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Old 11-16-2019, 03:35 AM   #1
pbishop
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Default Main and Rod Shim Sequence ???

TWO questions -


First, is there a 'sequence of order' for making shim adjustments for clearance/drag on 'main bearings' - either with the motor in the car, or out of the car and on a stand? If so, what is the sequence?



Second, is there a 'sequence of order' for making shim adjustments for clearance/drag on 'rod bearings' - either with the motor in the car, or out of the car and on a stand? If so, what is the sequence?
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Old 11-16-2019, 06:27 AM   #2
PalAl
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Default Re: Main and Rod Shim Sequence ???

This might help a little, I'll see what else I can dig up
Attached Files
File Type: pdf Main-Bearing-Clearances.pdf (887.3 KB, 126 views)
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Old 11-16-2019, 11:55 AM   #3
redmodelt
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Default Re: Main and Rod Shim Sequence ???

Rods or mains, in the car or out are fitted in the same way. You will note I said fitted not replaced.

Not sure what you mean by in what order? Do you mean check the mains then the rods or?

While checking both the rods or mains can be done under the car I personally would not recommend doing the mains with the engine in car but it can be done.



In the car I start with No 1 rod. I use aluminum foil instead of plastagauge. I fold a 1X1 spare to the thickness of .001-.0015. I check fit using the foil, if the crank is hard or snug to turn I call it good remove the foil, oil the cap, button it up and go on to the next one.

If it needs adjustment, after pulling the cap I check the thickness of the shim pack for each side. Often you do not end up with both packs having same number of layers on both sides. I take a layer off the thick side to start with then test fit. After that I go back and forth till I get the fit wanted. After final fitting of each rod, remove the foil and oil and replace cap, torque the nuts to 30-35FTP rotate the engine with the crank to check for binding for each rod as it is done.

I use the aluminum foil because experience has shown me that Plastagauge does not spread like it would in a shell bearing and get false readings using it.

While I have not done a test, I think using foil or Plastagauge requires the just about as much work, pulling the cap removing a shim and rechecking.

The rod shims as well as mains are laminated, each layer is approx .002 thick +/- some. If you are doing in car, just be prepared to be getting under the car and out from under the car multiple times for each rod.

If there are no shims, the refitting can be done but takes some experience to keep the caps flat and is not recommended for average person, would be better if new rods or main bearings are fitted if the babbitt is worn to much.
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Last edited by redmodelt; 11-16-2019 at 12:06 PM.
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Old 11-16-2019, 01:03 PM   #4
Bob C
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Default Re: Main and Rod Shim Sequence ???

Isn't there something about not taking more shims out of the center
main than the front or rear??


Bob
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Old 11-16-2019, 02:01 PM   #5
Patrick L.
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Default Re: Main and Rod Shim Sequence ???

Quote:
Originally Posted by Bob C View Post
Isn't there something about not taking more shims out of the center
main than the front or rear??


Bob

I've heard/read that. Makes no sense to me.
When I've done them in the car, I put slight jack pressure on the crank to seat the crank in the upper bearing. I'm one that uses plasti-gauge and set all bearings to .0015". The one exception is the rear main which I usually set a bit tighter. I also keep the shim packs equal thickness for one bearing. I usually have trouble peeling shims so I usually just sand them on a piece of glass.
Usually you'll find more clearance in the center main than the front or rear.
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Old 11-16-2019, 02:03 PM   #6
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Default Re: Main and Rod Shim Sequence ???

Bob good question. The down/power thrust(not talking back and forth) is on the caps more so then the block, so I would set all the mains to get the correct clearance. If there is more wear to the center cap from what I have read, I would not set the front and rear to .001-.0015 and leave the center at maybe .002+ by only taking off the same number of shims. As it is I have not really seen an engine that all the rods/mains needed the same number of shims removed for each rod or main when refitted. Without filing the caps, sometimes it is a compromise get clearance in the ball park, esp on a crank that is maybe a little worn or out of round.

