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Tractor Talk Discussion Forum

Measuring rod and crank bearings

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steve

06-07-2004 20:25:26




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Can anyone please help me understand how to measure all the tolerances on my crank. I also could use some advice on how to read a caliper dial. I also have some plastigauge measuring divice if anyone is familer with this but also not sure how to use it.




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Ron

06-08-2004 04:09:21




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 Re: Measuring rod and crank bearings in reply to steve, 06-07-2004 20:25:26  
The service manual has the "in-service" range of main and rod journal sizes. If OK, then you use new standard size bearings. Buy a couple of packages of Plastigage (it comes in different "sizes") and follow Ray's post being sure to torque the bearing correctly and not rotate the parts. Carefully remove the cap and match up the width of the Plastigage to the little gauge they give you.

If you are not comfortable with this or your journals are not in spec, get a machinist involved.

Note that there are about a dozen different tolerances on a crank and the rod and mains are the only ones you can do at home. A machine shop with the right equipment is required to check and correct the rest of them.

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Ray,IN

06-07-2004 21:13:47




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 Re: Measuring rod and crank bearings in reply to steve, 06-07-2004 20:25:26  
Start with your dial calipers, and insure they read 0.000 inches fully closed. I assume they read in inches only. The beam is marked in inches containing ten divisions equaling 1/10 of an inch each. Read the beam then add the dial reading behind it. For example: you read 1 inch and 2 tenths(2 of the 10 marks within the second inch), add the dial reading behing the beam reading like this 1.2(dial reading) inches. It's been a long time since using plastigage but I think you place a piece of it in the rod bearing, install the rod cap using the proper torque setting, remove the rod cap and read the plastigage width by comparing it to the scale accompanying the plastigage kit. The torqued rod cap squashes the plastigage consistently to the same width to reflect the clearance in thousandths of an inch each time and is very accurate- but no more so than the accuracy of the user.

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steve

06-08-2004 09:22:50




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 Re: Re: Measuring rod and crank bearings in reply to Ray,IN, 06-07-2004 21:13:47  
Hey thanks for the info. I measured the rod bearings and the crank bearings/journals and the plastigauge reads .003 inch. Is this OK and is it in specs? I also have a about 1/16 inch play in the crank in a push and pull method by pulling on the flywheel and pushing it is this OK?



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RAB

06-08-2004 10:34:57




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 Re: Re: Re: Measuring rod and crank bearings in reply to steve, 06-08-2004 09:22:50  
Only you will know whether they are in spec unless we know the actual engine model!
Crank end float is almost certainly not in spec. About a sixteenth of an inch is not really accurate enough, and 60 thou would proobably eat into your clutch free play setting, let alone tolerances for an engine.
Ovality on crank pins is important and we would not know whether the engine takes thin-walled shells, whether shims can be removed to adjust, or what. Are these plasti-gauge measurements on new bearings or old?
If the crank has been endfloating as much, or more, than you say there may be other issues with the crank/rod specs.
I think you need an expert eye cast across your installation before deciding on what needs doing.
Regards, RAB

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