my 2001 KX 250/500 conversion

[cutting torch]

Been riding the beast at the local MX tracks, and found out last night that both my head stay AND front engine mount are broken.  How are other engine mounts holding up on the conversions?  My engine mounts were gusseted and everything, oh well.  I need to add another pipe mount anyway.

Pics of the problem areas would help us with suggestions......

torch

[junk man]

I wounder if any other builds have broken front mounts ? and what kind of head stay he's using
If mine brakes i might sleeve the frame and use the stock engine plates off the 500 i was going to do this but the 250 frame is narrower and i didn't want to flatten the tubes but if it brake is on

just an idea JM

[BDI]

My 2002 is fine. My front mounts are simply the sock 250 mounts cut down. I did a bunch of practice welding on a junk 250 frame until I got my mig welds to look just like the factory welds and then went for it. As for my head stay I had a couple of funny comments made about my bike when I was building it. One was when I asked my buddy charlie tredwell who builds race car chassis if he thought my head stay was going to be strong enough. He said ya it would be strong enough for a shock mount on a trophy truck. I think the importance of and the designe of the head stay has been missunderstood by quite a few people, especially on the steel frame bikes. I realized how much demand was put on the head stay when I learned that the kx500 would blow fiber head gaskets do to the head flexing in the head stay area.

[KXer]

My forward enging mount had/ has a 90* gusset on it for strength.  The actual engine mounts are 3/16ish thick (think shock tabs), and the head stay was the piece together unit from Jfab, with double row tig welds.  It "seemed" to be bulletproof.

Does the head stay need to be rubber mounted?

I have yet to take it apart to see what failed on the head stay, I'm assuming the steel became brittle after welding, grinding, welding etc getting it 100% perfect.  Also have a good idea of how i will add a gusset down the center for the 3rd headstay for this monster.

[BDI]

If you try two weld thick metel to thin metal you will either get the thin metal way to hot in order to wled the thick metal and this will result in embrittlement and cause the base metal to fail. Or if you run at the right heat for the thin metal you will not get good penetration on the thick metal and you will have a cold weld that will break off the thick metal. I would imagine you had a hard time with this, probably did some grinding and some hole filling during this would be my guess.

[junk man]

hey kx'r we need to see where yours broke I'm thinking it cracked the down tube if so you could get a piece of 0.45 tubing and split it use about five inch piece remove your old mount and weld any cracks grind it smooth then slide half over the back side of the down tube and weld it top to bottom don't weld around the tube then use 1/8 inch flat plate  make your engine plate about four inch long and weld it to your doubler we'd like to help with your problem any way we can JM   note this might not be the best idea

I also used stock mount trimmed down so far its good  also BDI's   head stay is well built and definitely not a week link

[The Flyin Hawaiian]

I was gonna use thicker mounts on my bike but after reading BDIs comment Ill stick to the trimmed down stock mounts.

[KXer]

The engine mount crack is not on the frame or the weld, the steel gusset snapped. - will get pics tuesday ~ hopefully

The head stay cracked after the weld - again, I'll put pics up Tuesday.

Thanks for the input.

[BDI]

I like the idea of grafting the KX500 cradle into the 250 frame. Having never tried this I have no idea if it would work or not. The best thing to do is use the 250 mounts and do it just like the factory did in my opinion. I think this is one of those cases where over kill is your enemy. Also if you notice the factory starts there mig welds before the the mount and ends it after the mount. This is done so there is no cold weld to start a crack.

[KXer]

UPDATE:
Took the bike from so cal to Colorado.  pulled it apart, the headstay plate (that gets used to grab the 5 head studs) snapped in half.  This was because the nut came loose that holds the heads stay to the frame. . . my bad.  Gusset on the front engine mount was cracked, engine mount was not. . . yet.  Fixed both.

Rejetted for the elevation and the bike fired up.  let it warm up and then it died.  swapped the plug to find it was fouled.  Still would not start.  Long story short, somehow (I think) the stator wires got yanked causing VERY low spark.  It would bump start (after 2 trips around my brothers 4 acres) but it was running horribly.  Because Im stubborn, I kept at it and smoked the rings.  I now have no compression, Im just HOPING that I didn't blow any seals in the bottom end.

Brought the bike home, didn't get to ride the IMI mx track that is 3 minutes from my brothers house.  replacing rings, reeds, swapping back in socal jets and will have to look at the stator to see if whatever got pulled is repairable (But fear a new ignition is in order) - Anyone have a good running 500 ignition?