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Discussion Starter #1
Well it seems ive either cracked the ring lands on my number 4 piston or my headgasket simply went and was discharging all of my compression out of the combustion chamber.

CYLINDER NUMBER PRESSURE
1 149
2 150
3 147
4 89

Here is the rundown, my build is a d16z6 block with a y8 head and arp headstuds. vitara pistons 75.5 (2nd gen, black coating on skirts) on fjt custom length i-beam rods, crower stage 2 turbo cam and supertech valve springs, unported head. ar50 50 trim ching chong ebay turbo with ramhorn and ebay fmic. all tuned on neptune with a moates demon.

I was losing water into the combustion chamber figured it was a mis-torqued headgasket, replaced the headgasket and drove the car around, saw no issues with it consuming water anymore for about three days.

yesterday i did a 3rd/4th gear pull, i made sure the timing was dead nuts on 16 and even retarded the timing about 1.5 degrees before i took off and made sure it was full of coolant. Took off warmed up the motor a little bit and did the pull, at the top of third at 23psi it felt like it was breaking up, kind of like the same problem danz said he was having with his vitara build. At the begging of 4th gear the temp needle begins to rise and i let off as soon as i see it, I drive around the block cooling the engine off and the temperature goes back to normal, however it reached a peak of 3/4 up the gauge for a few seconds, what is really strange is that the AFRs were around 10:1 while in high boost, low boost around 11:7.

Get back to the house, suddenly i realize that its missing on 1 cylinder, pull the plug on the number 4 cylinder and its at 90psi. Pulled the head tonight and these are the results, i dont see a whole lot of cylinder scoring or any problems with the pistons except, piston number 4 has a very VERY minor melted/heat spot near the upper right corner of the intake valve relief.

If you guys have any suggestions let me know.






 

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Ferio inspired
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who tuned it, on what?

why are you beating on it if you're having issues?

most people would pull the plugs first and look at them, then do a leak down test, not a compression test
 

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Brokedick Millionaire
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exhaust, #4, will cause a lower compression number but car will still run ok without boost.

Until a bigger piece breaks off.

3 1/2 cylinder 1.5's are fun. Usually on DPFI it is a #3 exhaust valve that cracks. Either drop to 4th gear or turn off the AC when climbing hills in KY/TN.

Also sounds like a go-kart, still runs ok about 3000 rpms!

A well driven 3 1/2 cylinder 91 DX with a cracked valve and three people in the car will still walk a D15B7 Del Slow S 1.5 and make the most ungodly noise doing it.

Sounds like a go-kart :)
 

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Ok I thought it was a drop of water on it. Your description are awesome. I wanna go ride a go- kart now :)
 

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Discussion Starter #7
who tuned it, on what?

why are you beating on it if you're having issues?

most people would pull the plugs first and look at them, then do a leak down test, not a compression test
I did infact pull the plugs and examine them before i pulled the head, the plugs looked exactly as they do in the picture, oil spotting on them with no signs of aluminum.

Im tuning it on neptune and im not beating on it that was the first pull since re-doing the headgasket.

I think a half compression pressure loss is enough of a loss to pull the head without the use of a leakdown test, allthough i would have done it if i had a leakdown tester.

First pic tells everything, burnt a hole in the valve, or a piece cracked off.

afaik thats a drop of water but now you have me wondering.
 

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afaik thats a drop of water but now you have me wondering.
Looks like water to me. Bone is more often right than wrong. But, if that's a broken valve, I'll be surprised.
 

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Brokedick Millionaire
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Two drops of liquid by the spark plug threads, hole in exhaust valve.

Off Topic: Notice the different valve cut angle in the heads for biased swirl.

I ask for pics for a reason. That could be an oil drop, or a hole in a valve.
 

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That is not a hole in the valve :)
You can clearly see the there was some sort of light when the photo was taken.
By this I mean that if it was a hole it would not have looked like that.
 

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Discussion Starter #11
Two drops of liquid by the spark plug threads, hole in exhaust valve.

Off Topic: Notice the different valve cut angle in the heads for biased swirl.

I ask for pics for a reason. That could be an oil drop, or a hole in a valve.
That is not a hole in the valve :)
You can clearly see the there was some sort of light when the photo was taken.
By this I mean that if it was a hole it would not have looked like that.
Yeah last night after you made the comment i went down and wiped everything up, and double checked the valves, everything is in good order. made me worry a little.

Looks like im going to be pulling the pistons out today, we will see what i find.
 

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Discussion Starter #14 (Edited)




Sure enough 4th cylinder ring land was broken straight through however the rest of the pistons look fine, and there is no damage to the cylinder walls.

my best guess of the cause of failure is my fuel pump going bad, allthough it would be spread across all 4 cylinders, im guessing that because cylinder number 4 is the farthest away from the incoming cool water it gets the hottest, detonates and then blows the headgasket wich in turn perpetuates the disaster.
 
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