Primary Chain Case Leak Plunger A10

[Stu55Flash]

I can't get rid of my primary case oil leak. Had 3 goes so far. Chain case cover is now OK, had the clutch off and replaced the lip seal. Oil thrower is in place. Still oil comes down the back of the chain case like its coming from the shaft. The gearbox output shaft looked well centered.  Other than getting an expensive belt kit has anyone experienced this or got any suggestions? What about grease on the primary chain instead of oil?

Any advice gratefully recieved.

Stu

[bsa-bill]

Grease is a very poor lubricant on a chain and an even worse coolant.
My friend was advised to do this and tried it on a short run, result red hot chain.
Primary chain travels at a good rate of knots and needs the cooling effect of a dip in the oil as it goes around, doesn't take much but none is not good.

I'm only familiar with S/A Flash so you've lost me with the lip seal, but others will know what you mean so next reply might be more helpful

[chaterlea25]

Hi Stu,
I'm not over familiar with the plunger version either!, but!!!
Is the oil coming from the gearbox out along the sleeve gear bushing or / and out from the bearing along the splines to the sprocket nut?? or even the gearbox sprocket seal??
The gearbox quite often leaks out the shaft if the bike is left on the propstand

HTH
John O R

[Stu55Flash]

On re-looking at the BSA service sheets, at the very end of Sheet No 208 last paragraph, it says that the screw marked red should be moved to the hole next to the adjuster screw and the chain case modified on the inside to act as an oil level indicator.   I've done this now. It says elsewhere to put 1/2 pint in the chain case but after removing the re-located screw 1/4 pint pours straight back out. Leaving 1/4 pint in the chain case. It this enough oil? Has anyone else done this?

Stu

[A10Boy]

Its enough if its still "wetting" the chain. But beware, a dry chain will fry in about 1 minute.

[bsa-bill]

Plunger primary case capacity is given as 100cc which is less than a quarter of a pint (568cc = 1 UK Pint) so your ok at that

[Stu55Flash]

Spot on thanks folks.

Stu

[colindock]

In the Bruce main-smith maintenance manual it states the capacity of the chaincase as 1/6 pint (90cc)

[Rex]

The chain just needs to contact the oil for lubrication, so try 90cc or whatever and kick the engine over. The top surface of the top chain run should have fresh oil on it if there's enough in the primary.
i don't recognise these warnings of red hot and fried chains though. Some owners (including me!)  of bikes with especially leaky tin primaries use nothing more than a squirt of chain lube or regular oil before every trip, and the primary chain lasts just as well as those with better primary lubing and sealing arrangements.

[RDfella]

I agree Rex. Gave up putting oil in primaries years ago having got fed up with slipping clutches (and leaky cases!). My primary chains get boiled in grease and then are good for thousands of miles. What about rear chains - they're not in an oil bath? Or primary chain on racing machinery, where they last hours with no oil in sight?

[BagONails]

This is a vexed question currently and one that I am not qualified to answer. All I know is I have a bike which has a completely cream crackered primary and the P/O was doing just this, running it dry and squirting chain lube on before a run.

The primary chain runs at engine speed which is a hell of a lot faster than the final drive. It is also less than half as long so does a lot more revs over any given distance.  It is encased which keeps it clean but it also runs a lot hotter as it gets no cooling air flow around it. I think mine has been destroyed by running too tight, being misaligned and lastly by not being sufficiently lubricated.  In addition there are the clutch rollers which are left high and dry with no oil being flung around...not ideal.  P/O had greased these but there was very little left on the rollers and you could see where it had been flung out all over the inside of the clutch drum, probably the first time it started and got hot.

My plan is to replace all the fried parts, set everything up as well as I can, follow the good advice I've been given on this forum and run it with just enough oil to wet the lower run of the chain. If it still leaks a bit I'll find a way to live with it.

[Swarfcut]

   Plunger bikes have a metal slipper chain tensioner which requires lubrication, so oil in the primary case is a must, just deep enough to wet the chain. S/A models have a chain more tolerant to a lack of wet lubricant, not having the metal to metal friction of a tensioner blade.
  Better to stick with the original design if you can and strive for an oiltight primary case and remember to set the play in the chain when it's at its tightest point in the run.

 Swarfy.

[Greybeard]

Fettling the case edges with a smooth file, (across two sides at once) or emery cloth on a piece of glass and slightly chamfering the screw holes may be required. I use Hylomar Blue and a gasket. You should be able to get the case oil tight. I do not recommend Allen screws as they can be overtightened and distort the case.

[BSA_54A10]

My 29 model S has just a front cover as did all BSA's till some time in the 30's so the chains all ran dry.
I would have said they were all dry till the 1936 redesign but I am fairly sure the model G has a complete primary chain case .
So while primaries do take a beating, you can run them without an oil bath without problem, it just means you have to manually lube them regularly & I have found that the foaming O ring chain lube does an excellent job of it.
Down side is doing a multi day ride you do have to lube the chain the instant you stop while it is still warm

[chaterlea25]

Hi All
The vintage BSA's usually have the engine breather outlet pointing at the primary chain,  the oil mist exiting the breather helps lube the chain,
There is also a drilling through the mainshaft and a radial drilling to the inside of the cush drive sprocket which lubes the rubbing surfaces
People forget that the cush drive needs lube when running a "dry" primary 

It is not that hard to get the primary cases oil tight flat surfaces and good screw head seats are essential
The sliding plate can be a problem because all the pattern ones are shite
Most leakage comes from the riveted up joint "V" .  Seal that up with your favourite  goo,,
A cork or oil proof foam ring to replace the felt on the sliding plate stops another gap
The thick felt washer from SRM behind the adaptor works well too
On my SR I had to add a breather because I had sealed up the usual escape routes LOL

John