North American Turbocoupe Organization



Blown HG... Removed head and...
vegas_ss Offline
Senior Member
#1
Two of the pistons have what appears to be a small hole drilled in the center... These are in cly #1 and #4 #2 and d #3 do not have this hole in the piston.

Any ideas on what the deal is? This was a rebuilt motor I bought off of someone on this board a few years ago. Supposedly was rebuilt correctly. Really haven't had any issues except for the blown HG between #3 and #4


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1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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ZeroRain Offline
Member
#2
I have no idea! I can't imagine that there would be much if any compression...

Matthew
1987 Turbo Coupe Auto- gone
1991 Sport 5.0 Auto- gone
1996 LX 5.0 5spd- Gone
1989 Super Coupe 5spd- gone
1984 Turbo Coupe 5spd- newest project
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powerstrokin Offline
Junior Member
#3
I'm no expert by any means but I would guess it just means they were replaced... and the replacements happen to have those dimples. It doesn't look like they have a hole going all the way through.
'88 Turbo Coupe
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vegas_ss Offline
Senior Member
#4
It's not a hole in the piston, just some material was removed. Since this is a rebuilt motor, it appears that two must have been replaced.

The motor ran fine... until the HG blew between 3/4.

What's the best way to prep the block? I have a fresh boport head w/2.1 cam to go on it.
1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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Pete D Offline
Administrator
#5
I'm guessing that is the hole where the "center" for a lath contacted the piston to hold it in place while it was turned and machined on a lath. Just a guess.
Pete Dunham


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RDOG Offline
Posting Freak
#6
Are you going to go with a nice set of ARP head studs. I would since you are going to go with that big cam and high flow head.

Maybe contact who you bought it from and ask for the number of the machine shop. Ask the machine shop the part number that was used for the pistons in question. I had a shop build my short block that was supposed to be good/reputable, and they put nonforged/cast pistons in the block. I had to fight with the guy for over two weeks to get it done right. I havent seen forged pistons with a dimple drilled in them, but I have seen cast pistons that look like that. Not saying they are cast pistons, but they look like it.
1986 Turbo Coupe. Boport StageIII head, Boport 2.1, Performance Techniques 50 trim hybird, StageII.63, stinger 3" exhaust, Phenolic spacer, Boglog header,NPR FMIC intercooler setup, kirban fpr, bigrmotorsports fuel rail, diablo water meth kit, CAI, remote mount TFI, CHE rear adj control arms, MAC girdle, 8.8 rear disc, aluminum drive shaft, H&R lowerings springs Tbird Turbo Specific, y MAS!!
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vegas_ss Offline
Senior Member
#7
I'm just using a replacement set of felpro TTY head bolts. I do have a torque angle meter though Wink I got this motor over 2 years ago from a member on here from Linden, PA... Unfortunately I am having trouble contacting him and at this point, not much to do anyhow.

The motor has been trouble free except for the HG. I do have my old engine that suffered a dizzy gear episode... At the time I found this motor and figured it would be better to just swap the whole engine as this was a complete long block.

I will be using a fresh Boport stage 3/2.1 cam, ported/gutted intake, ported rfe6, stock ihi/intercooler, gillis and a set of flow matched rebuilt stock browntops. Once I get this running I can look at turbo upgrades, but for now... ihi is it.

I sure hope those pistons are forged... I'll clean them up and compare them to what is in the old motor. Hopefully the match the two center ones as I'm sure that all the pistons would need to be forged (or cast) due to weight issues.



1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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