Oil usage 1985 RZ350 US model

[Charliem]

I have an issue with an RZ350 I’m working on. I completely rebuilt the engine newly rebuilt crank all new oil seals and gaskets. I’ve pressure tested the engine and it holds 5psi for at least 10 minutes over the course of 2 1/2 hours it will bleed down to @2-3psi and hold overnight. Engine runs perfectly but sucks quite a bit of transmission oil into the combustion chamber right cylinder when running. I cannot find any cause, as far as I know if the engine holds pressure the right crankshaft seal is solid. Does anyone have any ideas where to go next.

[brrrappp]

you did a pressure test. Did you do a vacuum test? Same as a pressure test but you can use a brake vacuum pump. It sounds like the crank seal is leaking on the clutch side.

[MK]

My last right side crank seal issue could be diagnosed rather easily.
Bike was smoking excessively in rear mirror, though no unusual running noisees or whatsoever.
After a while smoking got back to normal level.

Leaned the running bike to the right side and blipped the throttle : smoke was back.
Leaning it to the left: smoke gone.

At home I did the counterprobe: filled up missing oil and smoke was back without lean angle.

In this case a broken bearing cage had damaged the seal and a complete disassembly was required.

In your case I'd ask, whether OEM Yamaha seals were used or aftermarket. If the latter one, you got my suspect #1.
Then you could have damaged them during assembly.
And last but not least there's the OEM maintenance manual error showing the seal installed the wrong way.
The castellated part goes to the bearing side, but usually it doesn't result in leaking when installed the other way round. (Over the years I have seen and also installed engines both ways and all were ok.)

Besides the seal, there could also be a leak somewhere at the mating case surfaces which should be sealed with Yamabond or similar sealer.
(but I agree that this likely would have shown up in a pressure test)

The really last way to get oil into the cylinder would be the oil pump. You could get the hoses off and run with 1:40 for a while to eliminate that possibility.

[Charliem]

you did a pressure test. Did you do a vacuum test? Same as a pressure test but you can use a brake vacuum pump. It sounds like the crank seal is leaking on the clutch side.

I have not vacuum tested the engine at this time, very rare to hold on pressure test but not under vacuum. But in my long life of building motorcycles/engine I’ve learned never say it doesn’t happen. I will run a vacuum check and report back to you guys.
Thank you.

Update: I vacuum tested the RZ engine today and it will hold 5psi of vacuum for several minutes. However I am not able to pull more than 5.5 psi of vacuum and it bleeds immediately down to 5psi. What is the correct pressure to test vacuum?

[Charliem]

I understand your reasoning, however if it was leaking through the crank case which I did seal with Yamabond it should show up on the pressure test. I have run into the oil pump issue in the past on RD350‘s and 400s but in both those instances oil was being sucked from the oil pump tank past the oil seal on the pump drive shaft into the transmission causing the transmission to overfill and leak out the overflow getting on the back tires. I will however check that. The right side oil seal was an OEM Yamaha seal and it was definitely installed correctly. I will however heck all your suggestions.
Check out my website www.forplayracing.com you can see my latest RD build
Cheers,
Charlie

[kpke]

Nice website Charlie. That is a beautiful RD350 you built. I wish I could help with your oil sucking problem.

Remember this day from 7 1/2 years ago? That was a fun gathering and ride.

https://youtu.be/2rozJw0AbbQ

You should set up another ride

How did this thread end up in For Sale?