Saw a thread about this topic not too long ago but it really didn't answer my question. My block was originally assembled at the machine shop and for reasons that I won't go into, I'm going to be re-assembling the short block myself after the block which has now returned from another machine shop. I don't know how the rods were assembled originally, stretch or torque, I'll try and find out and maybe they'll even know what the original stretch specs were, but I doubt they'll be able to tell me much more than we used the ARP stretch spec.

Here's the question. Can I or should I use the stretch guage method to install them now and would the spec's still be applicable using a bolt that's already been stretched, or should I just torque them using ARP recommendations. These are Lunati Pro Mod rods with ARP hardware.

Thanks.

 

If you are doing the disassembly, measure the stretch as they are installed now. I'd put the dial indicator stretch gage on a bolt, zero it, make sure it repeats as you take it on and off the bolt, then carefully remove it, remove the bolt and recheck it's length. Record stretch for each one. You'll be able to tell if it was overstretched (or understretched).

Assuming a bolt wasn't overstretched in the initial build, definitely reassemble using stretch. A .001 or .002 overstretch on a .0055-.0060 spec probably isn't cause to scrap the bolt. Any more would get my attention.

My bet is that you'll find stretch +/- .002 (at least) from spec at the minimum. If they are all overstretched a few thou, they were probably torqued without proper lube.

Hope it hasn't already been disassembled!

My $.02

 

Here's some intresting info. While building my LT1 I called SCAT to get the stretch on their rods and ARP bolts supplied with them. The tech told me to ignore stretch and torque bolts to 65lb as this is where they were machined to. If you ask most people on this board I bet that you'll find that to acheive the desired stretch on the bolts would require anywhere from 10-30lb of torque more. I called ARP on this issue and their tech told me that if the rods were made at 65lb then overtorquing them would cause tight clearances.....but he also told me that he reccomends measuring stretch not torque. So go figure!!!! I went the 65lb route.

Jason

 

I really wish when you measured the bore with the high TQ spec it actually changed.... I've increased the rod bolt clamping force 40% and haven't noticed a problem in a good aftermarket H-Beam.

BTW most of the time the TQ spec is going to be enough for what you are doing with the rods. If you want to get the last bit of clamping force out of them do it to the stretch spec. Most times people could get away with 8740 ARP's and putting them to the right stretch rather than upgrading the bolts.

Bret

 

Note that this is coming from an **** engine builder who measures stretch to the .0001, or at least as close as he can get. Tightening the rod bolds on an engine he builds is a long process. Been there, observed that.

I agree that for the average build, torque and proper lube is adequate.

 

Ya should see me fit rings and bearings.They kid me about measuring everything 18 times. I tell um the 18th time is to make sure the first 17 were correct.

Gotta love a perfectionist.