CONNECTING ROD CLEARANCE

[Rick Allen]

Trying to determine the connecting rod bearing clearance after I had my crank polished, shop said it was in good condition and only needed to be polished, not cut and use std. bearings. 

Under the engine section of the workshop manual, if I'm reading the correct specifications for what I am trying to measure, it lists the connecting rod bearing clearance as to being .00025 - .00275 inch.  

Is .00025 even measurable with plastigage, the green plastigage goes from .001 - .003 inch; or am I misinterpreting something here wrong?

[A0136]

Rick

Must be a misprint.  This is from a Avanti shop manual. 
 

[Rick Allen]

13 hours ago, A0136 said:

Rick

Must be a misprint.  This is from a Avanti shop manual. 
 

I also thought it could be a misprint, and it is also from the Avanti workshop manual, page 5 of general specifications, wonder if it could be some other type of connecting rod measurement?

 

[wildfelr]

RQB3263 /81/305 .... WOW ... I THINK THEY MISSED IT BY ONE DECIMAL POINT.... MANY MOTORS LATER .0015 IS ABOUT THE MINIMUM IVE EVER SEEN.... PLASTIGAGE TO CHECK  AND BRASS SHIM STOCK TO ADJUST ...DONT COVER ANY OIL PASSAGES ....WRG

[A0136]

Miss print or not .00025 ( 25 hundred thousands ) or 1/4th of 1 thousandth is not enough clearance. Oil is needed for lubrication and cooling of the bearing. While tight clearances will help keep oil pressure up, too tight and the bearing will burn up.  Plastigage  is not super accurate but when used correctly is a good way to check or double check clearance.  .001 to .002 is a good rod bearing clearance for a street driven Studebaker  V8.      I was looking in a 59-64 Studebaker shop manual for rod bearing clearance for 63 and 64 Jet Thrust and Super Jet Thrust  engines, the Lark and Hawk version or the R1 and R2. It shows .0005 to .002.  

[64Avanti]

.0005 is way too close!  Besides the need for cooling if the engine is revved to high rpms the big end of the rod will distort enough to pinch the bearing and you will end up with a spun rod bearing.   You should have more like .002 in of clearance. 

[64Avanti]

What I didn't say is that given the tolerances on the rod bores, crankshaft journal sizes and bearings it is possible to end up with clearances that are too small.  In that case you may need to make adjustment to the crank or the rod.   You will have to work with an automotive machine shop that knows what it is doing.  If you have a mild street engine and don't rev it very high then .0015 could be accepted.