Well, Mailman has got a plan (which, needless to say, involves polishing something) and a backup plan involving goopy stuff - and a reversion plan that involves slippery stuff in case the backup plan doesn’t work and finally, if the reversion plan flops and the GD#@#&*# leak STILL won’t stop leakin’, he can admit defeat and go to the hole-smash plan, do what I did last weekend and disguise his bike as a...well, a picture is worth, etc. etc....
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Well, Mailman has got a plan (which, needless to say, involves polishing something) and a backup plan involving goopy stuff - and a reversion plan that involves slippery stuff in case the backup plan doesn’t work and finally, if the reversion plan flops and the GD#@#&*# leak STILL won’t stop leakin’, he can admit defeat and go to the hole-smash plan, do what I did last weekend and disguise his bike as a...well, a picture is worth, etc. etc....
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Pete, that’s my plan D. :D Admit defeat gracefully and just accept my bike for the leaky bastard that it is. :shrug:
 
One had a 750 kit and with both pistons banging down it created a lot of pressure. I modified the vent box and it pretty much stopped it. On the other one, I had used some cheap seals and when they were replaced with OEM they stopped leaking. You can tell if its the case pressure by loosening the dipstick and then taking the bike for a ride. Be sure to tape the dipstick down so you don't loose it and put a rag around it for spillage.
 
One had a 750 kit and with both pistons banging down it created a lot of pressure. I modified the vent box and it pretty much stopped it. On the other one, I had used some cheap seals and when they were replaced with OEM they stopped leaking. You can tell if its the case pressure by loosening the dipstick and then taking the bike for a ride. Be sure to tape the dipstick down so you don't loose it and put a rag around it for spillage.

Well that’s an interesting thought. I made a modification to my breather , I made the openings smaller.
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To try and match the sized openings that the later model bikes had.
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In an effort to try and reduce the oily mess that the breather tubes make under the frame of the bike.
 
By design... and I'll be the first to say it wasn't Yamaha engineers finest moment.. but by design, it's a metal to metal compression seal. The steel inner bearing race seals against the steel spacer.... forced together with a gazillion lbs. of torque on the sprocket nut. When everything's clean and smooth... and the nut's tight, it's an effective seal. More than effective enough to prevent crankcase pressure from overcoming the 100 ft.lbs of torque forcing the sealing surfaces together. If CC pressure was that high, we'd be seeing rubber seals blowing out right and left.
 
By design... and I'll be the first to say it wasn't Yamaha engineers finest moment.. but by design, it's a metal to metal compression seal. The steel inner bearing race seals against the steel spacer.... forced together with a gazillion lbs. of torque on the sprocket nut. When everything's clean and smooth... and the nut's tight, it's an effective seal. More than effective enough to prevent crankcase pressure from overcoming the 100 ft.lbs of torque forcing the sealing surfaces together. If CC pressure was that high, we'd be seeing rubber seals blowing out right and left.

Hmmm I see your point on that. You know, I’m really all not all knotted up about this, to me this is just a puzzle that I’m enjoying working on. I could’ve lived with it the way it was, and may yet still. But if I can stop or slow this leak down then that’ll be a little win for me. As you stated, many things about these old engines were just the engineering of the day. The quirks that we embrace, part of the vintage charm!
 
Seals came from Germany, an EBay seller , calls himself The Kenosha Kid, they are the same seals the factory used. Can’t remember the name right now.
 
You know, I’m really all not all knotted up about this, to me this is just a puzzle that I’m enjoying working on. I could’ve lived with it the way it was, and may yet still. But if I can stop or slow this leak down then that’ll be a little win for me. As you stated, many things about these old engines were just the engineering of the day. The quirks that we embrace, part of the vintage charm!
I'd say stay the course buddy. Your spacer has rough edges. On metal to metal that's more than likely to leak. The (new) spacer could fix that, unless.... it also roughed up the inner race. In which you have 3 choices... replace the shaft bearing too.... try the RTV trick... or live with it. Me personally, I wouldn't live with it. Call it the bulldog.... or the airplane guy in me.... whatever... You're on the journey. See it through.
 
I agree if the pressure is high you would be blowing seals, however if you use the valves I used it would reduce the pressure or put it in a slight negative. I wonder if you could find a thin copper gasket that would fit between the spacer and bearing
 
I wonder if you could find a thin copper gasket that would fit between the spacer and bearing

Yeah. A copper crush washer. Those are used all over the XS650 to seal metal-to-metal joints and that might just work great on that output shaft.

Great call cra-z1!

Pete
 
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