Ichi-SannCoupe

Hey guys i apologize if this is a redundant question but ive got mixed answers through research.

Im doing a complete SR rebuild so i bought a motor with a blown HG and it was tested showing 0 compression. My question is, is it possible to have no compression with just a blown HG or is there other factors involved.(valves are not bent, no holes in pistons). Obviously the machine shop will determine if i will need a new head or block i was just curious because i have heard even with a blown HG there should still be SOME compression.

Mikester

I would 'think' that there could theoretically be zero compression at whatever cyl the HG let go at... but I'm anxious to hear what other, more competent people have to say.

Hopefully you won't need a new block or head; just some machine work.

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ANDY black s13

The HG can blow out between the cylinders and give zero comp readings
but it looks intact in the picture tbh
But I would be more concerned about what looks like detonation damage to the piston crowns, could be ring land area damage/collapse causing the zero comp reading

Ichi-SannCoupe

Yeah the motor had overheated. It just amused me that the head gasket had no visible imperfection . I will be going with forged pistons and nearly everything new , I was just worried about the block and head. I guess machine shop will tell the story. I've also heard that the Hg on the sr is like a "fuse " for the motor and it'll let go in order to prevent any further damage.

Mikester

It can be thought of like that I suppose... I look at it similarly... I'd rather have havoc blasting out from between the head and block vs/ through the head or block if you know what I mean.

Lots of people get upgraded HG's (and there is absolutely nothing wrong with that)... but then crank up the boost; never realizing that adding boost and not blowing stuff up requires tuning

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Ichi-SannCoupe

Yeah so fingers crossed that the machine shop will be able to take care of it, to my naked untrained eyes everything looks fine but we will see. I'm shooting for around 350 to the wheels on pump for a grip set up.

ANDY black s13

Check the exhaust valves for cracks running through the seat to outer edge
,and cracks spreading out from the spark plug hole is another thing I've seen on SR's, either will loose compression
might be worth finding another head from a known not boiled over engine for
future reliability on track

Ichi-SannCoupe

Some more pics, cannot find anything but once again im sure the machine shop will confirm everything. I got an enitre sr motor set for 300 so i shouldnt be complaining, just raised my curiosity as i thought 0 compression would cause some significant damage.

fliprayzin240sx

Which cylinders had 0 compression? Usually when i got SRs that had 0 compression, its usually the valves.

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sabdagr8

From my experience the timing could be off causing valves to be open wen they shudnt b which cud cause 0 compression(happened to me)

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W.I.D.S.I.O

Ichi-SannCoupe

I was told cylinders 1-2 had 0 comp,so im assuming the others werent even tested -__-. The motor was overheated without a doubt, would that cause timing to change?

sabdagr8

No overheating would cause a timing issue I was thinking maybe u had the car apart at one point and possibly could've adjusted the timing wrong, I did that n I lost compression in cylinders 3 and 4 I thought I bent valves be jus to be safe I readjusted the timing and the compression came right back

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Ichi-SannCoupe

Maybe burnt valves would be more relevant in this situation?

sabdagr8

Sounds like it

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OutToWinPAHC

Yah those valves dont look so hot, or I shuld say lookes like they have been very hot. Its really hard to say I dont know what your plan is but. I would clean the piston tops and wipe down the cylinder walls and inspect the hatch and walls in general. if all is well maybe you can get away with a re-ring, rod bearings, and complete head service. Maybe pick up a used head for spare parts or to service. I just had to do the similar to a beat RB20 I got

sabdagr8

Do u know how to test the cables for leaks

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Ichi-SannCoupe

cylinder walls also looked fine, no real gashes or deep scratches of that sort. IF the head is bad i will look into going the VVL head route.

Ichi-SannCoupe

Motor had been sitting for a while and opened. Now just looking for a credible machine shop in my area.