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Showing results for tags 'ring clearance'.
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Hello all! Hoping you folks can help me figure out my problem with a 4.6 stroker that I've built. After the first assembly there were no issues with the break-in process which followed the cam manufacturers directions using comp cams break-in oil and lube. I did the normal easy break-in driving for about 50-75 miles around town and then drove it to work, 50 miles one way. When I started it up after work it was knocking. The knock doesn't go away with time or heat, it gets quieter during running but slowing to idle it's there every time. I got it home and immediately tore it back down to find the #1 piston slapping and scoring the one side of the cylinder wall. I pulled the piston and found it somewhat tight at the wrist pin. I ordered a new piston due to the damage and honed the cylinder wall to clean up the scoring. The second assembly was fine and I did an abbreviated break-in again and all seemed well. I drove around for about 100 miles around town for a few days with no issues. Starting it back up the next morning though it was knocking again immediately. Tearing it down once again I found the exact same thing with #1, slightly tight wrist pin and all. None of the other pistons show any issues. I've replaced the piston once more, installed new rings and new rod bearings but I haven't reassembled the rest of the engine. The first rod bearing set had the oil hole but the second set did not. This last set didn't either, but I cut a groove using a dremel and cleaned it up just to get the extra oil. I went to a different machine shop following some recommendations that the shop installing the piston was causing possible issues. The new shop pin fit the new piston. The new shop is an old school engine machine shop and he offered me two possible causes.....air bubble trapped around the cylinder causing elevated temperatures, and too much fuel causing elevated temperatures and possible fuel wash into the cylinder. I went home and pressure tested the fuel rail. The injectors are holding and the spray pattern is good. I also run a wideband O2 sensor and I'm running between 14.5 and 15.1 on the gauge. He recommended pulling the thermostat on the initial running to clear out any possible air trapped around the cylinder, before reinstalling it. What am I missing....? Specs: 1990 4.2 crank turned down .010/.010 with all new bearings, thrust is at .002, plastigauged all bearings at .002 - .0025 1994 Cherokee 4.0 block, 4.0 rods, block bored .030 over and magnafluxed/tanked Quench is .062 using .040 head gasket New Icon ICC 944 pistons .030 over, verified at 3.902, new rings, down .022 in the bore Comp cams 68-231-4 cam and lifters Bosch 24lb fuel injectors, cleaned, checked and verified to be working normally Cylinder bores are 3.9045 and pistons are 3.902, .0025 clearance per manufacturer 190 degree thermostat Thanks in advance for any help everyone!