7M-GTE No comression Cyl 2 and 5

[raven]

The only thing I can think of is BHG but "Zero Compression?"
I have recently completed a BHG repair. HKS HG, ARP studs. after I finished it idled fine, ran fine except for some boost leak that I hadn't tracked down yet. I travel out of town for the weekdays so I left it with the Mrs. to drive around. She called me after 2 days saying that it would not start. I could hear on the phone, that it would catch, then immediately sputter out. Then all of a sudden, it caught and ran fine. The coolant low light was on so I had her add a little. Only took 3/4 of the reservoir to top it off. She ran errands for a few hours that day, and then again the following day. Saturday morning, I go out to have a look see, and it's sputtering out immediately again. With the accelerator on the floor, it will catch and run and stay running as long as I keep the RPM's above 1200, but as soon as the accelerator is released it dies. No visible smoke from the exhaust, but a heavy "Rich" smell.
I noticed some coolant leaking from the "Turbo return line?"( the line that runs from the turbo to the top back of the thermostat housing). When loosening the radiator cap, there is substantial pressure in the radiator, yet it is still cold.
Ok, so this is obviously another BHG right? Pressure is being introduced into the coolant system via a blowout between a cylinder and a water port.
I remove the plugs to perform a compression check, all plugs are dry. Now if I've got a BHG bad enough to introduce that much pressure into the cooling system, then surely I would have some coolant pulled into the offending cylinder?
I progress with the compression check. All plugs removed.
Cyl 1 - 175
Cyl 2 - 0 ( I checked this by removing and reinstalling the guage line 3 times)
Cyl 3 - 180
Cyl 4 - 185
Cyl 5 - 0 ( I checked this by removing and reinstalling the guage line 4 times)
Cyl 6 - 185

I removed the valve covers to see if maybe the timing belt had jumped. Nope.

When it runs, although rough, there is no audible evidence of a broken valve, rod or piston.

I have never seen a BHG so bad as there would be ZERO COMPRESSION

Coolant color - nice rich green
Oil - No mayo, foam or discoloration
Clues - None

I'm open for any ideas?
It's my only option right now for a chariot for the Mrs. and I am having to rent a car until I get this resolved. I will yank the engine again if I have to, but I'd like to be able to explain the symptoms before committing to that project again.

I really appreciate any ideas.

Thanks

 

[jdub]

Did you deck the block? Or, at least check it for flatness?

Was the head decked and a valve job done?

Do you have access to a bore scope?

 

[crisp]

A little puzzled by the #2 AND #5 at the same time, but a STUCK VALVE will give ZERO compression. (Dropped seat, etc... or otherwise stuck valve... but why TWO cylinders? Still thinking...)


BHG can AND WILL show "0", but it'd have to be a pretty bad BHG to "0" on BOTH cylinders, I'd think!


G/L as you diagnose and repair...


-crisp

 

[raven]

Did you deck the block? Or, at least check it for flatness?

Was the head decked and a valve job done?

Do you have access to a bore scope?

No to all 3

It blew the original HG directly between cyls 4 & 5, and never overheated. I left it sitting for a couple of years hoping to get time to pull the engine and do a complete rebuild. Unfortunately my wifes car failed, and I was pushed to try a repair instead of a rebuild.

I would expect that if it indeed blew another HG, then that would be the cause, I am just trying to reconcile the symptoms against what looks like the only answer. Man a bore scope would be nice.

 

[jdub]

My $$$ is on a BHG. The HKS MHG's are not tolerant (at all) of a standard machine deck surface...they require a RA spec of 30 or less. If the block or head decks were not perfectly flat, it definitely will not seal. Looks like you get to do the job again...if you are not going to get the block decked, I suggest you use an OEM composite HG. There's a 90% chance the head deck will require machining...I can just about guarantee it's not flat.

 

[raven]

Fair enough jdub. I read enough to know that I was taking a substantial risk by not pulling it and having the surfaces decked. Any theories as to where the compression might be going?

Thanks

 

[rayall01]

Fair enough jdub. I read enough to know that I was taking a substantial risk by not pulling it and having the surfaces decked. Any theories as to where the compression might be going?

Thanks

Coolant passage most likely.