speeder Posted March 6, 2003 Share Posted March 6, 2003 While performing a leakdown test on an L28, I tested each cylinder at TDC, and got horrible (20-90%!) readings. I know that the engine is not that bad. Then, with the leakdown guage connected, I then turned the engine CW a short distance through TDC so that the applied air pressure just began to push the piston down. at this point, evry cylinder inndicated less than 5% leakdown. I'm sure of my TDC position determination throughout this testing. 2 questions: 1. WTF!? What causes this phenomena? 2. Is this engine good? Thanks guys. Quote Link to comment Share on other sites More sharing options...
Guest Rick Johnson Posted March 14, 2003 Share Posted March 14, 2003 It could be your pistons rocking in the bore. My 383 small block would do this when it had the Piece Of Shxx Keith Black hypereutectic pistons in it. I would actually hear the pistons click as they rocked into another position and began to seal. I would go from 20% leakagae to 8% leakage as I turned the motor. When I measured the skirts I found they designed in too much cam grind on the skirts (about .002") so the piston rocked and piston slapped. It also burned 1 quart of oil in 300 miles. I complained to the engineers at Keith Black and they said they had to grind in all that skirt taper or the piston would seize when it got real hot during some racing applications. I think they had the dimensional stability part of their design all screwed up and just solved the problem with excessive taper. I put in TRW hypereutectic pistons in it with the block still in the car and all my troubles were gone. No more piston slap or oil consumption and it runs greeat. Quote Link to comment Share on other sites More sharing options...
speeder Posted March 18, 2003 Author Share Posted March 18, 2003 Thanks for that Rick - I suspect thet I have damaged the ring lands of the pistons, but the rings are still intact. I won't elaborate on the reason I think so, but just let us say that I wasn't too smart with tuning and use of boost on a set of cast pistons. The engine gets removed and torn down soon, and I'll post what I find. Quote Link to comment Share on other sites More sharing options...
speeder Posted April 9, 2003 Author Share Posted April 9, 2003 Well, the engine is disassembled and the story is told. All 6 pistons have chunks broken off their skirts on their "load" side, allowing them to rock in the bores. Very ugly. I'll post some pictures soon - Once past the horror of the situation, engine damage is fascinating. Quote Link to comment Share on other sites More sharing options...
speeder Posted April 12, 2003 Author Share Posted April 12, 2003 See my post in the Datsun L6 Forum "Weapon of Mass Destruction" for piston pics. Quote Link to comment Share on other sites More sharing options...
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