Compression Test Results, What Now?

[JT87NA]

Well I was having excessive blowby from my PCV system and some other problems with the oil draining from my turbo oil return so I decided to do a compression test. Before the compression test I did a block test for combustion gases in the coolant system and it came up Negative so no BHG. These are the results
Cyl 1: 180
Cyl 2: 180
Cyl 3: 60
Cyl 4:180
Cyl 5: 180
Cyl 6: 155

After the first test I tested all cylinders again and came up with the same results.
I tested cylinders 3 and 6 again after pouring a teaspoon of oil in the cylinder. The results were
Cyl 3: 65
Cyl 6: 175

So my question now is where to go from here. I am thinking something has to be wrong with the valves on Cylinder 3 for compression to be so low. Cylinder 6 is most likely the piston rings. I know at the very least I have to pull the head and inpect the valves that coincide with cylinder 3 but what should I do about the 6th cylinder? Also when I do pull the head do I have to resurface both the block and head? I already have an hks 1.2mm mhg and arps.

 

[evildoer]

well you shouldnt have to resurface the block but always should have the head inspected and resurfaced if nescary but it sounds like your ready for a valve job number 6cyl might be rings tho hard to say it jumped up quite a bit after oil

 

[IJ.]

JT: Has it ran lean or detonated?

Sounds a bit like the ring lands have collapsed in #3

 

[JT87NA]

No it hasn't been running lean. I have an lm-1 wideband. It was reading 10.5:1 at WOT. I just purchased a leakdown tester to see exactly what is going on. Hopefully number 3 is just a valve. I did have one of my shims spit out by some Gude cams I had installed, I forget which cylinder it was though, maybe the valve on cylinder 3 is bent and not sealing properly.

 

[IJ.]

No it hasn't been running lean. I have an lm-1 wideband. It was reading 10.5:1 at WOT. I just purchased a leakdown tester to see exactly what is going on. Hopefully number 3 is just a valve. I did have one of my shims spit out by some Gude cams I had installed, I forget which cylinder it was though, maybe the valve on cylinder 3 is bent and not sealing properly.

<fingers crossed it's something simple like a valve!>

 

[drjonez]

doubtful it's a valve prob if you're still getting 65 psi. sounds like a BHG or cracked piston to me....

 

[JT87NA]

doubtful it's a valve prob if you're still getting 65 psi. sounds like a BHG or cracked piston to me....

Is the car still going to run fine with compression at 65 and a cracked piston. I can't hear anything out of the ordinary and it seemed to be running stong, seemed is the key word. Thanks Later.

 

[JT87NA]

I just purchased a leakdown tester so I guess I will use that and try to figure out where the engine is leaking(ie valves, rings). The 7M is so damn frustrating. If I were to find out that the piston rings in cylinder 3 and 6 are the problem could I just replace the rings and pistons in those cylinders if needed? Any other advice is appreciated.

 

[drjonez]

i hardly think the 7M is your problem. ANY car and ANY engine w/the age + miles of your current one is going to give you problems....

 

[JT87NA]

i hardly think the 7M is your problem. ANY car and ANY engine w/the age + miles of your current one is going to give you problems....

It is a rebuilt engine from ATK with 17,000 miles on it and MHG w/ ARPS. Sorry for not clarifying.

 

[drjonez]

did you do a compression test after break-in?

 

[JT87NA]

did you do a compression test after break-in?

Nope, really wish I would have. The engine has a 3 year 100,000 mile warranty on it so I am trying to see if it is covered or not. But they will probably give me some bullshit about lack of oil or something like that so the warranty won't cover it. I never ran the motor low on oil, but who knows. Hopefully the leakdown tester gets here soon. Later.

 

[IJ.]

Best case would be dead valve but I still think it's collapsed the lands

DrJ makes a good point about running a comp test after break in, this will show any problems before they become BIG drama's (I mention this for any of the guys with reading this as it's too late for JT).

Big hassle with boosted motors is even if they're laying down they still make good power in an NA once it hurts itself it's very noticable not so with a Turbo to mask the pain!

 

[JT87NA]

Best case would be dead valve but I still think it's collapsed the lands

DrJ makes a good point about running a comp test after break in, this will show any problems before they become BIG drama's (I mention this for any of the guys with reading this as it's too late for JT).

Big hassle with boosted motors is even if they're laying down they still make good power in an NA once it hurts itself it's very noticable not so with a Turbo to mask the pain!

Sorry if this is a noob question but what do you mean by collapsed the lands? Right now I really can't decide what to do. First off I have to wait for ATK to see if they might warranty the engine, if that doesn't happen then I either have the choice of rebuilding or just buying a shortblock and throwing my head back on.

Edit: Is it the indentations in the piston that the rings slide into?

 

[IJ.]

JT: The Lands are what the ring sit on and pushes down, if a motor detonates sometimes they snap off!

Even if they don't snap they can squish down this traps the ring so it can't expand against the bore and you get low cylinder pressure!

A really bad case is when someone has used a ring groove cleaner and cut a bit hard, Motor detonates piston breaks then goes up piston starts coming down and the top of the piston + rings stays at the top until the next firing stroke then it's all over!

 

[JT87NA]

JT: The Lands are what the ring sit on and pushes down, if a motor detonates sometimes they snap off!

Even if they don't snap they can squish down this traps the ring so it can't expand against the bore and you get low cylinder pressure!

A really bad case is when someone has used a ring groove cleaner and cut a bit hard, Motor detonates piston breaks then goes up piston starts coming down and the top of the piston + rings stays at the top until the next firing stroke then it's all over!

Would I hear any strange noises with the engine running if this were to be the case?

 

[JT87NA]

Btw I just want to thank both IJ and Dr. Jonez for helping me out and giving me gppd advice, I probably could figure the shit out on my own but it helps alot having knowledgeable people giving you their opinions. Later

 

[IJ.]

JT: You're very welcome!

nah no real noise when the lands collapse but your leakdown tester will pick it up!

 

[JT87NA]

Thanks IJ, my leakdown tester should be here by next Friday so I guess I will know what is going on. Do I just listen to the exhaust, intake manifold, oil dipstick port and valve cover ports to diagnose how the air is escaping? For example if it is an exhaust valve then I will hear air escaping out the exhaust? If it is the pistons and rings where will the air be coming from, I am guessing the oil dipstick. Thanks guys. Later.

 

[IJ.]

Yep if it's pisons/rings you'll hear it from the dipstick, you could test it now just take the oil filler cap off and run it!

You'll feel it by putting your hand over the hole!