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I had a shortblock built by a shop (has aftermarket pistons, rods, stock Evo 88mm crank, bored 0.20" over 4G63 Evo 8 block) and noticed at TDC one piston stuck out a little higher than the rest while it was on my engine stand.
I checked TDC with a dial gauge and measured both Cyl 1 and 4, and got 0.004" above piston deck on Cyl 1 and 0.011" above piston deck on Cyl 4, there's about a 0.007" taper from one side to another. From North -> South (intake to exhaust) there's nearly zero change, the taper is from East -> West. I made sure to account for the piston rocking back and forth within the bore by setting my dial gauge in the dead center of the piston (values only changed by less than 0.001" when rocking piston). I had a local machine shop confirm my measurements.
Will this taper give any issues once the car is running? I'm building my Evo as a fun HPDE car with a FP Green, aiming to make 400-450~ whp on E85 and don't want to waste my time assembling this motor if it's going to give me a issue later down the line.
I have no idea. Local machine shop said it was likely milled at the oil pan rails instead of the mains. Less time to setup but possibility of taper. I'm a little concerned it could affect head gasket sealing. I'd rather just make sure it's not going to affect anything rather than assembling the motor, and having a issue later down the line due to careless machine work that'll be blamed on a bad tune or whatever.
At this point, it's even making me question the clearances and the rest of the motor (as in they just slapped it together without giving any ****s and sent it out ASAP once the check cleared) if they didn't catch that before shipping it back to me. It's a pretty reputable shop in the Evo/DSM world too.
If the deck was tapered, each piston would be progressively more out of the deck. Sounds like the one piston has the pin height off, or that rod is slightly long, or the stroke on that throw of the crank is slightly long.
That's actually what's happening. With my dial gauge setup just checking for differences in height between each piston (not measuring distance from deck), measurements seem consistent and repeatable even if my gauge setup isn't fixed, and I made sure to set TDC. I did some creative MS paint work to remove the logos off the piston face, but can assure you they're centered as best as possible to the piston (and the gauge placed in the same location every time).
Cyl 1 Cyl 2 Cyl 3 Cyl 4
Cyl 1: 0.0015" (set this closest to zero being the lowest)
Cyl 2: 0.0025"
Cyl 3: 0.0065"
Cyl 4: 0.0110"
Apr 19, 2019, 09:34 PM
