08 motor mounts cracking

[stoney55]

http://s1208.photobucket.com/albums/cc368/Jeremiah_Stone/ We have an 08 kx250f and the motor mounts have cracked twice now. any one else have this problem? or know why it is happening? it's not cheap to have welded and i have to think something is causing this that i can fix. thanks for any help in advance. Edited April 4, 2011 by stoney55
add photo

[D-K]

Probably your swingarm pivot axle is loose. It makes the engine vibrate more than normal. Tighten it.

[Pr1malR8gw]

Pictures would be nice?? I've not heard of motor mounts cracking.. I guess it's not impossible especialy if A. you're a top a ride, or B. you a bottom D rider trying to ride like an A rider and case repeatedly!

[D-K]

First!

[Pr1malR8gw]

Ohh don't play that BS game with me dk! PUNK!

[stoney55]

Pictures would be nice?? I've not heard of motor mounts cracking.. I guess it's not impossible especialy if A. you're a top a ride, or B. you a bottom D rider trying to ride like an A rider and case repeatedly!

That "B" description may describe me but this is my son's bike and he rides it pretty hard "intermediate class" BUT I'm sure these things are made for that. i will get a pic posted as soon as i can. thanks for the opinion but i'm doubting that it is riding technique

[Pr1malR8gw]

Dk's loose swingarm pivot bolt theory would also make sense.. That would cause the engine to vibrate and flex the mounts more then normal which could inturn cause them to crack.. How many hours are on the bike?? my 07 which has the same style mounts has 80+hrs of riding and they have yet to crack.

[stoney55]

The bike has probably 50 hrs or so, we just had a new top end put in it and thats when we found the breaks in both motor mounts originally. He just raced in the Mammoth Qualifier last weekend and when we washed the bike he noticed the new crack. pic is posted now. I will check the swingarm tonight. hopefully its something like that. thanks

[stoney55]

Not the Swingarm, it was tight and the bushings are fine. any other thoughts? thanks again.

[D-K]

Was the picture there originally? I just saw it now.

Why is there a "standard" bolt there?

Might not be so mystical after all. Someone (you or the p.o.) must have ran it with that bolt loose, causing the problems to begin.

The original bolt is fine threaded. That is to make sure it gets the proper torque. A standard bolt is a sign that something has happened, probably the whole bolt fell out and was lost.

Aluminum is very rigid, but does not stand up to rubbing/vibrations good. Welding can be done in so many ways, with so many different materials, it might be the "new" cause for the further problems, perhaps even the use of the different bolt can come into play.

Kawasaki did not put in a fine pitch thread bolt there just because it was funny, they had a reason. The nut you have also is not self locking. So it probably comes loose every now and then.

Enough of my ramblings and thinking out loud, if I were you, I would take the engine out of the frame, have a (very) good aluminum welder cut the old tab out and weld a new one in place. Then make absolutely sure the sides of the new tab was perfectly parallell and straight.

Then I would put the engine back in, tighten all mounts except this one, then if there was any gap, fill that up with washers so that it does not bend inwards when tightened.

Oh, and I would get a new bolt too.

The bolt has part.no. 92153A and the nut is 92210

[stoney55]

Was the picture there originally? I just saw it now.

Why is there a "standard" bolt there?

Might not be so mystical after all. Someone (you or the p.o.) must have ran it with that bolt loose, causing the problems to begin.

The original bolt is fine threaded. That is to make sure it gets the proper torque. A standard bolt is a sign that something has happened, probably the whole bolt fell out and was lost.

Aluminum is very rigid, but does not stand up to rubbing/vibrations good. Welding can be done in so many ways, with so many different materials, it might be the "new" cause for the further problems, perhaps even the use of the different bolt can come into play.

Kawasaki did not put in a fine pitch thread bolt there just because it was funny, they had a reason. The nut you have also is not self locking. So it probably comes loose every now and then.

Enough of my ramblings and thinking out loud, if I were you, I would take the engine out of the frame, have a (very) good aluminum welder cut the old tab out and weld a new one in place. Then make absolutely sure the sides of the new tab was perfectly parallell and straight.

Then I would put the engine back in, tighten all mounts except this one, then if there was any gap, fill that up with washers so that it does not bend inwards when tightened.

Oh, and I would get a new bolt too.

The bolt has part.no. 92153A and the nut is 92210

thanks, that bolt was replaced when we found the original cracks. why he put in a standard bolt i don't know. i agree it could have caused the second round of cracking now that you put it that way. great advise. thanks again.