Con Rod Torque

[alstarz88]

Hi

I am currently rebuilding my engine but having trouble with the con rods. I have replaced the big end shells and the bearing carrier shells I am using engine build lub and new bolts on the con rods but when I do them up to 20nm thena 90 degree turn they are extremely tight moveable but only just. before the 90 degree turn they feel more like what i am expecting move freely but with no play.

Can you please confirm the initial torque is 20 and that the final is a 90 degree turn and should they move freely or do they need to bed in before there free. I believe the bolts are designed to stretch under use.

Regards

Ross

[JFP in PA]

Hi

I am currently rebuilding my engine but having trouble with the con rods. I have replaced the big end shells and the bearing carrier shells I am using engine build lub and new bolts on the con rods but when I do them up to 20nm thena 90 degree turn they are extremely tight moveable but only just. before the 90 degree turn they feel more like what i am expecting move freely but with no play.

Can you please confirm the initial torque is 20 and that the final is a 90 degree turn and should they move freely or do they need to bed in before there free. I believe the bolts are designed to stretch under use.

Regards

Ross

First, I see you used new rod bolts which is good as you should never reuse the rod bolts on these engines, never.

Correct specs are 20 nM (15 ft Lb.) + 110 degrees of torque angle.

Edited March 11, 2012 by JFP in PA

[alstarz88]

then that is even tighter than what i'm doing them up and they are quite stiff already is that normal with new shells and bolts

[logray]

If you are using ARP rod bolts they need to be resized. Meaning, torqued out of engine, checked with bore gauge, then bored to proper size (resize).

If you are using stock rod bolts you shouldn't have to do this, but I would still recommend measuring both the crank journals and the rod bores to make sure you don't have a bad con rod or journal.

Also it is recommended to have the crankshaft and rods magnafluxed.

[JFP in PA]

then that is even tighter than what i'm doing them up and they are quite stiff already is that normal with new shells and bolts

Yes, but it begs a question: Are you torquing them dry or lubed?

Logray also has a point about checking the big ends for roundness after bench torquing them, as well as checking the crank.

Edited March 11, 2012 by JFP in PA

[alstarz88]

Bolts are dry shells lubed

[JFP in PA]

Did you run a thread chaser through the rod bolt holes first to be sure they are clean?

[alstarz88]

there clean can do them up by hand so the surfaces are nicely together then torque them. my concern is that the feel very stiff to the point of if i move them up or down they will turn the crankshaft

[logray]

There should be absolutly no binding and they should glide like they are floating on thick jelly or jam. They should never rotate the crank.

If it were me I would remove the rods, torque them on the bench (with fresh stock bolts since they are single use only).

Then take a good set of measurements, all the big ends, and of the crank as well. On my engine I found .003" clearance to be average, never less than .0025" and never more than .0035". If you are signifigantly under or over that there is a problem to address.

If everything looks good, reinstall the rods with NEW bolts again.

If there is a problem during measurment, the rods will need to be machined (or replaced).

[JFP in PA]

You need to carefully run a thread chaser through all threaded items, followed by a blast for clean compressed air to be sure the threaded areas are totally clean before any assembly is possible. If you have not done this, go back and do it, otherwise you will get all sorts of erroneous torque readings.

[JFP in PA]

there clean can do them up by hand so the surfaces are nicely together then torque them. my concern is that the feel very stiff to the point of if i move them up or down they will turn the crankshaft

They should not be this tight, go back and recheck the rod and crank sizes as well as clean out the threaded areas.

[alstarz88]

They were oval out by 6 thou

now replaced and balanced to within a gram