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Milodon Main bearing caps


FBBO Gold Member
FBBO Gold Member
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4:05 AM
Jun 1, 2020
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Lake Wales Fl.
Has anyone done this to their 383 or 440 motors. My motor guy says my old motor was trash due to the front main cap was lose. This seems to be one of the things that kill our motors. I was searching on the net and found that the Milodon caps can be used in the motor after extensive machine work done on the block. It is true that finding a motor shop is getting harder and harder. Think it might be the answer in steed of trying to find another block. I was wanting a motor to be bored less than 30 over in the cylinders. So, had to buy another block to meet my needs. My motor guy showed me the cap wobbled and moved in the register area. That would wipe out the main bearing. Also damage the crank. If anyone have thoughts on the subject would enjoy hearing them. Save our motor's.
If the cap "wobbled and moved in the register area", then it likely spun a main bearing, and yes, would need another cap to make the block work. Finding a used cap that will match the block at the parting line can be difficult. The new Milodon caps will work if the block has not been too damaged, but WILL require "Line Boring" to fit them. If a shop says that the new caps can be "Line Honed", they are wrong. New caps provide about 0.020" of extra material to fit them, and can not be honed, but rather must be bored to fit. With the cost of the Milodon main caps, and line bore, it could be cheaper to find another block. Caps also cannot be stretched out to regain the block fit because they are a ductile iron, and will break (don't ask how I know)... I occasionally will stretch rod caps to fit correctly, but they are a forged iron, and won't break with minor nudging.
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That info is rewarding. That is why I was asking the question. These blocks are getting harder to find and getting one that is in better shape than what you have. So, what was the results in the Milodon cap.
I don't understand your last question. "So, what was the results in the Milodon cap."
Did it brake or fail. Looking at their page for the replacement cap Thought it would be stronger. Understand about cast and other metal. Have not asked them if they are heat forged. Finding another block is getting harder and harder. There is no more junk yards where we can pull a motor that the car has low milage on. So appreciate the info. Thanks.
When a bearing spins, it creates an enormous amount of heat which allows the cap to stretch away from the crank/block which, in turn, pulls the parting line ends inwards. This is what makes the caps fit loose in the block. It is also the reason the caps are black as the oil is baked onto them due to the heat. A stock cap can work if it matches closely with the block at the parting line. What I mean by match is this; looking down the main bearing tunnel from the front, the hole was machined with the caps installed, so the bore is in the same plane between the two. Now, you get a cap from a different block, and it is not guaranteed that the bore is in the exact same spot as the original, so when the stock replacement cap is placed on the original block, it might not line up with the original hole, so it could be shifted to one side or the other. The closer the fit, the better the line hone will be. Milodon Billet caps are meant to be a high performance replacement for stock caps when the HP is increased greatly. They can be used to repair a block with a spun bearing and bad cap, but must be line bored to fit the caps. The cap I broke in the press trying to spread it out like I do rod caps, and it didn't work. But it didn't work in a most awsome way!! :thumbsup: