Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Rod bearings

Rod bearings

Post Mon Aug 21, 2017 5:07 pm

Posts: 569
Location: Wa, USA
I had to remove my cylinders due to a sleeve that slipped and after they were off, the rods did not flop freely to rest on the case mouth like usual. They moved OK by hand although there seemed to be a couple of spots that were a bit tighter. After some inspection, I found that they were all the way over toward the right flywheel and I could not move them back. Palmer's says that this is caused by the bearings being fitted too tightly. I broke everything down and found that they were indeed too tight. I had to use a puller to pull the rods off of the crankpin. First inspection prior to cleaning does not appear to show any unusual wear or heat signs. This bottom end has only 2800 miles on it. What are the pros and cons of measuring everything up and just putting in the appropriate smaller size rollers?

Post Mon Aug 21, 2017 5:48 pm

Posts: 2770
Location: Los Angeles, CA
Oldtime racer and engine builder Steve "Clem" Pettis had his own rollers and cages made. He set lower ends up to zero clearance. They always ran great and lasted forever.

Post Tue Aug 22, 2017 5:15 pm

Posts: 569
Location: Wa, USA
How did he deal with the tendency of tight bearings to push to the right? Mine were actually wearing the side of the female rod against the flywheel washer.

Post Tue Aug 22, 2017 5:26 pm

Posts: 3472
Location: Central Illinois, USA
Gosh Woody!

I was accused of "too tight" of motors.
Yet 'thrusting to the right' was never the problem.

I suspect other issues.

....Cotten

Post Wed Aug 23, 2017 2:04 pm

Posts: 5
Of course he did.
Last edited by kitabel on Wed Aug 23, 2017 6:26 pm, edited 1 time in total.

Post Wed Aug 23, 2017 2:56 pm

Posts: 170
Location: Carver, MN

Woody, I think that you'll find that if you measure carefully that the bottoms of the rods have gone out of round or "stretched" as it is often called. One rarely finds a used Harley rod that doesn't have at least .0005" out of round, with the top to bottom measurement larger than front to rear. And in most cases its not that the top or bottom of the race has worn away more, its because the rods have deformed (or stretched) so while the top to bottom measurement has gotten larger (stretched), the front to rear has gotten smaller (pinched). So when the factory went to a minimum crankpin bearing clearance of .0004" on late Evo's and Twin Cams, and then the rods stretched so that they were .0005" larger top to bottom and .0005" smaller front to rear, you end up with a .0001 press fit in one dimension. Lots of Twin Cam cranks were replaced under warranty because of "tight rods."

I would hone the rods round again and refit rollers to .0008" to .001" clearance.

Post Wed Aug 23, 2017 3:39 pm

Posts: 3472
Location: Central Illinois, USA
I observed that too, Lee!

On one Chief I did many years ago, I pushed out the male rod race and re-installed it at 90º before honing it for oversized rollers.

The owner breezed through the shop last week, so I know I would have heard if it had failed....

....Cotten
PS: And it pulls a hack, too!

Post Thu Aug 24, 2017 11:20 am

Posts: 569
Location: Wa, USA
Lee,
Measuring the rods showed exactly what you described. The male rod is .0004" out of round resulting in a plug fit side to side and .0004" clearance up and down. This one seems to have been too tight even before going out of round. The female is .0005" out on both sides and has clearance of .0003" to .0008". Looks like I have some honing to do.

The pressure to the right also wore the aluminum bearing cages quite a bit. Are good steel ones still available anywhere? The last shop I had work on this did me a "favor" and replaced my steel cages with aluminum.

Post Thu Aug 24, 2017 12:27 pm

Posts: 170
Location: Carver, MN

Woody, "JIMS" shows them in their catalog.

Post Thu Aug 24, 2017 4:16 pm

Posts: 569
Location: Wa, USA
Thanks, Lee. I found them.

Post Fri Aug 25, 2017 7:57 am

Posts: 3472
Location: Central Illinois, USA
Are the JIMS cages parkerized, Folks?

They should be...

....Cotten

Post Mon Sep 25, 2017 7:02 pm

Posts: 569
Location: Wa, USA
Another thing I found during this teardown was that the motor ate a couple of cam shims and some of it got caught between the flywheel thrust washer and the pinion bearing race. The washer needs to be replaced and there is some grooving of the case race face. It measures about .005" deep. The whole bottom end is new and otherwise shows no wear. I am thinking of setting this up in the mill and cutting the face of the case bushing flat again and then resetting the end play to the new surface. Any opinions?

Post Mon Sep 25, 2017 8:26 pm

Posts: 170
Location: Carver, MN

If you have tooling that is capable of cutting the hardened race it should work. I know that nothing I have would touch it, but I'm not a machinist by trade. Otherwise maybe it could be done with a surface grinder?

Post Mon Sep 25, 2017 9:49 pm

Posts: 1368
Location: Ojo Caliente,NM,USA
woody wrote:
Another thing I found during this teardown was that the motor ate a couple of cam shims and some of it got caught between the flywheel thrust washer and the pinion bearing race. The washer needs to be replaced and there is some grooving of the case race face. It measures about .005" deep. The whole bottom end is new and otherwise shows no wear. I am thinking of setting this up in the mill and cutting the face of the case bushing flat again and then resetting the end play to the new surface. Any opinions?


I chucked a NOS 741 case up in the lathe and took some off the drive race face. Was hard but not impossible with a carbide tool. I would expect the other side to be about the same.
Dave

Post Tue Sep 26, 2017 6:30 am

Posts: 98
Is this damage bad enough to make a difference?

Post Tue Sep 26, 2017 7:39 pm

Posts: 569
Location: Wa, USA
Dusty,
I figured that carbide would cut it. I don't have a lathe with enough swing, so I will be putting it on the mill.

Larry,
The bushing is grooved fairly deeply and the thrust washer on the pinion side is badly galled and must be replaced. If I have to go that far, I want a good surface on the case bushing.

Post Tue Sep 26, 2017 8:19 pm

Posts: 1368
Location: Ojo Caliente,NM,USA
If carbide wont leave a suitable finish a diamond wheel will. I used the lathe because the mill was in pieces. Still is come to think of it.
Dusty

Post Wed Sep 27, 2017 1:53 pm

Posts: 3472
Location: Central Illinois, USA
Many years ago, Folks,...

I saved a "Dragonman" botch for an associate in the same way, but I clamped a Dremel grinder to the toolpost to do it.

At the time, I was working out of an auto speed shop (with a larger lathe than mine), and the owner was quite annoyed. But since I repaired some planetary gears in the Clausing lathe's quick-change gearbox, by welding teeth up and grinding to shape, he let it go.

He still fired me eventually, for his other embarrassments.
I danced out the door grinning. And I don't dance.

....Cotten

Post Mon Oct 02, 2017 5:03 pm

Posts: 1731
Location: Interlaken, NY USA

I had a motor eat a cam washer a couple of years ago and decided to forgo the washer rather than risk a repeat performance.
DD

Post Mon Oct 02, 2017 7:10 pm

Posts: 569
Location: Wa, USA
DD,
I think that is exactly what is going to happen to my cams also. I the same thing happen in the late 70's with my WLA and left them out the next time. Apparently I am a slow learner because I tried it again. :?

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