Engine Rebuild - 1962 650SS

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. 

 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.

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 . 

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.
 

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. 

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.   

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 

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 

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

If this 650 is from 1962 it would have had a 3-start oil pump, low pressure return pipe feed to the rockers. The rockers would have used scrolled spindles.

Check carefully to see what is inside your cylinder head. A 6-start oil pump plus pressure rocker feed and scrolled spindles will flood the head each time the engine runs.

Both the early 650 and 750 engines used oil pumps with the 3 start worm/gear and low pressure return feed to the rockers.  The pump body would have been the high capacity kind usually stamped with an 'S' on the feed face.

A standard (earlier) pump will have a lower capacity due to its thinner gears but when a 6 start worm/gear is added will easily provide enough oil pressure to the bottom end.

The big 'BUT' being the conrods. If these have  bleed/splash holes and pressure fed rockers as part of the system then the safety margins will change. Especially if the pump is worn.
A new oil pump is not a bad move.

Alistair, Regarding the con-rod oil holes, if you are concerned that they could be drawing too much oil with a lower capacity pump (albeit operating at double speed) you could simply either get plain, undrilled big-end shells, or reverse the upper and lower shells, so that the blank (undrilled) shells are blocking the holes.  Cylinder lubrication will then revert to splash, as on all pre 6-start pump models.

Andy

Hi Alistair, 
if you go for scrolled rocker spindles, even just exhaust ones with a high pressure supply,  you will definitely get way too much oil up the top end.
It is my belief that the plain spindles were introduced in order to reduce manufacturing cost, not necessarily to make things better.

My mongrel 650 has 3 start gears for the 'S' oil pump, and originally was fitted with scrolled spindles and return feed to the rockers. 25 years ago, Mr Emery said I 'must upgrade' to the plain spindles/high pressure feed for reliability and a good idle. However, after getting fed up with not being able to ride more than 5 miles before a smokescreen appeared behind due to top end over oiling, I reverted back to the original system and all was well. 
I may be wrong,  but I believe that the cylinder head drain (and tappet chamfers?) were increased in size for the later engines too.
I will add that I use 20/50 oil, so the oil drain issues would have been much worse if using  a straight 30 or 40 oil.
Regards, George