Motor Replacement Options

What motors (excluding stock of course) can I fit into the 426 frame/setup? Do custom aftermarket motors that fit the 426 exist? How about newer 450 motors? What kind of work is necessary to make either work?

I'm not interested in purchasing a used 426 motor, and rebuilding the current motor is not worth the cost. So I figure, why not upgrade (if possible) to an entirely new motor. I'm not sure what possibilities exist...

What motors (excluding stock of course) can I fit into the 426 frame/setup? Do custom aftermarket motors that fit the 426 exist? How about newer 450 motors? What kind of work is necessary to make either work?

I'm not interested in purchasing a used 426 motor, and rebuilding the current motor is not worth the cost. So I figure, why not upgrade (if possible) to an entirely new motor. I'm not sure what possibilities exist...

I'd say the only close fit would be the 03-05 yz450f motors, and that's probably after modding the frame mounts. Realistically, since you don't want to spend on a 426 motor or rebuild the existing one because of the cost involved, the best option would be parting out the 426 and buying a slightly newer bike. Using a newer engine in that frame is certainly doable with time/$$$, but probably not viable economically, unless the replacement engine was VERY cheap or free.

As I recall, the swing arm pivot of the '02 has a different PN than the '00-'01. This may cause a fit problem at the rear hard point, but the steel inserts at this point can be removed and replaced with those from the correct year. The '02 swing arm was also different and could be a factor.

The '03-'05 engine should be very close to a bolt-in also, but could be subject to problems at that same rear mount for the same reasons.

In my opinion, if you are really at the point of needing a complete engine, and can't find a deal on a used one the correct year, you would be best off buying a newer 450 for what they sell for now and part yours out.

you don't want to spend on a 426 motor or rebuild the existing one because of the cost involved

its not that i don't want to spend the money for a used 426 motor, i just rather not. if i did, i might be buying a motor with more problems than its worth. its rebuilding the current motor that's not worth the price.

In my opinion, if you are really at the point of needing a complete engine, and can't find a deal on a used one the correct year, you would be best off buying a newer 450 for what they sell for now and part yours out.

i would have a traded up for a new model a long time ago but i want a green sticker for california. ca laws :bonk:

is there any custom motor that can be easily modified to fit the 426? if not, i think i'll end up rebuilding the current motor with a couple of upgrades

is there any custom motor that can be easily modified to fit the 426? if not, i think i'll end up rebuilding the current motor with a couple of upgrades

ok, how about rebuilding the existing engine with a 444cc kit?

ok, how about rebuilding the existing engine with a 444cc kit?

that's a good idea. i need to get my stock cylinder resleeved anyway...the company doing the resleeve can do the big bore for me when i send it in, right? do you think it would be any cheaper?

that's a good idea. i need to get my stock cylinder resleeved anyway...the company doing the resleeve can do the big bore for me when i send it in, right? do you think it would be any cheaper?

It's probably best to look up the 444cc kit and see what comes with it and who makes it, it should be easier from there to figure out which parts are needed. I remember seeing a few threads on the subject within the last year in this forum, shouldn't be too hard to dig up the info. Probably pretty easy if they provide a sleeved/bored cylinder and just have you send in the core exchange.

It's probably best to look up the 444cc kit and see what comes with it and who makes it, it should be easier from there to figure out which parts are needed. I remember seeing a few threads on the subject within the last year in this forum, shouldn't be too hard to dig up the info. Probably pretty easy if they provide a sleeved/bored cylinder and just have you send in the core exchange.

after researching your suggestion, i came up with this: 449cc bore, 97.5mm piston (Wiseco or JE), 13:1 compression, and '03 OEM 450 cam.

EDIT: or 444c bore, 97mm piston, 12.5:1 compression, and '03 OEM 450 cam

thoughts? will either work?

Edited by felix 222
after researching your suggestion, i came up with this: 449cc bore, 97.5mm piston (Wiseco or JE), 13:1 compression, +2mm stroke increase, and '03 OEM 450 cam.

EDIT: or 444c bore, 97mm piston, 12.5:1 compression, +2mm stroke increase?, and '03 OEM 450 cam

thoughts? will either work?

Where did you find a stroker crank kit?

Where did you find a stroker crank kit?

this is all i found. but i can't use it with my setup. never mind.

you don't need a sleeve, they bore your cylinder 2mm over and re-plate it .

you don't need a sleeve, they bore your cylinder 2mm over and re-plate it .
In fact, you should avoid sleeved cylinders.
In fact, you should avoid sleeved cylinders.

If youre going to a really large big bore you want a sleeve if you're using the stock cylinder as it adds rigidity. I do however prefer plated aluminum sleeves compared to iron sleeves in bikes when they're avail.

IIRC thumper racing has aluminum sleeves avail for KTMs. Not sure what their cyl sleeve material is for their YZ426 to 450 big bore kit though.

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