Okay,

I have a 90 miata with a 302. The engine was rebuilt before installing, ordered aluminum heads pre-assembled springs and valves. I chose to use an edelbrock intake and 600 carburetor.

The right bank at idle smokes out the tailpipe. When I hit the gas, the smoke stops. Any Ideas as to what would be causing this?

 

Wrong ring gap , rings upside down, rings not seated , valve guide bad , valve seal bad Pick one?

Also pcv system may be sucking oil in some bizarre way.

 

Working PCV system ? If pcv system is all good I would bet money on valve guides or possibly a cracked head. Any power loss issues ?

 

If it was the rings it would smoke all the time no ?

 

Hi,

Ok diagnosis should be as follows:

If the engine was rebuilt then the following tests will reveal the culprit. I am putting my money on a valve stem seal, since the smoke stops when you push the gas. but lets do the tests...

1) Just to be sure do a compression test on all cylinders (good to see if the rings have all sealed properly) but start on the bank that smokes (if any cylinder is low say over 20% lower than the others it is likely rings)
2) After that with the engine running, disconnect a spark plug wire one at a time and then see if the smoke stops (this stops the oil from burning) on any particular cylinder
3) If you identify the cylinder in question and the compression is OK. Then its the valve stem seal. These can get nicked on install or maybe faulty or the little spring slipped off and it wasn't picked up on install.

The rectification is easy and can be changed with the head on the car..and cheap about 1.5-3 hours start to finish when you have found the dud cylinder.

cheers