We have a new crank kit in a 390 rebuild, and with one piston connected, tested the rotation drag with a dial torque wrench. I get from 10 lbs to 22lbs around the revolution when starting from a stand still. I feel it should be closer to the same all around. My other engine was about 5-7lbs in total.

What is the thoughts from you engine builders? Am I overly concerned or is this OK to install?
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John

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In the cool still quiet of night, you can hear chevies rusting away.

 

i havent built engines,but having more pistons conected
would make the rotation smoother rather than a rough
up down resistence being felt.thats my 2 cents ,just a
thought,I ve only taken motors apart


Fe power

 

John, how easy does the crank spin in the block without any rods attached?

Barry

 

Did you plasiguage the main bearings yet John?

 

>We have a new crank kit in a 390 rebuild, and with one
>piston connected, tested the rotation drag with a dial
>torque wrench. I get from 10 lbs to 22lbs around the
>revolution when starting from a stand still. I feel it
>should be closer to the same all around.

This is a very unusual test indeed.
Does the piston have rings on ?
What sort of seal does it have ?
What sort of oil did you assemble it with.

This test is unlikely to give any indication of the "roundness" of the crank shaft, that can only be assertained with micrometers.

Palstigauge, will give you the difference in diameter at the point you measured.

I would suggest you are measuring ring drag and the experinecing the effect of changing piston speed that a reciprocating engine endures. Also at the speeds you are turning it you only have hydro-static/ boundary lubrication and no hydro dynamic.


My other engine was
>about 5-7lbs in total.
>
>What is the thoughts from you engine builders? Am I overly
>concerned or is this OK to install?

over stating my thoughts :- why are you emailling and not finishing the assembly.

 

Email from partner

Crank was poorly ground, egg shaped on the number two journal. Bill
put it his lathe and fixed it. Everything else was OK.
90 in-lbs to start rotation, 25 or so to maintain rotation. Was 25 ft-pounds or 300 in-lbs to start as you recall.

Starting on the timing gears then pistons in a few minutes. Should have it close to done this evening.

Thanks for the replies fellows.

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John

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In the cool still quiet of night, you can hear chevies rusting away.

 

[updated:LAST EDITED ON 18-Jun-02 AT 11:06 PM (EST)]I was a little confused by the open post
Now I'm bamboozled.

The number 2 crank pin was out of round ? ( or was it a main)
How far ?
How did you get the surface finish by turning it in a lathe
How did you balance the lathe to turn the crank.

Can ya give a "full" rundown on this little saga

 

 

Wayne, Bob took it back to the machine shop where he bought the crank kit from. After a lot of checking of the journals, one was found to be out of round. I posted what he sent me, but they don't know how it could happen. This shop can grind cranks, we had to buy one because of a 360 to 390 upgrade.

Bob is recording the drag on the crank as each piston is added. Don't ask, I don't know why, but the engine is better off now. IMHO
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John

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[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NCFTO] North Carolina Ford Truck Owners Group

In the cool still quiet of night, you can hear chevies rusting away.

 

OK so it was a crank pin (not a main).
I guess i always did by "feel" the test that is being done as I installed each piston.

But I always measured and checked clearance and roundness with a mic.

Out of round crank grinds are usually the result of "tired" or poorly setup (balanced) grinders.

It is good to understand