So had my car dynoed th eother day. 66 nova with LQ4 and a BW S475. After did a few pulls on the freeway as anyone would. When I got home, I noticed crankcase smoke coming from my catch can. I pulled all the plugs and they are fine. I put fresh ones in and the smoke still puffs constintly. I drove the car around a bit, the power seems fine, no missing or anything but it still keeps puffing this smoke. Its more that usual, im not just being worried about nothing. So last night I pulled the hoses off of the catch can, 1 per valve cover, it seems the smoke is only coming from the driver side. I pulled the valve cover and started the engine to see where the smoke was coming fro, it seems to be coming from the crankcase area. So then I did a compression test on the driver side, and all cylinders were between 100 and 118 besides #3. 3 is at 91. Still not a HUGE difference. I checked the pushrods and they are all straight. HMMMMM.

Broken ring land
Blown Head Gasket
Bad Valve

Whitch one guys? [/SIZE][/SIZE]

 

BTW: The motor was built for boost using factory parts. Gapped rings, headstuds, etc...

 

If you have the stock pistons still, I am going with a crack in the piston between the top and bottom rings...

 

Compression difference between cylinder #3 and the other high one at 118 (we compare compression differences from the highest to the lowest) is 29.6% Id say that is pretty HUGE.

Sounds like that is your problem.

 

I understand, all I was refeering to is if it still is at 90 psi then I dont think it could be a broken piston. If the piston was broke, I would think I would see around 50 psi or less.

 

Looking at the facts here....The smoke is coming from the valve cover? Pull the valve cover and take a look.

If you had blow by, a cracked pistons, etc etc. You would have a loss of power, smoke through the exhaust...I don't think thats the issue.

#3 compression is concerning considering the other 7 are 118.

 

I completly agree. The car idles, sounds, and runs perfectly. The #3 compression is making me wonder too. Maybe the smoke I see is water vapor? Blown head gasket possible? There are no other signs of a blown head gasket though. weird.

 

If it is a head gasket it wont last long.

 

Pull the head and take a look. You would only need a gasjet at that point u already gave head studs

 

Im going to throw a boroscope in there after work today. The only problem is if the ring land hasnt come apart yet then i will not be able to see much since I cannot see the cracks that would be on the side of the piston. Too bad there isnt an xray machine for engines!

 

It was rebuilt using new or used stock pistons? Did they hone the block? If so what was the piston to wall clearance?

 

Do a leak down test. You should be able to hear where the air is escaping too. If the piston is cracked, you should be able to hear the air coming out of your oil filler with the cap off...

 

This, a leak down will tell you what's going on very quick.