Bearing clearance

Peter J

Peter J

Well-known member
Hey guys,
I pulled the pan to tighten up the rods. Looks like a fairly new rebuild as the shims were in place. I pulled the caps, removed the shims and checked for .0015 clearance with plastiguage. The bearings look great. Problem is when I get between .0015 and .001 and re-torque the rod, it's frozen solid on the crank. I finally ended up adding shims again until I could get the crank to get it to turn. How stiff should it be? Any ideas?
Thanks Again
Pete
 
Were you removing shims on one side at a time? If not, alternate adding/removing shims from each side until the clearance is adequate. Depending on what the wear pattern looks like (or lack thereof) would dictate to me how tight I would make them.
 
Peter;

I have just done the same thing as you except that I use the "tin foil" method. I place the tin foil (Reynolds Aluminum wrap folded for two thicknesses ie 0.002") in the cap and remove shims, alternating from side to side until, with 35 lbs torque on the rod bearings, I can no longer turn the crank manually.

I then remove the tin foil from the cap and retorque to 35 lbs and check to ensure that the crank turns farirly easily. If it does - good to go. If it doesn't I remove another shim from one side.

On another engine that I had I snugged the rod bearings a little too tight and lost some babbit, from overheating I guess. On this engine I set the bearings so that the crank was very stiff to turn manually - too stiff as it turns out.

Dick
 
That's a puzzler. Why would we be measuring clearance if the bottom line is playing with shims? Actually thats the way I would tighten up the rods when I was a kid but I thought I'd be "scientific" this time. What about Les Andrews' spec. on .001"? By the way the crank journals look fine also.
 
Peter;

If I can't move the crank manually with the 0.002" tin foil, but I can move it without the tin foil, then the clearance is less than 0.002". The tin foil method also compensates for the weight of the crank when doing mains, but you are doing rods so that does not come into play.
 
Dick,
I guess that's what I don't understand. How could remove a shim and be able to move the crank? I seems the less shims, the tighter the rod. I still can't understand that if I get .0015 <> it freezes up?
Pete
 
I thought it might be a little OOR and that sure makes sense. I've got a cheepo mic. and I show about .001 variation. I did check one a second time but I got the same results. Maybe I'm dealing with a worn crank but their doesn't seem to be any abnormal wear at all on the bearings I've been playing with.
Pete
 
Hi Peter, You have to take into account a little "black magic" here. Here's what I mean: You need to know what the clearance was when you took the rod or main bearing apart - measuring by torque wrench or by feel note what torque the nut "broke free" as you unscrewed it from the bearing cap stud. So, you would measure with your plastiguage what the existing clearance is, then decide what shims to remove to get it to spec (0.001 - 0.0015) then PG it again with the shims removed and the caps re-torqued. PROBLEM: there is no guarantee that the castle nuts will line up with the cotter pin holes at the same torque as you dissassembled the caps! Furthermore, the brass shims are squishy, and will register differing thickness depending on what the actual torque is that the nuts are tightened to. Are you getting the picture here? Or, in other words, the constants aren't, and the variables don't.
Some of the guys have gone to using Marsden nuts to overcome these problems, and I have to say that I wonder why the whole hobby has not done so. Perhaps it is because they are hard to find in the necessary grade 8 or C-grade hardened steel.
The engine should turn over at no more than 50 foot-pounds of torque. Hope this helps you... Happy Motoring!

------------------

burlingtoncrankshaft.com
 
The last engine I took apart was a Model B block with a Model A "B" head. The car was driven with too much spark advance and after a few miles of pinging the pistons overheated and started to wedge in the bores. This caused the rod caps to have to pull very hard to pull the pistons down, and the rods were VERY much out of round.

Out of round rods can cause tightness, but still show a gap in some areas.
 
The babbitt on the rods are gray still so I assume they are relatively new and haven't been abused. I like the idea of sneaking out a shim at a time until it gets hard to turn then put it back but that still answer the specs. I try to snug them down between measurements to approx. the torque setting since that's how I originally discovered that the plastigage measurement and free rotation don't necessarly match up. Should I get free movement and guage it just to see what I have for clearance?
 
If you have 0.0015", it doesn't freeze up. However, if you place a 0.002" piece of tin foil in the bearing and bolt it up, it will frreeze up because you have a 0.0005" interference. Thus you know that you have a clearance of less that 0.002".

I'm probably not doing a good job of explaining it. The website "two doors and forty horses" has an excellent explanation of the procedure. For some reason the website currently does not work. I think that there was a post earlier about it.
 
