A bit of advice needed (oil leak from the back of the primary)

[bikerbob]

I have a 1956 swinging arm A7, I have made and fitted a modified sliding plate in the primary which has an oil seal fitted instead of the reverse oil scroll. To fit this I have had to machine off the oil scroll and the bit of the clutch sleeve that holds it for clearance. Thinking this would cure the persistent oil leak from the back of the primary I took the bike out for a run and found that the oil leak is now worse than before.

I stripped the primary down again to see if I could find the problem, no luck only thing I could think of was maybe oil was getting down between the aluminium boss I made to hold the seal and the back plate so removed it and sealed it with gasket cement and riveted it back again. after rebuilding it up again took bike for a run oil still coming out.

At this point I had decided to strip down again and put everything back to standard and put up with the slight leak of oil I have spare backplate and clutch sl;eeve and scroll. Left everything for a couple of days to think about it then had a thought the primary with the oil seal is now airtight with the scroll it is not so maybe pressure is building up and forceing oil out.

Removed the oil filler cap and fitted a rubber bung in with hole drilled in center with a temporary plastic tube fitted. Took bike for a run and now no oil leak. So now I need to fit a breather, do not want to fit anything that can be seen so the front of the primary is no good so has to go on the back possibly just below the magneto.

Have looked on the internet and there are plenty of breathers but I think they are all to big, there is not a lot of room behind there I could make a fitting in the lathe drill a hole attach it and lead a plastic tube away from it. I would prefer to fit a proper breather but where can I buy a small enough breather that is the help I need.
Thanks

adm edit: split the compact block of words into paragraphs, makes things much easier to read and grasp :O)
& title edited to reflect subject of topic, see https://www.a7a10.net/forum/index.php?topic=4723.0 #5

[Greybeard]

How is the primary getting pressurised? Is the engine breather not working so forcing pressure past the main bearing seal? Is the main bearing seal in good nick? Are you sure the oil is from the primary? I have ATF in mine, partly so I can tell what oil is coming from where!

[AdrianJ]

I wondered if Bikerbob’s oil was coming from the crankcase breather, or is there not one there on the S/A bike?
Greybeard - ATF in your primary chaincase? Are there any downsides to this? Is there a specific type of ATF to use? I’ve just rebuilt and haven’t filled it yet, it is just “moist” with engine oil oil.
Adrian.

[stu.andrews]

No problem with using ATF in the primary. I always used to so that it was easier to identify leaks!

[Greybeard]

I wondered if Bikerbob’s oil was coming from the crankcase breather, or is there not one there on the S/A bike?
Greybeard - ATF in your primary chaincase? Are there any downsides to this? Is there a specific type of ATF to use? I’ve just rebuilt and haven’t filled it yet, it is just “moist” with engine oil oil.
Adrian.

Don't overfill the primary. I can't remember the exact amount but they do not need very much jollop!

[ellis]

Chain case oil, I never put more than 180mil in and never had a clutch problem either. I also fitted a Yamaha breather elbow into the back of the inner chain case. I can't remember the part no but it was off a small capacity single and no leaks or pressure in the Chain Case.

ELLIS

[chaterlea25]

Hi Bob,
LOL the same thing happened to me when I went down a similar road years ago
I did write a post about it here a long time ago
The felt ring behind the sliding plate will act as a wick once the seal is fitted, I made a cork replacement
Dave Flintoft sells an oil proof sponge type replacement for the felt ring
The replica sliding and some old plates leak between the two rivited parts, and need a bead of sealer run around the joint
To add a breather I used some braided stainless brake hose and fittings and bolted them through the filler plug
It adds a talking point 

John

[Jules]

Interesting post this, I've been going through my bits lately and found an old chaincase outer that had a small hole drilled in the "cavity" where the fill plug/cap screws in ie outside of the seal surface but not obvious unless you look closely, and couldn't fathom why anybody would have done that - maybe this is why!! 

[Tomcat]

Type F is the ATF to use in a motorcycle clutch, Dexron is made to slip a little in car automatics.

[bikerbob]

Thanks for the replies to answer them, for some reason this bike has always leaked a very small amount of oil from the back of the primary  and it is primary oil not gear box oil. I have tried a number of times to cure this renewing sliding plate felt seal new scroll to no avail, I had a 1957 Gold Flash for 16 years with exactly the same set up and it never leaked oil from the primary.

When I modified the sliding plate I removed the rivets and enlarged the center hole fitted an aluminium boss to take the oil seal it also has a brass plate on the back with the center hole only a few thou larger than the gearbox shaft this allows adjustment of the primary chain without putting any load on the oil seal.

The oil is primary oil not gearbox oil  and I do not believe the crankcase oil seal has failed allowing pressue from the crankcase to get into the primary because when standard I was only getting maybe a couple of drops of oil after a run going onto the garage floor whereas with the mod I am now getting maybe a dessert spoonful of oil this I believe is because the primary is now airtight and possibly with everything spinning around in there at speed it is acting a bit like a fan and forceing oil out.

With the temporary bung with hole and plastic pipe fitted in place of the oil filler cap I went for a run and not one drop of oil has leaked onto the garage floor so I now need to a proper breather fitted to the rear of the primary case it has to be small as there is not a lot of room there and the only ones I have seen so far are to big they are approx 2" dia and 2.1/4" longI need something smaller.

[muskrat]

G'day Bob.
One of these little ones will do. https://tinyurl.com/y8w2jsmh or https://tinyurl.com/ybncoto5
Cheers

[bikerbob]

Thanks for that Musky will look into it.