8ba rod bearing problem

[3739ford]

Without removing the crank and taking back to the machine shop is there a way to remedy two rod bearings when tightened down you cannot turn it over. The motor does not have the heads on it yet just slowly rebuilding the motor.

[cadillac512]

Originally Posted by 3739ford

Without removing the crank and taking back to the machine shop is there a way to remedy two rod bearings when tightened down you cannot turn it over. The motor does not have the heads on it yet just slowly rebuilding the motor.

The problem may be the rods rather than the crank. Make sure the caps are on the matching rods and that they are on the correct way 'round. Then install one at a time to see which is the problem. Finally, you may have to remove the rods and measure them for out-of-round and size. Also the crank throw can be measured in-place with a 2-3" micrometer to make sure the size is correct. Bearing thickness can be measured with a dial caliper or ball-end mic to make sure you don't have an incorrectly marked/packaged bearing.

Terry

[3739ford]

Caps were installed on correct rods. I went ahead and pulled all the caps off and picture 2 and 3 the bearing has a spot that hangs your fingernail. These were new bearings and wiped clean and moly lubed before installing. The motor has only made two complete revolutions with pry bar on the fly wheel.

[JWL]

What are the details? Is this a fresh regrind crank with a larger fillet?

[3739ford]

It is a Mercury crank with 4" stroke that came with the 1CM block. The machine shop just polished it as it was in good condition. Had to bore the engine 3 5/16 to get a good clean bore. Reusing the original rods had the machine shop check for being round all were good. I had the machine shop install the new Egge pistons to the rods. When I picked the block and crank up I had the machine shop recheck the size bearings I needed. According to him I needed .20 under for the rods which I ordered. I cannot remember now where I ordered the rod bearings from.

[Kohnke Rebabbitting]

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Originally Posted by 3739ford

It is a Mercury crank with 4" stroke that came with the 1CM block. The machine shop just polished it as it was in good condition. Had to bore the engine 3 5/16 to get a good clean bore. Reusing the original rods had the machine shop check for being round all were good. I had the machine shop install the new Egge pistons to the rods. When I picked the block and crank up I had the machine shop recheck the size bearings I needed. According to him I needed .20 under for the rods which I ordered. I cannot remember now where I ordered the rod bearings from.

Using a so called good enough crank, could mean it can very in a few tenths in size. Mic closely the pins that turn good, compared to the one that doesn't. As previously stated, check Radius, a .001 to tight is enough to lock a motor.

The black marks in your bearings, are the spots that are touching.

Herm.

[Kohnke Rebabbitting]

Originally Posted by 3739ford

Caps were installed on correct rods. I went ahead and pulled all the caps off and picture 2 and 3 the bearing has a spot that hangs your fingernail. These were new bearings and wiped clean and moly lubed before installing. The motor has only made two complete revolutions with pry bar on the fly wheel.

Make sure you check, rod alignment!

Herm.

[Bob C]

If the old bearings were .020 and they just polished the crank why would
he say you needed .030 bearings.

[3739ford]

He whipped out his little measuring tool and dialed it up on the journal and without hesitation said .30 under.


I found this site interesting: http://pbwdist.com/catalogs/Mahle_Clevite_Bearing.pdf

[Ronnie]

Turn the bearings over chances the size is on them


R

[Lawrie]

Dont use a vernier caliper ,USE a micrometer,
Measure the crank pin diameter,(using a Mic)
Measure the bore of the rod,
Then measure the thickness of the bearing shell, using a 1 inch mic and a 5/16 dowel ,then subtract the dowel diameter from the reading and that will give you the bearing thickness.
Start with the rod diameter subtract twice the bearing thickness and you should have the crankpin size plus the clearance.
Lawrie

[JWL]

If those measurements are reasonably close to being accurate they represent one at .020 under and the other at .030 under.

[Gene1949]

find another machine shop. No REPUTABLE shop would grind a set of rod [journals] like that. God know what else they missed.

[JWL]

There is most likely no problem with having different size journals, with proper coordinating bearings. I would say no problem except for my inability to actually examine the conditions.

[3739ford]

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.

[40 Deluxe]

Originally Posted by Gene1949

find another machine shop. No REPUTABLE shop would grind a set of rod [journals] like that. God know what else they missed.

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.

[philipswanson]

Check it with Plastigage.

[Gene1949]

Originally Posted by 40 Deluxe

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.

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.

[rotorwrench]

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.

[cadillac512]

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