doing up a yz400 but have questions- lyles build

[peaceofwork]

do 426 heads breath better than 400 heads

are the cams any different between wr and yz motors 400 and 426

whats a good 450 auto cam to go to?

are some 426 cams auto comp relese?

i got a new 02 crank assembly so whats everything i,ll need to go with that?-different crank gear i,m hearing- what about the balancer?

will a wr400 fit in place of a yz400

thats enough for now lol thanks in advance for all answers

[Birdy426]

do 426 heads breath better than 400 heads

are the cams any different between wr and yz motors 400 and 426

whats a good 450 auto cam to go to?

are some 426 cams auto comp relese?

i got a new 02 crank assembly so whats everything i,ll need to go with that?-different crank gear i,m hearing- what about the balancer?

will a wr400 fit in place of a yz400

thats enough for now lol thanks in advance for all answers

400 and 426 heads flow the same...they are the same basic part

YZ and WR cams are the same, but cam timing is different between YZ and WR

Pretty sure 400 and 426 cams are trhe same, but not 100% sure.

Stock 03-05 450 exhaust cam is as good as any, but probably more expensive than hot cams now. Hot cams work well.

Only aftermarket 426 cams are autodecomp. never offered from the factory

I assume you mean to run a 426 top end for the crank question...you will need the 426 primary drive gear, balance shaft drive gear, locking washer and nut, along with the 426 piston and cylinder and gaskets. Run a new timing chain on your new crank! (400/426 balance shafts should b e the same...check the part number with one of the many on line parts lists)

I assume you mean will the entire WR motor fit in place of the YZ...yes...cases, cylinder, head, etc are the same. If swapping between years, you will have to deal with different diameter swing arm pivot bushings.

[peaceofwork]

thanks birdy

i been thinking about the big bores a lot and i noticed that more than a few of them blow.could it be that they stress a bored cylinder to much and they flex then destruction?

might a steel liner in the cylinder be a good bit stiffer and lead to a long happy existance ?

[peaceofwork]

new questions - i picked up a 99 wr 400 motor that i dont know mutch about but the valves are in spec and it turns over fine so i droped it into my 99 yz 400

i ,m wondering if i cause me greef by runing a wr stator with a yz cdi ?

we got the motor put in as it was getting really dark so after about 20 kicks back to the shed it went. it has fresh gas and when we leaned the bike over it flowed out on the ground from the vent tube but i,m just pondering if i need to run all yz or all wr ignition components?

last year the bike was running with a eline set up on the yz400 motor this year no fire yet off wr stator equipt wr 400 motor

any ideas any one?

[grayracer513]

To use a WR stator with a YZ CDI, follow these instructions:

https://www.thumpertalk.com/forum/showthread.php?p=10674552#post10674552

[peaceofwork]

thats pretty cool, thanks grayracer

[peaceofwork]

do crank bearings have to come from yamaha? i suspect odd internal and external sizes so yamaha might be having a custom bearing ? like when i did my 250f, i could get everything from the bearing house except crank bearings

[grayracer513]

It's not the sizes. YZF mains have a step machined in the outer race for the retainer plates. A bearing house could likely order them, but they would probably not be cheaper, and could even cost more.

[peaceofwork]

the local dealer wants 96 each and 89 for the timing chain

i,m gathering parts slowly

[peaceofwork]

update- ok guys i scored a 99 wr400 motor a while back put it into my 99yz

well it turned out that i had no spark so i unhooked the yz cdi then hooked up the wr cdi and wiring harnes, it then had fire it then started first kick and idled nice so i suspect the yz and wr stators need their respective cdi unit to run. any one else tryed mixing cdi and stators between yz/wr 400 426 bikes?

may be i just f,d it up some how on try one

[grayracer513]

The two ignitions operate on two different principles. To use the YZ CDI with a WR stator, follow this procedure:

https://www.thumpertalk.com/forum/showthread.php?p=10674552#post10674552

[peaceofwork]

greyracer thats a great link,and if you follow it over to supermotojunkie it tells a lot of usefull imformation about a batterieles lighting system.

when i build my new motor i,m going that way, but for now i just wanted to test out my 200 dollar wr400 motor,i,m so glad i got the wiring harnes and cdi included with my purchase.

does anyone have anything good or bad to say about aftermarket weisco timing chains?i,m weary knowing the story on their cranks but i like their pistons

[grayracer513]

If the timing chain is more than $45, skip it. They are most likely rebranded chains from the same vendor Yamaha buys from (Borg-Warner Japan). If they're made in China, walk away quietly.

[peaceofwork]

I called honda east Toledo today crank bearings are about a third of the price compared to local dealers ware i live 29.29 VS 96.00

and timing chain is 37.61 VS 86.00 ,

so after finishing my kx100 frame 125kx motor project the 2 yamie ones will be going ahead