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Engine Rebuild - 1962 650SS

Submitted by alastair_price on Mon, 02/09/2024
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Heavy Twins

My 1962 650SS expired on the run back from the MGP last week and I am now resigned to undertaking a complete rebuild in an attempt to create a reliable oil-tight unit with something resembling the original power output (i.e. not a highly tuned monster).
I don't know what has been done to the bike over the past 62 years, but I do know that although a belt drive has been fitted in the past, there was a significant and persistent oil leak from the primary chaincase. Although a new main seal was fitted together with new gaskets and liberal application of RTV to mating surface and screw threads and suspected porosity of apparent welding on the drive side case was covered with JB Weld, I could achieve no improvement.
I suspect that inadequate breathing may be a contributor to this hitherto unresolved problem.
A pair of what seem to be good-looking cases have been procured (although not yet received) as the basis for the rebuild.
First question is:
Is there a recommended go-to builder for Dominators, particularly 650SS?
Second question is:
Are there any modifications recommended for best chances of achieving reasonable reliability and oil-tightness? There seems to be a lot of contradictory information available with regard to oil pumps, rocker spindles and breathing.
Third question:
Is this something I could reasonably tackle myself, with any specialist engineering work such as replacement of valve guides & seats, barrel rebore and crank re-grind (latter two dependent on what I find upon dismantling) being outsourced to specialists?
Fourth question:
The crank will probably need dismantled for the sludge trap to be cleaned out. Is it advisable to have the crank balanced? If so, any recommendations?
Thanks in anticipation for any guidance.
 

Submitted by robert_tuck on Mon, 02/09/2024

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What was the expiry caused by?. Nothing difficult in these motors. Try to re-use orriginal parts if not damaged . These are tough old beasts . Its usually modern replacements and modifications that give the most bother. 

Submitted by alastair_price on Mon, 02/09/2024

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Whipped the rocker covers off tonight to find left hand exhaust rocker with 1/2" clearance.

I can see with a torch that the top end of the pushrod seems to have broken off!

Submitted by jan_nelder on Mon, 02/09/2024

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 a one way valve in the main breather, as used as a mod. on many Commandos , is usually vg for reducing oil leaks. Some use one sold for XS 650 Yams.
   Pete Lovell in Smethwick is highly recommended by many.

Submitted by alastair_price on Tue, 03/09/2024

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Jan,
The existing breather comes off the back of the left hand crankcase (via the timed breather disc at the end of the camshaft - will not know if that is even there, or if it is the correct one, until the engine comes apart).
The flexible pipe then goes to the froth tower on the top of the oil tank with a further pipe from the top of the tank to a spigot on the top of the rear chain guard.
Where should a one way valve such as that used on the Yam XS 650 be fitted?
Is this the same as a PCV?
For what it's worth, the engine number is 104135.

Ideally the breather NRV should be fitted as close to the engine as possible. Bear in mind that the std arrangement (with the timed disc) breathes through the camshaft and the drilling is not big enough. If you want the NRV to work properly it needs a pipe connection into the crankcase of a bore size that is the same as the NRV's spigot. The most unobtrusive way is to alter (divert) the current breather passage to connect directly with the crankcase so it bypasses the camshaft/timed breather. (means drilling a hole in the crankcase when its apart)  

Submitted by robert_tuck on Tue, 03/09/2024

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Pushrod was probably previously bent and straightened after being misslocated on fitting the head.  Amazingly they will run with the rod not properly located ,but damage is inevitable. A new rod and head gasket  may be the only parts needed . 

Submitted by alastair_price on Tue, 03/09/2024

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Received the Mick Hemmings Heavyweight Twin Restoration DVD yesterday - thanks NOC Shop people for your prompt despatch.

Watched the dismantling disc last night - really useful and very well presented.

Still to watch the re-assembly disc, but a mine of useful information which gives me some more confidence to tackle this myself.

The extra breather holes .jpeg is something like what you need to do, but half a dozen holes is going over the top a bit. You should aim for the same mm² area (or a little more) as the pipe spigot bore in the crankcase. The other two jpegs show other breathing arrangements that are too much intrusive (and look horrible)
Don't worry about the rest of the engines lubrication regarding 'the bellows effect'  putting a read valve breather (NRV) in the breather line has the same effect as the timed breather but with a better flow/action. The engines bearings will still get the required oil to function properly.
If you could see inside an engines crankcase when it is running you would see loads of oil being flung around....  Where did the photo of the extra breather holes come from? 

Elegant, NO, looks almost phallic!  Another reed valve breather that can be fitted and doesn't involve drilling holes is this one. the only downside is the cost.
https://nycnorton.com/product/reed-valve-breather-kit/

Submitted by philip_hannam1 on Tue, 03/09/2024

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Many 650,  Atlas and Hybrid 750 owners will inform you that their bikes are generally oil tight and remain so unless thrashed.
If your Dominator is pushing out quantities of oil when only ridden at moderate speeds then there are other problems which need to be sorted.  But this does not always mean sophisticated changes to the breathing system.
Piston and/or ring problems will allow blow-by which will pressurise the crankcases.
A worn main crankshaft seal or damaged crankshaft will let oil through into the primary cases.
Dodgy gaskets and/or poor mating surfaces don't help either.
Is the pressure Release Valve in the Timing Cover working correctly? Current reasoning is to shim the PRV up to only release at 55psi. Thus pushing more oil into the crankshaft and not into the Timing Cover.
Is the rotary breather valve on the Camshaft correct for the engine?
Copper washers for any oil pipes need to be annealed before fitting. Even the smaller ones.
Timing and Rocker Covers warp with ageing. Check them all for true flat surfaces.
Likewise, the barrels and crankcase mouth will distort with use.
Check all of the above before considering altering the breathing arrangements.
 

