I have never figured out how to go about changing the bearing clearances. If a bottom end is assembled and the clearances are not to spec how are they changed to within spec?

 

change the bearings.

i think the spec is all about how worn out the bearings can be.

so new one will be always in spec(should be i think)
and as it wears out u r going down the line.
i dont think u can adjust the physical clearance
besides buying a new bearing, and resurface the bearings or something.

 

that was very definitive information there sogabe, thank you

 

there really wouldn't be any reason to cheack the clearance on used bearings. if you're that close to the parts you'd be changing bearings. you'd want to measure and inspect parts after it's disassembled. if the diameter of the pins and mains isn't to spec you'd replace the crank or have it ground undersize. if it's ground undersize you'd run over size bearing to bring it within spec and if you replace it with new parts you'd run standard bearings. you'd still want to measure clearances with new parts just to make sure. plasti gage is pretty worthless but better than nothing, an inside mic or bore gage and OD mics are the way to go, or measure the holes and the bearing shells plus the crank and do the math. if you're really splitting hairs there are bearings made that are +.001 and -.001 and you can mix and match the halfs with standard shells to reduce or increase the clearance.

 

Yea that was more of my question. If it gets put together and the clearances aren't correct (with new parts) how you would correct that.

 

That would be how. I used plastigauge, with my new rods, machined crank, and align honed main bearing caps. I used the .010" over main/rod bearings. The plastigauge showed the .0025"-.003" clearances that I was expecting, so I buttoned it up. If I had used cheap rods (which I kinda did, but lets say even chEEper ones), and a few had .005" clearance or something, I could have bought a couple of bearings that were more oversized, to take up the gap. If my crank was machined poorly, and a few of the mains were taken further than .010", again, I could have used a bearing to take up the slack, or more likely, I would have raised hell with the machinist...
You can use plastigauge, and do ok, but if you plan on building a motor again, get the bore gauges, and micrometer set.