This will be my 1st time assembling an engine. I used a plastigage to measure the oil clearance on the main bearings. Here is what I found;
1 main .076 - .051mm
2 main .075 - .076mm
3 main .051 - .038mm
4 main .051 - .076mm
5 main .076 - .038mm
Should I be worried about number 3 and 5? All the bearings are 0.010in. According to the Engine Builder’s handbook by Tom Monroe, on page 120 (for those that have the book) .05mm is average for a street engine, but .02 mm is okay. Any help would greatly be appreicated.

 

you should be worried about all the numbers and you should buy some tools if you're going to try building an engine and forget plastigage. oil clearance should be around .0015 to .0025 which is way less that what you have.

 

if you are truly measuring with a metric scale, your measurements are running between .076 and .038 mm, which is varying between .0015" and .003".

.003" clearance is a bit on the high side, but not out of the ordinary for alot of rebuilds, even some race engines trying to wring out every last HP, and using heavy oil. It is also tough to guarantee that is what you are getting from using plastiguage. As a rough measurement to verify machine work was done properly, you're probably OK.

to be completely sure, you need accurate measurement tools. using a micrometer, you could in theory measure the bearing shells, and swap them around to get the set closer.

in all reality, if this isn't some max effort engine, you probably will never notice a slightly high clearance, but i would run 10w-30.

 

Thanks for the response. I have acccess to some of those tools by way of the Auto Hobby shops (some perks of being in the military)Will take the crank, rods and lt4 hot cam to do some measuring. Again this is my 1st engine build and looking to do it right the first time.