what would cause a instant compression loss?

[marsh63]

well i just did a cylinder head replacement last night. its a 1990 n/t eclipse 4g63 and i had the car running with about 180 lbs of compression across all the cylinders

now today i have 120 across 2 of them and 150 in the other 2 and it wont start. the timing is dead on and the valves are all seating fine. also when i added oil it went up to about 220 in each cylinder

so what is wrong with my car? could this be a headgasket? help me!!!!!!

i only ran it for like 20 minutes after i put the new head on it. im using a 3 layer cometic headgasket.

i have oil pressure so i dont think it killed my cylinder walls.

 

[DSM1G90]

also when i added oil it went up to about 220 in each cylinder

I'd still call it a ring problem since pressure shot up with the oil sealing up loss compression.


From experiences of some mechanics is that when a head is done, the bottom should be done as well since the head is now stronger and exposes tired rings.

How many miles is on the block?

 

[marsh63]

I'd still call it a ring problem since pressure shot up with the oil sealing up loss compression.


From experiences of some mechanics is that when a head is done, the bottom should be done as well since the head is now stronger and exposes tired rings.

How many miles is on the block?

i would have redone the bottom end but i was told before i got it that the bottom had about 50k on it so im lost. im still thinking about switching back to a composite head gasket.

 

[DSM1G90]

They key words here are: "you were told that....50kmiles". NOW, since you have no proof of the actual miles, how was that motor treated from zero to "50k miles"?

On normal driving, I can still see a tight motor. But, if it's been raced, rodded, and not broken in very well, I would then add a hundered or two to that 50k miles.

I'd still look into a bearing and ring job to the bottom.

K, here's another one to ask, or look for: How is your crankcase pressure - tons of blowby coming out of the dipstick hole? Oughta think on this one as well, for if you have excessive blowby, you'd better say "goodbye" to both of your crank end seals for they'll blow super bad with all that crankcase pressure.

Good luck in your finds to get your ride on the road. - DSM

 

[marsh63]

They key words here are: "you were told that....50kmiles". NOW, since you have no proof of the actual miles, how was that motor treated from zero to "50k miles"?

On normal driving, I can still see a tight motor. But, if it's been raced, rodded, and not broken in very well, I would then add a hundered or two to that 50k miles.

I'd still look into a bearing and ring job to the bottom.

one of my moms friend had it. he was an older male. he just got sick of all the little problems the car had. i doubt he drove it hard at all. the interior in it is amazing and the body is straight . the car is all stock.

im not saying that the rings are not bad and the bottom end isnt shot but im just thinking its something else.

i hope its something else cause i dont feel like having to 4g63 motors sittin on stands in my shop.

im going to try a few more things. cause when i had the head off the car everything looked fine and there was no scars or anything wrong with the cylinder walls.

could it be by flooding the motor that i washed out the cylinder walls to get me those compression numbers?

 

[mxer24]

does the oil smell like gasoline? tell tale sign for blow-by due to bad rings not sealing against the cylinder walls correctly. if you do take the bottom end apart, a qucik way to inspect the rings is run your fingers with little to no pressure on the edge of the rings perpendicular to the cross section of the piston. if they feel sharp = bad rings.

 

[hpexperts]

do a leak down test, it would tell if you have bent valves or if you out of timing, bad piston rings head gasket. etc.

 

[matt98eclipse]

do a leak down test, it would tell if you have bent valves or if you out of timing, bad piston rings head gasket. etc.

This is very true definatly do a leak down test but make sure the piston you are testing is at TDC.

 

[marsh63]

do a leak down test, it would tell if you have bent valves or if you out of timing, bad piston rings head gasket. etc.

sounds good ill try to get a tester from one of my friends. man i am hoping for the head gasket to be junk.

 

[matt98eclipse]

Some how my compression went it like a month ago it was 100,115,125,150 and i just did a test last night and it was 135,135,138,150. Its still not the greatest but it will do for now intell i get the money for a rebuild.

 

[92 GSR-4]

Hey Marsh63,

I believe the torque specs on 1G head bolts are 170+ Ft. lbs. Maybe that is your problem. An engine with 120 compression will run. Here is what I reccomend:

1. Check timing. Line your marks up, spin the engine over 6 times, and all the marks should line up perfectly. If not, your timing belt job was bad.

2. Try torquing your head bolts to 180 (stock head bolts). If they are ARP's then make sure they're torqued to whatever ARP specifies.

3. If your compression is still way down, swap the HG for a composite one (like a stocker). Its a NT, and I run 25 PSI on a stock HG with stock (used) head bolts daily. You have no need for a metal HG at this point. Not only that, the composite ones can seal better if your deck isnt perfect.

4. While the head is off, take the head down to the machine shop and have the valves checked for seating issues. Sometimes trash from where they machined it the first time gets into the valves causing them not to seat properly....causing compression issues.

5. If compression is STILL low and putting some oil in the cylinder causes compression to rise, then its time to take the bottom end apart.

Hope this helps, keep us posted!

