Don Terrill’s Speed-Talk

Any one experienced upper main bearings wearing a lot more than the lowers? This is on a BB Chev Dart block new build. 1 - 4 have excesive wear , # 5 still like new. Clearance 1 - 4 has .00275", # 5 has .0032".

AA Performance wrote: ↑Fri Aug 05, 2022 9:50 am Any one experienced upper main bearings wearing a lot more than the lowers? This is on a BB Chev Dart block new build. 1 - 4 have excesive wear , # 5 still like new. Clearance 1 - 4 has .00275", # 5 has .0032".

Personally, I would say that the 3rd from the rear counterweight on that crankshaft is not heavy enough; especially if this is externally balanced.
Could be lots of other things causing that, though.

How about a few more details ? Stock engine in a truck ? Supercharged in a boat ? RPM range.

BillK wrote: ↑Fri Aug 05, 2022 12:24 pm How about a few more details ? Stock engine in a truck ? Supercharged in a boat ? RPM range.

4.530" bore, 4.375" stroke 4340 scat crank, Dart 325cc heads with minor porting, 822 HP @ 6700, 758 ftlbs @ 5300, pump gas street car. It is internal balance. Freind had it built recently and does give it a hard time. Just wondering if he is giving it more than he should and whether crank is doing things it shouldn't.