Transom Bolt Stretch?

**Sovran** · 06-11-2015, 04:57 PM

British Wentworth. What a PIA. They were poor fitting fasteners to begin with. During a rebuild on my Rocket 3, I drilled, helicoiled, and replaced everything with metric. It stayed much tighter, and when I lost one from vibration I didn't have to mail order 1 bolt at a time.

**skeetbum** · 06-14-2015, 09:56 AM

Originally Posted by cray

I guess we just going to completely Hijack Searks post, but when I was a youngster I owned Triumph, BSA and Matchless twin and single cyl motorcycles. Talk about vibration, Red Loctite wouldn't hold those things together. Go for a 500 mile trip and you better have your tool kit and tighten everything up every couple hundred miles.

Triumph 650 Tiger Charlie. Rest every 100 miles and tighten every 250. Haven't had it for 30 years and still keep my eye out for the next one.

**Hanr3** · 06-21-2015, 08:03 PM

Originally Posted by Sovran

The best bolts I have ever used are stamped CAT on the head. They are almost indestructible.

I have seen them break!
I work at Caterpillar's testing facilities. Sometimes the purpose of the test is to determine how much force the bolt will take before failure, and failure comes in many forms. I get to paid to watch all sorts of Caterpillar testing.

As for bolts stretching, they all do when properly torqued to specifications. The purpose of torqueing a bolt/nut is to load the threads which stretches the bolt. This load is the mechanical bond. Over-torqueing bolts/nuts weakens the bolt. Too much load and it will shear in half. Not enough load and they will loosen.

**Scrapper** · 06-21-2015, 11:04 PM

Originally Posted by Hanr3

I have seen them break!
I work at Caterpillar's testing facilities. Sometimes the purpose of the test is to determine how much force the bolt will take before failure, and failure comes in many forms. I get to paid to watch all sorts of Caterpillar testing.

As for bolts stretching, they all do when properly torqued to specifications. The purpose of torqueing a bolt/nut is to load the threads which stretches the bolt. This load is the mechanical bond. Over-torqueing bolts/nuts weakens the bolt. Too much load and it will shear in half. Not enough load and they will loosen.

Exactly why you do not reuse many CAT bolts in a new rebuild. The injector hold down bolts for instance, 42lbs...loosen....42lbs...your done. If you replace the injector, you replace the bolt as they are built to stretch during torquing. Good point Hanr!

**Sovran** · 06-25-2015, 07:26 AM

Originally Posted by Hanr3

I have seen them break!
I work at Caterpillar's testing facilities. Sometimes the purpose of the test is to determine how much force the bolt will take before failure, and failure comes in many forms. I get to paid to watch all sorts of Caterpillar testing.

As for bolts stretching, they all do when properly torqued to specifications. The purpose of torqueing a bolt/nut is to load the threads which stretches the bolt. This load is the mechanical bond. Over-torqueing bolts/nuts weakens the bolt. Too much load and it will shear in half. Not enough load and they will loosen.

Agreed, but put a CAT bolt side by side to almost any other readily available bolt and there is a clear winner.
My favorite jobs were when I was called on to do failure analysis on low hour failures. Nothing quite like taking apart and sorting through the crumbs of a power train component to determine what part failed and what was resultant damage.

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