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Originally Posted by marcucci,Dec 28 2009, 01:49 PM
Based on this short summary, I would suspect that the cylinder suffered detonation (chunks missing?) and cracked a ring land, leading to the cylinder wall scoring.
Did you see any scoring on the other cylinders? It probably goes w/o saying that you should see none. Did you see any detonation damage on the pistons?
Did you have much carbon built up on the tops of the pistons? You should, otherwise... you probably are running lean.
I did see some scoring in #4 however it was slight. Yes, I did see some detonation damage to the head of the piston, there was a small piece missing where the piston met the cylinder wall. It's suspected the ring may have fractured and finally made it's way through the piston edge. As for carbon build up, there was some. Actually #3 looked like it had more buildup then #'s 1 and 2 which showed no scoring. This is my first damaged motor so I'm really taking my time to figure out what happened and correct it. I should know more tomorrow.
I highly recommend buying an used block vs a rebuild. No matter how good the rac shop say they are. It is always due to bad tuning, but that's very broad. U want to be safe, tune for 87 on a dyno by Shawn church (he has a KW rotrex S he daily) and run 91. Rotrex do NOT work better with lower compression.
Well, I finally got the motor out and it sure looks like detonation. I took a few pics (cylinder 3 is the one show and the worst, 4 was going and 1/2 had burn marks) but they really don't show the extent of the damage. The short block and head are over at Laskey racing (he said the pistons were cracked and the rings broken and crumbling) to get bored and sleeved with a Darton Sleeve. I think I'm going to drop the compression to 10:1 and bore it to 88mm. I'm hoping the head can be salvaged but there was quite a lot of buildup on 3 and 4. Since the motors out, I plan to get a Berk header and high flow cat (straight pipe for the track), I just received an ACT l/w flywheel. If the head can be saved, I'll do a valve job and put in dual springs with titanium retainers and new valves.
It's unfortunate that it happened but I did have a good time buying tools and pulling the motor out. I must say, the Helm's manual is a lifesaver! I took lots of pictures and used number tape at all questionable connections. Hopefully it goes back together as smooth as it came apart!
