Rod bearing clearance tight after machine work?
 

I have been collecting and getting parts for building my forged engine since a spun bearing.

Vehicle will be turbo application with hopes of future-proofing some increased power, should I chase it. Starting goal is 200-230hp range...
The crank was machined .01" oversized for the main and rod journals. Oversized bearings were purchased.

I installed the main caps, and plastigauge showed .0018 - .002" across all 5.

The problem comes up when installing the rod caps. With a clean surface, ARP lubricant, and triple checked; I am getting .0014" for clearance.

This is with the .01" oversized bearings.
This is too tight correct? What would be the path to correct this and get closer to the .002" clearance I am led to believe is what I want?

I also re-installed one of the old (stock) rods with the oversized bearing on a different journal and got the same .0014" measurement.

Note sure what bearing clearances you are targeting but you can use a stock 1/2 shell together with a 0.001 1/2 shell to gain 0.0005

Maybe I'm wrong, but you have to take measurements dry.

I believe he was referring to using the arp lube on the fasteners, which is required. No lube on the fasteners will cause galling.

.0014" is a bit too tight for the rods. .002" would be more ideal. Plastigauge is not the most accurate. You should have a machine shop measure them to confirm the clearances. Because of the timing belt and crank driven oil pump you should not run more than .002" clearance on the mains. If it turns out that the plasti-gauge measurement is bit on the small side you can run the rods but should reduce the mains back to .002". If indeed you are tight on the rods first check that bearings are correct. There are +.025mm and -.025mm bearings. If they are confirmed to be tight you only have a few options. Check the rod's housing bore diameter, enlarge if needed or have the rod journals polished.

plastigauge isnt as accurate as I like.

Dial bore gauge and calipers for everything IMO.

And nothing wrong if you went back to a standard bearing to run 0024 IMO. I'm like 0022-0023 on my rod bearings, I would have to look.

Otherwise you are talking about machining the rod cap's and honing everything to get where you want to go... not the end of the world.

I was under the impression that the acl bearings came in under sizes with the + or - .025mm (+- .001”) option. It appears they don’t and the only extra clearance bearing is the hx which is only offered in a std size. There is no other solution other than polishing the crank which is not ideal because it often results in a barrel shaped journal. A few ten thousands of an inch is doable. The other option is increasing the rods housing bore, but if it’s not on the tight side of the tolerance it would reduce the bearings fit (aka crush). Another option would be to try the king race bearing which from my experience do net a little more clearance.


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