8ba rod bearing problem

I still have the old bearings separated and marked where they went. If using plastigage what is the desired clearance on rod bearings. Just wanted to check and see how it would turn out. Perfect world would be getting them all the same and that is still option I'm considering. I want to change out front seal to one piece anyway since I'm back inside the engine.
 
3739ford said:
JWL, the front and rear measure the same 2.106 and the two middle ones measure 2.115. I got to ask since I don't know what is the downside of running .030 on front and back and .020 on the middle ones.
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Did you have the crank reground at the same machine shop? Even if they just polished it, should have measured/checked ALL the journals . . . so I'm still not letting them off the hook. :)
 
Gene1949 said:
find another machine shop. No REPUTABLE shop would grind a set of rod [journals] like that. God know what else they missed.
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Wait a minute Gene. Apparently this crank was ground in the distant past when it was common to do this. Either by customer request or the crank guy wanted to save a little wear on his grinding wheels. The engine apparently ran a long time set up this way, so it was not a problem; nothing overlooked.
 
Ford allowed more clearance on the connecting rod big end bearings than they did the mains. My old Mercury manual lists .0005" to .003" for rod big end bearing clearance and .001" to .0026" for main bearing clearances. Side play on the rods is .006" to .020" for two rods on one crank pin.
 
I'd have no problem running dissimilar sized bearings if their crank journals are round,smooth,and correctly sized to their respective undersizes. And yes...it's time to get a micrometer and check-OR-if not possible, careful use of plastigauge on every journal of this crank after determining undersizes with the caliper. The machine shop personnel really should have checked and noted every journal-shame on them.


Terry
 
When journal sizes are odd, I'd be wanting to make sure there was no runnout anywhere. That would make sure things are still concentric with the center line of the crank. There can be a problem if journals are polished too far. Some folks used to lap the bearings too so you never know what your going to find on these old cranks.
 
I removed the pistons/rods with bearings and have everything ready to go back to the machine shop tomorrow. I'm going to see what he figures out and tells me what the problem is. With my cheap measuring tool it seems to me the rod journal is not round, but more egg shaped. Will let you know what the outcome is.
 
40 Deluxe said:
Wait a minute Gene. Apparently this crank was ground in the distant past when it was common to do this. Either by customer request or the crank guy wanted to save a little wear on his grinding wheels. The engine apparently ran a long time set up this way, so it was not a problem; nothing overlooked.
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Precisely my point (distant past), customer request or "saving some wear on his grinding wheels" is a patch job.

Eyeballing a "polish" on a crank without measuring it is not something a reputable shop would do.
I doubt if the crank even had a bath after the polish.
The owner himself picked up on the original patch job (grind) AND egg shaping the journal, who knows.
 
I think you answered your own question when you measured the journals - two are at .020 and two are at .030 . . . a miss-matched affair. Now, if the journals are in good shape, concentric, no taper, etc -- then I can see no real issue with running .020 bearings on two journals and .030 on the others. Would I do it this way . . . well 'No' - but I'm a perfectionist and I wouldn't want the "next guy" to see an engine I built done in this fashion.

BUT - with all that said, if it is about spending less money - then you can probably put it together with the two different rod-bearing sizes - as long as the resulting clearances are correct.

On my Soapbox: What is still of concern is that the machine shop obviously didn't measure the crank . . . so what else didn't they measure? Quality machine work and correct clearances are everything in an engine build . . . .
 
GOSFAST said:
Very accurate statement here, not only on an individual rod journal but sometimes an occasional cylinder bore also! (See photo below, it's just one brand of a "portable" boring bar used at the time for very this purpose)

Many of these type repairs were done with the engine still in the ride, it's how it was done back then!

Thanks, Gary in N.Y.

P.S. At one time I had the "portable" crank grinder along with the boring bar pictured here, I still own this bar, the crank grinder went a long time ago. In retrospect it wouldn't have hurt to hang on to both?? Nice conversation pieces today anyway! I have customers today have absolutely no idea what the bar was used for when I show it to them?
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As a side note Gary, Rottler is having their annual open house to the industry this weekend. Everybody will be there. I first met the old man in 1955.
 
