I recently started my motor that i've built over the last couple years. Its a b5 a4, awm motor. mahle pistons, scat rods, 034 coated bearings. It sounded like a tub of marbles on its first start. Thinking the noise was from the lifters priming up i let the motor come up to temperature. I made sure the cylinder taper was in spec and not out of round. I also plastigauged the bearings to check those clearances. I popped the head off and i rotated the bottom and and saw that the lower part of the cylinder it looks like the skirts on the pistons polished up the side of the cylinder. i'm pretty sure the noise i'm hearing is the piston skirt slapping the side of the cylinder. what is causing this? lubrication? tune?
Fractured/broken ring, probably happened during assembly. What did you use to install the pistons? If you used a generic ring compressor I highly recommend you use a tapered ring compressor. They can be found for around 30-50 dollars...
Look here: http://www.euroexportinc.com/store/t...mpressors.html
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Bottom end was pulled apart and relubed prior to being installed back into the car. I used a generic compressor, which i never had an issue with before with other motors i built.
Its not just one cylinder so its an issue across the board. I had a difficult time starting the motor on the base maestro 630 tune. Originally i had an issue with the coil pack wiring and it wouldn't start. I fixed that and it idles at 14.5-14.7 afr so i don't think its from washing the cylinder walls down. Maybe its an issue with oil pressure? I pulled the rod bearings and they look clean and even. Wouldn't that be the first sign of an oil issue?