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2.5L DOHC Head Gasket Failure *PICS*


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109 replies to this topic

#101 Tech1967

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Posted 08 February 2007 - 07:36 PM

Looked at my block again today. The passenger side is even worst but the thermal inequality would appear to be front and back which would explain why that side will show oil at the front corner too.

Had an interesting conversation with my machine shop about my heads. I left everything to their descretion and they planed the head because of the grooves the sealing rings cut. Told me Toyota guys were JB welding the grooves in the block during assembly for the same issue. I'm splitting the block and taking that to be machined too. It just barely made spec for flatness. Hope to hell it goes back together without too much trouble.:dead:

#102 nipper

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Posted 08 February 2007 - 08:19 PM

You've had plenty of time to consult your library, any facts on this?


I have been researching this alot, across all boards. It seems something happened in the mid 90's where HG failures started showing up on many makes. Some engines were as small as 2.0L, others were V-6's (honda toyota GM chrysler subaru to name a few).

http://www.babcox.co.../us/us80222.htm

I tend to agree with this with one addition. Open deck/Hybrid deck design all came into fashion starting in the 1990's. Even honda has had an issue with it.

Look at this

http://hondaswap.com...sed-deck-64559/

Look at the dramatic difference between open and closed. A hybrid is a open deck with more support.

The alarming thing is that ALL theories for all open/hybrid deck design leans to lack of support of the cylinder liners or complicated dynamics involved to make a system that seals.

In my professional opnion, early HG failure (below 40,000 miles) is a probelm of supporting the sleaves, and or an assembly issue at the factory. Anything above that is the Sealing dynamics of the gasket itself.

From a nissan Performance site:

"The weak point of the VQ (nissan) block is its open deck construction and freestanding bores. Nissan did this so the cylinder top end would be more evenly heated to reduce hydrocarbon emissions. Open decks also lend themselves to die casting better. The bad part about this is when the engine is loaded hard, the unsupported cylinders walk around compromising head seal and eventually cracking from the pressure."

What happened is that the theory got ahead of the technology with the open/hybrid deck. In Subaru they finally got the combustion chamber to seal properly, but the sealing forces were lower around the edges of the gasket. I don't know what causes it to happen on the same place externally every time.

The Gasket technology just wasnt up to the job. Now all across the board HG failure has almost disapeared. Its taken almost 10 years to come up with a good head gasket.

It's been a very long learning curve. Not only do they have to redesign the HG, but they als have to make sure it doesnt interfer with emissions.
Once en engine is certitifed, they can make lower emissions on a change, but not higher emissions.


Just my observations and thoughts.


nipper

#103 grossgary

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Posted 08 February 2007 - 10:30 PM

another reason for failure. trying to play games with materials. the mid to late 90's dodge engines (neons) with cast iron blocks and aluminum heads were a materials engineering failure. they blow headgaskets worse than any subarus.

#104 nipper

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Posted 08 February 2007 - 10:52 PM

another reason for failure. trying to play games with materials. the mid to late 90's dodge engines (neons) with cast iron blocks and aluminum heads were a materials engineering failure. they blow headgaskets worse than any subarus.


I heard that if you have a neon, expect to blow a HG. Its so bad every one will need to be replaced at some point.

Problem isnt a steel block, its a steel open deck block. Steel blocks and aluminum heads have been around a long long time.

nipper

#105 WAWalker

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Posted 09 February 2007 - 10:10 AM

So rather than stopping the cylinder movement they have come up with a magical moveing gasket design.:) Sounds good to me. Would seem that this gasket is keeping up with the cylinder movement in the SOHC engines. Now they just need to refine it a little so that the fire ring and water jacket areas of the gaket can move independently of one another.

As far as the DOHC engines go, I will have to see it to believe it. I'm sure it looked good in the drafting program, real life has a way of finding the weak points.;)

#106 nipper

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Posted 09 February 2007 - 10:56 AM

So rather than stopping the cylinder movement they have come up with a magical moveing gasket design.:) Sounds good to me. Would seem that this gasket is keeping up with the cylinder movement in the SOHC engines. Now they just need to refine it a little so that the fire ring and water jacket areas of the gaket can move independently of one another.

As far as the DOHC engines go, I will have to see it to believe it. I'm sure it looked good in the drafting program, real life has a way of finding the weak points.;)


Untill emissions change again and we have another 8 years of growing pains.

nipper

#107 WoodsWagon

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Posted 14 February 2007 - 06:10 PM

, and or an assembly issue at the factory.


I'm leaning a bit towards this option. I have noticed on both the EJ25's Ive taken apart, a 1998 and a 1997, that the lower center headbolt seems like it isn't nearly as tight as the upper center headbolt. This is on both sides of the engien. The two center headbolts are supposed to be cranked tighter than the 4 end ones. This might be part of the problem, somehow the headbolts weren't torqued right on assembly.

#108 nipper

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Posted 14 February 2007 - 07:46 PM

I'm leaning a bit towards this option. I have noticed on both the EJ25's Ive taken apart, a 1998 and a 1997, that the lower center headbolt seems like it isn't nearly as tight as the upper center headbolt. This is on both sides of the engien. The two center headbolts are supposed to be cranked tighter than the 4 end ones. This might be part of the problem, somehow the headbolts weren't torqued right on assembly.


They were correctly done at the time. BUT (big but) for some odd reason (read sarcasim) Subaru changed the torqing method of the head bolts. So i wouldnt call it an assembly error, as much as an engineering error.

nipper

#109 WAWalker

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Posted 14 February 2007 - 08:17 PM

The change in the torque procedure didn't really change anything. In the end you get the same result.

#110 nipper

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Posted 14 February 2007 - 08:27 PM

The change in the torque procedure didn't really change anything. In the end you get the same result.


i didnt say it fixed the problem :-p

nipper




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