[Supras] #5 cylinder damage, bhg

[berniek at technicaldevelop.com]

Fred:

Sounds as if you had foreign material enter the cylinder.  I'm somewhat
concerned about the HKS air filter I'm using because the foam pores are so
large.  I had a '90T I was going to upgrade after having it since '92, but
rust here in the northeast, and the fact that it had 156K miles on the
clock discouraged me.  It was starting to need upholstery work as well. 
Then it had a BHG (original gasket, with 72 lb-ft torque.

To make a long story short, I sold it as-was, and got a '91T from Houston,
no rust and 103K miles.  Seemed to run well, but was low on power.  I
figured I'd get the jump on a BHG by installing a Cometic, lapping the
block with a circular lapping plate driven by a small gearhead motor. 
After getting the head off it was obvious that it already had suffered a
BHG and was repaired.  But #1 cylinder was scored, and the piston did not
come up to the deck, so it may have hydrolocked during the BHG and bent
the connecting rod.

By that time I had already started to freshen a JDM engine I got.  I
reused the stock bearings as they were fine.  No bearings had any wear,
including the thrust sections (it came from an automatic, but mine is a 5
speed).  I reused the stock pistons thinking I never had any reason to go
above 15 PSI boost.  Well, now that is 17, but I don't dare go higher.  I
did consider forged pistons, but Weisco due to the longer skirt for less
rocking and the fact that like stock pistons, the wrist pin is offset
1/16" toward the thrust side to keep it a little quiet.  That is not true
of JE pistons.  I also have a 57 trim CT26, but with the wastegate passage
bored out and no turbine clipping.  Mine was also done by Performance
Techniques.

Did the head myself also, as the valves just required lapping (took the
head and block to be surfaced at a shop, though).  Also refinished the cam
journal caps for correct clearance (they always wear, especially on the
last exhaust side).  Made valve spring shims from bored out washers, and
set clearance using shims and buckets salvaged from scrap heads on ebay
(they were cheap, but heavy to ship) and some surface grinding of shims. 
The engine went togther well, with the Cometic gasket, ARP studs, 550cc
injectors, Lex, Walbro, '98 mounts (very strong).  Now also have a
recirculated Raptor BOV, Treadstone IC (like Spearco), homemade 2-1/4"
hardpipes.  Engine does have piston slap until the thermostat opens,
expected.  Also have 3"  Random Tech and HKS exhaust pieces.

Man, lunchtime is over.  Gotta get back to work.  Let me know if you need
anything additional I can help with.


BernieK



> There was scoring on the exhaust side of # 5 piston skirt and cyl wall,
> the
> oil ring and # 2 ring were kind of stuck just above the scoring. Not sure
> if
> it was caused by the scoring or that caused the scoring. This motor always
> had kind of a piston slap odd noise when held about 2000-2200 rpm  in
> neutral.
> But it drove out fine for 60k miles with the noise, I got the car with 94k
> on it years ago.  Cylinder didn't hydro lock, just kept losing coolant
> after
> the last hard 16psi run on the stock head gasket.
>
> What bearings did you use when you rebuilt yours, I have used cleveite 77
> many times in small and big block chevys but this is my first time going
> thru a 7M. I am now considering forged pistons, if I can find a good deal
> on
> them . Jims post makes sense.
>
> I like the performance techniques turbo, I had my CT26 done 7/06, 57 trim,
> no clip, bored out inlet housing.
> Any suggestion would be appreciated
>
> Fred
>
>
>
> ----- Original Message -----
> From: <berniek at technicaldevelop.com>
> To: <fbnetrazor at hotmail.com>; <supras-request at supras.com>
> Sent: Tuesday, February 12, 2008 4:46 PM
> Subject: Re: #5 cylinder damage, bhg
>
>
>> Just curious as to what happened.  Did the cylinder hydraulically lock
>> from coolant due to the BHG?  Or was the damage there before the BHG
>> from
>> running too much boost with stock pistons?
>>
>>
>> BernieK
>>
>
>