Just finished compression test

[talonDSMerr]

From cylinder 1-4: 150, 150, 120, 80.
The car still runs and drives fine, but loses power after 4000rpm. Can worn rings cause compression to drop so much? There are no coolant or oil leaks, but I think the head gasket is blown between cylinders 3 and 4. What other causes could there be? How might I go about fixing? I am kind of torn between buying a longblock and trying to rebuild it myself. In the end, won't they both end up costing about the same amount? Thanks for any input.

 

[toofast82]

Is it smoking blue or white? You may just have a blown headgasket or it could be fried rings

if you had bad rings i would think there would be some blue smoke at some point whether it be idle or acceleration. you probably have a bad hg, i would just replace that if its the case.

could be bent valve or something like that as well, but your shortblock may still be all good

 

[92AWDHX40]

Yes it could be a blow hg, you can loose coolant when it leaks into the combustion chamber and leaves as exhaust. Well rings arent that bad pull the head off, and pop the pistons out. Rings arent that much, change the hg at the same time of course, done.

 

[talonDSMerr]

toofast82 - The engine isn't smoking at all, the exhaust is white, but I think it's because it's really cold out, but I could be wrong.

iugrad92turbo - How can I pop the pistons out without taking out the block? I was also under the impression that whenever I change the rings, I should have the block at least honed.

I didn't think it was anything major (knock on wood). I'll try pulling the head when I get the opportunity and replace the headgasket and check if any valves are bent.

Any tips you might have for when I do?

would the car even be able to run if it had bent valves? Compression is good on the first 2 cylinders, wouldn't all valves get bent if timing skipped?

 

[1_2befast]

Depending on how bad the valve bent it is quite possible that the car will run pretty well. It doesn't take much for a valve to not seat properly.

 

[92AWDHX40]

Ive had 2 dsms and valves bent equal not running. At least in my case, and you can pull the head drop the oil pan remove the rod and bearing caps and push them out from the bottom. Ive done this before.

 

[talonDSMerr]

I think I will keep the stock bottom end intact, I'll drop a cap of oil and do another compression test to make sure the rings aren't shot. I'm leaning towards getting the head machined while it's off and replacing the valves, guides, springs, etc. Then I can just bolt it back in with a new headgasket, and hopefully it'll be good to go.

 

[92AWDHX40]

Good idea, im not sure about the rings but i understand the head ache it can be. Throw some arps on there as well. A bit more than oem head studs. Get a timing belt, balance, and a new tensioner. You should be all set, i put some new lifters so no more ticking. Do it right do it once and its one less thing to worry about. Good luck.

 

[toofast82]

Yeah i would do the test again with oil. If it checks out good, then look into the headgasket, then valves. you may want to get the head leakdown tested and resurfaced for the new hg.

 

[throwedgsx]

Putting oil in the cylinder isn't going to tell you much. Your compression will ALWAYS be higher if you do that. Oil sits in the dish of the piston.

 

[talonDSMerr]

Thanks. I'm crossing my fingers the rings are good, if they aren't I'd have to pull the block because I'd want it honed, and I probably will go for pistons with higher compression, among other things I'd want to get done while I'm there. Just a whole slew of things I don't think I'm prepared for experience- and financial-wise. Thanks again for the tips.

 

[throwedgsx]

How many miles are on your bottom end?
Your rings are probably fine. Are you pushing coolant? Oil in coolant or coolant in oil? Those are your first signs of a blown HG

 

[talonDSMerr]

150,xxx miles on the bottom end. If putting oil in during a compression test doesn't help, how could I find out if the rings are good or not? Last time I checked, coolant wasn't discolored.

 

[throwedgsx]

It'll help a little but you're compression WILL be higher so don't just assume that becuase the compression is higher with the wet test. Do a wet test and see how long it holds compression.

 

[92AWDHX40]

Check the wet test again and let us know, my block and rings were fine when i got i had lotts of miles on it so rings are probably ok.

 

[talonDSMerr]

How long should it hold for? If I do the tests a minute apart, how much should it have dropped if the rings are good? I get what you're saying with how compression will be higher no matter what now, since oil is not compressible, less space to fill.