Others may have different op, but this is what has worked for me.
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Old 11-16-2019, 05:49 PM   #7
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Default Re: Main and Rod Shim Sequence ???

pbishop there is a lot of info here on the "Barn" if you do a search

Try this https://fordbarn.com/forum/showthrea...3525&showall=1
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Old 11-16-2019, 09:16 PM   #8
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Default Re: Main and Rod Shim Sequence ???

Quote:
Originally Posted by Patrick L. View Post
I've heard/read that. Makes no sense to me.
When I've done them in the car, I put slight jack pressure on the crank to seat the crank in the upper bearing. I'm one that uses plasti-gauge and set all bearings to .0015". The one exception is the rear main which I usually set a bit tighter. I also keep the shim packs equal thickness for one bearing. I usually have trouble peeling shims so I usually just sand them on a piece of glass.
Usually you'll find more clearance in the center main than the front or rear.
What the reference is to, the middle main, as most know, the hanging weight of the flywheel, causes the the crank to bowed, center bearing up, and rear bearing down.

In a center bearing, you can find .003, to .020, or burned out.

So, if the front is wore .004, and the rear is say wore .006, and the center wore .010, and you adjust all to .001-50, T

That would be No. 1 tightening of 002-50.

No. 2. would be .008-50.

No. 3. would be .004-50.

So when adjusted, to .001-50 thousandths, you have a bow in the crank, and when it runs, it will flex, which is a good way to break, a crank, and will have a vibration.

The other thing that happens, is the off center main will eat the bearing out until the pressure gets off the cranks center main bearing, from the bow, held in the bearings, after adjustment.

Herm.
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Old 11-17-2019, 08:00 AM   #9
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Default Re: Main and Rod Shim Sequence ???

Quote:
Originally Posted by Kohnke Rebabbitting View Post
What the reference is to, the middle main, as most know, the hanging weight of the flywheel, causes the the crank to bowed, center bearing up, and rear bearing down.

In a center bearing, you can find .003, to .020, or burned out.

So, if the front is wore .004, and the rear is say wore .006, and the center wore .010, and you adjust all to .001-50, T

That would be No. 1 tightening of 002-50.

No. 2. would be .008-50.

No. 3. would be .004-50.

So when adjusted, to .001-50 thousandths, you have a bow in the crank, and when it runs, it will flex, which is a good way to break, a crank, and will have a vibration.

The other thing that happens, is the off center main will eat the bearing out until the pressure gets off the cranks center main bearing, from the bow, held in the bearings, after adjustment.

Herm.




I'm not quite sure what you're saying, but, thats OK. I guess we can maybe agree to disagree. I certainly don't do this as often as you, but I haven't ruined a bearing or crank yet. [ for whatever thats worth].

I like the bearings [ rods and mains] at .0015" [ no more than .002"] with each side of the shim pack equal thickness.
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Old 11-17-2019, 09:01 AM   #10
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Default Re: Main and Rod Shim Sequence ???

PalAl - Excellent article. Thanks!!
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Old 11-17-2019, 01:44 PM   #11
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Default Re: Main and Rod Shim Sequence ???

Not trying to start an augment but wouldn't the centrifugal force of the spinning flywheel and down ward power stroke negate the bow?
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Old 11-17-2019, 04:11 PM   #12
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Default Re: Main and Rod Shim Sequence ???

I like the bearings [ rods and mains] at .0015" [ no more than .002"] with each side of the shim pack equal thickness.[/QUOTE]


Me too.

Herm.
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Old 11-17-2019, 04:45 PM   #13
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Default Re: Main and Rod Shim Sequence ???

Quote:
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Not trying to start an augment but wouldn't the centrifugal force of the spinning flywheel and down ward power stroke negate the bow?
The crank would be out of alignment at the bearings, the worst, at rest, and when running, the centrifugal force of the flywheel, tries to put the shaft back into a straight line, it has to force its self free, wearing the bearings, and enlarging and flexing the shaft. 3-4 thousandths in all 3 bearing, not much of a problem, any larger adjustments, can be.