 

[marsh63]

Hey Marsh63,

I believe the torque specs on 1G head bolts are 170+ Ft. lbs. Maybe that is your problem. An engine with 120 compression will run. Here is what I reccomend:

1. Check timing. Line your marks up, spin the engine over 6 times, and all the marks should line up perfectly. If not, your timing belt job was bad.

2. Try torquing your head bolts to 180 (stock head bolts). If they are ARP's then make sure they're torqued to whatever ARP specifies.

3. If your compression is still way down, swap the HG for a composite one (like a stocker). Its a NT, and I run 25 PSI on a stock HG with stock (used) head bolts daily. You have no need for a metal HG at this point. Not only that, the composite ones can seal better if your deck isnt perfect.

4. While the head is off, take the head down to the machine shop and have the valves checked for seating issues. Sometimes trash from where they machined it the first time gets into the valves causing them not to seat properly....causing compression issues.

any body know the torque specs for a 1g n/t with stock head bolts?

5. If compression is STILL low and putting some oil in the cylinder causes compression to rise, then its time to take the bottom end apart.

Hope this helps, keep us posted!

i just checked the timing and its still dead on. im going to tear into it tomorrow if i get time. but that is alot of torque for the head bolts i think. idk chilton repair Manual said like 48lbs. and the only reason i put the metal hg on is cause i had a extra new one sitting around at my house that i never used due to i need to bore the motor i was going to use it on.

 

[DSM1G90]

the interior in it is amazing and the body is straight . the car is all stock.

...AND that is a keeper right there. You can almost return that vehicle to mint condition and consider it a collectable.

Good luck with it - DSM

 

[JeffGST]

Putting oil in cylinders during a leakdown test are to see if your rings are bad. If the compression increases, it means you got leaky rings.

Not true.

The wet test does not work with DSM's. It only works on pistons that are designed with domes. Our pistons are dish style, so that when you pour oil on the pistons, instead of it dripping out along the rings, it just puddles in the middle of the dish.

A wet test will ALWAYS INCREASE COMPRESSION in a DSM because the oil that is sitting in the dish is now displacing the air in the cylinder. It increases the overall volume of the piston, and you will get a higher pressure reading.

 

[92 GSR-4]

Marsh I'm telling you that torque is too low. Re torque them down to the spec in my manual and see if anything changes. I would torque it a little tighter, but thats up to you. Here's whats in my manual. I think you may have looked at the incorrect torque specs. Hope this helps

-Seth

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[dsm-onster]

45 ft-lbs plus the number of turns he did DOES come out to about the ft-lbs in that manual. You mentioned 140+ ft-lbs earlier and that is incorrect by times 2. And that manual is only good for up to 1992 4g63s. The Mitsubishi published FSM stated that 1993-1994 (7-bolt) 4g63 head bolts should be torqued to 14ft-lbs the 1/4 turn and then one more 1/4 turn.

The mls head gasket has to have a certain sheen (ra) on the surfaces. They have to be clean enough to show a reflection. Did you get this type of finish on your surfaces?

And yes, when I put oil in my cc when running a compression check, the compression ALWAYS goes up, even with a blown head gasket.

 

[marsh63]

45 ft-lbs plus the number of turns he did DOES come out to about the ft-lbs in that manual. You mentioned 140+ ft-lbs earlier and that is incorrect by times 2. And that manual is only good for up to 1992 4g63s. The Mitsubishi published FSM stated that 1993-1994 (7-bolt) 4g63 head bolts should be torqued to 14ft-lbs the 1/4 turn and then one more 1/4 turn.

The mls head gasket has to have a certain sheen (ra) on the surfaces. They have to be clean enough to show a reflection. Did you get this type of finish on your surfaces?

And yes, when I put oil in my cc when running a compression check, the compression ALWAYS goes up, even with a blown head gasket.

thank you. yeah im going to order a new head gasket tomorrow. im just going to go with oem.

 

[vancitydsm]

Ok well there are a few things you can do. Add a bit of oil to each cylinder and crank the car with the plugs out and the fuel pump disabled, ( fuse or connnector in back seat) crank and crank until all that shit is out.. Put a few drops of oil back into the cylinders. Put the plugs back in and try to start with the fuel pump enabled again.. did it work? If not a trick i learned at work was to take off all the spark plugs and attach them to the wires and lay them over the plug tubes, make sure the thread or body of the plug is touching the motor for ground and crank the motor. If you see big flames comming out of each cylinder you have a descent spark/fuel combo. BUT if the spark is not strong enough it would work with the plugs and no compression but with compression the spark sometimes isnt good enough. It has happened to me but in this case i would lean more towards a compression issue. If what i said earlier doesn't help the problem, and you want to know exactly where its leaking from. Do a leak down test. Very simple and effective way of diagnosing. Just set your timing to tdc and #1 cyclinder on compression stroke this means the piston is at the top and the valves are closed. Apply shop air pressure to it and listen for leaks. If no leaks go to next cylinder by rotating it 180* and doing the same to cylinder #3, then another 180* and do it to cylinder #4 and finaly another 180 to cylinder #2. I THINK you have a bad gasket or your head/block are not true enough for the 3 layer metal gasket. IF ITS NOT A RACE CAR WHY PUT RACE PARTS IN?!??! just put a nice thick gasket in im sure its your problem man.

