Anyone ever blow a HG, yet have no visual signs it was blown?

VadersV6

Active Member
Joined
Sep 9, 2004
In case you saw my other post about oil out the dipstick tube...
Ive got the heads off, and I'm planning on getting them decked since someone decked them with a sander. I had 130-135psi in all cylinders, cold motor, except #5 which had 60psi. I pulled the heads, and see no obvious sign the HG was blown. All the pistons have quite a bit of slop in the cylinder. The cylinders are a little ovaled out from the piston skirts, but just barely enough to have worn away the cross hatch just in that area. I really dont have engine rebuild money and Im really hoping for a HG issue. I poured a bunch of oil in that cylinder, and not a drop has seeped past the rings in 2 days. Maybe the oil ring is good and the top ring is broken...who knows. But the main question is, has anyone blown a HG, or better yet, replaced a HG and the problem, whatever it was, went away even though you saw no sign whatsoever it was bad?
 
In case you saw my other post about oil out the dipstick tube...
Ive got the heads off, and I'm planning on getting them decked since someone decked them with a sander. I had 130-135psi in all cylinders, cold motor, except #5 which had 60psi. I pulled the heads, and see no obvious sign the HG was blown. All the pistons have quite a bit of slop in the cylinder. The cylinders are a little ovaled out from the piston skirts, but just barely enough to have worn away the cross hatch just in that area. I really dont have engine rebuild money and Im really hoping for a HG issue. I poured a bunch of oil in that cylinder, and not a drop has seeped past the rings in 2 days. Maybe the oil ring is good and the top ring is broken...who knows. But the main question is, has anyone blown a HG, or better yet, replaced a HG and the problem, whatever it was, went away even though you saw no sign whatsoever it was bad?


vader have you checked the cylinder head/ valves on the cylinder thats low? could be a vlave stuck open just the ever little bit. along did you do a leak down on that cylinder with the rocker assembly off the head. might be a lifter holding the valve open jus ever so slightly.

HTH
Pat Broughton
 
Use some kerosene instead of oil in the cylinder, it is thinner and will find a bad ring. Try the kerosene in the intake and exhaust ports to find a bad valve, if you do not have a spring compressor. Post a few pictures of your head gaskets, there might be failure that you do not see, that someone may be able to see? A leak down would have told a better story, as stated above. If the cylinder holds kerosene, then I would suspect a bad valve, also. A flat cam would also cause low compression in a cylinder, as the engine isn't breathing properly.
 
One of the first things I did, was pour some windex in the combustion chamber of the bad cylinder, and it didnt seep at all. I cleaned up the heads last night and took a closer look. I popped the valves out and checked them out a bit. The point where the exhaust valve pinches down in diameter is pretty smoked...like exhaust temps were way higher than they ever should have been. The exhaust valve seats on the passenger side are all toast. Not toast from being fried, but from having way too many valve jobs. The heads look like they've been rebuilt at least 6 times. The heads have been surfaced beyond the scrap mark. The seats were done with stones, and done many times. One of the exhaust valves are sitting alot deeper than the others (causing alot of lifter preload, but this isnt the bad cylinder). The valve is so much deeper than the others, I would suspect it had 30 pounds less seat pressure than the others. I really havent checked the cam, but I would expect a cam would have to be pretty flat to lose half its compression, so why didnt it run like it had a flat cam....
 
Maybe I'm missing something but what does a cam going flat have anythign to do with compression?...during compression stroke both valves are closed...has nothing to do with a flat cam...low compression is usally caused by:

1) blown HG
2) bent valve
3) bad(damaged/broken) piston ring
4) hole in piston

...probably some others but I think those are the common ones
 
Nevermind...thought about it more and if the intake lobe was gone the amount of air being pulled in would be lower thus lower compression...
 
Having a flat lobe will lower compression, if it's wiped out enough. If the valve is only seeing .100 lift or so, the cylinder cant fill very much and will lower the reading. I have a strong feeling the pan will have to come out and so will a piston and rod.
 
If a cam lobe was that flat though it would be very obvious just by turning the motor over...the rocker would barely move...
 
I have a strong feeling the pan will have to come out and so will a piston and rod.

Brent I have a feeling the whole motor will have to come out, I know your trying to avoid the unavoidable, just yank it and do it right, your a smart guy dont let it get ya and do a cobble wobble cuz you'll be back to square one in a few months.

I know youve expressed your feelings on just offloading the whole damn car but with the economy. 1 you might not get any offers anytime soon and 2 you might not get another one anytime soon and if you sell it and get stuck driving a used honda prelude....well

I got set of 8445 heads sitting here..there yours for shipping

40 over slugs were offered as well from betminesfaster

The save Brent foundation
 
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