I know this was answered recently, but I can't find it. New Molnar H beam rods w/ Molnar ARP 2000 bolts. Free lenght of the bolts vary .010" from short to long. The preferred method is either stretch OR torgue plus angle. I did both, measureing free length of each bolt, then torquing to 30 ft lbs and turning it the additional 60 degrees it calls for. Then when I measure the bolt stretch, they are .0066"-.0071". Molnar spec's call for .0062"-.0064".
So..... Should I back off on the 60 degrees a bit to get the proper stretch, is the additional stretch OK?
Also, the torque required to get to the 30 lbs plus 60 degrees is about 82 ft lbs. Other ARP 2000 bolts that I have used called for aa torque of 72 ft lbs for the same size/length. What is most important here or am I trying to over think this?

Thanks, Brian

I don't know, but in your case I wouldn't take any internet advice unless you know and trust them. I would call ARP w/the bolt length and diameter and tell them your situation. Too much at stake there.

I started a thread about rod bolt stretch about two weeks ago.

The only effective way to do the stretch method is to use a long box wrench with the gauge installed and watch it for the proper stretch. I called both ARP and Scat (I have Scat I beam small block rods with ARP 8740 cap screws) and both said forget the stretch method, just use the torque spec. You really can't do both methods.

Also, the guy at ARP told me that once you slow down your pull and are trying to get that last little bit on it, the bolt head is just twisting.

The stretch method sounds easy enough but it's not, at least for me it wasn't. You need a long enough wrench to get the proper leverage because you need to be able to swing it quickly and smoothly. I don't have a real long wrench so I tried different combinations of breaker bars and attachments and none of them worked great. The wrench kept slipping off and I rounded off a few bolt heads.

I fumbled around with this several times, doing it over and over again trying to get the stretch right. One bolt I actually measured to be stretched beyond it's limit. I mentioned this when I was on the phone and the guy at Scat said I should replace the over stretched bolt. I started thinking about it and did not feel comfortable with how the whole thing went and ended up replacing all the bolts. Probably not necessary but I didn't want to worry about having a rod come loose at the wrong time.

Hope that helps.

The last set of H beam rods I had used ARP 2000 bolts, recomended torqueing the bolts to 72 ft lbs. They also included a bolt stretch spec. I never put a stretch gauge on them. I torqued those rod bolts many times during the original build and later freshen ups (checking rod bore, then bearing clearance, then instalation, ect), and put over 1000 passes on that engine. I don't understand why now, all of a sudden, what we've done for so many years is invalid.

Thanks, Brian

All the ARP rod bolts(8740,2000, L19 and so on) I've check for stretch in a rod vise have never come close to being as long as they wanted with the recommended torque I do tighten them starting at the recommended torque and add 5 lbs at a time , after loosening them back up first and then retorquing them until I find the torque spec. needed with that torque wrench to get them in the middle of the recommended lengths, IE recommended from .0059 to .0064 I shoot for .0061 to.0062 . I have seen 25 ft. lbs difference on a set of Oliver billet steel rods on thier ARP 2000 rod bolts I called Oliver and they said to forget the stretch method and use the torque plus so many degree method. I ended up recording the torque needed for each bolt location and use that torque wrench to torque them in that motor, I furnished those speacs. and location to the customer

I don't get that either. I don't necessarily think it's invalid though. Only thing I could come up with is that fastener MFRs. feel like it's a more finite measurement and that a perhaps a torque spec alone does not provide that little extra amount of clamping force. Seems to me like torque + angle would be as good as stretch but that's still only a measurement with a wrench, you're not actually measuring the fastener's ability to clamp based on it's length. I guess they believe that a fastener must have slightly less clamping load if it's not stretched to a certain point. Who knows.

The confusing part to me with my rods was that Scat put two specs in the same line - 64 ft. lbs, and a stretch "limit" of .0046". They don't say where the stretch should be though so you are left to guess. Do you go right to the limit or just under? What if you are a little short, then what?

Again, I found it tricky to get it to where I wanted it which was .004", there was no consistency. I was either under or in one case over. I figured it should not be this hard so I abandoned the whole thing and decided to start from scratch. Torquing the bolts took 10 minutes, even with two steps and a double check.

I didn't think ARP even gave torque specs for their rod bolts and insists that they be installed using either the stretch method or the torque plus angle method.

Eagle gives torque numbers for the ARP bolts used in their rods. But when I compared how much the actual torque was after installing a set using the torque plus angle approach for ARP 8740 bolts, it was quite a bit more than the 63 pounds Eagle said to use.

The problem with just using a torque wrench is it doesn't take into account the friction of the threads. IIRC ARP used to quote different torque values depending on what kind of thread lube you were using.

The torque plus angle method should give you the most consistent results because the thread pitch dictates that X degs of rotation will always be .00Y" of stretch.

Kevin