I have a 2001 Bayou 4x4 that I have slowly brought back to life. Current status is that it runs well but smokes (light blue) under heavy acceleration. Light acceleration it seems okay. If I rev it in neutral to about ½ throttle it will produce a steady stream of smoke. At idle sometimes no smoke, sometimes a little after a fast run. So that would normally mean oil rings on the piston as opposed to valves but here is what I checked:

Compression is 160 lbs. I know that compression can be good and oil rings bad
Valves are adjusted to spec
Timing was checked
Leakdown test – This was done on a warm motor at TDC. About 90% air leakage coming from exhaust (at 100psi). In fact if I disconnected from gauges I could actually blow through the hose and get air to come out of exhaust. I double checked TDC and did the test again. Same result. This would typically mean that the exhaust valve is bad.

Here is my confusion. Can a bad valve produce smoke all the time? If the valve wasn't closing wouldn't that show on the compression test? I was expecting if my compression was good and oil rings bad then the leakdown wouldn’t show loss (as the compression rings would hold the air). I was not expecting the valve to apparently not close.

Any thoughts would be appreciated!

 

By your leak down test you know you need to pull the head and repair what's wrong. At this point you might as well pull the cylinder and check the piston to cylinder clearance and have an over size piston installed if the cylinder is able to be bored and the piston and rings are worn.Bad feeling to just repair the head and still have it smoking.

 

I appreciate the reply. I'm trying to tech myself how to diagnose and repair. I know that fixing the valves and replacing the piston and rings will solve the problem. I don't might taking the head off, fixing and realizing that I might have to dig deeper. I'm trying to figure out could a bad valve cause the smoking on acceleration I am seeing or is a bad valve masking the issue with the oil ring and that is why compression is good but leakdown shows valve (perhaps I have a valve and oil ring issue). And could my compression still be good with an exhaust valve that is not sealing properly?

 

Worn valve guide seals or a worn out valve guide itself could be leaking oil into the combustion chamber causing the problem or rings loosing seal against the cylinder wall when warm can cause oil smoking. Or a combination of both.Repairing one area alone is just like doing a valve job on one side of a v8 engine only,usually doesn't work too good for long. Guess I was a tech too long and didn't want to have to tear things back down again. If this is the original piston,you know it and the valves have been working a long time together.

 

Good analogy. I think I will replace valve seals and piston/rings (after having it honed). I won't do the valve guides as (I believe) that requires a lot more work (having them removed and replaced). Based on what I am seeing I believe replacing the valve seals (looks pretty easy) and the piston/rings (not too bad) will solve the problem. Just to confirm I believe all this can be done with the motor still in the frame right (I am thinking yes)

 

In the frame, I really don't know,but if like most engines this size you can. Some Bayou owners on the forum can tell you if it can or a good manual would for sure.