Topic: Shifter cover gasket leak... Advice?

[Dunk]

I have a leak at my shifter cover gasket along the bottom. It drips while sitting but while running it will drop more rapidly after a short ride. I had replaced the gasket a while back and it dripped just as bad. I just got my new gaskets and removed the cover and found the enter two screws along the bottom of the cover were a bit wet with oil on the threads. All others were dry. So it does appear to be leaking from this cover. Last time I used a line sander to lightly skuff/flat the cover and lightly cleaned the engine sealing surface by hand with some fine sandpaper. I used a very thin coat of RTV on each side of the gasket.

Not sure if I should try a similar approach again or try the gasket dry? Any tips? It was leaking enough oil that I could not ride the bike for risk of oiling down the tire. Not sure if it could be leaking from anywhere else in this area but I was watching it seep from the lower edge of this gasket while idling on the center stand. Any tips are very welcome! Thanks!

[nancy]

Hi Cadunkle....how about from the big seal behind that....behind the sprocket actually.  Common leak here. Is easily accessed and pried out to replace. Mine leaked all over the floor under my LHS - near shifter - sprayed over the rear a bit. The oil pools here - so maybe u are chasing a leak that starts from elsewhere?
After pulling off the front sprocket I found the seal behind it was slightly out of position. Tapped it back in with a piece of wood and a mallet. Been good for 6 months since. Most would renew the seal...I have short arms and deep pockets.
Regards
Mark

[Dunk]

Thanks for the input Mark. My first thought for this leak after replacing the shift cover gasket was the chain oiler gone crazy. I pulled the sprocket cover and watched there while it ran and found nothing there. Adjusting the oiler out it leaks profusely but all the way in it hardly drips at all even in gear. I did not in fact watch explicitly for the sprocket seal, but I think I would have noticed that. I will double check for a leak around the sprocket seal after I put the shift cover back on.

[nancy]

Another cause of leak in that vicinity is the junction of the Alternator cover and the gearchange cover, where the wiring enters through a rubber gusset/block, wedged into the case. This leaks. I pulled mine and squished in some sealant and pushed the rubber block back into it till it set.

[Dunk]

Thanks, I had not even thought of that. I got the cover back on with RTV on the gasket, will add oil back in the bike tonight and see if I still have a leak. I'll definitely have a closer look at those areas you mentioned, in case it's leaking there and just dripping down making it look like it's coming from the shifter cover. Hoping for the best.

[Dunk]

OK Here's the deal. I think I replaced that gasket for nothing. It isn't leaking there now but at this plug/switch right next to it. Before riding I hit this area with brake cleaner and wiped it all dry. Now this plug is wet and dripping slowly. What is this? Do I replace the whole switch? Is there a seal I can replace?



Also note I went for a ride with my oil cap loosely set on the tank and not turned tight. I get a lot of oil vapor out of the cap while running and if I put the cap tight I get pressure building up. Just turning the cap to loosen it when it goes loose it'll jump up in my hand and hiss as the pressure releases.

After getting back from my ride around town I let it idle in the garage and put the cap on while watching where I found the leak. Within 30 seconds the very slow drip turned into a fast drip and I had one drip of oil from farther back on the right side near the tank. So with everything sealed up it's building pressure and forcing it out any weak spots.

Is the CB750 crankcase vented? Maybe my vent is plugged? Is there a line from the crankcase to the air box somewhere that I should check? Or if the system is sealed does this mean I have a lot of blowby and my rings are shot? The bike seems to run good. Could probably use a carb adjustment and sync to smooth the idle a bit but it runs smooth and has good power. It has 26,780 miles on the odometer.

[MCRider]

That is the neutral light switch. It is installed with an ORing around its body, and sealing against the case. You can replace that ORing. But I give it 50/50 that the switch itself has given up and is leaking internally, to the external.

Put it in neutral, remove that 6mm bolt (10mm head) that holds that tab in place, that holds the switch in. Grab the switch with some open jawed pliars on the flats and wiggle and curse and worry it out. Mostly pull. Others may have a better system.

[nancy]

Cadunkle
In answer to the venting - yes. There is a vent pipe that runs from the back of the lower case and goes to the oil tank (not the airbox) . ..and there is also a vent pipe that runs out from back of the HEAD and must vent to atmosphere..or the airbox...
Mark

[Dunk]

Thanks for the info on that neutral switch. I found a diagram and it looks like an 18x3 oring on there. I was going to just order a new switch but looks like they're about $60 so I'll try the oring first. I'll clean the switch real good while it's out. Hopefully that will do it. I'm getting sick of draining fresh oil and trying to keep it clean to reuse.

