Leaky Primary

rockitdoc · Sep 14, 2017

I'm running a belt drive primary on my '74 850. Everything is new. I mean a total restoration. But, to my dismay, oil from the crankcase is leaking into the primary past the crankshaft seal. Like, 2-3 ozs when the bike just sits. Should I replace the crankshaft seal (again), or is this to be expected? And, if expected, oil on the belt can't be a good thing, right?
Thanks for any insight in advance.
S

Nortoniggy · Sep 15, 2017

If it's doing it while it's sitting it could be oil in the sump getting down the threads of the inner chaincase to crankcase setscrew. You would have to have a lot of oil in there to be high enough to get to the seal. Over what sort of time does it sit for it to happen? You could try leaving it with sump plug out and a tray to catch oil.

Most belts don't like oil, so you are right to be concerned.

fireballjrd · Sep 15, 2017

Not sure oil is passing through crankshaft sea l : this is very high level of oil . check the 3 screws maintaining the primary case on the crankcase : put some loctite or sealant on them . this solved the issue on my 750.

rockitdoc · Sep 15, 2017

Nortoniggy said:
If it's doing it while it's sitting it could be oil in the sump getting down the threads of the inner chaincase to crankcase setscrew. You would have to have a lot of oil in there to be high enough to get to the seal. Over what sort of time does it sit for it to happen? You could try leaving it with sump plug out and a tray to catch oil.

Most belts don't like oil, so you are right to be concerned.

Good advice. I will seal the threads on the bolts as a first go.

rockitdoc · Sep 15, 2017

fireballjrd said:
Not sure oil is passing through crankshaft sea l : this is very high level of oil . check the 3 screws maintaining the primary case on the crankcase : put some loctite or sealant on them . this solved the issue on my 750.

Great minds think alike. See post prior to yours. Thanks. That could explain it and an easy fix. I will let you know.

o0norton0o · Sep 15, 2017

Higher crankcase pressure contributes to case leaks. Adding a reed valve breather to your crankcase reduces crankcase pressure and usually reduces leakage too.

rockitdoc · Sep 15, 2017

o0norton0o said:
Higher crankcase pressure contributes to case leaks. Adding a reed valve breather to your crankcase reduces crankcase pressure and usually reduces leakage too.

I have the Comstock breather at the rear/bottom of the crankcase. That 'shouldn't' be the issue.

swooshdave · Sep 15, 2017

rockitdoc said:
o0norton0o said:

Higher crankcase pressure contributes to case leaks. Adding a reed valve breather to your crankcase reduces crankcase pressure and usually reduces leakage too.

Click to expand...

I have the Comstock breather at the rear/bottom of the crankcase. That 'shouldn't' be the issue.

Where does it breathe to?

rockitdoc · Sep 16, 2017

swooshdave said:
rockitdoc said:

o0norton0o said:

Higher crankcase pressure contributes to case leaks. Adding a reed valve breather to your crankcase reduces crankcase pressure and usually reduces leakage too.

Click to expand...

I have the Comstock breather at the rear/bottom of the crankcase. That 'shouldn't' be the issue.

Click to expand...

Where does it breathe to?

The valve is attached to the block at the left rear position (block had to be machined to accept the valve) and breathes up to the oil tank.

rockitdoc · Sep 16, 2017

I took out the lowest bolt holding the inner primary to the block. Low and behold, it was oily and it looks like someone had helicoiled it. That would lead to leaks for sure. I cleaned it well with carb cleaner and coated the bolt with high temp, black silicone gasket maker and put it back together. I'll wait til tomorrow to try it out to make sure the silicone has cured, but this 'should' do it. If not, at least I know that the helicoil has to come out and a larger tap needs to go in to fix the threads. Fingers crossed. Stay tuned.

ashman · Sep 16, 2017

Leave the helicoil in it should be right if done right just seal it, not a fan of using silicon but as long as you don't over do it, did you seal all the bolts or just the bottom one.

Ashley

gripper · Sep 17, 2017

I think the three screw threads are are all helicoiled as standard.

ashman · Sep 17, 2017

gripper said:
I think the three screw threads are are all helicoiled as standard.

Yes I through that as well just looked at my old crank case but had to much dirt a crap around the threads to see properly, they been under my work bench for over 10 years.

Ashley

Torontonian · Sep 17, 2017

Shitty thread of bottom 3. Hopefully you installed primary main seal correctly.

Leaky Primary

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