Main and Rod bearings on rebuild

[dshanks]

I have a 48 Cub which I recently did an overhaul. I ordered new standard size bearings as I did not think it was worn all that bad nor had the crankshaft been tooled down.

The engine does not turn over easily and the starter is labored and gets hot quickly.

I've been told that you should easily be able to turn the engine on a cub with the fan belt, and that the crankshaft should have some slap (move forward and back). Is this true?

The main bearings are too tight when torqued down. Isn't the standard size the thinnest, and each time the crankshaft is tooled down the new bearings have to be thicker?

Should you be able to push the crankshaft forward and back? The center bearing has sidewalls that are snug and would prevent this.

I probably need to remove the crankshaft and have a machine shop check it out.

Any advice is appreciated.

[tst]

use green plastic gauge to check the bearing clearance, no machine shop needed to do this, this needs to be done when installing bearings to check for correct clearance

[Ahab01]

Use plastigage on the crank journals and bearings to see if they are too tight. Order them on amazon or get them from your local auto parts store. The bearing clearances are in the manual as well as the process for making the measurements. you just need the plastigage and a reliable torque wrench. See page 1-34 in the service manual

Did you measure the bearing journals before purchasing the bearings? Did you liberally apply assembly lube to all of the components / bearing surfaces when you were installing them?

I just rebuilt my cub motor this past winter and it was a little sticky when you first get it all together but it would turn by hand with some effort. I also don't remember any "slop" in the longitudinal axis of the crank once installed. It sounds to me like you have something that is way too tight or the tolerances are not right. Pull it back apart and double check all the clearances and look for wear marks on the bearings and cylinder walls is the best advice I can give you.

I thought I read on here that there is a difference in the early year cubs for the center bearing flanges, but don't quote me on that. Perhaps someone with a little more cub time can confirm or deny that statement.

[Ahab01]

Correction, page 1-50 in the service manual for the crank main bearing measurement with plastigage.

[ricky racer]

Do you have the bearing caps all oriented correctly? Everything should be match marked so each cap goes back in the correct location and the correct orientation. Once you know that is correct, plastigage the clearances.

[Glen]

Hi,
Below is the Cub service manual, it has lots of info. The engine is in section 1, I would read it before working on the engine. The manual tells how to use Plastigauge to measure the crankshaft bearing clearance. The bearing clearance at each journal should be measured.

http://farmallcub.com/rudi_cub/www.clea ... index.html

The crankshaft should only have a small amount of end play.
Page 1-04 says .004" - .008" clearance, or end play. You have to measure it with a feeler gauge.

I don't know why it would be tight if you put in standard bearings, they are the biggest, and would be the loosest fitting. Don't run the engine with 1 or more bearings that are too tight, it may damage the bearings or crankshaft. Check them one at a time with the plastigauge.

If the crankshaft measures standard size, and is still good, and the plastigauge shows that the bearings are too tight, then maybe the bearings are marked wrong, and are too small.

[Gary Dotson]

I'd bet you have a bearing cap on backward or you have mixed cap location. With each cap that I install, I make sure that I can feel the end play (side play on the rods). It's only a small movement but you should be able to detect the it.

[outdoors4evr]

There is some crankshaft movement allowed front to back. It will find its home.
Regarding the tightness, there is probably something assembled wrong. Look for a rod or a rod cap that is turned the wrong way.
Did you lubricate the bearings when installing? Dry bearings or thick assembly oil may contribute.

[Glen]

Hi,
The main bearing caps have numbers stamped in them, and have to be put on in the right positions.
The connecting rods and caps have numbers stamped in them, and have to be put together with the numbers aligned, and facing the camshaft side of the engine.
The Cub service manual shows how to assemble them. Pages 01-35, and 01-50, in the manual I posted above, show how to assemble them. Maybe you knew already.

[ricky racer]

Hi,
The main bearing caps have numbers stamped in them, and have to be put on in the right positions.
The connecting rods and caps have numbers stamped in them, and have to be put together with the numbers aligned, and facing the camshaft side of the engine.
The Cub service manual shows how to assemble them. Pages 01-35, and 01-50, in the manual I posted above, show how to assemble them. Maybe you knew already.

The motor I've got apart right now has no markings on the main bearing caps. When I pulled the each one off, I looked for markings and when I found none I carefully placed each one back in place and match marked them so they go back in the proper orientation. I was surprised to find no markings.

[Gary Dotson]

If you find no markings on the cap, the lock tang on the bearing insert should always be on the same side.

[TallCoolOne58]

Other than the excellent advice already offered here, the only other item I can think of, that's easy to miss, is correct install of the center bearing, which is covered in the service manual, in order to ensure top and bottom bearing half alignment, for proper crush, and consistent top and bottom end play.

I recently completed an "underhaul" with new mains and rod bearings this past spring. I worked slowly and carefully. I do understand that measuring, using plastigage, keeping hands, tools and parts as clean as possible, and even triple checking your work for proper cap number and orientation is tedious, but necessary. Along with checking for proper crankshaft rotation (no binding etc.) after each bearing is replaced, but it helps pinpoint the problem bearing quickly as your job progresses.

[dshanks]

Thank you all for the good advice. I took it apart again and took the crankshaft to a machine shop. It was slightly bent. they were able to straighten it and honed it down to .10. I ordered new bearings and installed. Still tight. The starter won't turn it but it does turn ok with a crank.


I have not used plastigage but I have used a micrometer. I did verify that all the rods and bearing caps were in the correct order. The rods have numbers but the rod caps have T, V, U, and F stamped on them to match them up. Anyone know if those characters stand for something?

I've taken it to a professional. Hopefully they will be able to work out the kinks.

Thanks

[Glen]

Hi,
Good that you had the crankshaft repaired.
If the engine turns normally using the crank, and if the starter is the original, the starter could need repair. The brushes and bushings get worn, and it doesn't turn as fast as it should. If this is the problem, it won't work right unless it is repaired.
There is a bushing at each end of the starter, if they are worn, the big part of the armature can rub on the magnets in the starter, then it will run slow, and use more power than normal.

You have to take the starter apart to see if the armature is rubbing, but you can remove the band, and look at the brushes, using a light. The commutator, where the brushes run on, should be clean and shiny also. Clean it with fine sand paper if needed.
The ends of the band face down when putting it on again.

Below is your previous post, I wrote info there about repairing a starter. Follow the links in my post.

viewtopic.php?f=1&t=104145

A starter repair shop can repair it if you prefer.

Below is a pic of a Cub armature where the large part of the armature has rubbed on the magnets, you can see the marks at the ends of the large part.