As another side note, I own both a "in-car" crankshaft grinding machine and boring equipment.

I saw the crank grind done once and the operator was very skilled and efficient. The job was a new Rambler 6 cyl. that was under warranty. As far as I know it survived the warranty period and is still going. Grin.
 
JWL said:
As another side note, I own both a "in-car" crankshaft grinding machine and boring equipment.

I saw the crank grind done once and the operator was very skilled and efficient. The job was a new Rambler 6 cyl. that was under warranty. As far as I know it survived the warranty period and is still going. Grin.
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Hey John: Was sitting here scratching my head - trying to imagine how the rod journals could possibly be ground in the car (given the stroke/throws of the crank). Did this magic gismo somehow handle the rods as well? I'd love to see that machine in action! And I imagine it would take a hell of a skilled operator to use it!
 
In car work was usually done on warranty situations where the car was still in near new condition and there was less chance of heavy wear or bending on any of the rotating components. Older components with a lot of wear and tear should get more scrutiny to insure serviceability. A dedicated crank grinding machine is the best way in that situation. Checks are simpler that way and repairs would follow as necessary.
 
Bored&Stroked said:
Hey John: Was sitting here scratching my head - trying to imagine how the rod journals could possibly be ground in the car (given the stroke/throws of the crank). Did this magic gismo somehow handle the rods as well? I'd love to see that machine in action! And I imagine it would take a hell of a skilled operator to use it!
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It was for Rods, NOT mains.

Herm
 
Kohnke Rebabbitting said:
It was for Rods, NOT mains.

Herm
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Hey Herm - just checking . . . RODS, not mains??? I can see a fixture for the mains working, but the rods - that has to be complex! It would have to somehow rotate/articulate with the crankshaft rotation - that seems to be a hard situation to ponder - unless it indexed off the mains in some fashion.

Just curious!
 
The grinder has a hook opposite the grinding wheel, there was a motor to turn the rear wheel, or fit in the place of the starter to rotate the crankshaft , the grinder moves with the rod journal. It can only make the journal round, but the center of the journal will move if the wear was only on one side
 
I had a crank ground in the car on a Chrysler 383. The wheel on the grinder was quite skall and the starter turned the crank with the lugd removed
 
Bored&Stroked said:
Hey Herm - just checking . . . RODS, not mains??? I can see a fixture for the mains working, but the rods - that has to be complex! It would have to somehow rotate/articulate with the crankshaft rotation - that seems to be a hard situation to ponder - unless it indexed off the mains in some fashion.

Just curious!
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The best one was built by Sunnen, Model KN, look on E-Bay. It was made to be used just for Rods mostly when just one pin went bad. You jacked the car up, pulled the pan, put an electric motor and V-belt to turn the crank, the machine was clamped to the pinand the metal was ground the main part of the pin, and centered of, I Think ????????? off the Radius to keep the same stroke.

Herm.
 
rotorwrench said:
Ford allowed more clearance on the connecting rod big end bearings than they did the mains. My old Mercury manual lists .0005" to .003" for rod big end bearing clearance and .001" to .0026" for main bearing clearances. Side play on the rods is .006" to .020" for two rods on one crank pin.
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Most bearing books have a maximum, and minimum for any given crank. On say a 2" crank, the actual minimum size should be .002 thousandths, and plus, one more .000-50 for a maximum.

If you set a 2" crank clearance to .000-50, or even a .001, the crank when hot will expand about .002 thousandths. So what happens is the crank pushes bearing material out of the way until it has the clearance it wants to get enough oil to the bearing to cool the bearing, and stop its expansion, so why waste bearing material, and taking a chance on smearing a bearing.

Depending on how fast the car is driven, most of the time will determine what the bearing clearance will be when, Cold, or Hot.

Herm.
 
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