CB350 Left Crankcase Cover Oil Leak

[spazzyfry123]

Hello all. I've a '71 CB350 I picked up a couple months ago that I've been tinkering with in the garage. After diagnosing a few small issues, I have a big issue with the left crankcase cover leaking oil that I cannot seem to rectify.

Quick back story...
I first realized the leak from the lowest point of the cover after about 10 miles of riding. I parked the bike and noticed a decent amount of oil around the kickstand. Essentially, the oil is leaking from the cover, hitting the frame, and running down the kickstand. If the bike is cold, nothing leaks. The bike only leaks once it has warmed up and is running (both while running and after it is cut off). It seems like it is a combination of thermal expansion and pressure buildup from the crankcase causing the leak.

Assuming a bad gasket, I picked up a Honda OEM paper gasket. After cracking the cover, I see it is all RTV or similar - no paper to be found. I do the normal checks and cleaning and reinstall in a "star" pattern. I "torque" the phillips down using a manual impact driver without going too nuts. All surfaces are smooth and free of debris. I crank it up and ride a couple more miles - leaking worse than before.

Okay... So I tear it back apart and use the black RTV in combination with the paper gasket. This time I spend about 2 hours or so replacing this gasket to make sure I'm not overlooking something. Zero debris left on any faces, all surfaces are straight with no apparent deformations. I reinstall and tighten a bit past finger tight to allow the RTV to cure slightly for ~15 minutes or so then I crank down in the "star" pattern once again. Let the bike sit about 24 hours before I fill up with oil and crank it up. It is essentially raining oil out of this cover now. The leak seems to be coming more towards the clutch cover side instead of the lowest point of the crankcase cover. I've given a video to show just how bad the leak is.

https://youtu.be/SPnEK8eAD8I

I'm at a loss. Has anyone else experienced this? My final guess is the alternator wiring which goes through its rubber grommet on the cover. With that said, the rubber is in good shape and is fitting in the cover just fine. As I understand it, this cover isn't necessarily an oil reservoir whilst running, but more of an expansion tank. Is this true?

Another set of eyes or opinions on this would be great. What are your thoughts? First "obvious" problem causer would seem to be mismatched surfaces, but it all seems true.

Thanks!
-Tyler

 

[Barnburner]

As I was reading I was planning on suggesting the grommet/seal on the wires coming from the stator into the chain case, but it sounds like you've inspected that already. While the alternator area doesn't hold oil it is open to the case in spots and thus some gets through and gets flinged around (which makes timing with a strobe messy unless you have a modified cover). I'd also check the oil seal around the gearshift spindle (Part 14 below). I had this leak on my CL175 last year and it caused a steady drip of oil. It would collect behind the chain cover and pour out when I put the bike on the side stand. My only other thought would be perhaps your left crankcase cover is warped. Have you tried putting it on a perfectly flat surface (like glass) and checking for warpage?

 

[carnivorous chicken]

Also check the O-rings that are on the three mounting bolts for the cover.

 

[xb33bsa]

SHIFT SHAFT ,CLUTCH PUSHROD OR C/S SEALS
DO NOT USE RTV , NEVER use it or silicone anywhere that oil is involved
and if you use it anywhere else it must be allowed to fully cure 24 hrs ,2 hrs is not nearly enough time
how can a perfectly flat clean gasket surface with a new dry gasket leak ? the answer is it can;'t , so then you move onto another cause
also check the breather hose for kinks or blockage

 

[spazzyfry123]

As I was reading I was planning on suggesting the grommet/seal on the wires coming from the stator into the chain case, but it sounds like you've inspected that already. While the alternator area doesn't hold oil it is open to the case in spots and thus some gets through and gets flinged around (which makes timing with a strobe messy unless you have a modified cover).

Surely there isn't enough oil in the crankcase cover for the bike to continuously leak for quite some time after the bike is turned off (meaning not flinging around oil as the internal bits are stationary) if the wiring grommet was the culprit? That seems to be too high up on the cover to leak as badly as it is if this cover isn't acting as a reservoir.