Submitted by peter_shand on Tue, 03/09/2024

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Your statement   'Many 650,  Atlas and Hybrid 750 owners will inform you that their bikes are generally oil tight and remain so unless thrashed' means the breather system can't cope. It would be ok if it just had to cope with a 500, but as the cc's grew its short comings are evident in the propensity for the oil to escape when the throttle is well rung.    

Submitted by alastair_price on Tue, 03/09/2024

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Thanks Peter & Philip.

The leakage is only on the drive side - not chaincase oil as it has a belt drive.

This is the one where I had a recent thread where the consensus was that it had been welded some time in the past and the weld may be porous.

I had fitted a new crank seal, but there was a comment that the replacement seal might not have been of the best quality.

I replaced the complete oil pressure relief valve assembly - piston, 2nr shims & spring and the oil pump nipple seal against the inside of the timing cover.

I don't know whether the breather valve is the right one (how would I find out?), nor even if there is one fitted yet as I haven't split the cases yet.

I am going to rebuild using a good set of used cases (recently purchased) to rule out weld porosity and want to take every possible step to build an oil-tight unit, so any pointers towards best practice "whilst you are in there" regarding breathing would be appreciated.

In the course of the rebuild, new rings will be fitted at the very least - worst case would involve a rebore with new pistons and rings - together with a top and bottom end rebuild.

 

Submitted by robert_tuck on Wed, 04/09/2024

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Hi Alastair , If the piston and rings show no sign of blowby and  ring gaps are within used tollerances  I would not mess with it.  My experience is that many  bikes are laid up and not used due to " improvements "not working as well as the status quo,  , many do not even get run in again properly before being pulled down again later to correct faults that were not there in the first place. 

Submitted by ashley_cutler1 on Thu, 05/09/2024

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If you fit a PCV, then be aware that these can cause corrosion in the engine. We have seen some engines with them fitted that have more corrosion in the them than engines without. This we think is due to short stop start journeys which is not good for any engine with or without a valve fitted. Not sure about the Domi's but a Commando engine will need a good 12-15 miles to warm through the engine and heat the oil in the tank to decent temperature. 
The PCV seems more common now, fitted to a lot bikes that come through the workshop - a bit like electric starters.   

That is why the best place for a NRV breather is as close to the engine as possible, to reduce or eliminate the condensation trap. In that respect the sump reed breather is excellent. Some of the bikes i see that have a reed NRV fitted have them situated at a distance from the engine, presumably to hide them behind side panels or oil tanks etc  making for a length of pipe that is a classic condensation trap. The best solution is to ride the damn thing for a decent distance.

Hi Peter, 
I am in a similar situation as I am rebuilding a 650SS motor that has been stored for quite a while. 
Where would you suggest the NRV be positioned to get the best benefit. I appreciate that to ride for longer is the best solution. 

Regards 
Phil 

As close to the engine as possible. a reed type NRV preferable, There is the XS650 type that has a right angle between the pipe spigots and a straight version fitted to yamaha 125.s and the like that is much cheaper from ebay    
Like this    2023 BENELLI BN125 BN 125 EGR VALVE 110011070000 •1   Just found it for a buy it now price of £12.50

Submitted by george_farenden on Fri, 06/09/2024

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Hi Alastair, 
here is a picture of the Yamaha 125 valve I have on my 650.
I removed the 'Maltese cross' bits from the end of the cam as I wanted to make sure it worked before I made any changes that were unable to be reversed.  Doing so meant that the reed was in control of crankcase pressure.
Having proved to myself that it works brilliantly, should I have reason to split the cases again I would do as Peter suggests and make the hole from the breather tube attachment direct into the crankcase. 
Regards, George 

Attachments
Yamaha valve.jpg

Thanks George - that installation looks good.
However, I have pulled the trigger on the sump plug type.
Just to clarify, you completely removed the timed breather disc assembly at the end of the camshaft so all breathing is controlled by the new reed valve?
Did you have breather-related problems before?
Alastair

Submitted by george_farenden on Sat, 07/09/2024

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Hi Alastair, 
yes I did suffer issues, especially as I enjoyed opening the throttle a bit! That's why I went modern. As has been said earlier, the breather worked on a 500 fairly well,  but as the engines got bigger so did the problems.
Me? I'm happy as my bike is for riding, not showing - most of it did come out of Norton factories,  but not at the same time...
I got fed up of drive side seals going west and since the mod all has been good.
Regards, George 

Submitted by john_oldridge on Sun, 08/09/2024

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Hi Alistair,  I have the same Yamaha reed valve fitted to My M50 and Venom, as shown by George, and can strongly recommend  them.

As suggested by Peter, fit as close as possible to the crankcase, and give them a good clean every couple of years, the Yamaha type are very easy to dismantle.

Regards John O

 



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