Rod bolt/main bearing thread stretch?

I think most of that " stretch to yield " bolt spec happened in the last 20 years.. I dont remember any ( off hand) for the 1950-70 era that recommended changing out the bolts.

Edited by steve(ill) - 23 Sep 2022 at 9:36pm

All fasteners do stretch, some acceptance criteria was established as to bolt shank thickness or thread departure from concentric or depression at Detroit Diesel and Cummins engines when I was first learning engines.  As little as .002 in thread region as to that was the max allowable for rod or smaller fasteners on engines.  Head Bolts, Main Cap Screws, Stud  systems were all inspected similarly, where those were based on Shank Length.  Cummins allowed .015 stretch on Main Bolts, Detroit allowed .012 according to what I had in some old class room notes I found on Head Studs.  Would require engineering dimensions of which not many still remain for Allis machines.  

Hunt4Allis wrote: r... It's on a 1972 60 horsepower diesel 4 cylinder that I'm rebuilding in frame. Thanks Matt

Modern high performance engine builders (think NASCAR, etc.) don't use torque wrenches on rod bolts, they use a special tool that measures the actual stretch of each (always brand new) bolt as it is tightened.

Your 1972 60 horsepower diesel 4 cylinder engine 'may' fit that criterion

These connecting rod bolts may not be available, unless I'm just that terrible at searching for them?

Hunt4Allis wrote: I cannot believe these are over $100 per bolt? That seems a bit insane, I could see if it were a NASCAR rod bolt or something...

I've read to use blue medium loctite on these bolts when reassembling? I'm assuming they should be completely dry and free of oil when I do that correct?

Okay when I removed them there was no lock washers or any type of mechanical fasteners on the rod bolts.(other than the nuts which I'm unsure of their type, I think some had slits cut in them about halfway)
Using blue loctite is something someone told me to do, I will look in the manual

Edited by Hunt4Allis - 24 Sep 2022 at 4:41pm

yes, there are various ways to make a nut LOCK onto the bolt.... the book should say to replace the nuts after use... or add loctite to OLD nuts, etc...

Gotcha

Those ARP bolts are not torque to yield. They are simply torqued to a certain stretch, of .008" and 80ft lbs is what it takes to make them stretch that much. In my puller, I've reused those AGCO/ARP bolts numerous times. I also check the bolt stretch with my stretch gauge. Torque to yield bolts would have you torque to say 50 ft lbs, then turn them a half round stretching the bolt in the process. Special bolts made to work that way, and are one and done. People tend to mix up torque/turn method, and torque to yield, which is stretch bolts. You can definitely feel the stretch bolts stretching while turning them the half turn. 

Edited by injpumpEd - 26 Sep 2022 at 8:00am

Problem with loctite is unless the blocks been boiled theres still oil in the main cap holes. A drop of oil on the threads and under the bolt head is all you need. This ensures the torque is true. I've never took an older engine apart that had loctite on mains or rods. Timing gears yes, never bottom end. The disposable bolts have a narrowed shank. That enegine shouldn't and that why they're expensive. Dont sell enough.