36LB Rod side clearance question...

Randy

Randy

Well-known member
Is there a spec for rod side clearance on a 36LB 21 stud flathead? I'm used to building later small block Fords where you measure the rod side clearance with a feeler gauge, so was surprised to find a lot of rod side clearance, like several hundred thousandths, on a 36LB I'm looking at. It just seems like all of the oil pressure would be lost from all of that clearance. There are no flanges on the bearings to keep them located and they will slide back and forth between the crank throws.

Another way to put it would be, do you measure the rod journal side clearance with a feeler gauge or a tape measure?

Thanks!
 
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I thought '36 will have a flange on the sides of the bearing like most rear main bearings only on the inside to control side clearance, mine do. I guess later inserts are flangeless and the crank surface does it. So you have 81 series inserts and not 48, I would guess. Also takes a bunch of hassle on some to get them to "float" and not bind on the rods. Check the archives for a description on how it's done, I worried through it with reconditioned rods, but can't explain it myself, been a few.
 
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Barry WNY said:
I thought '36 will have a flange on the sides of the bearing like most rear main bearings only on the inside to control side clearance, mine do. I guess later inserts are flangeless and the crank surface does it. So you have 81 series inserts and not 48, I would guess. Also takes a bunch of hassle on some to get them to "float" and not bind on the rods. Check the archives for a description on how it's done, I worried through it with reconditioned rods, but can't explain it myself, been a few.
Click to expand...

I AGREE,

You need the earlier bearings as stated above and be sure they do "Float" when you install them.

Chris
 
You have the wrong inserts, they should be flanged bearings. Everdently you don't have the old bearings that came out of the engine. Walt
 
I believe .006-.010 is recommend for street and .012-.015 for compitiom. However, every builder has his own ideas.
 
Thanks for all the input. This is an assembled engine, I've only pulled the pan off to inspect it. So the rod bearings are supposed to have a flange on each side to fill up that gap? I've never seen anything like that. There are two insert halves for each of the 4 pairs of rods and those insert halves are supposed to be flanged?
 
Randy said:
Thanks for all the input. This is an assembled engine, I've only pulled the pan off to inspect it. So the rod bearings are supposed to have a flange on each side to fill up that gap? I've never seen anything like that. There are two insert halves for each of the 4 pairs of rods and those insert halves are supposed to be flanged?
Click to expand...
That's wild. You could pull one out & size it, get a set and change them out one at a time but then I would have to wonder what surprises are with the mains, piston pin keepers, ring end gap & stagger, piston orientation (FRONT in front), oil tube plugs, valve clearance etc...
The rod bearings are overpriced so would proceed with caution. If standard size, good buys on the 'bay.
Also, running like that would the rods have a chance of bending? Someone with 'sperience may know.
 
This engine was rebuilt but never fired, there's no carbon on the pistons, everything looks new. I'm wondering if they didn't try to prime it and got no oil pressure so never fired it? You're right, it certainly puts everything into question. Thanks!
 
There were some rods made with small lock cuts in where the bearing seats to lock the rod bearings to keep them from turning. These were thick bearings like the full floating but with no flanges. We rebuilt a Canadian 59-C about 25 years ago and tried all over the USA and Canada and I even call Federal Mogal and Clevite and couldn't locate bearings. One company went down in the basement and found the drawings but hadn't made any since the early 50s, the other company couldn't find any record of ever making them. Call Harvey at Dennis Carpenter he knows about them. He said at the time they had several barrels of the rods but never saw a bearing. He said they resized the rods and put floating bearings in. I was a little worried about the lock cuts riding on the bearing surface but that's what we did and as far as I know the engine is still running. I don't think they had a lot of side clearance. G.M.
 
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Installing floating bearings is a mathematical operation.
1. Measure crank dia.
2. measure the thickness of the bearing shell
3. These numbers determine the rod bore.
Example:

Crank= 1.998
bearing shell thickness. .110
Times 2 = .220

.002 clearance on crank and in rod= .004'

Add 1.998 + .220 + .004 = 2.222"

Now if your parts don't add up right you have to compensator for the change. One place to look is the thickness of the shell, some are as small as .108".

I have a box full of used bearings that are good and I interchange to get clearance.
I do not like to use Ford OEM bearings, these have a tendancy to flake, ahd was one reason we went to a Fule flow oil filter.

Ain't this fun??
 
I forgot to mention. After you get all the numbers right, you have to wavk em with a hammer to get them round. This is the tricky part.
 
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