Check it out, I'm not sure which year is which, but one has a hole leading back into the crankcase area, while the other doesn't. Anyone know what it's deal is? To help keep excess oil off the seal?? I also noticed a different shape on the gear where it slides onto the crank snout, but I don't think that matters since both sides of the crank are just flat.

 

fwiw, parts list shows different part numbers between years.


88 crx si 15110-PM3-000
90 crx si 15110-PM3-010 BODY, OIL PUMP

 

the 88 and 89's are technically 100% the same along with the 90 to 91's. but compare an 88 to a 91; they're not 100% the same. There's going to be minor differences in the series.