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Massey Harris & Massey Ferguson Tractors Discussion Forum
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main bearings

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8njohn

08-09-2007 06:48:42




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This more a general question about engine rebuilding than anything, but, when rebuilding an engine due to bottom end wear, where the bearings are bad enough that it is affecting oil pressure. What would be the actual bearing clearance? It is hard for me to explain, but when all new you might have .003 thousandths of an inch clearance, and you get say 55lbs of oil pressure. What would you suspect would be the figure when the bearing are bad enough that your oil pressure falls and indicates the need for new bearings?

Sorry for the confusion, kind of a hard thing to clearly ask.

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Don-Wi

08-11-2007 13:37:28




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 Re: main bearings in reply to 8njohn, 08-09-2007 06:48:42  
I think the range that is too much is about .005". Many cranks are ground only .010 under factory specs, so it aint much at all. As a machinist myself I can tell you .001 can make you or break you, and scrap a very expensive part otherwise.

Take A 2 tool steel for instance, which is an air-hardening steel. If you make a boo-boo, you gotta start all over. You can't weld on it because as the name suggests, it hardens just by cooling in air. That also causes problems cutting it. Gotta keep it cool at all times or it gets hard realy quick. (I know, a little more info than you asked for)


Donovan from Wisconsin

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DavidP, South Wales

08-09-2007 11:32:39




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 Re: main bearings in reply to 8njohn, 08-09-2007 06:48:42  
Hello John,
Wear is important but so is ovality. Mains and big-ends should be checked in the vertical and horizontal planes at each end of the journal.
MF give the figure for wear and ovality which must not exceed 0.0015 inches. Regrind or replacement is then required.
Cheers
DavidP, South Wales



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