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Old 04-29-2020, 07:48 PM
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Default Any Ford engine builders in the house? have a question.....

Putting together a 302 from a fox body mustang GT
It had excessive main bearing wear that was giving it oil pressure fits. From what I have read this is the achilles heel of these engines. So, I had the crank cleaned up at .010 off the rods & .020 of the mains.

Checking things before re-assembly and the spec I am finding via google on the crank mains range is 2.2482 to 2.2490. so I was looking for 2.229 or less on the freshly ground crank, but I am measuring 2.2295. Is that a little too snug? Maybe .001 bearing clearance.?

I am unsure what the main bearing gap should be but I am guessing .0015 - .002" ?

any thoughts or insight.?

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Old 04-29-2020, 08:43 PM
hurryinhoosier62 hurryinhoosier62 is offline
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Do you have access to a Mahle bearing catalog? All the suggested bearing clearances are listed in there. If I remember correctly there is also an online version in the PDF format. .001 for a performance engine main bearing clearance is way too tight. Normally on a performance engine it's .001 for every inch of main journal size. I would suggest you start with .002 and go from there.

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Old 04-29-2020, 09:53 PM
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Thanks for the tip on the clevite / Mahle catalog. The book confirms the sizes I listed above & shows "vertical oil clearance at the following.

Std shaft diameter
2.2482 / 2.2490

vertical oil clearance
0.0005 / 0.0029

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Old 04-29-2020, 09:59 PM
hurryinhoosier62 hurryinhoosier62 is offline
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Quote:
Originally Posted by 68ragtop View Post
Thanks for the tip on the clevite / Mahle catalog. The book confirms the sizes I listed above & shows "vertical oil clearance at the following.

Std shaft diameter
2.2482 / 2.2490

vertical oil clearance
0.0005 / 0.0029
At .002 you should be OK. SBFs can be a little quirky, especially on their oil systems. Be sure to disassemble the oil pump, thoroughly clean it and double check all clearances and bypass valve operation.

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Old 04-29-2020, 10:49 PM
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Quote:
Originally Posted by 68ragtop View Post
Putting together a 302 from a fox body mustang GT
It had excessive main bearing wear that was giving it oil pressure fits. From what I have read this is the achilles heel of these engines. So, I had the crank cleaned up at .010 off the rods & .020 of the mains.

Checking things before re-assembly and the spec I am finding via google on the crank mains range is 2.2482 to 2.2490. so I was looking for 2.229 or less on the freshly ground crank, but I am measuring 2.2295. Is that a little too snug? Maybe .001 bearing clearance.?

I am unsure what the main bearing gap should be but I am guessing .0015 - .002" ?

any thoughts or insight.?
Usually it’s more to the rear seal being notorious for leaking at 150k and less oil (if the owner isn’t watching) hurts the back bearings.

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  #6  
Old 04-30-2020, 06:18 AM
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Thanks Guys, I have a feeling this might put me at less than .002" I will torque down the main caps & measure the inside of the bearings, or plastic gauge them. Most of the cranks I have had turned measured at max spec to .0005 under. So when this was half a thusands over it has me concerned. Its going into a completely stock 1983 with something like 170? hp, so I don't think it needs to have racing tolerances, but I don't want to squeak a bearing either.

The measurements I posted just above are from Mahle's book. is the .0005 they list the wiggle room? And if so is that only on the thrust bearing?

Here is the page From Mahles book & I am using their clevite 77 bearings. I should have posted this right up front. Let me know your thoughts when you have time.

I don't build a lot of engines, but normally I just measure the crank journals & if they are at spec or slightly looser & install them. Also, for what its worth I am using a calibrated mitutoyo caliper, Not a digtal slide micrometer.


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  #7  
Old 04-30-2020, 10:04 AM
hurryinhoosier62 hurryinhoosier62 is offline
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Calipers aren’t the best method to measure a crank journal. I have no problem with home builders using Plastigage. Using a mic accurately is an acquired skill that comes with use. It’s funny( odd, not humorous) to see the difference in journal sizes obtained between a novice using a mic for the first few times and someone who has used a mic thousands of times. I’ll reiterate what I said last night; stay around .002 and you should be OK.

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Old 04-30-2020, 01:04 PM
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Dang, micrometers is what I am using, not calipers. When I said "not a slide calipers" it would have been better to use the right word. My bad.....

So, moving forward I put the bearings in & torqued the caps to spec. measured the crank journals & Placed the micrometer in the vice. Zero'd out the bore gauge in the mic & measured the bearings.
They are for sure a little too tight. .0009 to .00165 I will run the crank back to the machine shop. Better that its too big than too small I suppose.
Not sure why I always want to call anything that measures from the outside a caliper. Sorry for adding to the confusion.

I will see if he can resize so I have .002 - .0025


These are my measuring tools, Hopefully after this I will call them the correct thing

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78 S/E Trans am W72, WS6 Auto
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80 Indy pace car Trans am
89 Trans am GTA
  #9  
Old 04-30-2020, 03:49 PM
hurryinhoosier62 hurryinhoosier62 is offline
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Your tools are fine; Mits are good quality. At this point you have two options: re-polish the crank or align hone the main saddles. Of these two, align honing is the easiest way to gain the clearance you need.

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  #10  
Old 05-20-2020, 10:14 PM
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Thought I would follow up. Machine shop polished off about .001 on #1 & #5 & .0005 off the centers. clearances measured great afterwords. all just a fuzz under .002" Engine is back together, in the car & running great with gobs of oil pressure now.

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  #11  
Old 05-21-2020, 01:06 PM
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If you are building the motor to make the same amount of power and same usage, then the cap-walk problem is most likely going to come right back. A HUGE percentage of Dart Windsor block users started off by trying to make good power with a stock block. I'm one of them :-)

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