Rick Allen Posted August 11, 2023 Report Share Posted August 11, 2023 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? Link to comment Share on other sites More sharing options...
A0136 Posted August 11, 2023 Report Share Posted August 11, 2023 Rick Must be a misprint. This is from a Avanti shop manual. Link to comment Share on other sites More sharing options...
Rick Allen Posted August 11, 2023 Author Report Share Posted August 11, 2023 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? Link to comment Share on other sites More sharing options...
wildfelr Posted August 11, 2023 Report Share Posted August 11, 2023 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 Link to comment Share on other sites More sharing options...
A0136 Posted August 12, 2023 Report Share Posted August 12, 2023 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. Link to comment Share on other sites More sharing options...
64Avanti Posted August 13, 2023 Report Share Posted August 13, 2023 .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. Link to comment Share on other sites More sharing options...
64Avanti Posted August 13, 2023 Report Share Posted August 13, 2023 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. Link to comment Share on other sites More sharing options...
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