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M- Main Bearing Questions

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Joe

09-01-2001 20:10:33




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Plan on replacing main bearings in 1951 M.

Is is OK to remove all three bearings at the same time or is it better to remove and replace the Main Bearings one journal at a time?

Also front main journal seems to cause engine to be too tight even though Plastigage shows it to have a clearance of about .005. I can loosen bolts and it turns much easier. Any ideas why?

Thanks for all the good advice in past.

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Joe

09-02-2001 20:55:47




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
Thanks to all for the words of wisdom. Will get back on it later next week and will keep you posted. Happy Labor Day Holiday!!



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Dale13

09-02-2001 14:52:35




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
Make sure the backs of the bearing inserts are DRY,if you have oil on the back side they will be tight.



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Ralph

09-02-2001 09:11:30




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
All: Just a comment about plastic guage while engine is in the tractor. I simlpy take my smallest hyd jack and a wood 1X2 and apply UPWARD pressure on the crank on the NEXT journal closest to the flywheel. It only takes maybe 100 pound of pressure to eliminate any sag in the crankshaft. Takeing the engine out and placing upside down is extra work for only a slight more accuracy. I also apply a coat of light grease to the bearings for first start up so they'er not dry. ralph

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Zonie

09-02-2001 08:35:43




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
I'd check to make sure you have the front main bearing cap going on the right way. if you had it turned around it probably would cause the bearings to bind up.



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Andy Martin - Need to hear from Farmall engine rebuilders

09-02-2001 06:59:37




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
Maybe we'll hear from some experts on engine rebuilding, but I wouldn't replace a 0.005 clearance bearing on an M unless I needed the practice. If you have the engine upside down and dry, that represents 0.0025 running clearance (crank centered in bearing) and the specification for M is 0.002 to 0.003. If the engine is in the tractor, it is hard to get an accurate plastigage reading on main bearings because the crank will sag a little, and you are only measuring a little. If the bearings look good, they probably are, no matter how old they are. I am convinced some of my M's have the factory bearings. You just about can't mic the main journals with the crank in, either, to know whether to buy undersize bearings. Main bearing failures are not real common on M's, in my experience. But I only work on my own tractors, however I do farm full time with them so they are worked extended periods under load.

You can put a piece of lead shot on each end of the plastigage to try to lift the crank up while you are measuring the bearing, but I'm really not sure if that still gives you a good reading.

Now let's hear from some real experienced Farmall rebuilders on replacing M manis in the tractor.

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The Red

09-02-2001 00:03:39




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
Joe I experienced the same problem when I rebuilt a 1951 H 2 1/2 years ago. I did a lot of priming with the starter engaged and spark plugs out before I fired it and had no problems. It was also hard to turn by hand after installing the new bearings.



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Andy Martin

09-02-2001 07:15:49




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 Re: Re: M- Main Bearing Questions in reply to The Red, 09-02-2001 00:03:39  
By the way, Red, and Bill, I was not insinuating the either of you were not expert engine rebuilders, just that the issue of 0.005 clearance was not addressed in your replies, nor the issue of crank sag for checking a crank in the tractor.



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The Red

09-02-2001 07:27:19




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 Re: Re: Re: M- Main Bearing Questions in reply to Andy Martin, 09-02-2001 07:15:49  
An expert engine rebuilder I am not. I am always learning something each day.



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Bill Smith

09-01-2001 23:11:05




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 Re: M- Main Bearing Questions in reply to Joe , 09-01-2001 20:10:33  
I always replaced bearings all at one time. That is engine taken off and over turned and working on it upside down. Working on it right side up, you might want to do one at a time. I always (with engine upside down) would replace all intended bearings and then torque the entire main and rod caps to speck useing plastiguage and then take all bearing caps lose again. I would then see if the plastiguage would correspond with engine specks on clearance. If all checked out OK I would put bearing caps on and torque back to speck. Doing this with engine upside down is easier and probably more accurate becuase the weight of the cranke will not smash plastiguage before you do the initial torque. No gravity concern when doing it upside down. The crank is alot heavier than your bearing caps in other words. I always plastiguage with dry bearings and if it checks out OK I prelube the bearings when I reinstall the caps after checking clearance. You will have to check the specks to see of .005 is acceptable. You might do a plastiguage check on the entire width of new bearing. Maybe it is .005 at a certain point, but .001 out on the edge or something. If you put plastiguage all across the bearing, maybe a variance will be found.

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