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g96nt 09-19-2010 12:44 PM

t7 motors; which piston usually burns, first?
So, I know in DSMs, the #3 is usually the first to go, and show signs of knock. partially because of it's placement on the fuel-rail, and partially because it's inside, and doesn't get to shed heat so quickly.

I was driving home today, and did a spirited pull in the wagon, and it started smoking. when I got it down to idle @ a stop-light, it was idling pretty rough.
when I get home, I pop the hood, and notice oil and coolant on the rear-drivers' side of the motor, which is a little odd. (I assume bad HG)

when I did a compression test, I started with 3, then 4, then 2, then 1
the numbers looked like this: 190, 190, 185, 60 psi.

Is it common that the #1 piston goes? I went to it last, thinking it was the least-likely to be melted... or, it it more likely that I REALLY blew the HG pretty bad?

FWIW, I have a td04, 3" exhaust, FMIC, CAI, and it was tuned as such.
I have recently added t5 cams, but have yet to have it tuned.
I didn't think the car would need a re-tune with just cams, but I'm thinking I will, soon.
(please don't post to tell me I need to tune it)

zingZACH 09-19-2010 12:47 PM

Out of curiosity, who did the tune?

And usually 3 is the common one to have problems. I have also seen 1 fail though.

Sorry to hear!

jssaab 09-19-2010 01:06 PM

Too bad I have seen one as well... did you run a wideband on that motor?

g96nt 09-19-2010 01:27 PM

Steve Hayes did mine about a year and a half ago. It only boosts to 15psi, and on the wideband, it was high-11's low-12's @ WOT (on a dyno)
It's worth mentioning I did just swap to a H.O. t7 head, and it's possible the headgasket didn't seat correctly. (also possible I didn't torque the ARP's enough.)

This motor never overheated, according to the SID, (never went over 102*)
with the old, and new head on it.

I kind of assumed that #3 would be the most-likely, as well... I was a little shocked to see #1 be the low one.

The motor isn't making any noise, idle doesn't dip... seems normal, aside from sounding like a subaru, and having no balls.

oh well... if I have to, I'll pick up some JE's or whatever, hone it, and go back at it.

DrewP 09-19-2010 04:27 PM

I have like four Cyl. #4's in a row go on roasted B2x5 engines at the shop.

mike d 09-19-2010 04:33 PM

What did you torque the ARPs too? and did you have the head decked before installing??

its an end cyl (either 4 or 1) to toss an HG, most the time ive delt with blown ones those are the two that kick out first

however, this is c900/9000 experience talking, i think cyl 1 (or is it 4, its the one closest to the dizzy) usually blew due to the intake mani design. 9-5s are much more symmetrical

g96nt 09-19-2010 05:12 PM

the head was planed, yeah.....
the ARPs get tightened to 105lb/ft
the only thing is that I didn't use oil or the moly lube.
I'll take a look @ the head with a straight-edge when the head's off again.

g96nt 11-15-2010 10:34 AM

well, I finally got it apart today.
#1 is cracked. it's not in pieces, but it's cracked.
Also, the lower compression ring is cracked, and fell out when I popped it out of the motor.

The good news was that there was zero scoring, the rod bearings looked good, and the oil pan/pickup were pretty clean. (aside from some RTV scraps)

so.. a stone-hone, and wossners are the plan. I may have it done in '10, but I doubt it.
having the 9-3 means I donlt have to rush.

a couple crappy pictures:

Saabeh 11-15-2010 12:12 PM

Nice! In the pics, the crank looks scored on number 3 I think? Like spun main bearing? Might just be stains.

g96nt 11-15-2010 12:48 PM

no scoring. they're all perfectly fine.

Raven18940 11-15-2010 01:07 PM

Wow, boom.

saabkid37 11-15-2010 01:37 PM

looks like a classic t7 failure to me.

g96nt 11-15-2010 02:49 PM


Originally Posted by Saabeh (Post 792555)
Nice! In the pics, the crank looks scored on number 3 I think? Like spun main bearing? Might just be stains.

are you talking about the 2nd from left? that's the rod bearing, still on the crank. Everything's fine in there. just needs a hone, and we're off!

Dudethe9-5isfast 11-19-2010 12:34 PM

Just curious as to why you changed your mind from JE to Wossners ?

g96nt 11-19-2010 02:10 PM

I'm not going to have this car forever, And I'm trying to keep it as civil as I can (for resale) Trying to explain to anyone why the motor makes so much noise @ startup isn't what I want to be doing.
I'd perfer to buy the 4032's which have less expansion/contraction difference, and worry a lot less about warm-ups, and blowby.

JE aren't junk, by any means, but they're just not the most D/D-friendly.

stromer 11-19-2010 05:56 PM

Looks nice :cool:

Mine was #3, for reference. Luckily it happened shortly before my test drive and the Saab dealer rebuilt the engine.

Dudethe9-5isfast 11-20-2010 06:11 AM

I have the ceramic coated JEs in my daily driver for 30K miles at this point without any piston slap etc at startup

JZW 11-20-2010 08:25 PM

I like the woessner, they are high quality and I get no piston slap on cold mornings, defintely less than the Je pistons I was running before and the woessner pistons do have a coating on the skirts, just like je.

The woessner pistons are a little bit lighter too, I have been very happy with them so far and have them in my Viggen and my 700bhp race car.


JZW 11-20-2010 08:26 PM


Originally Posted by saabkid37 (Post 792578)
looks like a classic t7 failure to me.

I would agree, looks just like my viggen did and other t7 piston failures I have seen. T7 pistons are on the weak side, no doubt about it...

mike d 11-21-2010 05:22 PM

our of curisoty, how far have people taken the T7 rods? they look pretty beefy, and Ive barely every heard of them popping?

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