Dick;
Why are you getting in a p-----g contest on this subject when you're absolutly right. I use this method with great results as long as you have a round jounal...works with rods too!
Bob F
 
INTERFERENCE FITTING OF BEARINGS
Mike Flanagan had posted his description of interference fitting of the main bearings in the Model A engine. Because of the weight of the flywheel and the flexibility of the Model A crank,plastigauge my not be a reliable method of adjusting the bearing clearances.
Here's Mike:
How do you check the clearance on the bearings? It is not QED but can be done if you can lay on your back and work with oil and grit and grime falling in your eyes.
First you gotta drop the pan, let it sit overnight to get all the oil that will fall out to do so. You are still going to get oily. Pull the damn oil pump out and lay it aside. You can shine a flashlight up in there to see which way the tang is oriented to reinstall and with it out there won't be so damn much blood on it to clean off it.
Then I start with the center main. This one requires that the valve cover be taken off as the nut is in side there. The other nut is between 2 and three outside on the other side. Remove the cap being careful to keep the shims on the same side as they came from. Visually inspect the bearing for cracks and places at both the front and back that look as if it has been compressing the babbitt
and pushing it forward or to the rear. Bad signs if so. To check the clearance, use a piece of aluminum foil .002 thick. The heavy duty she buys to do heavy-duty things is .002 but the regular like you cook a baked potato in is .001 so you fold it. You want a piece as long as the cap and about 1/2 wide. Lay this in the cap and with the SHIMS BACK IN THERE put the cap
back on and tighten it up. Now you want to see if the motor will turn with the obstruction in
place. Stick a 6" punch in one of the balance holes in the crank throw so the pull will be
consistent each time you check. You are looking for lockup with the obstruction in there and
free without. The shims are increments of .002 or .003 depending on which the rebuild used.
The steel shims are generally in .002 and the brass in .003. Peel 1 increment from one side at a
time, one from one side and if that doesn't lock it up then do one from the other side. Yes it
tedious; just be glad you didn't by a space shuttle. Once you get this bearing to lockup then
remove the obstruction and replace it and tighten it up again and see if it will rotate. If it won't
turn with the 6" punch then put that dame shim back in and run it another 3k.
Do the rear next then the front. The rods adjust exactly the same way. When you finally get a
bearing adjusted like you want it put some pre-lube (engine assembly lube) on there before
putting it on there for the last time. Torque to whatever you has been using (75 minimum) and
go. The rod nuts torque to 40.
To put the pan on there install the oil pump using a 3/8 fine thread bolt in the plug hole in the
side of the block to retain the pump while you install the pan. Finger tight as the threads are
actually national pipe threads but the bolt will work in there. Get some 5/16 all thread and make
yourself some cheaters by cutting 4 pieces 4 or 5 inches long. Screw them into the pan rail and
let 'em hang down. Slip the pan over them and start a nut. Then it is a matter of tightening the
nuts incrementally in turn and thereby winching the pan up against the spring on the pump.
The gaskets and sealer is a matter of choice but my opinion is that the silicone belongs in the
bathroom. I use permatex red personally. When you put it all back together put some of the oil
down the dist hole so the valve galley is oiled. It should not have lost any oil but I like to make
sure.
Lotta work laying on your back
 
Mike,
Thanks for the explination of the tinfoil. For some reason I didn't get the idea of putting the foil ON the bearing surface. I kept thinking why the hell put tinfoil where you just took a shim out. Now THAT makes sense. I still think my journels are OOR to some extent. I like to know who or what rebuilt this engine with new rods and an oval crank.
Thanks Everyone!
Pete
 
To make sure there is no confusion on Mike's description, the doubled up aluminum foil is now .002" thick and 1/2" wide and the length of the bearing. The width being side to side as mounted in the engine and the length being front to rear as mounted in the engine.

If a person got mixed up and ran the foil from one side to the other side (bolt to bolt) on the bearing cap, you'd now have .004" total on the sides and .002" on the bottom.

Another method I've used is to mount a dial indicator to the block using a magnetic base, then put the point of the indicator on the crank web next to the bearing being checked. Now, you'll have to carefully pry the crank up and pull down as close to the web as possible without rotating the crank. This can be a bit tricky, but will save having to R & R the bearing caps a bunch of times to check and shim. I used this method a couple months ago and removed .012" shims from the center and .006" from the rear main bearing caps.
 
Tom;

Interesting idea on checking the bearings with a dial indicator. Could you also use a bottle jack to push up the crank to check the clearance?

Dick
 
Dick Deegan said:
Tom;

Interesting idea on checking the bearings with a dial indicator. Could you also use a bottle jack to push up the crank to check the clearance?

Dick
Click to expand...

Yes, a carefully bottle jack would work. I used a block of wood and a 2 x 4 to lift the crank. I then zero'd the dial indicator, removed the jack, and pried down on the crank with a large bar, and read the dial indicator.
 
Tom;

Thanks for your reply. That sounds like a good procedure. Even though I have just checked and adjusted both rods and mains using tin foil, I am going to double check using your method today. We'll see how accurate I am with the tin foil method. I really like this method since it does not entail removing caps (usually several times). I'll let you know how it turns out.

I guess that this would work on the rods as well as the mains??

Thanks again

Dick
 
The rods might be more of a "moving target" when you apply force to check the clearance. Maybe exactly at BDC would work?
 
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