[Tempest68]

455, sum-2802 cam, 6x-4 heads, stock rockers. Should have been ablout 9.5 static compression.

I did a compression test on my engine, and it seemed i had a sudden drop in pressure on 7 of 8 cylinders (read 105-110psi, 150 on 8th). The head gaskets seemed worn/blown out some, so i replaced them, and also installed new hydraulic lifters(one was going bad). I hadnt tried firing the engine up yet, just tested the compression after adjusting valves now its only 115-125psi, but the lifters werent pumping up since i hadnt tried running it yet (i did presoak before installing). Would the lifters sagging cause that much of a pressure drop versus normal numbers ?(approx 150-180s id assume). Side note, the heads did get some minor milling and stem seals before installing too.
The engine used to run great, then started acting funny one day after getting a little hot, then quit wanting to run at all. Thats why i was pretty sure it was just the gaskets. It had great oil pressure, about 40psi at idle, 65-85 off idle(think it was the higher).
If i need to rebuild hopefully i would just need rings, and probably bearings since id be tearing down that far anyway. If it needs bored, what do you guys think of the Summit/Federal Mogul/Speed Pro rebuild kits, or are there better for the money?

[screamingchief]

A "dry" compression test only tells a fella part of the story,to get more of the story one needs to next do a "wet" compression test,then to get the rest of the story,one really should do a leakdown test as well,that all should be done before tearing into the motor and making any changes.

And it's a pretty good idea to throw in a cooling system pressure check as well,just for good measure.

Your low cranking compression problems could have absolutely nothing to do with the headgasket sealing at all,the problem could be lots of other things.

Proper diagnostic procedures can save lots of headaches,and untold sums of money.

IMO,rare would be the case when headgasket issues would affect virtually all the cylinders all @ once.

Far more likely problem affecting the whole engine after an overheat condition as mentioned would be damaging the rings.

The "wet" compression test,and the leakdown tests both would have made that situation extremely obvious to diagnose via those tests results.

Anyhow,in my experience the lifters not pumping up would likely make it kick out higher cranking compression numbers as SOP,not lower.

That's what happens when you run Rhoads lifters,they'll kick out higher cranking compression numbers vs. a fully pumped up standard hydraulic lifter,as the Rhoads lifters bleed down much easier.

That's also often what you see when cam lobes go flat as well,one (or more) holes way higher than the rest.

So ask me,you probably still have a problem somewhere.

Good luck with this.

Bret P.

[chiphead]

Was the suspect lifter on the #8 cylinder? What was the problem? A worn lifter foot could very well indicate a bad cam or other valvetrain problems. Is a proper adjustable valvetrain installed?

Don't crank on it with those new lifters. I think you need to break those lifters in, assuming the cam isn't already ruined.

[67bonnie455]

I would not test compression on an engine with a new lifters that has not been run to pump up the valve train. Also VERIFY the lifters are set correctly (like you tightened them to 20 lbs, but the needed to be set like a Chevy due to the seats/valves being ground..).

I agree it should be pumping over 155psi with 6X-4s (about 9.2:1) Did it start to use oil or turn it dirty after it was over heated? Was there deposits in the motor?? All bad signs of engine damage.

SC is correct, rings and pistons are most suseptable to over heating damage. If is was my motor, I would run it to get the lifters pumped up and set correctly and then perform a wet/dry compression test. Un hook the distributor power, pull all of the plugs, and with a friend, take a reading on a cylinder while turning over with WOT for 3-4 compressions on that cylinder. Using a pump oil can and a piece of vacuum line on the can, pump several pumps of 10w-30 in the cylinder and take compression again (this is hard on oil cans and your fingers!). If the wet compression is more than 10psi higher, you have ring or ring/cylinder damage. If is it more than 20, it will effect it. If it really pops up like 30+, not good.

If this is indicated, I would put Risolone or another very good pentrating oil like Kroyal in the cylinders and let soak for day. Won't cure scored pistons, cylinders, or rings, but it can help if rings are stuck and not too damaged. It is something to try. Poor wet/dry test can only be really fixed with wrenches and parts.

Best of luck.

[Tempest68]

This is was lead up to the problem. The car ran great, only a few hours time on cam, and oil pressure was great 65-80 psi, engine seemed fresh. When i drove it to my home to do some work, it ran hot while idling too long, about 230-240F for maybe 10 min. After that it did run a few times, but wanted more initial spark, instead of normal 12, it wanted 18-20 to start up and idle. One day it decided it wouldnt run at all. It would fire and sputter then die.

The cam is in perfect condition, arely any wear marks at all, and the engine wont run (the original reason to start diagnosing), so i cant really wear in the lifters. The lifters were set correctly (adjustable rockers, not stock). Ill try a wet test and see what happens. I also had my heads done while they were off, so i need to mill the intake before i can attempt to fire it up again. I did the dry test and rocker adjustments with intake and valley pan off to make sure the lash was right. I did prime the oil system multiple times while testing. Theyres no oil in coolant or vise versa. There was a bit of fuel from the many many times it had been cranked and not run, either trying to start or running tests. Any moisture (spilled coolant from heads, or wd40 to prevent rust) that sat in the cylinders, never drained down past the pistons while sitting for weeks,which gives me hope of a good seal still. Also, the head gaskets were atleast very worn, the reinforcing rings? around the cylinders were almost egg shaped, no longer round. If it wasnt blown, it was probably on its way to. Im just trying to give as much info as i can. I havent had alot of time to work on it.

[ultraman]

Is there any possibility the timing chain jumped?Low compression and having to change the ignition timing point to that.

[El Camaro]

If the wet compression is more than 10psi higher, you have ring or ring/cylinder damage.

Ten; really?