Topic: Oil Coming out of Exhaust

[cb650guy]

Hello All,
I finally gave up on my 1980 CB650C and sent it off to a mechanic.  The mechanic gets the bike running (probably for the first time in 15 years) and oil starts coming out of the exhaust.  He said its fixable but if I know I can't afford for him to do it.  If I wanted to tackle this problem myself where would I begin looking?

Thanks,
Adam

[KingCustomCycles.com]

How long did it run?  I have had them smoke and spew oil for 5 miles or so until it cleared up.  Don't let old oil in the pipe bother you.  The good news is someone may have filled the cylinder at some point in the past to preserve it and you are seeing the results. 

[cb650guy]

I should have been a little more clear.  I got the bike to idle once or twice before I sent it off to the mechanic.  I never let it run for more than 5 minutes and I never saw oil.  The mechanic got the bike running properly and he was running the bike for approximately 15 minutes before oil started coming out.  I wasn't there when it happened but by the description on the phone it was NOT a small amount of oil.

[Hush]

Could be valves or guides are worn and the start-up has begun the oil flow down from the head/cam area.
I would run it a bit longer before passing judgement on the motor as KCC pointed out sometimes over oiling was done for a reason like storage.
The fact that it "runs" means the plugs are not fouling which would be the case if the rings/pistons were shot.
My guess would be an oil "O" ring somewhere has perished with age and will need replacement.

[camelman]

That "oil" could even be from raw gasoline getting into the exhaust.  If you were trying to start it for a while and couldn't get it running, then you have definitely passed a lot of raw gas into the exhaust.  When raw gas mixes with carbon and gets heated up, you'll get an oily looking liquid.

If it were my bike, I'd consider keeping an eye on the oil and running it for a couple miles before passing judgement on pulling the engine apart.

Camelman

[cb650guy]

All of this is great advice.  Thanks guys.

I am definitely going to ride the bike a little before making any decisions.  Any ideas as to why the bike has to run for 15 minutes before oil starts coming out of the exhaust?

Adam

[KingCustomCycles.com]

The oil or fuel mix is laying in the bottom of the pipe and it takes some heat to get it to vaporize and flow out.  That is the 15 minute delay.  If it were a pressure leak, and I don't know of any place that it would exit the pipe, it would leak all the time and increase with throttle (pressure) also, if the oil is very black it is no doubt not engine oil but a mix of oil, gas, water, and carbon.  Run it a few miles.

[Kong]

First off there are very few ways any appreciable amount of oil can get to the exhaust system at all and its particularly hard for it to happen to an engine that keeps on running.  If you have very bad valve guides on the intake side then under deceleration when vacuum is at its highest some oil can be sucked into the intake and if the cylinder is missing like hell then it can pump that oil right on through to the exhaust but in that case the cylinder would not be running - or at least it would have a severe miss and horribly fouled plug.  Bad guides on the exhaust side don't do that because there is no vacuum on that side, there's pressure in fact.  You see the only other possibility is a holed piston or badly broken rings, and with them once again you'd have a bad miss.  Now if it does have the miss this is your best bet on what the problem is, broke rings and a trashed piston.  I can't say if fixing it is within your abilities or tool set, but to be honest about it this would not be a repair that you couldn't not do with a little patience and asking a few questions.  There are much harder jobs and parts should be easy enough to find at reasonable prices.

[MCRider]

There are times in the cycle when oil can be sucked down the exhaust guides into the cylinder and blown out the exhaust. That is because the cam has "overlap" and for brief periods there is suction while the exhaust is open. The CB750 first came out with no guide seals on the exhaust side. By K2 they had them, to clean up the running.

So it could be valve guide seals, intake and exhaust. They get old and brittle with age and don't do their job.

Doesn't explain the delay and other symptoms, but there you go. I would expect an old motor that's been sitting to smoke this way.

Guide seals only are relatively easy. We have discussed here many times the techniques for replacing them without removing the head, just the rocker cover and rockers. Would be happy to cover it again.