Topic: 1975 CB750 - Grey smoke coming out of right cylinder...

[heylaerz]

Hey guys,
I'm trying to troubleshoot an issue that just started with my 1975 CB750 and I wanted to see if anybody had ideas on what might be the problem. After starting the bike up and riding it for a mile or so I'm seeing grey smoke come out of the far right cylinder where the spark plug goes in and possibly at the connection between the exhaust pipe and the engine. I've checked the spark plug here and both the area around the spark plug well and the plug itself are pretty fouled.

Here's a quick video that shows some of the smoke: http://youtu.be/cV3hCZXZRIY

It also looks like I have an oil leak coming out of the engine between the two cylinders on the right side. I've attached a picture where this can (kind of) be seen. My guess is that this leaking oil is heating up and is causing the smoke after the engine gets hot.

Any thoughts on what might be causing this and where I should start? I've searched the clymers manual and I can't seem to find anything related. Should I check my compression? Do I need to replace the gaskets or is that not likely the issue? I'm willing to learn but at this point I've only done basic mechanical work.  Thanks for the help!

Lars

[bjbuchanan]

Up high could be valve cover gasket or breather/pcv

This leak could clear up after a bit of riding. It isn't a dangerous leak per se so give the bike some good heat cycling, maybe some seafoam and see if magic happens. A lot of the time with bikes that sit the leaks clear up

[Tews19]

I am with BJ... I would be worried about the bolt heads showing that are in the engine.. The ones holding the header on..... You may not want to open up a can of worms by taking the header off.

[bollingball]

I would take the pipes off dig out the old gaskets clean it good to shiny metal and through the bolts in your bolt bucket. Get some studs and nuts and new copper exh. gaskets.
But that is just me.

Ken

[RSchaefer]

Kinda looks like smoke from oil leaking onto the header and burning off, so you need to find the source of the oil leak.  It does not look like smoke coming from the combustion chamber under pressure (#4).  You could let the header cool and then clean off as much of the residual oil around that engine location.  You may have to kinda drench the area with a solvent and use a brush to get down into the spark plug hole, etc. to get all the oil gunk out.  I assume its not a right front fork seal?

Start it back up and let it idle and keep an eye on that location with a high intensity light to see if you can see some oil seeping into this location.

[flybox1]

I would take the pipes off dig out the old gaskets clean it good to shiny metal and through the bolts in your bolt bucket. Get some studs and nuts and new copper exh. gaskets.
But that is just me.

Ken

+1!
studs, nuts and new copper gaskets.
get it really clean once the headers come off.  if it reoccurs, you'll have a better idea of where its coming from.

anything coming from the valve cover gasket area?

[Jerry Rxman Griffin aka MuthaF'er]

Start with the tach cable. The seal could be bad. Work your way down from there. Valve cover gasket. USUALLY an engine removal job! Everything else IS an engine removal job. Head gasket from loosened cylinder stud nuts due to stretched studs. Cylinder stud seals. Rubber sealing 'pucks' under the cam towers. Cam tower studs leaking through.

I'd also replace your bolts with the correct studs.

[heylaerz]

Thanks for the ideas guys. I'm gonna pick up these guys (and a bunch of other stuff) from Dime City: http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-exhaust-parts-muffler-exhaust-gasket-kit-16-5977-4.html

but it sounds like I should also snag new studs and nuts. I did some searching but I'm not sure which I need. Anybody have links on which I should pick up?

As for the actual troubleshooting, the video doesn't do it justice (I'll post another later) but I rode it yesterday and it's got a decent amount of smoke when she gets heated up that looks like it's coming out where the spark plug goes in on the top of the far right cylinder. I'm gonna start by picking up some SeaFoam and some engine degreaser to try and find the leak. Once I trace it, I'll go from there. Let the adventure begin =]

Lars