As for the venting... That would explain why I'm building pressure. My previous two CB750s had the hose from the valve cover tucked down low where the carb bowls vent to. This one has that hose connected to the oil tank. There is also a smaller diameter line as you said, connected from the lower case to the oil tank.  I'm assuming the valve coer should be vented to atmosphere and the oil tank should also be vented to atmosphere? If so that's how I'll run the lines, and i think I'll be golden after I get this neutral switch leak sorted out.

[nancy]

Cadunkle,
You definately should change that hose from the valvecover so it vents to air!!! That will be a cause of much pressure, released at the whim of your engine and may indeed explain the LHS pooling. I have been there and done that! My bike was spiriting oil from the head also...took me many weeks before I noted the hose connection between head and oil tank! What made it worse, was I was th eidiot who connected it that way!
Other hoses vent as u mentioned. With th epressure reduced - u shouldn't get rear end splatter either.
Regards
Mark

[Dunk]

Alright so I began my quest for an oring. Tried two hardware stores and 3 auto parts stores and ended up getting two 400 piece oring assortments, and stopping by the Honda dealer to order one that will be here next week. Honda says it's 18mm x 3mm but not sure if that's ID or OD,  I'd assume ID. My oring kit has a 18 ID x 3.5 OD and 18 ID x 2.5 OD so figured I'd try it and see if it would work or if I should wait.

No love getting the switch out. The frame rail is in the way, no way to get a socket on there. The oil pan and misc other stuff is in the way to use a wrench. My metric offset (deep) wrenches only go down to 12mm and all my crows feet are standard. I guess there's nothing left to do tonight except play drink the beer.I'll try Sears tomorrow as I need a pair of 1-7/8" wrenches and was planning to go tomorrow to get those. Seems like my plans get foiled every step of the way. I'll have this thing ready by winter, I swear! lol

[MCRider]

Alright so I began my quest for an oring. Tried two hardware stores and 3 auto parts stores and ended up getting two 400 piece oring assortments, and stopping by the Honda dealer to order one that will be here next week. Honda says it's 18mm x 3mm but not sure if that's ID or OD,  I'd assume ID. My oring kit has a 18 ID x 3.5 OD and 18 ID x 2.5 OD so figured I'd try it and see if it would work or if I should wait.

No love getting the switch out. The frame rail is in the way, no way to get a socket on there. The oil pan and misc other stuff is in the way to use a wrench. My metric offset (deep) wrenches only go down to 12mm and all my crows feet are standard. I guess there's nothing left to do tonight except play drink the beer.I'll try Sears tomorrow as I need a pair of 1-7/8" wrenches and was planning to go tomorrow to get those. Seems like my plans get foiled every step of the way. I'll have this thing ready by winter, I swear! lol

I knew it was a bear to get out...and that's with the engine out. Never tried to pull one with the engine in.  Good luck.

[Dunk]

Yes ranger, a '71 CB750... I found my offset 10mm wrench and went at it today. With that I was able to get the bolt out. The switch came right out no trouble, and I immediately found the source of the leak... There was no o-ring on there at all. Buttoned it back up with a new o-ring.

Went to fire it up and leaking all over, fuel out of one of the carbs. Pulled the bowl, float, and needle, and cleaned it. Reinstalled and no leak. Went for a little ride and I don't see any oil leaking anywhere but that carb is leaking fuel again. Not sure if it's float level, bad needle and seat, or junk in it. Oh well, at least it seems my oil leak is fixed. May try cleaning it out one more time and if no dice maybe try to set float level and if no love then a rebuild for the carbs. I'll be happy when I can just get on the bike and ride with no worries.

[gregimotis]

Went to fire it up and leaking all over, fuel out of one of the carbs. Pulled the bowl, float, and needle, and cleaned it. Reinstalled and no leak. Went for a little ride and I don't see any oil leaking anywhere but that carb is leaking fuel again. Not sure if it's float level, bad needle and seat, or junk in it. Oh well, at least it seems my oil leak is fixed. May try cleaning it out one more time and if no dice maybe try to set float level and if no love then a rebuild for the carbs. I'll be happy when I can just get on the bike and ride with no worries.

Stuck floats are a common cause of overflowing carbs.  Installing the bowl gasket slightly crooked is one cause of stuck floats, I believe there is an article in the FAQ about wear on the float bowl hanger assembly causing this also.
Often it only happens only once in a while and can be remedied with some light tapping (screwdriver, flashlight, stone, etc) on the offending carb bowl.