Frame cradle cracks above front motor mounts

[rider624]

Hey guys. I'm in need of some suggestions on what may have caused these cracks so that I can fix them correctly and keep them from occurring again. Any insight is greatly appreciated!!!

Don't know why these things flipped on me when I uploaded them, then again, I'm more of a motor guy than a computer guy.

First should be the pic of both tubes cracked just above the front motor mounts. 2nd is the left tube, and 3rd is the right.





My guess is vibration, cause I can't seem to find anything else that looks like a root cause. The headstay mounts are both in perfect shape with no signs of fatigue. I'm out of ideas though, and I need to get this thing fixed! 4 weeks off the bike now, and I'm getting antsy!!!

[craigf40]

how is your head stay

[ScooterInVegas]

Pictures of your head stay please.

[Gmbond]

Looking at the contact surface of the motor mounts I'd say it was loose and allowing vibration and movement. Looks like the motor has "rubbed" into them.

Did you use a high grade bolt, loctite and how tight was the fit of the motor in between, was it shimmed to take up any gap?

[AlisoBob]

http://www.bannedcr500riders.com/board/ ... hp?t=12421

[iggys-amsoil]

Looking at the contact surface .... was it shimmed to take up any gap?

Thats what I'm going with.

I would also add a gusset or doubler on the inside, better yet a angle covering the front and inside.

[seanmx57]

Looking at the contact surface .... was it shimmed to take up any gap?

Thats what I'm going with. .

X2

Looks like the bolt put tension on the rails sucking them in because it wasn't shimmed. The vibes would eat it up quick if the motor needs work.

[rider624]

The head stays are NOT cracked or fatigued in any way. The fit is very tight as the markings you see on the frame are from working the motor into the frame. Grade 5, 7/16 bolt through it all with red loctite. Was tight when I pulled it apart.

I guess the "vibration" was the right way of thinking as I thought, but like I said, everything was tight, so I'm kind of at a loss. I thought for sure when I found the cracks, it was going to have broken head stays.

I like the idea of maybe using some angle for the new brackets, but I'm also considering machining the cases out to insert some urethane, or neoprene or rubber bushings to try and reduce the vibes as well. Any thoughts on this?

Thanks for the info and ideas guys!!! Please keep it coming!

[rider624]

I just caught the comment about the motor eating it up if it needed work. I must have needed work as it blew up BIG TIME. I think the guy who bored out the cylinder to put the 1.25 over piston in when I got the motor, bored it too big. Cause it appeared to be a piston slap caused explosion of the piston, which led to the cylinder skirt dropping down into the crankcase and punching a hole through the bottom of the cases as it LOCKED UP TIGHT. Soooooo, I guess I should have put that in the first post as well.

Just a little more background, bike's been together and working perfectly (other than vibrating like a Harley) since the build was completed in August of 2010. So I didn't think anything about the vibration. I guess I should have thought differently about it!

[seanmx57]

How much did you have to spread the frame to get the motor in.

[asteroid500]

The engine to mount surface areas in your picks show that they arnt bolting together square to each other.
this will cause uneven stress & ultimately frame failure.
Shim the bugger up on your refit .... weld up the cracks 1st

[Kuma]

I would replace the rails with new i peice units for the repair and not even attempt to weld up the cracks.

[AlisoBob]

I would replace the rails with new i peice units for the repair and not even attempt to weld up the cracks.

Yup, there readily available now...

[rider624]

Right on guys. Thanks for the info. I've still got a length of tube from when I originally built it, so I was thinking full replacement as well. Hopefully round #2 goes longer than 18 months!