 

[vancitydsm]

Oh ya if you want to skip all that stuff just take off your cams and all your valves will sit, then just apply air into your cylinders and check for leaks. if air leaks outta the oil gallery its fine, thats just some air passing the piston rings. Don't use the hose from a 2 piece compression tester cause the hose usually has a check valve in it.

 

[hpexperts]

Oh ya if you want to skip all that stuff just take off your cams and all your valves will sit, then just apply air into your cylinders and check for leaks. if air leaks outta the oil gallery its fine, thats just some air passing the piston rings. Don't use the hose from a 2 piece compression tester cause the hose usually has a check valve in it.

ye man do a leak down test before taking things apart its easy.

 

[dsm-onster]

. . . If not a trick i learned at work was to take off all the spark plugs and attach them to the wires and lay them over the plug tubes, make sure the thread or body of the plug is touching the motor for ground and crank the motor. If you see big flames comming out of each cylinder you have a descent spark/fuel combo. BUT if the spark is not strong enough it would work with the plugs and no compression but with compression the spark sometimes isnt good enough. . .

Interesting. But basically tuning your engine into a torch can't be good for the masses.

 

[92 GSR-4]

I like all the criticism on this board when you try to help. The information posted before hand indicates a mis-torqued head. On the other hand, a car making 120 compression across the board WILL run. How do I know? My backup car fires up every day, on 120 PSI, and still runs mid 13's with a 16G and a stock sidemount. You be the judge. I recommend re-torquing the head, since a metal HG is reusable. A mirror finish is NOT required to make it seal, especially if you use copper spray, however I still recommend a composite (stock-like) head gasket.

 

[dsm-onster]

You're getting irritated because you and others said the wrong things and get called on the carpet for it. The informtion does NOT indicate a mis-torqued head. It's my job to curb misinformation no matter how well meant.

Like now! YES!!!! A mirror finish IS required for a MLS headgasket to seal properly. The Copper Coat isn't strong enough to seal out the imperfections. It will fail before a stock composite will fail in the same conditions. No reason to install a +$100 headgasket if it isn't better than a $16 special from Partsdinosaur.com. Too many have done this and failed for it to be an acceptable route with a metal headgasket.

But, I do agree that an engine can run with 120psi compression. One of mine runs high 11s as a FWD with 125-135 across the board on a fresh rebuild. I have FP2Xs. So the cylinder filling at 250 (starting) rpms is much lower than stock cams. So, retorquing the headbolts won't help it start again. No matter how high the compression numbers may yield.

Marsh63, why not double check your timing marks? . . . That would rid you of one possibility.

 

[92 GSR-4]

Called on the carpet? What are you talking about? As a wiseman I would suggest using your knowledge to help this guy figure out what he's doing instead of becoming a keyboard Jockey and pushing others who are HELPING around. I wonder how many engines you've built, with a fresh rebuild making only 120PSI compression? Cams wont affect compression buddy...your valves still seal... And yes a METAL HG will seal on a standard finish on the deck surface. I like to rebuild a block without decking a head, and 30PSI on a cometic with some copper spray works just fine...for me. Maybe when you build an engine it doesn't work out that great.

Oh yeah. I said I thought the torque was 170+ Ft. Lbs. It is actually 70+ Ft. Lbs.... I guess I made a mistake, but at least I was close and consulted my manual anyway. You got me. Go have a party, . Care to rip the rest of my post apart, or just try to stick me on 1 typo?

 

[dsm-onster]

I've rebuilt more engines than the age you are acting.

Called on the carpet? What are you talking about? As a wiseman I would suggest using your knowledge to help this guy figure out what he's doing instead of becoming a keyboard Jockey and pushing others who are HELPING around.

I have lent a hand. You've given him misinformation. In the very least, I've pushed away those trying to help that will just fall in the mud with this guy.

I applaud you efforts!

I wonder how many engines you've built, with a fresh rebuild making only 120PSI compression? Cams wont affect compression buddy...your valves still seal...

CLEARLY, you've never even checked the compression of a dsm (or any engine) with a cam swap, have you?

What the He!! is cam timing, duration, and Volumetric Efficiency? Sealing early or seaing later, which affects your top end? Which effects your lowend? What do you consider 250rpms?

And yes a METAL HG will seal on a standard finish on the deck surface. I like to rebuild a block without decking a head, and 30PSI on a cometic with some copper spray works just fine...for me. Maybe when you build an engine it doesn't work out that great.

Just because it worked for you, that doesn't mean that it works for everyone. If you knew ANY thing about rebuilding more than one engine, you would know that what may be ok for one may not be for another. Your job is to guarantee a seal, a proper clearance, a wet start. No matter what.

So what have YOU contributed?

 

[92 GSR-4]

Marsh63, why not double check your timing marks? . . . That would rid you of one possibility.

Wow. That advice sounds familiar? Oh yeah, look at my very first post in this thread. That was my first piece of advice. So does curbing misinformation on this board mean copying exactly what I have already suggested? Or maybe somehow I was wrong by suggesting that and now your right? I'm confused..