I'd also check the oil seal around the gearshift spindle (Part 14 below). I had this leak on my CL175 last year and it caused a steady drip of oil. It would collect behind the chain cover and pour out when I put the bike on the side stand.

This is too far back on the bike and in a different compartment, no? The leak is originating from the big left crankcase that covers the alternator (which is a separate cover than that of the shifting assembly's: the clutch cover)

My only other thought would be perhaps your left crankcase cover is warped. Have you tried putting it on a perfectly flat surface (like glass) and checking for warpage?

No, I have not taken the cover off. In actuality, I didn't figure out how to disconnect the wiring from the cover. Any pointers on this? I didn't really try all too hard to figure it out, but I don't have the bike here in front of me as I waste time on the internet at work right now. I am seriously hoping that if something is warped, it is the cover and not the casing.

 

[spazzyfry123]

Also check the O-rings that are on the three mounting bolts for the cover.

Just to make sure we're on the same page, this is the entire left crankcase cover that is leaking, not the smaller one that has "Honda" printed on it. It is leaking from #1 on the image below, not #4.

 

[spazzyfry123]

SHIFT SHAFT ,CLUTCH PUSHROD OR C/S SEALS
DO NOT USE RTV , NEVER use it or silicone anywhere that oil is involved
and if you use it anywhere else it must be allowed to fully cure 24 hrs ,2 hrs is not nearly enough time
how can a perfectly flat clean gasket surface with a new dry gasket leak ? the answer is it can;'t , so then you move onto another cause
also check the breather hose for kinks or blockage

The RTV was cured for 24 hours before any oil was entered into the system or the bike starting up. I'll be tearing it back apart tonight hopefully. Definitely getting tired of buying new oil, though Side note, "C/S seal" is?

Where is the breather hose? Again, I'm sitting here at work and trying to think off the top of my head. Are you implying that if this is blocked that it is causing too much pressure and oil is being "pressed" out of the gasket somehow?

 

[xb33bsa]

pressure buildup is not likely to push past a fresh new gasket on a nice clean surface more likely past a bad gasket or bad seal
if the breather is somehow blocked then some pressure will build with heat,and pressure can be generated right on startup if there is significant blowby past the rings,this would be seen as smoke coming out the breather hose
the hose it is under the tank coming off the valve cover the black hose about 9/16 diameter
c/s =countershaft the transmission output shaft there is a major seal behind the c/s sprocket and it is holding back oil which is being pumped there in the system
pull the sprocket cover off,clean the area maybe pull the sprocket as well fire it up and look for leek some talcum or flour will help spot the leek

 

[carnivorous chicken]

Just to make sure we're on the same page, this is the entire left crankcase cover that is leaking, not the smaller one that has "Honda" printed on it. It is leaking from #1 on the image below, not #4.

Nevermind -- I was thinking stator cover. Brain fart.

 

[Barnburner]

I don't think enough oil would be generated from the grommet to cause a continuous leak. I agree with xb33bsa that pressure caused by a blockage may make a poorly sealed area (whether from a bad gasket or a warped cover) leak more than it should. I also like the idea of cleaning everything really well with a degreaser then drying it and dusting flour all around the installed left crankcase cover (including behind the sprocket/clutch/chain cover) and trying to pinpoint the leak.

 

[spazzyfry123]

Unfortunately life has taken priority, and I haven't touched the bike in forever it seems. While this leak has been tearing at my heartstrings, it has me thinking that if the cover is warped (has to be, right?), what type of surface finishes are typically recommended for the machine shop given the OEM paper gasket is being used?

 

[xb33bsa]

we already explained how to find the leak,a warped coved is not your problem use some flour or foot powder to find the leak there is no reason to keep pulling off the stator cover except to clean off all the RTV.RTV , never use it on oil containing cases

 

[Tune-A-Fish]

8) Most likely the one on the right. if the one behind the flywheel/stator your in luck! you could have a fresh motor when yer done!... Just kidding it's likely the little one in the middle, find the kit and doemall