Strange compression test results after overhaul

ElectronVTEC · Jan 10, 2003

It just only gets worse before it gets better

Before my new head/headgasket I tested compression
4-1 - 150 - 130 - 155- 150

Leakdown showed it to be partly rings, partly headgasket, so I left the rings and decided to change the headgasket. I changed the gasket with the motor out so it wasn't exactly hard, used a 4-layer mitsu metal, with ARP studs -torqued at 80 ft-lbs in 4 steps, proper sequence.

Now that everything is back in, I get:

4-1: 155-155-120-120

What in the hell... cam timing is spot on, base ignition is spot on, car won't idle for crap and stalls upon throttle input (after it's been revved to about 2000 RPM). Only pulls about 4# of vacuum at idle. Now, it's been brought to my attention that the head I used might have had some bent valves... nothing horrible (not that I could tell by lookin at it at least) but the possibility remains. I was under the impression (after searching for the last 2 hours, heh) that I'd get almost no compression at all if I had bent valves, is this true? Second, a buddy of mine "assembled" the valvetrain in this head and it was his first time. He went by the manual but still, could this possibly be a cause? I've decided i'm gonna just rip out this head and HKS cams and re-install my old head with factory cams until I sort out this problem, then re-install the new cams later. Any help or advice would be appreciated, we're all stumped over here. Thanks again, Todd.

ijsaul · Jan 10, 2003

I would leak down test it again to try and figure this one out. Depending on "how bent" the valves are you may only loose down to 120 I suppose... How did the valves get bent supposedly? 120 on two right next to each other after 150 in them would usually sound like HG.. Good luck. -Ian

darktalon92 · Jan 11, 2003

The fact that your 1&2 results are both 120 leads me to believe that yes you have slightly bent valves. Do a leakdown test and listen in the exhaust pipe for bent exhaust valves and intake for bent intake valves.
I had the exact same situation, the two lower cylinders were both 140 and they were both side by side, and the leak down test I did told be bent exhaust valves. I finally took off the head and sent it in to get decked, cleaned and newer valves installed, the machine shop said in fact bent exhaust valves in those cylinders, how they got bent? maybe just carbon deposits on the piston tops, who knows, I bought the car like that.

All it takes is a very slight bend so that they don't seat propaly, visually they will look fine, I looked at my old valves when they came back from the machine shop and they all looked fine, yet they weren't.

Now for your stalling, well bent valves that still pull 120 on the compression will not cause the car to pull 4 on the vacuum and stall. My car ran just fine, but it did idle a little rough. You may want to check your timing marks again, I thought mine were fine when I put the head back on, yet they were 2 teeth off giving me a lumpy idle and 9 on the vacuum, plus higher compression. You might also have a vacuum leak, maybe a vacuum hose was left off. Just do a intake leak test to find out if you have an intake leak.

If I were you I'd do an intake leak test to see you have a vacuum leak, if nothing comes from that then I'd check your timing marks again, I know its a bitch to have to take the timing belt cover off again, but you may have to do it.

Hope this helps.

ElectronVTEC · Jan 11, 2003

Well, I did a leakdown and got 4-3-2-1: 5%, 7%, 55%, 45%... the exhaust was a hummin when I did 1 & 2, and I could hear it in the I/M with a stethoscope. The head is almost completely off now, so I'll see exactly what's goin on soon, probly tomorrow. I know for a fact i don't have a vacuum leak, I've tested up to 40 PSI WOT and i get nothin, it holds air for quite awhile. The timing marks seemed fine, but we're redoing the timing belt so that will be redone as well. I also found out my new front main seal that I got with my front cover is leaking... wtf, i'm starting to hate this car. That's all for now, thanks for the help! Todd.

colonelfox · Jan 12, 2003

Welcome to the world of DSM's. Here, have a tree. :tree:
The belt could have been off a tick, but that wouldn't have been enough to bend a valve.

ChrisAWD · Jan 12, 2003

well, i'm glad you removed that suspect head. I had a head installed which I now believe had at least one bent valve(it was rebuilt from a SHITTY ass machine shop, that cuts corners). Anyway, after 500 miles a valve broke halfway up the shaft, fell into the combustion chamber and smashed the shit out of the top of the head, and cracked the piston in half. luckily the cylinder walls miraculously came out unscathed.

also, remember you can't reuse that headgasket. I've gone through like 4 hg's in my car and 2 of them had less than 500 miles.

ElectronVTEC · Jan 13, 2003

Results: 1 bent exhaust valve in both 1 & 2. Shine a light in the intake port, you can see a nice line where it's bent back, it's also got some burrs in it, not sure how that all happened. Tomorrow i'm ordering a new timing belt and the standard mitsu head gasket (was going to re-use the metal one, but i pitched it anyway

) Could these bent valves cause the low vacuum it was pulling? I would think since they were not closing i would be in constant overlap (leakdown was 55% in 2, 45% in 1) and not able to hold much compression. 120 does seem like a lot for compression in terms of holding vacuum but I still think this was causing the rough idle. Any thoughts? TIA, Todd.

colonelfox · Jan 13, 2003

It would cause a rough idle yes. It would also cause compression to leak out the bent, unsealing valve, causing a low vacuum. They could be bent just enough to cause a small leak, but not enough to cause a total leak before the cylinder makes a complete stroke, and recompresses.
Why not reuse the metal gasket? They're reusable as long as it's not bent.

ElectronVTEC · Jan 13, 2003

it's not bent at all, I was just told not to re-use it. Hell the car has basically just idle'd with it on, so I'm not really sure. Either way though, it's worth the $70 or whatever to just use a new gasket so i don't have to do it again. Can I get a witness in heya

Thanks, Todd.

Brandon92DSM · Jan 13, 2003

unless you really feel you need a metal HG, its best to just use a stock one with ARP studs.

Im glad you found your main culprit, but a fraction of the blame could also be sent to the metal HG. (which I think you mentioned.)

You didnt happen to say if you had the head and block re-surfaced. If you didnt, its very possible your metal HG didnt seal properly anyway. They are much less forgiving as far as imperfections in the mating surfaces compared to a stock (softer) gasket.

92tealTSI · Jan 13, 2003

Brandon92DSM said:
You didnt happen to say if you had the head and block re-surfaced. If you didnt, its very possible your metal HG didnt seal properly anyway. They are much less forgiving as far as imperfections in the mating surfaces compared to a stock (softer) gasket.

Thats what I was thinking. I can honestly say I think the metal HG is reusable, but it would suck if you reused it and it ended up just leaking. Good to hear you found out you had some bent valves (well its not good, but good that you found the problem). Hey man, if you ever need help working on the car, give me a PM, id be glad to help you out

ElectronVTEC · Jan 14, 2003

Well, both the head and block will be well cleaned before the new metal gasket goes on. Since I was only at 5-7% leakdown in 3/4, I gotta think that HG was doin it's job like it should. Time will tell, and I don't anticipate needing a new HG before the new turbo goes on and well... um... i'd rather have the insurance

. Thanks again for everything guys, and Brian keep in touch man. Todd.

92tealTSI · Jan 14, 2003

New turbo eh? Which one do you plan to go with? I thoguht you were gonna max out the 14b?

Mike

Strange compression test results after overhaul

ElectronVTEC

ijsaul

darktalon92

ElectronVTEC

colonelfox

ChrisAWD

ElectronVTEC

colonelfox

ElectronVTEC

Brandon92DSM

92tealTSI

ElectronVTEC

92tealTSI

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