Main bearing clearance ?

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Model T Ford Forum: Forum 2012: Main bearing clearance ?
Top of pagePrevious messageNext messageBottom of page Link to this message  By david schwichtenberg on Friday, November 02, 2012 - 02:18 pm:

can any tell me what the main bearing clearance is on a model t is? I am wanting to rebuild a engine with out rebabbetting the mains. with out shims I have .005 clearance and was wondering if I could use this as is?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett on Friday, November 02, 2012 - 03:22 pm:

Should be closer to .0015"-.002". You can trim the caps with a file or belt sander to tighten them up. Many of the caps I see as a babbitt guy show signs of this kind of thing, some are really crude. Whatever you do, go slow and easy, and clean the caps after trimming them.
Erik


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, November 05, 2012 - 06:18 am:

For all of the work that you'll put into this, it would be best to replace the babbit. If not, you'll end up with an engine which can't easily be reworked (shim removed), plus, you'll be moving the crank centerline away from the cam centerline.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, November 05, 2012 - 06:57 am:

The front and rear mains in the block mainly wear in the cap, while the mid main bearing also tends to wear upwards into the block due to unbalance in the thin crankshaft + weight of the transmission. You have to check carefully with a straight edge towards the front and rear main babbitt into the block wether there is any play between the straight edge and the mid main babbitt. If it's just a little, you may be able to scrape/work with timesaver on the front and rear mains until you get it straight again. You don't want to adjust the mid main so the crank gets bent - it'll shorten the time until it cracks considerably.
Rebabbitted caps are available from the vendors if you don't want to file the caps.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Monday, November 05, 2012 - 07:25 pm:

Scott I think you meant to say that sanding the caps will bring the crankshaft closer to the cam shaft not farther away. Even so, its good to recognize that David will not be disturbing the babbitt in the main saddles, all he will be doing by sanding the caps (sanding using a flat block, never a file) is closing the clearances from the underside. The tiny amount the crank will actually move toward the cam because the clearance is closer is probably a good thing considering most timing gears have quite a bit of lash.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Monday, November 05, 2012 - 08:48 pm:

The rear main on the Model T crank always wears the most, on a Model T. That is because the transmission is supported in front by the rear main, and the back of the transmission is supported by the ball cap, for that reason, the crank will not arch, or bow on the middle main, as bad as a Model A Ford.

The Model A is the center bearing that wears the most, because of the weight of the flywheel not being supported, as good as a Model T.

David, if you have .005 thousandths with out shims, you are way out of round. If you go down .00350, that will leave 2, or 3 thousandths after that just to get the hole level, and the oil will be going out the part lines as fast as it gets in. With that much clearance, you will have a large egg shaped hole. You never did say if your crank mic's good enough to use?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Tuesday, November 06, 2012 - 06:03 am:

Richard, yes, you are right. That's what I meant. Thanks for pointing out the correction.


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