failed compression test

[wanna-be]

compression readings as follows: sp1:0 sp3:0 sp5:120 sp7:150 sp2:170 sp4:170 sp6:165 sp8:160.

also #1 spark plug was broken see pix and #2 sp blackened see pix

block is under warranty but need to know problems/causes before i make claim so i can defend claim.

sp-1

sp-1

sp2

sp-2

--------------------


"Good judgment comes from experience, and a lotta that comes from bad judgment"
Glastron 1900 5.7L
2005 Dodge Neon SXT-5speed

 

[Don S]

Re: failed compression test

Timing or lean condition.

 

[rs2k]

Re: failed compression test

Uh-oh. That's not good. The lack of a reading on 1 and 3 say there a problem between them. I'm going to guess here: It could be a completely blown head gasket, or a cracked head. If only cylinder 1 had the low reading I'd guess that the broken spark plug cracked the piston or gauged a big scratch in the cylinder wall. You may also have a hole in your pistons. That spark plug insulator look a pretty white. It could be that precognition caused spark plug damage and put some holes in your pistons.

 

[Don S]

Re: failed compression test

The plug in the second picture looks melted and burned off, not broken.

 

[rs2k]

Re: failed compression test

I think you're right. I was looking at the first image more than the second. It's hard to tell as blurry as they are. I think you might have some holes in your pistons caused by detonation or pre-ignition. It may just be a coincidence that it is happening on two pistons that are right next to each other. What do the other 6 plugs look like?

 

[wanna-be]

Re: failed compression test

Don, your right it looks melted not broken. r2k, theres no air leaks around head nor water and oil is clean. could sp1 over heat and burn hole in piston?

 

[wanna-be]

Re: failed compression test

sp2,4 a little blackened on one side, 6,8,3,5,7 are white. but 1,3 look a little rusty

 

[rs2k]

Re: failed compression test

I really don't think that it's a blown head gasket or a cracked head, but it could be. The only thing that makes me say that is that cylinder 1 and 3 have low readings together and they are right next to each other. What symptoms did you have when the you decided to take out the plugs and do a compression check?

 

[Don S]

Re: failed compression test

You have to do the tests and record things before you take it all apart.
I assume it still runs, if so, start it and get it to idle down to around 700 if you can. Then check the timing. Then speed it up to 3000 rpm and check (and record) the advance timing.
Do a leakdown test on the 2 low cylinders and listen to where the air is going. This won't tell you anything about how the carb was adjusted, and a lean condition will cause your problem.
Then the only thing left is to pull the head and look.

 

[rs2k]

Re: failed compression test

sp2,4 a little blackened on one side, 6,8,3,5,7 are white. but 1,3 look a little rusty

White is very bad. They need to look tan. White means that those plugs are getting way too hot. When running at peak EGT the gasses inside the cylinder can get hotter than the aluminum pistons can stand, detonation also knocks the heck out of the pistons and everything below it. It's like taking a sledge hammer to them. Running too lean on the rich side of peak EGT and/or having too much advance can destroy an engine in short order.

 

[wanna-be]

Re: failed compression test

The symptoms were insufficient power for a 5.7L. The timing is set at 12 btdc at 700 rpms about the same at 1500 rpms. never ck's at 3k.

 

[rs2k]

Re: failed compression test

Assuming you have around around 25? advance than 12? is way to much. You should look at your manual but you usually don't want to go higher than 8? at 700 RPM, sometimes 6? for a higher compression 5.7.

It really depends on what you're getting at 3000 RPM though. What kind of out drive do you have. I'm going to assume that since it's still under warranty it's a newer engine with electronic ignition and fuel injection. If that's so then you really need to check your manual for the correct timing procedure.

 

[wanna-be]

Re: failed compression test

its a 91 model... 2-bbl carb, thunderbolt distrib-no points. 8 is the standard but a mechanic told me to adv to 10 or 12 was ok. alpha 1 od. why are some plugs white yet others are blackend and 1,3 look rusty? where is a guide to do a leak down test?

 

[wanna-be]

Re: failed compression test

read up on detonation/preignition sounds like thats what i got...most spark plugs are white and timing at 12 at 700 rpms, didn't ck at 3000, could be the culprit. if so this ain't covered by warranty...ouch. i guess i'll tear it down and inspect pistons. thanks guys. any other advise you have is appreciated.

 

[rs2k]

Re: failed compression test

It depends on your warranty. If something failed that was not supposed to (like a knock sensor) than it may still be covered. Depending on what you like to call easy, the easiest thing to do is either a leak down test or pull the head. I would personally pull the head. It's not too bad of a job if you can get to the engine easily.

If the engine does not have much run time and nothing got mechanically damaged, all you need to do is tear it down and replace the bad components. It really depends how much of the cylinder wall has worn away. It's possible the engine may have partially seized at some point.


Here's a melted two stroke piston:
http://www.theultralightplace.com/images/piston3a.jpg
http://www.theultralightplace.com/images/piston3b.jpg

Here's a 4 stroke piston:
http://www.max-boost.co.uk/max-boost/images/LET/melted_piston.jpg

 

[dontask]

Re: failed compression test

You have to do the tests and record things before you take it all apart.
I assume it still runs, if so, start it and get it to idle down to around 700 if you can. Then check the timing. Then speed it up to 3000 rpm and check (and record) the advance timing.
Do a leakdown test on the 2 low cylinders and listen to where the air is going. This won't tell you anything about how the carb was adjusted, and a lean condition will cause your problem.
Then the only thing left is to pull the head and look.

No need to pull the head to look, find a shop that has an Olympus style flexible borescope. Pull the spark plugs insert the scope and save the wrenching. If you had the plugs pulled already when you went to the shop the charge should be reasonable. With the block under warranty this is the least intrusive approach to make a direction decision. The warranty holder may want the engine as an assembly not a basket case, if it goes that direction.
The detail on these scopes is amazing, quality enough to use in million dollar jet engine combustion chambers. Plumbers use borescopes, Doctors use borescopes (colonoscopy), mechanics are catching on.

 

[JustJason]

Re: failed compression test

White means the plugs were steamed cleaned from water ingestion. Water would also explain the rust on the electrodes. Was the rust on the same plugs as the no compression cylinders?
Me tinks that you may have a water leak at the intake manifold gasket feeding into those cylinders. It would explain the white plugs, rust, and 0 compression. Now all you need to to is find out if you tuliped some valves or smoked a piston.

 

[wanna-be]

Re: failed compression test

No need to pull the head to look, find a shop that has an Olympus style flexible borescope. Pull the spark plugs insert the scope and save the wrenching. QUOTE]

thats good advice because the warranty prohibits tampering with engine. however i called a few shops and no one has a scope...might try calling my surgeon.

 

[NoKlu]

Re: failed compression test

You have a new motor under warranty, yank the motor and get it to the warranty shop and let them deal with it. Let them make the decision. If they won't warranty the motor get it back and fix it yourself. Did you have it installed at a shop or did you do it yourself?

 

[bruceb58]

Re: failed compression test

I wouldn't yank the motor. What if it turns out to be just the heads? Need to do a cylinder leak downtest to see where the air is leaking first. If its into the crankcase then you will know if it involves the piston or not.