Crankshaft main and rod bearing clearance

[Mike41H]

I have just finished measuring the crankshaft journals on my 1941 H. Both the main and rod journals are about .001”-.0015 under low limit. Which would result in having a main bearing clearances between. 0035”-.005” and rod bearing clearances .003”-.004”

the journals are all within.001” for roundness. Does anyone have any experience with running these clearances?
I would like to avoid spending $300 -$400 on turning the crank if possible 

Thanks

[HydroTek]

Used to get .002 under bearings
check the old bearings to be sure they have not been changed
should be stamped / marked on the bearings 

...but it's an H it will be fine as is
unless you are planning to do more than just collecting / show 

[snoshoe]

59 minutes ago, Mike41H said:

I have just finished measuring the crankshaft journals on my 1941 H. Both the main and rod journals are about .001”-.0015 under low limit. Which would result in having a main bearing clearances between. 0035”-.005” and rod bearing clearances .003”-.004”

the journals are all within.001” for roundness. Does anyone have any experience with running these clearances?
I would like to avoid spending $300 -$400 on turning the crank if possible 

Thanks

Paper shimmed many a crank. Used to use the counter tickets. White and yellow sheets were about .0024. Pink was .0026 and the carbon was .001. Target is .002 on tight side of crank. No tighter than .0015 anywhere. Cut paper so it only goes halfway up either end of cap.

[DT Fan]

11 hours ago, snoshoe said:

Paper shimmed many a crank. Used to use the counter tickets. White and yellow sheets were about .0024. Pink was .0026 and the carbon was .001. Target is .002 on tight side of crank. No tighter than .0015 anywhere. Cut paper so it only goes halfway up either end of cap.

I love reading tips like this one. Then I think, if only I can remember this if it ever comes up!

[acem]

Dad got discharged from the navy after WWII. Cars were nearly impossible to find. 

He bought a model A that had been rolled. He and some friends chopped the top off with an axe. Not too bad since they were in southern New Mexico.

After a while it developed a knock. Dad sold it to a poor Mexican cheap. He dropped the oil pan and found the loose rod. Took the cap off. Cut a piece of belt and wrapped it around the crank a few times. Reinstalled the cap, oil pan and oil. Drove it for a few years changing the leather belt bearing occasionally.

I've heard of people using hard pork rind for a bearing. 

[rustred]

16 hours ago, Mike41H said:

I have just finished measuring the crankshaft journals on my 1941 H. Both the main and rod journals are about .001”-.0015 under low limit. Which would result in having a main bearing clearances between. 0035”-.005” and rod bearing clearances .003”-.004”

the journals are all within.001” for roundness. Does anyone have any experience with running these clearances?
I would like to avoid spending $300 -$400 on turning the crank if possible 

Thanks

till you post what the new brg. clearances you have, its hard to know what your actual clearances are. seams like you just removed the old brgs. and checked the crank ?? no telling how much wear the brgs. have .  .0015 is ideal on a reground crank with new brgs.   .004, .005 is at the max wear level and means brg. time for sure. at .005 things will just wear that much faster especially under load, due to less oil pressure. plus running  a thicker oil like #40, 20-50. of even the diesel 15-40 would help. there will be a lot more than 3-400.00 than a crank turning , thats only part of an overhaul.  

[dale560]

20 hours ago, Mike41H said:

I have just finished measuring the crankshaft journals on my 1941 H. Both the main and rod journals are about .001”-.0015 under low limit. Which would result in having a main bearing clearances between. 0035”-.005” and rod bearing clearances .003”-.004”

the journals are all within.001” for roundness. Does anyone have any experience with running these clearances?
I would like to avoid spending $300 -$400 on turning the crank if possible 

Thanks

Don’t worry about it on an h or M they can be pretty worn and still run a long time. Your oil pressure will drop but just don’t worry. Unless you want to shim bearings. We always kept actual shim stock on hand for various things years ago.

[Mike41H]

I would like to say thank you to everyone for the advice.

The clearance I listed would be with new bearings. I’m considering shimming to bring them in a little closer to specifications.

