How tight should the rod bearings fit?

Sam Eubanks · Jan 6, 2011

I am rebuilding an engine which includes new connecting rod bearings. I originally torqued the connecting rod bolts down at about 50-60 ft lbs. I learned they should be more like 42 so I loosed them and re-torqued them. I noticed that the connecting rods will move side to side (rattle) just a little on the crank. Mybe it was like this before and I just didnt notice. Did I squash the bearings when I overtorqued? Should I order new ones? Just looking for opinions. New ones are 40 bucks.

As always, thanks!

glennster · Jan 6, 2011

if you have the clearance specs for the bearings, zip on over to napa and get some plasti-gauge. its a thin wax like string that compresses when the bearing is torqued. there is a chart on the package that will give you the clearance when the bearing is torqued to spec. most insert type bearings do have a little "wiggle" to them.

rustyfarmall · Jan 6, 2011

(quoted from post at 11:32:16 01/06/11) I am rebuilding an engine which includes new connecting rod bearings. I originally torqued the connecting rod bolts down at about 50-60 ft lbs. I learned they should be more like 42 so I loosed them and re-torqued them. I noticed that the connecting rods will move side to side (rattle) just a little on the crank. Mybe it was like this before and I just didnt notice. Did I squash the bearings when I overtorqued? Should I order new ones? Just looking for opinions. New ones are 40 bucks.

As always, thanks!

Did you measure the crank journals with a micrometer before you ordered the bearings? Did you order the correct size? Did you use "plasti-gauge" to ensure the fit was correct? Crank bearings come in several sizes, ranging from "standard" for a crank that exhibits NO wear and measures well within factory specs, to 0.001", 0.002" undersized all the way down to 0.020" undersized. The undersized bearings are made to accomodate normal wear, but the crank journals are required to be "miced" to know which undersize is needed.

Sam Eubanks · Jan 6, 2011

Will Do. I"ll go get the plasti-stuff.

As Always, thanks for your advice.

Sam

Allan in NE · Jan 6, 2011

If they "DON'T" move side to side, then ya gots something way bad wrong and it won't run 10 feet.

There is a .001-.0035" "oil clearance" built into the crush. Put 'er back together and you'll be just fine.

Allan

Allan in NE · Jan 6, 2011

If they "DON'T" move side to side, then ya gots something way bad wrong and it won't run 10 feet.

There is a .001-.0035" "oil clearance" built into the crush. Put 'er back together and you'll be just fine.

Allan

Bob · Jan 6, 2011

Properly fitted connecting rods/bearings will ALWAYS slide from side-to-side within the limits of the journal width. There HAS to be enough play (typically in the .0175" to .0035" range) for the bearing to "float" on a film of oil. Much tighter and the bearing will lack lube, overheat, and seize.

If I were to worry about anything overtightening the bolts would have done I'd worry about stretching the bolts and weakening them.

Typically, if the bolts are replaced the "big end" of the rod should be checked by a machine shop with a rod machine.

NDS · Jan 6, 2011

Torque wrenches are good and should be used BUT I have seen a lot of them that were pulled down until they felt right and they went out and made a hand for years. Personaly I can not remember bad rod bearing in old Farmall have seen lots of bad mains though.

Heat Houser · Jan 7, 2011

You did not squash the bearing inserts at all since the cap "bottoms" on the rod shoulders (where the bolt holes are). What you have done is to over torque the bolts which may have taken them beyond their yield point. You may want to consider replacing the bolts with new.

Note, your movement from side to side indicates that you did not and could not squash the bearings......the cap/rod shoulders prevented this.

M Diesel · Jan 7, 2011

(quoted from post at 07:24:58 01/07/11) You did not squash the bearing inserts at all since the cap "bottoms" on the rod shoulders (where the bolt holes are). What you have done is to over torque the bolts which may have taken them beyond their yield point. You may want to consider replacing the bolts with new.

Note, your movement from side to side indicates that you did not and could not squash the bearings......the cap/rod shoulders prevented this.

Zactly.

I gotta ask. Is this torque spec'ed on oil, or red/white lead?

BTW, mains are harder to oil than rod ends.

How tight should the rod bearings fit?

Sam Eubanks

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glennster

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rustyfarmall

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Sam Eubanks

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Allan in NE

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Allan in NE

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Bob

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NDS

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Heat Houser

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M Diesel

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