1.8nb Bearing clearances
 

Hey guys and gals. First time poster. Long time reader. I've starting the adventure of my engine rebuild. So all forged internals and new 84mm pistons and acl bearings. I have had the crank ground and they said to use .25 bearing which I have done for the main bearings. And using plastiguage I got with in spec.

Now stuck on the rod bearings. I didnt re order new bearings for the rods as didn't think about it at the time. So now I have gone to install rods on to the crank pistons 1 and 4. And I have a gap of 0.1mm/0.004. So what I'm asking is first what are the clearance needed. On street only car. Turbo in the future? I believe this clearance would be very max? Correct if not. But want to bring closer to normal spec. What bearings would do this? Should I just use .25 bearings as well? And what would the clearance be then? 0.075? Can anyone help me out?

Typically if the mains are ground to use .25 oversized, so are the rods. Were they not?

If you try to use .25 oversized rod bearings right now, you'd have ~.009" clearance if my math is right. You want .0015-.002". Use a mic to measure the rod ends of the crank, report back.

So I assumed they were but will have to check with them.

So so size of crank where rods connect. Not sure exactly what this part is are as follows
P1 44.690mm
P2 44.691mm
p3 44.689mm
p4 44.694mm

So all look to be fairly close I believe. And this was an average as they didnt seem to be 100 % perfectly round. The gap I get with standard bearings (not the correct size I know) was 0.100mm / 0.004 inch. What do u think?

So doing some math my self. Just to check.

+0.25 bearing = 0.0098 rounded to 0.010

0.004 plus the extra 0.010 from the bearing would that be 0.014???

I think you measured your .004 clearance incorrectly, the diameters you measured come out to be .010 smaller than stock, so they need .25mm/.010 oversized bearings.

Here's the page of specs from my haynes manual if it helps in the future. Lists oversized bore diameters, but not rods and mains.

https://cimg3.ibsrv.net/gimg/www.mia...f9ebc6e686.jpg

So I will order .25 over sized bearings then. What would my clearances be then?

Get the proper measuring tools and do math. Plastigauge isnt all that accurate.

Inside dial bore gauge and outside micrometers in the proper size to set the bore gauge.

If you want to measure the bearings properly you want a micrometer with a rounded anvil.