I only farm part time and only intend to use this tractor to plant a couple of acres corn and give wagon rides on Saturday and Sundays in October 

 

 

 

[HydroTek]

You can just shim one half with standard copy paper 90 pound is about 3 thousands 
I suggest the cap half 

most any fine woven paper can be used -- just need to look thru your stash to see what is available 
get your micrometer out and measure a few to see what will work to suit you 

as @snoshoe mentioned , you only make the shim to about 2/3 of the bearing
dont usually need much on the sides -- so stay short about 3/4"

put just ever so little of the old permetex aviation cement on the bearing cap to hold the shim in place 
just a smear with your finger will be enough to glue the shim

Beer can will also work, but I don't have one handy to measure right now -- may be too much

[stronger800]

I’ve heard of old timers shimming bearings with tin cans. (I thought they were kidding). I had no idea Paper shimming was a thing 

[snoshoe]

Federal Mogul used to make tapered metal shims. That allowed you to shim the whole bearing half. Kept that part round. When our stock ran out is when I started paper. I have pulled engines apart 15-20 years later. Could still read the print on the paper.

[Matt Kirsch]

 

[560Dennis]

Suggest you grind the crankshaft ,with those measurements. 

[560Dennis]

Also another tip is replace oil pump spring ,both woodruff keys on drive gears.  , check bottom pump housing plate for flatness with straightedge,  must be flat. Replace gasket with .005 gasket with Correct IHC  from DEALER,Like Messicks. 
I found the oil pump gasket from Steiner is out of spec at .01 + don’t make that mistake. 

[dale560]

This topic is getting a little out of hand for a H crankshaft.  The .001 extra isn’t a big thing on that slow speed low compression engine.  Have been through a lot of H and M plus other letter series engines. The crankshaft forging and machining wasn’t spectacular from new. Have actually seen crankshafts with flaws ( pitting or missing iron) from a long time ago they are still running. The mfg process from  80 years ago was not the same as later high speed engines.
Also when people talk about shimming bearings in engines this was common in the earlier years up until the 1980s. The thing that is different now is most bearings are aluminum behind the bearing surface. The old bearings that took well to shimming and worn crankshafts were copper plated. The copper bearings tolerated imperfections and dirt or tight spots better. 
 

The worst thing that will happen on your H is lower oil pressure, but more than enough to run forever.

[HydroTek]

Several ways to skin this cat
and has not been mentioned if the engine had 2 under bearings or not

"Babbit" is a mixture of metals and the recipe has changed with the differences in technology and opinions of engineers

Some engines have lasted longer than others as those that work in the mechanic field have seen
The copper layer in bearings was used in the softer babbit formulas  -- with the aluminum used in the harder babbit bearings

[rustred]

5 hours ago, Matt Kirsch said:

 

i have seen a lot of worn engines, but this one takes the prize ! nothing but scrap there. i would hate to hear the rattling happening also,... maybe it was have another beer , as no radio to turn up !  Squatch knows what he is talking about and does good work. and a perfect example of wanna be mechanic.lol.

[dale560]

1 hour ago, rustred said:

i have seen a lot of worn engines, but this one takes the prize ! nothing but scrap there. i would hate to hear the rattling happening also,... maybe it was have another beer , as no radio to turn up !  Squatch knows what he is talking about and does good work. and a perfect example of wanna be mechanic.lol.

This guy is making a mountain out of a mole hill. All the problems he listed on that block come with the age of it. After 75 years yes you might have to deck block and counterbore sleeves. The rod bearings were moving but they did not spin more than one revolution over time. If they had did anymore the would have spun and welded to rods.

i have seen D9 engines overhauled at caterpillar shop have patches on side where block was punched through.

And again an engine that old having shimmed mains or rods isn’t a big deal. 

[rustred]

6 hours ago, dale560 said:

This guy is making a mountain out of a mole hill. All the problems he listed on that block come with the age of it. After 75 years yes you might have to deck block and counterbore sleeves. The rod bearings were moving but they did not spin more than one revolution over time. If they had did anymore the would have spun and welded to rods.

i have seen D9 engines overhauled at caterpillar shop have patches on side where block was punched through.

