<VV> Cracked Pistons

[Mike Stillwell]

 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

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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