Blown HG again??

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ATL240
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Blown HG again??

Post by ATL240 »

My car won't start! So I checked the compression and it is very low (30-60psi) on pistons 1,2,3. Piston 4 has normal compression. The car was having overheating issues the day before but nothing bad enough to blow a HG. The oil/coolant are not mixed either. what else could it be?
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Post by nismoautoxr »

put a couple capfulls of oil in each of those low cylinders and rerun the compression test.

Also when you are running the compression test , take the rad cap off and see if it appears that compression is getting intot eh cooling system . Most times it will puff out if its that blown and check for funny blowby at teh valve cover too.
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Post by NateDogg »

Oil and coolant mix and blown headgasket are not mutually inclusive...is it a stock motor? Maybe it's ring lands...
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Post by ATL240 »

Thanks nismo, i'm gonna check it better in the morning. What do you mean by "blowby at the valve cover"?

NateDogg: It's a KA-t with a cometic head gasket, built bottom end, stock head, arp heads & main studs. Was running 13 lbs of boost on a t3/t4

What's confusing is the car was running great the night before, then in the morning it lost so much compression that it wont even start.
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Post by NateDogg »

Forget the cometic and go with a Felpro.
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Post by nismoautoxr »

by blowby I mean anything that is positive pressure in the crankcase. There should not be pressure puffing out the valve cover ever but say if you have a problem with the rings or ring lands...it would be allowing pulsating pressure to go to the crankcase past the rings there by producing what is known as blowby.
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Post by ze12o »

Was your head and block decked? The cosmetic gasket requires a stupid flat surface. Look into felpro for cheapness if you want mls go for crawford.
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Post by basic »

the cosmetic cares more about surface finish than flatness. you could have a perfectly flat block and head with a crappy surface finish and still have issues. The surface finish matters.
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Post by ATL240 »

The head gasket IS BLOWN. I have blown a felpro and a cometic HG with this motor. So if I wanted to go with cometic again I would have to get the head AND block decked/refinished again? Which I would have to pretty much rebuild the whole motor again. Or just the head?? Please help me out, I really want to do this the right way. I want to run 20 psi on a t3/t4.
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Post by nismoautoxr »

bottom line is there is something wrong whether it be the block deck finish or the straightness of it , or the head being warped or possibly trying to reuse some hosed bolts .

Dont know anything about the motor as far as what bolts/studs/cr etc but I personally have had no problem with felpro gaskets so long as everything is straight and they are not as picky about the finish on the surfaces like the cometic is . Ive never used cometic because I have never seen the need to in my applications but just my personal opinion,,,,composite head gaskets worked for ages before cometic existed . Just a little food for thought. G/L
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Post by ATL240 »

nismoautoxr wrote:bottom line is there is something wrong whether it be the block deck finish or the straightness of it , or the head being warped or possibly trying to reuse some hosed bolts .

Dont know anything about the motor as far as what bolts/studs/cr etc but I personally have had no problem with felpro gaskets so long as everything is straight and they are not as picky about the finish on the surfaces like the cometic is . Ive never used cometic because I have never seen the need to in my applications but just my personal opinion,,,,composite head gaskets worked for ages before cometic existed . Just a little food for thought. G/L
How much power are you running with the felpro? And it has ARP head studs torqued to FSM specs. JE pistons with 9:1 compression ratio. So to check the straightness of the block can I do it myself or take it to the machine shop? Thanks for the help!
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Post by sdaigle240 »

nismoautoxr wrote:There should not be pressure puffing out the valve cover ever
i dont know what worth this post is but the valve cover always puffs air out. clearly you know your stuff from your posts but it puffed on my tired motor, it puffed on my rebuilt motor, it puffed on my blown motor. certanily more so in blown form but it always moves air. id love to have my pcv port bigger then the VC to make that the path of least resistance.


was there machine shop work between all these HG failures? sure is a lil fishy. personally.... if you really think it crapped out from sealing and not warping, i would slap a felpro at it and run it. i just put together a motor to run low 400hp/tq and went felpro myself. somethings up though ive "slapped" several felpros on with no issue.
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Post by NateDogg »

ATL240 wrote:The head gasket IS BLOWN. I have blown a felpro and a cometic HG with this motor. So if I wanted to go with cometic again I would have to get the head AND block decked/refinished again? Which I would have to pretty much rebuild the whole motor again. Or just the head?? Please help me out, I really want to do this the right way. I want to run 20 psi on a t3/t4.
If you want to run 20psi you'll need meth injection, e85 or race gas.

I wouldn't run more than 15psi on pump gas alone. Gas isn't what it used to be...

BTW my engine makes 450whp on a felpro and arp 10mm head studs with meth injection and 94 octane.
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Post by ATL240 »

sdaigle240 wrote:
nismoautoxr wrote:There should not be pressure puffing out the valve cover ever
i dont know what worth this post is but the valve cover always puffs air out. clearly you know your stuff from your posts but it puffed on my tired motor, it puffed on my rebuilt motor, it puffed on my blown motor. certanily more so in blown form but it always moves air. id love to have my pcv port bigger then the VC to make that the path of least resistance.


was there machine shop work between all these HG failures? sure is a lil fishy. personally.... if you really think it crapped out from sealing and not warping, i would slap a felpro at it and run it. i just put together a motor to run low 400hp/tq and went felpro myself. somethings up though ive "slapped" several felpros on with no issue.
YES. After I rebuilt the motor I put a felpro. Blew at 20 psi. Then I took the head and the machine shop checked it. Cleaned everything up, and put a cometic. ran it for a while at 7psi, no problems. then it blew at 13 psi. So I don't know what to do know.
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Post by nismoautoxr »

Im only speaking form my personal experience with felpros and have never been at a higher boost level than 15 and somewhere in the neighborhood of 275-300 at the tires.