And again an engine that old having shimmed mains or rods isn’t a big deal. 

well im glad u think that, as to me its way past worn out.  plus the pistons in backwards, tells me who did that job. and yes you can have a patch on a block, but the rest would be done to spec. in a caterpillar shop.

[dale560]

51 minutes ago, rustred said:

well im glad u think that, as to me its way past worn out.  plus the pistons in backwards, tells me who did that job. and yes you can have a patch on a block, but the rest would be done to spec. in a caterpillar shop.

The pistons backwards are a bit iffy but it ran. And from the looks of it it ran a long time. I fixed a 3010 diesel one time that had a main cap backwards. It ran 15 years like that. Sad thing this was 1991 the 3010 was on let’s second engine then. I put a crankshaft , camshaft and John Deere kit in it. Plus checked the injectors and shimmed them. It has ran without a hiccup since then. 
But I am saying any of us can have mistake and assemble something wrong. The cat block isn’t a boat anchor because pistons were in backwards. That is just being dramatic.

[acem]

A performance trick on a 70s and early 80s chrysler 318 was to install the pistons backwards.  The wrist pins were offset slightly for longer wear.  They made more power installed backwards (but didn't last as long).  Recommended in an old Direct Connection Manual (factor Chrysler performance group).  Ran one for years and it was noticeably quicker in a car.

[Binderoid]

On 1/16/2026 at 7:44 PM, HydroTek said:

You can just shim one half with standard copy paper 90 pound is about 3 thousands 
I suggest the cap half 

most any fine woven paper can be used -- just need to look thru your stash to see what is available 
get your micrometer out and measure a few to see what will work to suit you 

as @snoshoe mentioned , you only make the shim to about 2/3 of the bearing
dont usually need much on the sides -- so stay short about 3/4"

put just ever so little of the old permetex aviation cement on the bearing cap to hold the shim in place 
just a smear with your finger will be enough to glue the shim

Beer can will also work, but I don't have one handy to measure right now -- may be too much

Why the cap? I would  have thought  just the opposite. 

[Gearclash]

23 hours ago, dale560 said:

This guy is making a mountain out of a mole hill. All the problems he listed on that block come with the age of it.

I thought the same thing.  Aside from the severe pitting on the block deck I saw nothing that wasn't fixable, or indeed an atypical problem of an old well used engine block.  The pistons being in backwards, while it is a novelty, has no affect on the future usability of the block. Ditto the shimmed bearings.  The block needed the main bearings to be resized and line bored, plain and simple.  While it is extra cost to do that, it is not some kind of unheard of procedure.  Rod caps can also be resized.  

Speaking of assembly mistakes -- I recently pulled apart the rear housing of a Maxxum transmission and found that one simple looking part had been installed backwards, and the result left the pinion bearings loose with predictable results. 

[rustred]

16 hours ago, dale560 said:

The pistons backwards are a bit iffy but it ran. And from the looks of it it ran a long time. I fixed a 3010 diesel one time that had a main cap backwards. It ran 15 years like that. Sad thing this was 1991 the 3010 was on let’s second engine then. I put a crankshaft , camshaft and John Deere kit in it. Plus checked the injectors and shimmed them. It has ran without a hiccup since then. 
But I am saying any of us can have mistake and assemble something wrong. The cat block isn’t a boat anchor because pistons were in backwards. That is just being dramatic.

i agree the block is not toast, as its about the least worn thing . yes it can be decked and line bored and what ever else it needs.  it appears squatch didnt want to spend that kind of money on it. and to get all them parts in shape would be quite a few thousand dollars.  i cant get over that crank at how much wear it has. i know i would not spend that on it either.

[dale560]

24 minutes ago, rustred said:

i agree the block is not toast, as its about the least worn thing . yes it can be decked and line bored and what ever else it needs.  it appears squatch didnt want to spend that kind of money on it. and to get all them parts in shape would be quite a few thousand dollars.  i cant get over that crank at how much wear it has. i know i would not spend that on it either.

They must have been running bad oil or had dirt infiltration along the way for the crank to be worn that bad.