Excessive oil loss through breather, '75

[Cleaner802]

I've had this bike for 2 years now. Last year ran it with worn out rings in the right cylinder and and oil loss out the exhaust. Had the top end rebuilt this spring by a older local mechanic who owned Yamaha dealership and shop in the 70s when these bike came out. Oil loss through the breather began after the rebuild. I've tried different oil levels, inline check valves on the breather tubes, and most recently the Heiden Breather w/ reed valve, to no avail. Pictures include the oil loss after a 10-15 min ride and the oil level in the bike post ride (stick resting on the threads: no oil on the stick, screwed in: oil on front and back of the stick). Bike runs great with some small popping back fire on decel (I know I have crappy pods) Really would like to get this figured out so I can ride this fall.Time to tear it all apart again? Too nervous to go for a long ride with that kind of oil loss. HELP!

 

[jpdevol]

I suspect that the rings aren't sealing causing excess crankcase pressure, but I'd first want a compression or leakdown test. Then I'd want to examine the breather itself to check for misassembly letting too much oil out (there's a screen and baffles in there). I guess you have, in fact, verified the oil is leaving via the crankcase breather?

 

[nj1639]

There's a baffle in the engine head right behind the breather, it's easy enough to overlook during reassembly and frustrating to see it on the corner of the bench once everything is reassembled.
Only way to find out if it's missing is to tear into it. One of the problems of others taking care of your baby.
Not saying it's the issue but......

 

[gggGary]

Yes start with a compression test, then if it's a low a leakdown to see where it's getting out.
https://www.xs650.com/threads/crankcase-vent-using-a-reed-valve.61188

 

[Cleaner802]

I suspect that the rings aren't sealing causing excess crankcase pressure, but I'd first want a compression or leakdown test. Then I'd want to examine the breather itself to check for misassembly letting too much oil out (there's a screen and baffles in there). I guess you have, in fact, verified the oil is leaving via the crankcase breather?

Yes, only through the breather. Original Breather was in good condition, assembled correctly and not missing any parts, and Heiden Tuning breather saw no improvement.

 

[jpdevol]

Yes, only through the breather. Original Breather was in good condition, assembled correctly and not missing any parts, and Heiden Tuning breather saw no improvement.

Well that's pretty crazy! Are you running 20W-50 oil?

 

[Cleaner802]

Well that's pretty crazy! Are you running 20W-50 oil?

Yes

 

[gggGary]

Not much else to say til you get a compression test done. Often the local auto store will loan out a compression tester. Get the thread in style not the rubber tipped type.

 

[cra-z1]

You probably want to do a leak down test along with compression. Then you can tell if its leaking past rings or valves.. Like GGGary says