No compression

[pepsi21463]

Well let me start off by telling you what happen in order of events. I was driving on the highway in 5th gear and did a little pull up to about 100mph..maybe 12psi on my GT3082r. My brand new motor has around 1,000 miles on it.

Well I heard kind of a loud pop, and the car got very sluggish. Then I saw the smoke comming out from under the hood and immediately through the vents. I immediately pulled over the car into a parking lot and popped the hood. Not really to my surprise the dipstick was sticking about 4 inches out and oil was all over the place. I called AAA and had the car towed home since I didn't have any cloths or extra oil.

Well today I turned the car on and revved the motor very slightly and heard a knocking noise, only under load. So I quickly checked my PCV and that was working fine, shut off the motor asap and did a compression test.

Going from right to left on the block the test read:
150-150-150-0

The last one never read anything and I tried two compression testers. I saw the piston moving and I felt air comming out of the spark plug hole. I know now I should try a leakdown test but is there anything else I could try, or look for?

 

[xXaTaXx]

Well let me start off by telling you what happen in order of events. I was driving on the highway in 5th gear and did a little pull up to about 100mph..maybe 12psi on my GT3082r. My brand new motor has around 1,000 miles on it.

Well I heard kind of a loud pop, and the car got very sluggish. Then I saw the smoke comming out from under the hood and immediately through the vents. I immediately pulled over the car into a parking lot and popped the hood. Not really to my surprise the dipstick was sticking about 4 inches out and oil was all over the place. I called AAA and had the car towed home since I didn't have any cloths or extra oil.

Well today I turned the car on and revved the motor very slightly and heard a knocking noise, only under load. So I quickly checked my PCV and that was working fine, shut off the motor asap and did a compression test.

Going from right to left on the block the test read:
150-150-150-0

The last one never read anything and I tried two compression testers. I saw the piston moving and I felt air comming out of the spark plug hole. I know now I should try a leakdown test but is there anything else I could try, or look for?

Similar to the (very very very) unfortunate problems happening to the guy who wrote this-
http://vfaq.com/mods/kill.html It sounds like you've probably blown your piston rings or cracked your lands.

EDIT: That knocking noise is probably the combustion blowing-by the piston (I'm not sure so don't quote me on that)

You can still 'feel' the air moving because even with broken rings/lands, the incoming air will be moved towards the top of the cylinder (large surface area of piston head). But, without a complete seal around that piston, as soon as the air meets resistance (closed spark hole by comp. gauge or spark plug), it will blow-by the piston and therefore making that cylinder unable to acheive even 1psi.

Assuming you listed those compression numbers in CYL1-CYL2-CYL3-CYL4, so I'd have to say you probably need the CYL4 Piston removed and at a most likely replaced (since you've run that motor after this incident). Hopefully that piston hasn't messed your bore/hone on the cylinder wall.

--
Good luck
Chris

 

[pepsi21463]

The problem is this block has been rebuilt several times. To my knowledge the previous owner never rebuilt it, but this will be the third time we've had to open it up. After the first two builds the car was brought to a much better DSM mechanic. I'm wondering if all that maching on the block eventually took it's toll and the piston rings suffered. Is that possible?

 

[GVR4592]

If you have 0 compression, something is really messed up. I broke all of the ring lands on a piston and still had some compression. My guess is there's either a hole in the piston, or the valves are bent/broken.

 

[pepsi21463]

Would bent/broken valves cause my dipstick to shoot out?

 

[GVR4592]

It depends on what happened in the bottom end. If the valves hit the pistons hard enough anything can happen. Do you have balance shafts?

 

[pepsi21463]

No, they were taken out during the rebuild.

 

[autonut]

Is it possible that you threw a bearing? Ive repaired 2 that when the rod bearing went, the piston then was able to move up higher than it should and bent the valves, and then no compression in those cylinders. Knocking noise under load almost sounds like a rod bearing. Doesnt take much of a rise to collide with valves with the tight tolerances you guys are putting in these motors.

 

[pepsi21463]

Well it doesnt sound like rod knock. My first rebuilt motor had rodknock and that had a pretty distinguishable sound. This really isnt a knocking, it's a quiet, heavy, knock. Not has fast as a regular rod knock.

I'm going to pull off the valve cover and check if a rocker arm busted off and a valve got stuck open.

 

[autonut]

Yeah, you're right, a rod knock is usually pretty fast. Main bearings can knock too, but not with the frequency of the rods. Never heard a broken rocker before, just a collapsed lash adjuster and that is more of a heavy tap tap tap. Hope you find it.

 

[1997GST]

have you at least pulled the spark plug yet for that cylinder to determine if it's a piston/ring. Floated valve sounds like the case to me. I've cracked ringlands before and rings, they still give a little compression. A lost valve will yield none for sure. I figure if it was a cracked cylinder it would effect another one too. I don't know how the 4g63 takes to losing sleeves tho.

 

[pepsi21463]

have you at least pulled the spark plug yet for that cylinder to determine if it's a piston/ring. Floated valve sounds like the case to me. I've cracked ringlands before and rings, they still give a little compression. A lost valve will yield none for sure. I figure if it was a cracked cylinder it would effect another one too. I don't know how the 4g63 takes to losing sleeves tho.

Yeah I pulled the spark plug, thats how I did the compression test...

Heres some pics after I pulled the valve cover. I'll have better ones tomorrow, it doesn't look like anything is too bad.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

 

[pepsi21463]

Much better pics... As you can see the valves look okay, but how bad would my piston rings have to be for me to get 0 compression?

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.