My rebuilt short block small block has all SAE threads except the block to bell housing are 10mm metric.

anyone else run across this?

 

Starter bolts started going metric around the early 90s.

Maybe you ran into a later casting rebuild.

 

I've seen that on the S10 4.3 blocks.

 

I ran the bell bolts in ARP site. Gen 2 shows only 3/8/16. Gen 3 LS shows only 10mm.

Fact that every other bolt on block is 3/8 may suggest that someone re tapped for the larger 10 mm for reasons unk. We have not installed starter so will check that...

 

The S10 4.3 blocks had 10mm for the bell housing, but the other bolts were 3/8-16.

 

Blueprint just postd this to me in email:

We have a few blocks that use metric bellhousing, motor mount, and starter bolts. GM decided to change those in the late 90’s. If we get a block that has those metric bolt holes, we include those metric bolts with the engine. We do not install metric helicoils in engines that had standard bolts.

The metric bell housing bolts were not in shipment. I will check parts listed in shipment. That is why mechanic gravitated to SAE.