Even in the K. R. Wilson Model T, and A Tool catalogs, I think he mentioned that effect. Every one should read these. Lots of information.

Thanks,

Herm.

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Old 11-17-2019, 04:49 PM   #14
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Default Re: Main and Rod Shim Sequence ???

Quote:
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Not trying to start an augment but wouldn't the centrifugal force of the spinning flywheel and down ward power stroke negate the bow?
Mr. Red, I missed the word " NEGATE ", short answer, No.
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Old 11-17-2019, 05:42 PM   #15
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Default Re: Main and Rod Shim Sequence ???

Thank you.
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Old 11-18-2019, 11:31 AM   #16
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Default Re: Main and Rod Shim Sequence ???

This is the one problem with the de-shimming theory of repair. The centerlines of the bearing bores gradually go off center as they wear. If one wears a lot more than the others no mater which direction of oblongation, it puts the crank in a bind when you deshim the mains since it will still be off center. Rods are not so much a problem in this respect.

My last boss was an Army retiree. Back in the 50s when he was changing MOS from truck driver to aviation mechanic, he was going through school for a several months as I did when I was in the Army. One of his classmates wasn't too far away from home and he had an old model A to drive back & forth. After each trip his center main was starting to knock. He would go around the billets and find someone that needed some new boots so he could get there old ones and cut the tongue out of them. He would pull the pan off and put the tongue piece in the center main and bolt it back up. He would take off on the weekend and come back knocking each time. I guess this lasted quite a while because my old boss got out of the school and never saw the guy again but the car was still operational. I though I was conservative but that would have been just too much work for me.
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Old 11-18-2019, 12:02 PM   #17
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Default Re: Main and Rod Shim Sequence ???

Quote:
Originally Posted by Kohnke Rebabbitting View Post
I like the bearings [ rods and mains] at .0015" [ no more than .002"] with each side of the shim pack equal thickness.

Me too.

Herm.[/QUOTE]



I think I understand what you were trying to say, but, there was still some question. I understand about the 'bow', I'm not a big fan of that 60# wheel and only 3 bearings. But thats 1930s stuff and what we have to deal with. Every bearing I adjust I then make sure the crank turns freely. Maybe we're just taking different directions to get to the same place.
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Old 11-19-2019, 12:15 AM   #18
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Default Re: Main and Rod Shim Sequence ???

Thanks for the informative discussion. So I think that I get it … about the normally greater wear on the center main. It seems that the best procedure for an "in the car" adjustment would be as follows.
First set up the front and rear bearings to .0015 - .002 and note the amount of shims that were removed.
THEN, take that same number of shims out of the center main and just live with the slightly greater clearance at that bearing. Thus avoiding the bowing that would have resulted from going to .0015 - .002 at that center bearing.
Makes sense to me .
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Old 11-19-2019, 12:51 AM   #19
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Default Re: Main and Rod Shim Sequence ???

Millions of A's have no doubt had their mains 'tightened' with no thought given to any bowing of the crankshaft. How many, percentagewise, then broke their crankshafts? (Not counting the ones hopped up and raced, obviously).
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Old 11-19-2019, 09:51 AM   #20
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Default Re: Main and Rod Shim Sequence ???

I don't know about millions since there were only around 5 million made but I'm sure a lot of them were shade tree repaired. A lot probably ended up in scrap iron drives during the war too. If a crank broke, you just went to the junk yard and bought another engine or you went to the used car lot and bought another car. It depended on how much money you were making at the time. During the war, folks had to make due with what they had since auto manufacturing dried up but there were still used cars available from service men going overseas. My Pop sold his 35 Tudor in Florida before he and his crew left for the ETO. He bought a 41 Tudor after he got back in late 1945.
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