damage. I wonder if the cases are distorted somehow? When you remove the pistons and before you split the cases, maybe you could check if the flywheel runs true. No point in stripping it again if it is true, is there?
Looking closely at your photos ,it appears that the distance from c/l of pin to bottom of skirt is greater on the new pistons. That does not in itself explain the height of the scrape on the skirt. However I think the rod face IS making a contact with the inside edge of the skirt and forcing the piston over into the case . Clean up the pistons and shorten the skirt and you may find disaster averted. You should get your money back or correct replacements but I won't hold my breath.
The overlap looks like half an inch. I don't see how pistons could do that. But bent con rods might. That's my theory....
If that was the case you would have eroded the lateral play on the small end, if you have, the small end of the rod would have rub marks on piston machined face that is adjacent to the small end of the rod.
The portion of skirt that has damage is no different in height, if anything less, than the adjacent pistons, this is not an issue with the pistons. The point fore and aft looks slightly lower but has not sustained any damage it seems, being the lowest point and if free of damage suggests also pistons are not at fault.
Seems reply is not working at the moment.
I have turned the crank over & nothing appears to be wrong.
Before using the conrods I put them together they were flat, I inserted gudgeon pin, they were still flat together.
I have however found that the barrel wont mate with the casing leaving it about 10mm off, it is also rocking on timing side cam barrel extrusion, I must have forced it down with bolts, so this could be a reason? looking down the conrods look central .
The bottom spigots should go into the crank case. So it should not be possible for pistons to touch cases..unless barrel is back to front!
A photo of the inside back face bottom edge of the pistons may help. David, if 99 long skirt pistons are fitted then they will go further down than the barrels and hit the casting flash in the cases. If you are right I will buy you a beer next time we meet.!.
Here at the pics of the inside back edge that were scraped
Looking forward to it, Robert!
And the offending conrods
The overlap looks to be very small, doesn't it? I see it was a Plumstead bike like mine (letter P), and my PO who put mine together said the fit up left a lot to be desired! Maybe it's simply that the case castings were never finished off correctly, and the extra few thou on the piston diameter was the last straw. So trim the hole with a burr in a Dremmel?
I have a Dremel and it has been a revelation ,doing all sorts of tasks I would not have expected. What I have not found is a blade that will cut alloy without smearing . Something like a tct blade in minature needed. The piston issue may be just down to AMC sloppy finishing ,not clearing casting excess . That's what you get with a "FAKE" Norton !!.
Well guys, this ex carpenter should leave engineering alone, while easing fixing holes in the barrel while being aware that the right hand cam enclosure was touching casing it has finally come to me that the scraping on the rear casing was due to the skirt of the barrel, being too tight & cutting its way down into casing, you may say why hadn't I tested all this out before going so far, my only defence is that I started off using the old engine casing that was a par with barrel but due to a stupid thing that I did, too embarrassing to quote, I proceeded then with other casing and I guess assumption that there would be no problem.
Scrapes on the pistons & stiffness have not yet been exposed but who knows it may be another stupid thing I have done, sorry guys for not employing a professional to give me an engine that works.
With these old motors even the really old hands expect to find a few surprises , wrong parts made to work ,new parts that are poorly made to indifferent patterns , missing parts that are not clearly shown on the literature,anything is possible . don't beat yourself up, most of the satisfaction is in getting the thing to run reliably and efficiently. Something I have learnt is don't try to renew original parts till you are sure you have better replacements, and don't throw anything away!.
I have ground the case to accept barrel, I have discovered that the pistons are larger at the bottom I found that they were tight but after moving them I believe they will be ok I guess the reason is so they don't flap about which is probably a bit of an exaggeration.
Because the conrods didn't go round absolutely smoothly feeling a very slight binding in a place or two I have broken them back down, I can see some shining up but I'm at a loss as to what it means, I cant go back to the machine shop for them to have a look as they will be closed, so Robert if I sent some pictures would you be able to give me your opinion on how they look?
Sorry to be a pain. Cheers
All pistons are tapered with the bottom largest as the heat from the combustion chamber makes the top of the piston expand more at running temps. The shine on the bearings is where they have contacted the crank journals, did you lubricate the shells with assembly lubricant before torquing up the con rod bolts.
I have no doubt that the rods are slightly oval, Something that happens over time. The Ideal would be new rods. And they are availiable,if a little expensive. The next best thing would be to get the rods re-sized,but as you say,not practical at present. You could give them a thorough clean ,and the back of the shells to make sure there is nothing there. I am guessing the shine is near the ends of the shells where they meet?. In the old days they would have "scraped" the bearing to releave the tight spots, I don't think you can do that with the shell facing you have.If it were mine I would scrape the rods (not shells) at the tight areas a thou or so till it all turns freely.Also give the crank journals a polish with very fine carburundom paper. All at your own risk. I have done this before and no problems but its usually frowned upon!.You could get a plastigage Kit thro the post to check bearing/journal clearance.Also check the big end caps not switched.
An interesting thread, I assume the early barrel that you have used is spigoted did your old barrel have spigots? I have had a similar problem with my '67 650SS which the previous owner fitted with a barrel from a Manxman [spigoted] I had the engine rebuilt with GPM pistons and found in my case the skirt touched the flywheel but the piston also touched the head both problems were cured by a bit of light machining. I also believe the pushrod length was shortened when the spigot was removed.
After looking at the pics hopefully you can see shining areas do you still think that they are oval?
Both barrels have spigots Allan
Those shell photos are exactly what I expected to see. Running too tight , no clearance for the necessary oil boundary.
I didn't use assembly lube but used oil, when I took them apart they were wet with oil so lubrication was not the problem.