<VV> Cracked Pistons

[Rick Norris]

I'll chime in here. As Mike alluded to the number 5 piston being a problem.
All the dropped 140 valve seats I have seen were on No. 5. Also the area of
the No. 5 piston is where the tempering air for the heater is drawn from the
upper shroud aka Turkey Roaster. Almost every street Corvair I've seen has a
leaky hose here if it has one at all. I have seen this opening plugged with
everything from a factory cover plate to a piece of cardboard. Sometimes the
hose will appear to be intact as far as can be seen but somewhere between
the firewall thru which it passes and the heater valve box connection it is
compromised. In my street 67 vert I capped the nozzle on the heater blower
valve box and pop riveted an aluminum cover over the upper shroud opening
after removing the nozzle. Works for me.


Rick Norris
1st CORSA President, 1971
www.corvairalley.com
Hurricane WV

 

-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Mike Stillwell
Sent: Wednesday, January 22, 2014 12:07 PM
To: virtualvairs at corvair.org; James Cuneo
Subject: Re: <VV> Cracked Pistons


 While I would NOT call myself an engine guru, I've always been
taught/trained/told that TRW (now Sealed Power) Forged Pistons with drilled
oil return holes seem to last the longest in a turbo motor. I picked up an
NOS set of older long skirt .020 over TRW's for my stock 180 turbo. They
still come up on Ebay pretty frequently. I've seen some pretty high
compression, 4 bbl, E flow turbos run pistons set up like this and live.
 As far as #5, it often comes up as a problem for dropped seats on 140's as
well. I don't know the air flow dynamics under the shroud, but the evidence
seems to suggest that it runs a little hotter at that spot on all of them. I
always, even in bone stock cars, block off the fresh air bleed in the top
shroud by #5.

 Mike
 YS-117

--------------------------------------------
On Wed, 1/22/14, James Cuneo <jamescuneo at hotmail.com> wrote:

 
 Guys,I need some help from you engine
 gurus out there.I have cracked 3 pistons in the #5 cylinder  in the past
four years. 2nd time I thought it was a  coincidence that it was the same
cylinder, third time, now I  wonder what is happening in #5 that sets it
apart from the  others.What I have:2G rochester carb modified.F/B turbo on
 140 heads. Clarks Hi Tech pistons D cut to 8.25 crCrank,  flywheel,
Pressure plate, rods, pistons balanced.TB20 otto
 cam329 turbo dist.Wide band o2 sensor, cruise afr 14.5,  boost afr
12.0SafegardWater injectionSecond time this  happened was just last august
so I recently installed water  injection. Was doing a tuning run last Sunday
when after a 5  second run at 10psi I felt the piston give way. Safegard
indicated no knock. I had done a lot of homework on water  injection and was
sure this would be the cure to this  problem, it was not. Spark plugs all
appear dark brown, #5 a  little lighter brown in color. Piston failure mode
is a  crack forms in land between
  #2 ring and #3 oil control ring, then travels to oil return  slot in #3
groove.Questions: 1. what is unique to #5  cylinder running hot, lean? I can
imagine the hot air off  the turbo being distributed there. 2. Is there a
better,  more appropriate piston to be using?I have decided to  replace all
6 pistons with new. It appears there are only 2  choices of forged pistons
easily available, Clarks brand and  Sealed Power, which one?I appreciate all
and any  advice.Thanks, Jim Cuneo39 year corvair owner, Journeyman
 
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