When I said puffing I guess I should be more specific . When you leak compression to the crankcase like say you have a bad piston problem then the puffing wil be substantial plus you would see it in you boost guage if it is mechanical and that is the context to which I said that , but that is beyond our HG discussion .

In your original post you said that #4 was the only cylinder that showed correct compression so I thought that maybe the cylinders were washed or the engine got extremely hot and relaxed the rings which is why I said do wet test with a little oil to try and isolate that suspicion.

Rule of thumb for checking deck straightness is to take a straight edge and lay it across the deck of the block (thoroughly cleaned block) and check to see if you can fit a feeler guage under it anywhere. Industry standard seems to be .003" is bad but I dont trust myself or a straightedge enough . If I really wanted to cure my problem I would take the block and the head and timing covers to a trusted machinist and have him check it all .
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Post by sdaigle240 »

can always grab a leak down tester to see if its the rings. that really sucks man, sounds like you took the time to do it right and it still didnt work. i guess at this point its try the felpro bandaid or pull it all out and start over.
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Post by adamky »

Call me skeptical, but I can't see a Cometic gasket being destroyed with only 13 psi, even if you had massive amounts of detonation. A cometic is a strong gasket, and when installed properly, it's not going to "blow" easily at all. You're more likely to destroy a forged piston than blow a Cometic MLS HG.
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Post by azS13 »

from what I read the cometic wasn't installed under the near perfect conditions everyone claims they need. OP said he had the machine shop check the head after he blew the felpro...
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Post by adamky »

Very true. If the cometic wasn't specifically machined to a smooth surface of 50 RA or better, then it's likely to leak. The people who have problems with Cometic typically never had the surface properly prepped. I'm going to assume it's just a badly leaking headgasket and possibly another issue. Cometics don't "blow" easily. Only way to really tell is take the head off and check it.

Also, what are you torquing the head studs to?
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Post by ATL240 »

adamky wrote:Very true. If the cometic wasn't specifically machined to a smooth surface of 50 RA or better, then it's likely to leak. The people who have problems with Cometic typically never had the surface properly prepped. I'm going to assume it's just a badly leaking headgasket and possibly another issue. Cometics don't "blow" easily. Only way to really tell is take the head off and check it.

Also, what are you torquing the head studs to?

You are right, I never told the machine shop I was going to run a metal HG. So i'm guessing it blew because the surface was not 50 RA.

I'm taking off the head tomorrow and getting it checked by my machinist, also checking the block with a flat surface. Going with a felpro and hoping for the best!

And i'm torquing to FSM specs.
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Post by nismoautoxr »

doesnt ARP give a specific torque when using their stud kit?? Im just wanting to know for personal consumption . Typically the studs I have installed for other people have manufacturer specific specs that differ from the FSMs torque specs .

Also , I have not used a cometic nor do I care to google it but do you guys use any type of spray on these gaskets such as high tack on installation . I can remember when the whole DSM and chrysler 2.0l headgaskets used to leak oil and they switched to the MLS gasket we had to use a tacky spray on both sides of the gasket per their instructions. Thats the reason I ask that .
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Post by sdaigle240 »

arp head studs are 62 ft lbs iirc

for cometic, many people use copper spray. supposed to work well.
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Post by nismoautoxr »

thanks for confirming that . I know I have on just about every MLS I have installed but that is on factory installed MLS gaskets such as Hondas and DSMs and have not had a problem
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Post by ATL240 »

I was thinking this could have been happening because of the head lifting in boost. It would only overheat when I hit boost. Should I torque the head studs to 70 lbs?? I'm working on her right now.
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Post by NateDogg »

I torqued mine to 75 and I think I might be pushing some coolant...it's weird because I did a 0-120mph run yesterday and it didn't push any coolant but some days I see it leak a bit out the top of my circuit sports overflow tank. Maybe its from cornering really hard...I dunno.

Have you bled the system properly with the front end in the air and the hvac fan on full hot?
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Post by ATL240 »

NateDogg wrote:I torqued mine to 75 and I think I might be pushing some coolant...it's weird because I did a 0-120mph run yesterday and it didn't push any coolant but some days I see it leak a bit out the top of my circuit sports overflow tank. Maybe its from cornering really hard...I dunno.

Have you bled the system properly with the front end in the air and the hvac fan on full hot?
Yes, I bled it, and took the thermostat out. I got the head out tonight. Talk about back pain!
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Post by adamky »

I used copper spray and torq'd the studs to 80. I've run up to 15 psi, and even had audible detonation one day, and mine is holding strong.
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Post by sr20drag »

We've run a felpro to 19psi on 93 pump with 10mm head studs torqued to 80lbs and copper spray for 2 years on a KA-T. felpro requires 70ra not 50.
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Post by project-c2 »

I just blew my Cometic HG running 21 psi boost. I don't blame the HG though. I readily admit to not checking surface finish, although, I just checked straightness and had no more than .001" wrapage. Gonna use a FelPro perma torque.
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