5.2 Build - main bearing size code identification

[DougS550]

Well…the rest of the story is that I don’t actually plan to use this motor as-is. I bought the block and pistons with the intent of building a 10.2/1 5.4L stroker. I got the rods basically for free and found a good crank so I figured I’d go ahead and assemble a stock predator back-up and convert it to a stroker later. So yea, I’ll be going through this again in a couple months with a 3.840” crank without a ford size code to go by.

Man that sounds great. I was thinking about buying a crate engine or a used aluminum big block to play with and maybe build it my way, and then drop it into my GT. It's just a toy, I don't care about matching numbers or would of could of should of, just having fun. Good Luck

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[engineermike]

I guess I was right....straight from Ford:

 

[DougS550]

I’m currently building a basically stock Predator short block. The ford procedure for selecting the main bearing thickness, or “grade”, is described here:

https://www.mustang6g.com/forums/threads/bbq-tick-test-request.117273/page-2#post-2467476

However, the code on the block is:

I have reason to believe the main bearing code is the first string of characters, but I also have reason to believe it’s the second string of characters. So which is it?

And before anyone suggests it….yes I’m dead-set on using oem bearings not aftermarket.

Hey Im with you on using OEM bearings. Let us know what the current bearing sizes are and the increments they have between sizes. Thanks

 

[engineermike]

Hey Im with you on using OEM bearings. Let us know what the current bearing sizes are and the increments they have between sizes. Thanks

You buy the bearing by the grade and mix/match, yielding 5 possible combinations. Ford doesn't tell you the actual thickness of the grades. I guess I could measure the corner and see what it is for a grade 1 and 2, at least. I trust Ford's numbers over my own, though.

The block and crank have a manufacturing tolerance (not to be confused with service tolerance) of +/-0.0005, so the clearance could vary+/-0.001 at the same bearing thickness. Since there are 5 combinations of bearings, that would mean they're splitting up the 0.002 into 5 possible segments of only 0.0004 each, meaning the manufacturing clearance tolerance is actually +/-0.0002.

The service spec on the clearance is 0.0011-0.0025, or +/-0.0007. This means that the service tolerance is about 3x greater than the manufacturing tolerance.

Most machine shops use the service tolerance as a go/no go, but you can see the OEM is much more precise. This is why I use OEM parts and prefer OEM final machining/finishing as much as possible.

 

[DougS550]

You buy the bearing by the grade and mix/match, yielding 5 possible combinations. Ford doesn't tell you the actual thickness of the grades. I guess I could measure the corner and see what it is for a grade 1 and 2, at least. I trust Ford's numbers over my own, though.

The block and crank have a manufacturing tolerance (not to be confused with service tolerance) of +/-0.0005, so the clearance could vary+/-0.001 at the same bearing thickness. Since there are 5 combinations of bearings, that would mean they're splitting up the 0.002 into 5 possible segments of only 0.0004 each, meaning the manufacturing clearance tolerance is actually +/-0.0002.

The service spec on the clearance is 0.0011-0.0025, or +/-0.0007. This means that the service tolerance is about 3x greater than the manufacturing tolerance.

Most machine shops use the service tolerance as a go/no go, but you can see the OEM is much more precise. This is why I use OEM parts and prefer OEM final machining/finishing as much as possible.

Do you plastic gauge or use another way to set the gaps?

 

[engineermike]

Do you plastic gauge or use another way to set the gaps?

I could….probably already have some…but no measurement method I use comes within an order of magnitude of accuracy to what ford does. They have 25 divisions within a thousandth of an inch. Im lucky to get 4…. I just don’t think I’m going to learn anything from it.

 

[DougS550]

I could….probably already have some…but no measurement method I use comes within an order of magnitude of accuracy to what ford does. They have 25 divisions within a thousandth of an inch. Im lucky to get 4…. I just don’t think I’m going to learn anything from it.

I must be missing something. If you polish your crank/ROD journals how do you know the exact gap clearance of each journal?

 

[engineermike]

I must be missing something. If you polish your crank/ROD journals how do you know the exact gap clearance of each journal?

I’m not polishing the journals. Like I said earlier…I much prefer the oem machining and finishes.

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