Farm Equipment - Mixing 201 Connecting Rods and Caps

Print Page | Close Window

Mixing 201 Connecting Rods and Caps

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=203338
Printed Date: 23 Nov 2024 at 1:28am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: Mixing 201 Connecting Rods and Caps

Posted By: wjohn
Subject: Mixing 201 Connecting Rods and Caps
Date Posted: 22 Sep 2024 at 7:29pm

I've been struggling with new con rod bearing clearances in the WD engine I'm rebuilding. Crank was ground .030 under and is right on the money, but a couple of the rods give me .001-.002 INTERFERENCE when I torque them down and measure with a dial bore indicator set to a micrometer for the corresponding journal on the crankshaft. Swapped in several new sets of bearings with no change.

For kicks I grabbed a random cap off of a junk set of rods I have, and voila, the bearing clearance is spot on. I'm thinking there's something up with my engine's original caps.

It looks like my options are to either have a machine shop resize the connecting rods, or swap the caps from the bad rods onto these rods. Is mixing and matching caps acceptable or not?

-------------
1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45

Replies:

Posted By: Les Kerf
Date Posted: 22 Sep 2024 at 9:44pm

This is not normally considered to be good practice but if the parting lines match and the bore is round (within reasonable tolerance) it should work just fine

Posted By: AaronSEIA
Date Posted: 23 Sep 2024 at 5:44am

Are you using the shims per the service manual?
AaronSEIA

Posted By: IBWD MIke
Date Posted: 23 Sep 2024 at 6:23am

While mixing and matching rods and caps is not generally a good idea and would make me uneasy. At the end of the day, round is the most important thing. You've got the right gauge to check them. If they are round when the bearings are installed and torqued and the clearance is correct, I'd run them. Not like this thing is going to turn 8000 rpm. The other option is to have the rods resized. Your call really.

Posted By: Boss Man
Date Posted: 23 Sep 2024 at 3:27pm

I'd use the original caps with the original rods and have them machined. As Aaron said these originally came with shims.

Posted By: wjohn
Date Posted: 23 Sep 2024 at 7:12pm

I am using a 0.010" factory shim pack on each side per the manual. Things are still all wonky.

Everybody is very much correct that the right thing to do is have the rods/caps resized. I am getting impatient with this engine but I should do it right and not just select fit caps and rods and hope they're close enough.

I chatted with my machine shop tonight and while he doesn't touch tractor stuff very often, he called a guy up and we confirmed that the con rod big end bore spec is 2.4995-2.5005. I wasn't able to find that in any literature I had so I will recheck mine after torquing down tonight or tomorrow night. He's going to check and see if he has a mandrel that big. I think he said big block Chevy engines have smaller journals and big end con rod bores than this WD engine does, ha.

I'll drop them off after checking them.

-------------
1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45

Posted By: wjohn
Date Posted: 23 Sep 2024 at 9:31pm

Okay, .010" shim packs in the rod w/ no bearing inserts. Nuts torqued to 40 ft-lbs. I am within +/-0.0002" of the 2.5000" spec I was given when I measure around the rod bore. It can't be an out of round issue, I don't think? That is well within spec.

New 0.030" bearing insert installed. The .010" shim packs gave me ~0.001" of bearing crush which is a little below the 0.0015" spec the AC manual calls for, but that should be good enough to get an accurate measurement of the bearing diameter when things are torqued down and definitely not be overcrushing the bearing or stretching the rod cap.

I have 0.006" of clearance when measuring with a dial bore gauge zeroed to the micrometer reading from the crank journal, which measures 2.3446". The AC manual says 2.374-2.375" for the standard rod journal diameter. Since I had the crank ground 0.030" under that is spot on. Clearance should be 0.001-0.003" per the manual so I am 2-3x what it should be.

Are the aftermarket bearing inserts just hit or miss?

I am trying to use this as a learning experience - just not sure what I am supposed to be learning here at this point, ha.

-------------
1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45

Posted By: steve(ill)
Date Posted: 23 Sep 2024 at 10:10pm

I have always used the .010 shim as a STARTING POINT... AS the crank and bearings wear, you can take out 2-3 thou to tighten things up..

I have never run into this before with a NEW bearing, but since the crank was turned and the bearings are undersize... i guess its possible something is off 1-2 tho... If your going to use the ORIGINAL CAPS, youi might need to add 1-2 thou to your .010 shim to get the right clearance ??

-------------
Like them all, but love the "B"s.