Frame bracing / bash plate

[Nathan S]

i can't see how it would reduce much, if any flex on the lower rails considering that the engine mount bolts tie both sides of the rails together anyway. If the motor is a snug fit, as it should be, between the mounting lugs, that in itself reduces any flex down the bottom of the frame. Re welding the old welds is the best way to reduce flex in my opinion, and also reduce the risk of frame failures at fractured weld seams.

I've owned a few 1980s KX frames that have broken the lower engine mounting plates off the frame. The 86 frame had cracked on the lateral tube that runs between the footpegs.

Best as I can figure, these failures can only happen because the frame is flexing around the much more rigid engine cases. The weld-on skid plate would seem like a good way to add rigidity to that section of the frame - and (in the case of brittle 80s KX frames).

[smed]

it was definitely not done by a works team...

I think MR Geboers might like to argue with you mate

[Nathan S]

No no - its my KX frame that was certainly not done by a works team.
Not unless there was a works team that employed a drunken chicken to poop metal together...

(And I'm no god of welding myself...).

[smed]

Yeah I get ya now after re reading your post , I would be guessing that the one on the Geboers 500 was done by HRC when they were building the frame so no probs when done properly,I always thought the welded in bashplates were pretty damn trick myself    

[Paul552]

The bike featured in the transomoto artical has a 19" rear.
I assume that would be pre 85 legal even though the bike came out with 18" rear.

Would it be a improvement in handling having a 19" rear

Opinions??

I also think the bash plate looks trick

[mainline]

Less weight, but less sidewall ?

[FourstrokeForever]

i can't see how it would reduce much, if any flex on the lower rails considering that the engine mount bolts tie both sides of the rails together anyway. If the motor is a snug fit, as it should be, between the mounting lugs, that in itself reduces any flex down the bottom of the frame. Re welding the old welds is the best way to reduce flex in my opinion, and also reduce the risk of frame failures at fractured weld seams.

I've owned a few 1980s KX frames that have broken the lower engine mounting plates off the frame. The 86 frame had cracked on the lateral tube that runs between the footpegs.

Best as I can figure, these failures can only happen because the frame is flexing around the much more rigid engine cases. The weld-on skid plate would seem like a good way to add rigidity to that section of the frame - and (in the case of brittle 80s KX frames).

Interesting.....Maybe the KX's used seamed round bar rather than extruded tube? I know Harley's still use seamed bar....
If any part of the engine mounting points are a loose fit or flogged out like alot of the old magnesium cases and alloy mounting plates, there will be undue flex created if this is not corrected. The way I see it, most flex would be at the swingarm pivot area due to the length of the arm. I dunno, maybe I'm looking at it the wrong way. Adding a welded on skid plate can't hurt, just make sure all the engine mounting points are a snug fit first. And that includes the head stay mounts as that is an integral part of adding rigidity. 

[Nathan S]

Old Kawi frames seem to be made of a fairly brittle material. A high carbon steel, at a guess.

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19" wheels are legal because 19" wheels have existed since forever.

They weigh less, and the lower sidewall is supposed to help handling. I know Magoo reckons it was a good move on his Evo bike. There's also a few extra choices for dedicated MX tyres in 19" (especially in 125-friendly sizes).

[Paul552]

Thanks Nathan

Makes sense.