My H23a1 failure analysis


Well-Known Member
Aug 21, 2016
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I wanted to start a thread for the H I had that recently exploded on my way to work. Some things I found while taking the engine apart. First the cam journal on number 2 piston had deep scoring. So deep in fact it made a hole in the aluminum. My guess is when the mechanic who adjusted my valves did that job he over-tightened the cam caps. This resulted in the cam really having issues.

Next up is the piston. I managed to hammer it out through the top of the block. There is deep scuffing on the sides which is indicative of overheating. Im thinking because it was running rich for a while it was getting oil dilution which could have further messed with that cylinder due to lack of lubrication on the cylinder walls. The top of the piston has carbon all over it (expected) with no hotspots so it doesnt look like a misfire.

The car was running rich because I never hooked up the o2 during the swap and the ECT sensor was bad for a while so since the car never saw it was warming up it probably ran rich constantly to try to warm up the motor. Replacing the thermostat could have been too little too late as there was already damage done.

I couldnt really get information from the crank bearings because the rod destroyed the whole journal/bearing when it broke into pieces. I cant say for certain what made it fail but I think these were all heavy contributing factors. So fuel dilution, overightened cam possible binding a little, lack of lubrication on cylinder walls and overly rich operation conditions paired with a heavy load at the time of failure. If anyone has anything to add that would be cool.

Note to self: Dont drive the newly swapped F20b until the o2 is installed lol.