Posts
109
Joined
6/7/2019
Location
IE
Hi everyone been a whil since iv been here just wanted to pop in and share my new build
Using a 2017 kxf 450 chassis with 1998 kx250 motor plans as followed
Rebore to 300cc
Boyesen rad valve
Light port work
Front fork update air forks suck
Vortex twin map cdi
Ktm 300 exhaust system because of availability and price
So pretty much it for now looking for guidance on welding the frame if anyone can help I will upload pictures of the motor mounts and mods to the front rails
This is pretty much as far as I have got
Just picked up this cylinder off ebay 250 dollars posted to Ireland I remember a day when I could have got a new one for that
Do not try and butt weld those joints. You want to insert similar size ID AL parts inside where the joints are. Then you push each joint together (if you can get a small interference fit that is a good thing). You also want to drill holes in the existing parts you see so plug welds can be used to join the frame joints to the internal solid pieces of AL stock. Then after the plug welds on both sides of each joint.... then weld up the seems.
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See that hole on the closest side of the "Y". That's one of the plug welds to the inter part inside the fame. There is another hole on the other side of that one (180 degrees)... the plug welds were done first... on all joints. 2-4 plug welds per joint. The welds were later ground down and hand sanded/ finished so you don't see them. You just see the joint welds. But you need the plug welds and internal AL stock provide on either side of the joints to make it much stronger then a joint weld. Make sense?
I did all the fab work ... cut all the parts etc.. but had a PRO do the welding on this part. The guy is well known in the bicycle industry for welding AL. He did a great job and was super reasonable for price.
As you can see in the pic above the extension is a slip fit so a solid weld can be achieved
Original way it was welded above
This is just a rough idea of the upper cylinder head mount it will be extended upwards more and down to the end of the y piece should also add strength to the joint which will be plated at the front also
As you can see in the pic above and below the lower engine mount extends in each direction of the joint so there's no fear of the failling
What do you guy think everything is just rough cut for now just for ideas but will be refined and machine finished before welding
It's good... I used a lot of overlap on the internal AL over the joints... But your use of a engine mounting to bridge the joint also should for sure ad more structural help...
I did originally plan to insert the rail extension down into the lower rail like yours originally but I found the 2 extensions in a scrap yard and some how thats the exact length they were i try my best not to spend money where possible 😅
goodies starting to arrive in went with a hgs pipe from a 2007 kx 250 with i will be using a insert to connect the pipe to the cylinder I will be getting 3 inserts made with different size inner diameters to change how the pipe will work to my liking
Also picked up a set of kyb yamaha forks brand new little or no use which will be gripped into a set of xtrig rocs I have on the way
I also purchased a used vortex dual curve cdi just out of curiosity and the fact it has 2 settings changeable by switch on the handle bar one in full power mode and the other wich changes timing which should help the fact this bike will be used for enduro
Another build i have coming together at the minute 1997 cr250 complete rebuild top to bottom kind of a mix between Stock styles from 1997 to 1999
More goodies in xtrig clamps replacement clutch cover and vortex dual cdi full power and traction setting if anyone can tell me I have a 98 harness and the stator plate is connected to the loom no plug the vortex loom has only 4 wires red ,white green ,white and white yellow only the original 98 harness i have 2 extra yellow wires the went to the igniter box just wondering could these be used as a power source for a fan and led light also just to clear up the vortex is from a 2001 starter plate from a 98
If anyone has a shortbody airstriker with a stic block id appreciate a good deal
Front end almost complete just waiting for some bremdo goodies to show up front master and clutch master and brembo caliper
Wossner 72mm piston and Fresh rod kit should keep the engine reliable for a long time searching for a set of oversize radiators to suit 16 to 18 kx250f or 450f if anyone has a mi t set for the right price
Stuck between these two styles big fan of the simple green kit bit the 01 PC kit is growing fast would like to here your guys thoughts
Sorry late on this but one key element when building frankenbike (I did one my self few years ago) is make sure the position of the center of the front sproket is really similar to the original position. This can have a huge impact on the handling of the bike. Maybe is the angle of the pictures but your look higher than the original position. Good luck with the build
Thanks for the info mate if your referring to the the first photo that was just a rough position for the pic lol its actually a lot lower now not to low tho I had a lot of interference with the expansion chamber and right side rad aswell the frame is welded up now and I should have it back tomorrow evening so I will post pics and see what you guys think this is the first time iv done anything like this so will either be an absolute disaster or work out good 🤣
Pit Row
So this is my carb and air boot situation 2006 kx250 airboot fits quit well and gives a straighter carb positioning to the cylinder but now I have a lager gap between the carb and reeds I will be using a 5mm to 10mm spacer because of the lager bore 300cc to add to the crankcase volume with boyesen rad valve so that should help abit only other option I have is to weld an extension to the carb where it connects to the air boot or extend the rubber between the rad valve and carb
That's kind of a good problem to have. You can do some pretty cool stuff there.
I would design a 3D printed plastic part between the carb and air boot and mount with correct size piece of rubber tube in to the carburetor. Carburetor too far away from the cylinder intake will hurt your power band
I have a few carbs there I have the loger version of the airstriker which fits better but rather the shortbody always found a engine more responsive and jetting to be more predictable I have done more research and as u said the further away will kill performance so I'm just going to modify the boyesen rad valve for the straighter position of the carb and leave the rubber joiner as is and extend the back of the carb I will still be using a reed block spacer
Yes, closer is better. Look around at shifter cart intake, carb and reed setups. That will give you a better idea of what you want to do with it to make good power.
I have looked at shifter karts and all for some inspiration couldn't find a kx250 one tho more cr250s than anything
So havent been on in a while but have been realy busy but have almost finished the bike
So plans have changed as i have progressed true the build just a spec list for the sake
Engine:
Sr250 factory crank with new wossner rod
Rebored to 300cc port matched and port job done
Vortex dual map cdi actually the second because first one i bought didnt work
Boyesen rad valve with 10mm spacer
Brembo hydraulic clutch working with a hymec slave cylinder
Brand new keihin pwk shortbody
Have used the original airbox with a 2003 kx250 air duct needs a spacer to reach the carb but looks good
2005 kx 250 full hgs exhaust
Chassis:
Yzf forks
Ohlins rear shock
Green xtrigs
Brembo front and rear brakes from a ktm
New sm pro talon wheel set waiting for a rear 18 as im using this as a enduro
Thats all i can think of at the minute
Will upload more pics the weekend when hopfully its ready run for the first time
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