I put the rods/pistons in my 225 today. These are the rods I used ARP 142-6001 bolts in. The stock rod bolts are torqued to 45lbs, and ARP bolt specs are .0055-.006" stretch, or 50lbs if you don't have stretch gauge.

Like I do with every engine, I torqued the bolts to the specified amount (50lbs) using my Snap-On torque wrench and ARP assembly lube on the threads*. As with every engine, there is not enough stretch. I checked each bolt and got .0035 -.004" max.

So....I increased the torque. It took 70lbs. to finally hit .0055". This is something I've seen on pretty much every engine I've assembled, it's not a unique occurrence. I'd guess ARP will tell you the clamping strength of the bolt is way under spec at .0035" stretch. Some food for thought if you are using a torque wrench alone.

*I fully cover both threads AND underhead of the nut with assembly lube. I've found that if you leave the underhead dry, it wastes a good bit of the torque effort. I'd guess a dry underhead on this application would give you .003" or less stretch at 50lbs..

Thanks for the info, GregCon. Nice to see some comparison measurements!

FWIW, I have always overtorqued my stock fasteners to 55, basically using the "feel" of it and thinking 45 ft-lbs was not enough. I guess this says that maybe I was feeling the stretch... When I did the torque-angle method for my K1 rods and ARP bolts, I went a bit past the angle they recommend (about 5 deg more). K1 specified using torque-angle or stretch methods, and that torque alone was not acceptable.

Lou

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Home of Slant6-powered fun machines since 1988

Yea...there's a lot to be said for 'feel' when it comes to tightening a fastener. Running the ARP's to 70lbs. 'felt' a lot better than 50lbs. I wish I had a way to read stretch on blind fasteners...

You can! Done it many times...

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There's no such thing as too much cam....only not enough engine!

precision grind the bolt head flat then use an ultra sound gauge
to measure the bolt length in the free state and then in the torqued state,
the difference is bolt stretch

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I mean a method I can afford lol

If you have a mag base indicator stand, that along with components in your pics......

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There's no such thing as too much cam....only not enough engine!