main bering torque

Skip Burney · May 12, 2017

Guys the service manual talks about only nuts. My engine has bolts through the caps and when I torque it down to 80 FT/LBS it is locked up solid. I have the correct main bearings for the crankshaft so that isn't the problem. Is there a different torque value for the bolts vs the nuts

Ultradog MN · May 13, 2017

Not sure if I'm following you.
Are you saying when you torque the main caps down you can't turn the crank shaft?
If so you have a bearing clearance problem.
That's why you always use plastigauge when you assemble an engine.
Plastigauge them and post back with your results.

TheOldHokie · May 13, 2017

(quoted from post at 00:24:18 05/13/17) Guys the service manual talks about only nuts. My engine has bolts through the caps and when I torque it down to 80 FT/LBS it is locked up solid. I have the correct main bearings for the crankshaft so that isn't the problem. Is there a different torque value for the bolts vs the nuts

You are going to hear different stories but my old copy of the FO-4 says quite explicitly - 75-85 lb-ft for both nuts and cap screws. And before somebody takes exception I understand why people think "that doesn't make sense" but that is what the book says.

As to the "binding" problem I doubt it is bolt tension. Get out your micrometer and bore gauge and check the main bores for round and measure the oil clearances with something more accurate than a piece of plasti-gage. Are you sure you have the correct caps (especially the oil pump) and they are all on the proper main and in the proper orientation?

TOH

Ken(Ark) · May 13, 2017

I read this quite often and the problem is usually the rope seals . People ( myself included ) sometimes get in a hurry . A person really needs to install the crank and lubed bearings with no seals then get a feel of the force needed to rotate the crank . Install the seals and rotate . Each time you add a component you feel the rotation .

Like most things you gamble your money is well spent . Plastigauge is not as accurate but it will give you a good indication if you are in the acceptable range . I will say the micrometers and dial bore gauges are very inexpensive these days .

Skip Burney · May 13, 2017

Same caps in the same position arrows pointing forward and no pistons in the block yet, crank and bearings match. My only guess is that the rear seal is binding it up. I will retorque at 75 and see.

TheOldHokie · May 13, 2017

(quoted from post at 10:42:20 05/13/17)
I read this quite often and the problem is usually the rope seals . People ( myself included ) sometimes get in a hurry . A person really needs to install the crank and lubed bearings with no seals then get a feel of the force needed to rotate the crank . Install the seals and rotate . Each time you add a component you feel the rotation .

Like most things you gamble your money is well spent . Plastigauge is not as accurate but it will give you a good indication if you are in the acceptable range . I will say the micrometers and dial bore gauges are very inexpensive these days .

I second the comments about the seals. Bolt it up without them and see what you are getting.

At best plasti-gage is a "good guess" at the clearances and plenty of testing has shown it can be off by as much as 100%. It also won't readily identify out of round bores or mismatched caps the way a bore gauge will. Decent micrometers are inexpensive, a decent dial bore gauge not so much. But if you are going to build engines a dial bore gauge is well worth the price and I waited way too long to pop for one ;-)

TOH

Skip Burney · May 13, 2017

Backed everything off,used another torque wrench, retorqued it at 75 ft/lbs and it turns just fine.

Skip Burney · May 13, 2017

I just took it back apart and measured both the bores, journals and everything was spot on. Same caps on the same journals as when I took it apart. All of the arrows on the caps were pointing forward and it was locked up tight. I m not a fan of plastigauge at all either haven't used them in 30 years I just don't trust them. I reassembled everything and used another torque wrench and used 75 ft/lbs and it turns just fine now. I m guessing it was a tight rope seal.

HFJ · May 13, 2017

glad it's fixed, skip - but you're scaring me. i hope my torque wrench hasn't gone rogue too, and it turns out i've got 120 foot/pounds on the head :shock:

HFJ · May 13, 2017

or 30 :lol:

R Geiger · May 13, 2017

(quoted from post at 14:03:14 05/13/17)
glad it's fixed, skip - but you're scaring me. i hope my torque wrench hasn't gone rogue too, and it turns out i've got 120 foot/pounds on the head :shock:

That is why we had to have ours recertified yearly working on Helicopters.

HCooke · May 13, 2017

Yep. Rope seals really tightens it up. May need to jump the started with 12 volts or pull it to start it.

Skip Burney · May 13, 2017

Its not the wrench its the rear seal

Skip Burney · May 13, 2017

No it wasn't my wrench its the rear seal that's locking it up,

main bering torque

Skip Burney

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Ultradog MN

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Skip Burney

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