Several years ago when I was riding and racing my KX500 a bunch, I was getting subframes from a fellow named Darren in the UK. They were much better than OEM or AC Racing's beer can offerings, but unfortunately I would still crack them occasionally at the stinger pass through area.
At one point Jonathan Bell, also from the UK, had mentioned he was working on a one piece sub frame / air box combo, but I don't know if he ever put those into production?
There is also Johnny "True Torch" in Santa Ana who made chromoly sub frames for the Team Green desert team. I spoke to him once about remaking a batch of them, as he still has his jigs, but I believe it would take a large group order to really gain his interest.
Anyhow, my question here is...besides the options I've mentioned above, is there anyone else out there who has taken on the task of producing new KX500 sub frames that can withstand some modern day MX abuse?
Hell yeah, awesome photo. Bump, hope you get some interest in getting some made. Loved building mine.
If you build them, they will sell. I miss mine.
How many would it take to get an order started?
I dig the gold rims...
I have one spare subframe, but I've had thoughts about building up some spare subframes if I crack the first one. I'm far to busy to tackle any more projects this year. It would be useful to have some photos of cracked subframes, especially to identify the most common crack locations and where the cracks start.
A few years ago I purchased some weldable 7000 series tubing from a bicycle shop in Europe with a similar profile to the Kawasaki subframes. The 7000 series aluminum is substantially stronger than 6061 before and after welding. 6061 requires a heat treatment after welding to regain full strength in the heat affected zone. 7075 Aluminum alloy tubing is considered non-weldable without heat treating, but the bicycle and motorcycle industries have tubing with low 7000 series alloy codes (like 7005 and 7005-scandium) that age out to higher strength over a short time following fabrication. You can heat treat it to T6 for even greater strength. The bicycle people have a lot of information published on this topic.
For some reason, I have it in my mind that AC Racing uses common 6061 for their subframes. If this is the case, it would be useful to know if they're heat treated after welding or not. If they crack near the welds, it may be an indicator that they are not heat treated.
I had my KX out to a buddy's farm/track on Saturday to test & tune a shock upgrade. I'll take it to Washougal this weekend.
The Shop
Man if I could ride like you I'd buy you 10 subframes! Awesome Pic!
Back in the day I had 3 Kawi 500's and a local guy would straighten them and re-weld them.
That complete frame and tank are from a 1989 KX250.
That tank, tall seat foam and modern cambered pegs give the bike a very modern rider triangle.
Build thread:
https://www.vitalmx.com/forums/Bike-Builds,46/1990-KX500-Classic-Looks-Modern-Handling,1394778
Interesting that you improved your KX500 by using 89 KX components - I've replaced the forks on most of my 500s (current 97 KX5 included) by swapping out the front end for the 89 KX RSU fork setup to improve it for my use (also installed those on my 93 CR250 and the transformation on that bike was nothing short of night-and-day). Back to the future?
While the feel of the USD forks might be preferred for MX, those 89 RSU forks are outstanding for offroad. I'm told the DRZ RSU forks are a newer/more readily available option that offer the same benefits but I've never tried them.
My forks are from a 2013 YZ250 (KYB 48mm SSS components).
I machined custom clamps to correct steering offset, steering stop, bar position and run the 1990 number plate.
Last month I built a new shock with a HSC adjuster and shorter overall length to drop the rear end. So far I love it.
The frame, subframe and tank are the '89 KX250 components. The rest of the Kawi parts are original 1990 KX500.
Everything is in that build thread I linked above.
I think I’m gonna bring you a new project bike
It started life in 2000 as a Team Green built KX500 complete with frame hoops (KDX200 style engine protection) and has one of their hand built). Since then, someone’s messes around with the PC Suspension and…I think it’s time to bring that bike into the present…
The tank you used looks a lot like the ‘97 KX500 tank which is an honest to goodness SR knock off part…GREAT profile and very works-like. I think the ‘07 500 tank might be slightly sleeker?
That sounds like a really cool project with some history behind it. I would imagine it has all the gussets and welds done to the frame to make it more durable. I'd love to see what that looks like.
My tank was only made for the one year ('89 KX250) so it's super hard to find them.
Doc Wob sells an aluminum replica and I've heard there's a company making rotomolded plastic replicas very recently.
What was the company that made aftermarket subframes before?
Yeah, I saw the build thread - very nice and much more involved than the ones I've owned. I was just thinking how both of us were "improving" the later KX5's with parts from the older 89 KXs... making newer, better by going back to the older. Now that's what you call progress!
Thankfully, my front end swap is as easy taking the triple clamps/forks assembly off and installing the ones from the 89. (So easy, even a Village Idiot could do it!) On most of mine I would modify and install the rear fender from a 93(?) KX250 to get rid of the snow-shovel-looking stock one and give it a flatter, sleeker look.
I think I've still got the seat from an 89 KX250 somewhere in my parts collection - we used to replace the stock seat on the 1st gen liquid cooled KDXs with the 89 KX seat. Does the 89 KX250 tank slip right onto the stock KX5 frame and does it mate up to the stock KX5 radiator shrouds? (I know you used the 89 KX250 frame but didn't know if it would fit the 500 frame) If so, I might consider picking up an 89 OEM repro tank and doing the tank/seat swap on mine to go with the rear fender.
I agree on the OE pipe mounts - not durable and hideously expensive. We started fabbing our own years ago using a design very similar to what you've come up with with much better results than the stock ones were giving.
Also, what paint stripper did you use on the pipe? Ever since they removed MEC from the formulation, the ones I've bought aren't very effective and I've yet to find a good replacement.
I still use Jasco brand stripper, but it all sucks these days. That pipe and the swing arm took a few applications over two or three days to come clean. Total pain in the butt compared to the old stuff... More "Progress".
The 1989 KX250 tank is a direct fit to the 500 frame. I don't think any others will fit..
Very little difference between the 1989 KX250 frame and my 1990 KX500 frame. The ignition mounts were different, the linkage tabs are different and some 500 exhaust pipe mounts need to be added. I decided to cut up the 250 frame in case I hated the bike when it was done.
My look into subframes was actually started by going down another rabbit hole. I mocked up a YZ tank and seat before I built the KX500. If a CR500R pipe and silencer are used with a modern YZ or KX shock body and a YZ250 / YZ125 tank, a custom subframe and airbox will allow a much more modern rider cockpit. Seat to footpeg and footpeg to handlebar would be essentially identical to a current Yamaha YZ250... The frame profile fits the YZ tank & seat well. The latest 2022+ YZ bodywork is even better and should fit equally well. Here's a photo of that mock up. I may revisit this in the future as a bolt on system.
Good info, thanks.
BTW, VMX has new 89 KX250 tanks available. It says they're molded from the OEM parts and they get good ratings, so hopefully they're a quality item.
That must be the one a buddy sent me a photo of. I searched and found the product thanks to your post...
It looks decent and has the bronze (or brass) threaded inserts like an original tank. That's cool!
http://www.vmx-service.eu/en/4865-tank-kx250-88-89.html
That's it.
I've heard good things about them (but can't vouch for them personally) and they get good ratings/reviews, so hopefully they don't disappoint. They're usually on eBay for about $250 + $35 shipping; less than the asking price of some raggedy ones I've seen.
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