Connecting rod side clearance

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Model T Ford Forum: Forum 2018: Connecting rod side clearance
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Eddie on Saturday, May 12, 2018 - 10:25 am:

What should the side to side clearance be on rod bearing surface at the crankshaft journal?
On my engine I have up to .040"
This is fairly recent rebuild


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Azevedo on Saturday, May 12, 2018 - 10:35 am:

Dave, that is excessive. I believe that the specification is 0.005 to .007 in. with a maximum of about 0.018" Make sure that the wrist pin, which can move back and forth since it is fastened firmly to the rod, does not drag along the cylinder wall at either extreme. Unfortunately the only remedy would be rebabbitting the rod bearings.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Saturday, May 12, 2018 - 10:48 am:

It would be interesting to survey the established Model T engine builders on this forum to see their opinions on rod side clearance with splash oiling.

On musclecar V8s with pressurized oiling, the conventional wisdom is that excessive rod side clearance results in excessive oil being pumped out of the big end rod bearings, reducing oil pressure and splashing excessive oil around in the crankcase.

However, some Mopar V8 stroker kits use big block Chevy rods or aftermarket rods with narrower big ends than stock, and they seem to run fine. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Eddie on Saturday, May 12, 2018 - 10:48 am:

I am having a connecting rod rebabbitted .

Unfortunately the re- babbitting shop and my crankshaft are hundreds of miles apart.

Is it practical to have a rod poured and bored to size for the journal
diameter, then leave the babbit width oversize and hand fit to the crankshaft?

The wrist pin end looks OK, as it is centered in the piston.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Saturday, May 12, 2018 - 06:46 pm:

I think Larry Azevedo says is right. I had an engine that had excessive side clearance and had been "rebuilt". It had 0.060" side clearance on one of the cylinders and less on the others. The one with the most clearance was really talking! I pulled the inspection door and watched as someone turned the engine over. The rod would shift to one side, bind up and snap back to the other side. An indication of a bend rod. I wouldn't have thought that the rod was bent prior to pouring and machining it out if it was bored while in a jig??? Perhaps someone had assembled the rod by holding the "beam" of the rod in a vice and tightening the rod bolt in the piston? The rod was sent back for rebabbitting and straightening. I measured the width of the rod journal and sent that along with the diameter of the crankshaft. I'm sure when the crank was turned, the thrust area at the rods was "cleaned up" too so it was no longer "standard". I kinda think that a lot of "rattling" T engines my be caused by this excessive side clearance.
Verne Shirk
Wichita, KS


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Andreasen on Saturday, May 12, 2018 - 09:11 pm:

Swell.........I just finished putting all four rods/pistons in my block this afternoon, then patted myself on having an assembled short block. Now that I think about it they were a little sloppy sideways. Just like Dave, the crank and rods were done by two different people.

I think I'd better go out and measure a few things..........


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Andreasen on Saturday, May 12, 2018 - 09:29 pm:

Well, the results are in. I have .032" side play on each rod. The rod builder did a wonderful job, but it's MY fault that I didn't measure the journal width. Looks like they're going back. More money. Oh, joy.......


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Bender Tulsa Oklahoma on Saturday, May 12, 2018 - 10:18 pm:

George
If the rod is straight and not twisted the clearance will not cause a problem. .032" side play will not let the wrist pin scuff the cylinder wall. IMO. Dave yours is not a problem also.

When cranks are re-ground the grinder will touch off the radius and this makes the bearing surface longer. Not uncommon.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Saturday, May 12, 2018 - 10:24 pm:

All I do these days are model T engines for rebuilds,
I will not build rods with out having the crank shaft, to many variables in sizes.

For the quietest engine as possible my babbit work is at Ford specs.
Rod pin is 1.505" and babbitt width is 1.500" so 1/2 a thou is all you need.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George Andreasen on Saturday, May 12, 2018 - 10:28 pm:

Mike........are you serious?? PLEASE pat me on the head and say "Now, now....it's going to be okay."
THANK YOU!

I've been stomping around the house for the last hour, cussing myself for being so dumb and planning to call the rod re-builder on Monday. You just saved me a bunch of money that I don't have at the moment!

If there's anything I can do for you....mow your lawn, paint your house, put your kids through college..........

I'm a lot happier now.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Sunday, May 13, 2018 - 08:07 am:

Silly me, I just re-read what I posted, what I meant was 1/2 of the thou's Ford used on side clearance, today's machining and oil is much better, like the oil clearance on the babbit, Ford specs for that was .002" 1.248" crank and 1.250" bearing but we can and I do 1/2 that for fresh engines.


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