Checking my type 4 main bore surfaces

[mark-s]

I've read about the 'fingernail test', but thought it applied to where the bearing seats in the saddle. Checking the bores in my type 4 CU code case, the bearing mating surfaces are smooth, but my fingernail catches on the very edge of the saddle in places on #2, #3 & #4 - most noticeable on #2. Is this cause for concern? Any comments on the condition generally?

click on the pics for larger images.



Fingernail catches here:


This is #1:


This is #3:

This is #4

[Piledriver]

Your case looks great, but that or the fingernail test really mean nothing.

The "fingernail test" a pretty reasonable test for a T1, not for a T4, and not perfect for T1s, but it's a valid quick check on T1s to see if it is hosed..

The T1 has an oil groove running down the outside of the bearing, so as the bearing beats itself into the soft magnesium, the area at the oil groove doesn't get beaten, and if the "rise" can be felt with a fingernail, it's due an align bore. (still not definitive, but makes for a fast filter when sorting through a pile of blocks)

T4s big mains have the groove on the ID (crank) side of the bearing, so it all gets beaten down ~evenly.
(the "burr" on the outer edges of the T4 block may... or may not mean anything)

You can get a good feel for it snapping a #3 shell into the saddles or such, but the only sure way is to measure with the proper equipment. T4 cases sometimes get tighter, rather than looser, and egg shaped is more of an issue.

Also, don't forget to check for separation at the center main, all torqued up they really should touch, Jake suggested using carbon paper (very thin) to do a pull test, if it could be pulled out, it was too wide.
I would measure some, but don't have any.

OTOH IIRC Jake used a significantly higher tq than the manual says, but he also used ARP through bolts a lot.

[mark-s]

Thanks for the advice, I'll certainly check for separation although I don't have carbon paper either, but I'll just use a bright light source.