KAZU Posted April 30, 2014 Share Posted April 30, 2014 I bought my 240z in 2000. It came with a L28 rebuilt from a company ATK. I replaced the L28 with a RB26 almost 4 years ago because L28 won't idle properly. Now I'm parting out the L28. Bearings were good. All top rings are broken into pieces. Pistons are 0.75mm oversized. The top ring groove of the No. 2 Piston is seriously damaged. I am not going to rebuild it but what would you guess the cause of this? Quote Link to comment Share on other sites More sharing options...
steve260z Posted April 30, 2014 Share Posted April 30, 2014 Block was bored too wide? Rings bouncing around with piston slap??? Maybe.? Quote Link to comment Share on other sites More sharing options...
Xnke Posted April 30, 2014 Share Posted April 30, 2014 Detonation can have damage patterns like that, but will usually show some pitting or other damage to the piston crown and cylinder head as well. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 1, 2014 Share Posted May 1, 2014 Detonation can have damage patterns like that, but will usually show some pitting or other damage to the piston crown and cylinder head as well. I would have expected to see broken ring lands from detonation that severe too. It almost looks like the piston melted around the ring groove in the second pic. Quote Link to comment Share on other sites More sharing options...
KAZU Posted May 1, 2014 Author Share Posted May 1, 2014 Thanks guys. I recall my memory when I put an engine management system using waste spark coil pack on it, I tried to run it with wrong firing order and timing. This might easily cause detonation. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 1, 2014 Share Posted May 1, 2014 I tried to run it with wrong firing order and timing. This might easily cause detonation. Ya think? Quote Link to comment Share on other sites More sharing options...
KAZU Posted May 1, 2014 Author Share Posted May 1, 2014 Ya think? I am not sure. Another fault I did may be that the car had been running for a while with 300zx coil on plug using MSD DIS-4 with waist spark wiring. The engine won't rev without the MSD box. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 3, 2014 Share Posted May 3, 2014 Detonation. Detonation. Detonation. Quote Link to comment Share on other sites More sharing options...
50th anniversary Posted May 5, 2014 Share Posted May 5, 2014 Wrong engine oil? Quote Link to comment Share on other sites More sharing options...
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