dumb question.

[RobVG]

The bolts that bolt one of our rock grapples to the rotec bearing on the hanger came loose.

I can tighten them until the bolt stops but there's a flat washer under the bolt head thats still just a little loose.
Whats going on? Did the bolts grow or did the holes get shallower? I've never seen this before.

5/8" x 2" course grade 8. 24 total.

 

[walkerv]

take one bolt out mesh the threads against a new one and see if it is stretched? almost sounds like the bolts are a tad too long and wasnt fully clamping down on the washer and now the washers are a little thinner then they once were?

 

[RobVG]

take one bolt out mesh the threads against a new one and see if it is stretched? almost sounds like the bolts are a tad too long and wasnt fully clamping down on the washer and now the washers are a little thinner then they once were?

That's a good idea.

Why didn't i think of that....:scool

 

[lantraxco]

Yup. My suggestion would be some longer studs not bolts so you know they have full thread depth in the Rotek and some hard spacer tubes, usually can get something that will work from CAT. The longer the fastener the more spring it has before it stretches and won't come back. YMMV

 

[RobVG]

The longer the fastener the more spring it has before it stretches and won't come back. YMMV

That i did not know. Thanks

It's a good set up, the current rotek is about 6-7 years old. It could be age related but the operator just told me it has been vibrating a little after the rotate motor was changed.
I reused the old pinon gear because it had some life left in it. Whatever the vibration, it may have caused it to come loose.

I need to get a chance to take things apart and get a better look.

 

[kshansen]

Yup. My suggestion would be some longer studs not bolts so you know they have full thread depth in the Rotek and some hard spacer tubes, usually can get something that will work from CAT. The longer the fastener the more spring it has before it stretches and won't come back. YMMV

Good idea! Some people don't understand why some fasteners, like say exhaust studs on many engines, have those long spacers. Or why some bolts are necked down in the middle or some studs are made with threads the full length . A bolt or a stud is, as lantraxco says, a spring. If you stretch a short spring it can only stretch a little more before it either breaks or exceeds it elastic limit and will not spring back. If you have a bolt or stud with only short amount of threads at one end and the rest of the length is larger than the minor diameter of the threaded area the only part that will give under stress is the short section of threads outside of the hole in the housing. Now if the stud is fully threaded and has a, say 2 inch spacer there is now a full 2 inches more of the stud that the stretch is spread over. This also works for bolts like many connecting rod bolts. They will have the unthreaded section of the bolt cut down to a diameter the same or even less than the minor diameter of the threaded area. This again allows spring action without exceeding the elastic limit of the bolt.

 

[kshansen]

If there is room for spacers I would go that route with the longest you can comfortably use with out causing interference, say a 2 inch spacer then use a bolt 4 inches long with a hard washer under the head of the bolt or use a stud long enough to bottom in the hole and add a bit more length to allow spacer, hardened washers and grade 8 nuts.

Grade 8 studs are available at:http://www.mcmaster.com/#standard-threaded-rods/=13hxk2j

Or a Cat dealer, both places would also be able to supply the hard washers and nuts.

 

[ETER]

Thanks kshansen...I have always wondered what the deal was with the decreased diameter somewhere between the head/flange and threads, and now I know!:drinkup
Regards, Bob