 

[throwedgsx]

Correct...

Do the test on each cylinder. Get it to your max pressure and time it for a minute and record how much the pressure dropped.

Also your readings on cylinder 1 and 2 are good. If you're rings were bad most likely all cylinders would read pretty constant and much lower than 150

 

[talonDSMerr]

I won't be able to do the wet test for a while, my tools and compression gauge aren't with me and I'll be going on vacation soon. This helped a lot though, in terms of determining what could be wrong. I will most likely leave the bottom end untouched, and send in the head to get resurfaced, machined, and have new valves, guides, and springs installed by a vendor. Looking at FFWD. I'll keep everyone up to date when I get the chance to pull the head and take some pictures.

 

[xlMcMlx DsM]

Leakdown test. That'll tell you where your compression is going. Warm up the car, take off the radiator cap, plug the PCV system, and pressurize the low cylinder. If the coolant bubbles, blown headgasket. If you take the oil cap or dipstick out and hear air, worn rings(some air there is normal) If you open the throttle and the sound gets louder, leaky intake valve seat. If you can hear it leaking in the exhaust, leaky exhaust valve seat. I don't know if that's everything, but that should narrow your problem down.

 

[talonDSMerr]

I got a leakdown tester off ebay and tried to do the test this past weekend. After hooking everything up, the highest pressure I got was 20psi and I could hear the leakdown tester leaking like crazy... $46 down the drain. So I skipped the tester and connected my air compressor to the cylinder and pressurized it to 95psi. I listened for leaks but couldn't hear anything. I also did the wet test again on cylinder 1 and compression rose from 80 to 150, so I'm not suspecting the valves anymore. I'm not sure why I couldn't hear leaks from pressurizing the cylinder though...

 

[talon187]

if you change the headgasket make sure you have the head resurfaced. you could also go with a mitsu 4 layer headgasket with arps its all up to you. When i bought my car the headgasket was changed by the last owner. I had driven it for about to months and then it went again. when the head came off the gssket was fine. the head was way warped so good luck!

 

[talonDSMerr]

I bought the OEM mls head gasket and ARP head studs thinking it was just the gasket, but I'm not burning or pushing coolant or mixing coolant with oil. Also, I thought I'd be able to confirm it if I heard leaks around the headgasket while pressurizing the cylinder, but no, I didn't. So I'm not sure what it is anymore, and I might just run this engine til the end of it's life and replace it with one in better condition when that happens.

 

[91tizzy]

I bought the OEM mls head gasket and ARP head studs thinking it was just the gasket, but I'm not burning or pushing coolant or mixing coolant with oil. Also, I thought I'd be able to confirm it if I heard leaks around the headgasket while pressurizing the cylinder, but no, I didn't. So I'm not sure what it is anymore, and I might just run this engine til the end of it's life and replace it with one in better condition when that happens.

Not a good idea dude...dont ruin a good six-bolt....just break down and pull the head. It will take a weekend and guaranteed you would find the problem...that or get a REAL leakdown tester and do it right. Such a bad conclusion to come to.

 

[JEFFREYCASTGSX]

Thanks. I'm crossing my fingers the rings are good, if they aren't I'd have to pull the block because I'd want it honed, and I probably will go for pistons with higher compression, among other things I'd want to get done while I'm there. Just a whole slew of things I don't think I'm prepared for experience- and financial-wise. Thanks again for the tips.

If you dont want to pull the motor out and just want to replace the rings then you can still do that. Just disconnect the engine mounts, jack it up, drop the oil pan, pull the head, and from there you can pull the piston out. You can hone it yourself. Just know that the main bearing are gonna have to stay. It will also be easier to replace all the other stuff too.

 

[habitatguy187]

Not a good idea dude...dont ruin a good six-bolt....just break down and pull the head. It will take a weekend and guaranteed you would find the problem...that or get a REAL leakdown tester and do it right. Such a bad conclusion to come to.

Definitely man, you don't want to risk doing all that extra work do you? Just take it somewhere that can do a leakdown test, and watch them do it.