Jump to content
Sign in to follow this  

Broke engine mount bolts--WHY?!?

Recommended Posts

Reinstalling my engine, I was torquing down the engine mounts. Luckily these that gave me trouble were the upper mount where I only gotta replace bolts and not mess with tapping the frame threads.

But still, how do bolts that HOLD THE ENGINE IN PLACE for 200 hours just sheer off like butter with 60 Newton meters if torque?? Anyone had this??

I know I know, can't tarnish the sanctity of KTM. Must be the 200 hard hrs of riding that fatigued them.

ImageUploadedByThumper Talk1406522235.890026.jpg

The sheered bolts are different lengths, but here's a clue to the problem--they're supposed to be the same length!! One of the three was fine. Probably cost like $9 each.

Share this post


Link to post
Share on other sites

Have you ever dropped that torque wrench? I have seen my friend do it with a torque wrench that had been dropped onto the cement floor a few times. It was a cheap model.

Share this post


Link to post
Share on other sites

Have you ever dropped that torque wrench? I have seen my friend do it with a torque wrench that had been dropped onto the cement floor a few times. It was a cheap model.

 

I've dropped it from my stool, only a foot off the ground maybe.  But still, to break off these bolts takes a ton of force.  And why did the 3rd one not break?  It's obviously the faulty bolts, maybe the torque wrench too.  But it's a good wrench, Craftsman.  I've recently tested it compared to other wrenches and it's been spot on, consistent too.

Share this post


Link to post
Share on other sites

I've dropped it from my stool, only a foot off the ground maybe.  But still, to break off these bolts takes a ton of force.  And why did the 3rd one not break?  It's obviously the faulty bolts, maybe the torque wrench too.  But it's a good wrench, Craftsman.  I've recently tested it compared to other wrenches and it's been spot on, consistent too.

 

Yea if it tests fine compared to the others I would say its good.

 

I think the reason the 3rd didn't break is because of slight differences in the bolts and/or different metal fatigue ....this is a guess....but I wouldn't expect them all to break at the exact same torque amount....some might fail slightly higher or lower.

 

Oh and also....did the threads have lube on them when you torqued them? general rule is lubed threads require 15% -25% less torque. I

Edited by RBI

Share this post


Link to post
Share on other sites

Yea if it tests fine compared to the others I would say its good.

 

I think the reason the 3rd didn't break is because of slight differences in the bolts and/or different metal fatigue ....this is a guess....but I wouldn't expect them all to break at the exact same torque amount....some might fail slightly higher or lower.

 

Oh and also....did the threads have lube on them when you torqued them? general rule is lubed threads require 15% -25% less torque. I

 

Thread lock.  WOAH I just remembered!!!  A few weeks ago when I disassembled the motor, those upper engine mount bolts were a little loose.  Two of the three bolts were maybe 10 ft lbs tight, only one of them was snug.  I thought to myself that thread lock was an absolute necessity for motor mounts. 

 

That's probably the root of my problem. 

Share this post


Link to post
Share on other sites

Ah so the wet thread lock acted as a lubricant.

 

Btw, I know the feeling.....its the irony of the whole situation.....breaking bolts with a got dang torque wrench and a service manual.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×