<VV> measuring and adjusting bearing clearance

[djtcz at comcast.net]

----- Original Message ----- 
> From: corvair at mts.net 
> Subject: Re: <VV> Engine building - bearing clearance 
> 
> 
> I am measuring the inside of the bearing bore in a torqued block, using 
> snap gauges and a micrometer. 
> 
> I measure the crank, the journal is (for example, and from memory) 
> 2.0985". 
> I measure the corresponding bore with snap gauge (.001 shells installed), 
> then mike the gauge, and get 2.0991". 
> 
> So my clearance is .0006 - too small. 
> 
> I want .0010 more clearance, so I substitute 2 STD shells instead of .001 
> shells. 
> 
> Remeasure, and now the bore measures 2.1011 and clearance is .0026" 
> (pretty 
> big). 
> 
> That's what makes me think that a single .001 shell takes away .001 
> clearance and a pair of them takes away .002. 
> 
> It's confusing me. Assembling with plastigauge will assuage my concerns. 
> 
> Les 
> 
---------------------------------------------- 

Good tolerances to work to on page 35 here 
http://mahleclevite.com/publications/EB-40-07.pdf 

A good way to use snap gauges is set them a little long ( bigger than diameter to be measured) with handle snugged a little. One way is to position them with the handle angled about 10 degrees to the crank centerline, then loosen the lock, then snug the lock. Then rotate the handle to force them to roll thru the bore being measured. This way they center on the bore and get forced to the smallest measurement, which is the diameter. Then measure gently with a mike. Repeat 100 times for repeatability. I'd check the rod and main housing bores for size, roundness, and taper without inserts first. 

Plastigage is an excellent check, but strictly +/- a thousandth or so. 

A bore gauge works best to measure bearing ID. Some will accept no other method for determining clearance. 
If the inserts don't get seated tight in the case or rod with proper roundness and size when torqued up, something is wrong. Since we already qualified the rod and case bearing bores as round and taper free, Start by looking for several thousandths "crush" or "nip" from the half insert shell ends being "proud" of the mating surface 

Mahle/Clevite says Mixing std and 001 shells to adjust clearance is OK. page 25 here. 0.0005 inch is a pretty small adjustment of one bore of the main line alignment 

I'd check the crank rod and main journals for size, roundness and taper with a mike. Then I'd check the runout of all main journals measured with a dial indicator, with the crank supported on front and rear main journals. Less than 0.002 inch is good. 0.003 or 4 is probably OK. Then I'd trial assemble the oiled crank with all main bearings with good clearance, torqued in the case. If the crank turns 360 degrees freely, the block alignment is good enough for me