98 yzf400 -426 mod

hi i am new here and i have a 98 yzf400 and want to convert it to a 426 and have a few qustions

am i right in thinking the parts i need are a 426 con rod a 426 pistone and a 426 cylnder.

from the recherch i have done i beleive i can use my head

secondly will a auto decomp cam from a 450 fit my head i red somewere that there might be a slight difrence in the pitch for the cam chaine is this right

also what would be a good starting point for jeting i have a standerd header with a white bros can the e series one

i would be verry greatfull of any help many thanks edwin

hi i am new here and i have a 98 yzf400 and want to convert it to a 426 and have a few qustions

am i right in thinking the parts i need are a 426 con rod a 426 pistone and a 426 cylnder.

from the recherch i have done i beleive i can use my head

secondly will a auto decomp cam from a 450 fit my head i red somewere that there might be a slight difrence in the pitch for the cam chaine is this right

also what would be a good starting point for jeting i have a standerd header with a white bros can the e series one

i would be verry greatfull of any help many thanks edwin

why are you trying to do a 426 conversion? unless your motor is smoked already the power differance will not justify the cost, and you would find yourself further ahead selling it and buying a yz450.. old ones are cheap enough now

but if you have some attachment to the 400 but "need" a bigger motor you would probably be further ahead buying an aftermarket bore kit like this http://www.lukesracing.com/luksr/yz400f.htm its ~$500 for the cylinder, piston and gaskets and will probably make more power

as far as the cam goes you can get a used early yz450 exhaust cam, there are plenty of details about that in this thread http://www.thumpertalk.com/topic/56257-yz-450-cam-mod-please-read/page__st__960__p__2979654#entry2979654 or if you are worried about the pitch differance (it works fine) you can buy the hotcams cam specific for your motor and it will work good but will cost more

I would wait for your bore kit to tackle the jetting, and if you buy that kit from lukes, I imagine they can tell you where to start. If you want to mess with it now and all you have is an aftermarket can the stock 175 main is probably big enough, if its running rough and you cant get it right by adjusting the pilot screw, you probably need to clean the carb out.

there is a user jetting database here http://www.thumpertalk.com/topic/604117-1998-99-yz400f-user-jetting-database/ but there arent many examples of the older bikes

interesting questions- if the 400 was getting a rebuild any way you would likley be getting a new rod and piston gaskets, so why not go 426? cylinders are cheap on ebay.

26 cc more isnt much would you even notice an improvment over 400?

would 426 cams help?- compared to 400 cams? are some 450 cams a direct fit and improvement?

i,m thinking a fresh cylinder and piston with good tight clearance would make the most difference except for say maybe that 444 kit

some one educate me and give your ideas on what to do with an old yz 400 thats allready had the head done- i love that old bike as its semi street legal

While 26ccs might not sound like much, it IS a noticable improvement...especially if you need to rebuild anyway. The change in my 426 going to 444 was a smaller step (18 ccs vs 26 ccs), but was quite noticable with my (and other 426 riders) "rectal dyno". The other advantage to going 426 on a 400 motor is the small end rod bearing is bigger, and thus more durable. If you replace the entire crank with a 426 crank, you get a third benefit. the primary drive gear (and balance shaft drive gear) are splined rathe than keyed. Again, an increase in durabilty. When I rebuilt my 426 a few years ago, the cost of the big bore kit was very competative with the cost of a replate, piston and gasket kits. Cost of the 426 rod vs the 400 rod is a wash.

Only 2002 426 cranks are splined for the counter balance gear.

good information guys i ,v had this bike apart for about a year- i just wait and watch ebay i dream of finding a 444 cylinder cheap so if i do then its a 426 rod etc hell maybe i,ll find a rebuit 426 crank

whats a good aftermarket rod and piston to run?

Only 2002 426 cranks are splined for the counter balance gear.

Negative. My 01 426 has a splined primary drive, as do several others I've helped rebuild. The 00 426 retained the keyed arrangement, but 01 and up are splined.

That's correct. The change from a keyed to a splined balancer drive gear was made in '01. The '00 crank is listed by Yamaha as "not available", and is replaced by a 5JG-11400-21-00 crank that has a revised rod and bearing as well. You'd need a 5JG-11536-00-00 balancer gear to go with it.

Negative.  My 01 426 has a splined primary drive, as do several others I've helped rebuild.  The 00 426 retained the keyed arrangement, but 01 and up are splined.

You're right,my badI just didn't want him thinking all 426 cranks were splined.

My thinking was in going 426 was cylnder verry cheep now and easy to get in good cond.

Pistons seem more available in uk and as such cheaper with more choice

Bigger wrist pin

More hp the 426 cylnder has more meat and can be bored out bigger and replated for a futher increase in hp

Bike needs rebuild anyway and I could always sell the 400 cylnder wich would then mean it would no more than a rebuild anyway

Sounds like a good plan!

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