Seized my motor today

And I forgot to add, that before you put the new crank in, be sure to put the tranny in first. I think the book shows putting the crank in first, but you'll need the extra room for your hands when your putting the transmission assembly in.

Ok I was wondering about the shift shaft, but wasn't sure. The book really doesn't give details, just a diagram and the order things come out. Problem is it references other sections, that reference still others, so it's hard to know if I got everything. Thanks guys, I'll let you know how it goes.

BTW, I checked Lukes racing and I cant seem to find a crank kit for the 400, only for 450s. I sent them an email to ask, but do you have any other suggestions?

Ok I was wondering about the shift shaft, but wasn't sure. The book really doesn't give details, just a diagram and the order things come out. Problem is it references other sections, that reference still others, so it's hard to know if I got everything. Thanks guys, I'll let you know how it goes.

The book is hard to follow. Read this: http://www.thumpertalk.com/forum/showthread.php?t=458222&highlight=engine+rebuild Its a complete tear down of a 250F (picture by picture), but its pretty much the same as your bike.

There a few very small parts that will fall out ...
And a couple more under the neutral switch, now that you mention it. Remove that first, too.
And a couple more under the neutral switch, now that you mention it. Remove that first, too.

Yeah, I almost forgot about the spring and the pin. They are on the end of the shift drum, under the switch.

Ok thanks guys. I got it apart today, pulled the crank, then loosely reassembled the cases and covers to keep the engine internals clean. I'm not really sure how long it's gonna be apart for, as I really cant afford to order all the parts right now so I'm trying to keep everything fairly assembled and closed up.

Here are some pics from today

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powroll explains how to turn a 400 into a 426 with yamaha parts on thier website. did you cut the paper off the oil filter to look for trash down in the pleats?

buy a stroker crank assy from Powroll?

According to the powroll site they machine your stock crank. That means buying a $200+ crank, then adding another 400 for machining. No thanks. I didn't even pay half that for the bike to begin with. Also they dont seem to sell cranks either. Anyone know who does?

According to the powroll site they machine your stock crank. That means buying a $200+ crank, then adding another 400 for machining. No thanks. I didn't even pay half that for the bike to begin with. Also they dont seem to sell cranks either. Anyone know who does?

I would get an OEM Yamaha crank.

If your cam drive sprocket is OK, then you can rebuild your crank using the connecting rod from a 426. This will allow you to use a 426 piston and cylinder, even a 444cc big bore kit, on your 400. I'm fairly certain that a 2000 model 426 crank can be used (a 2001/2 would require more parts to convert because of changes to the primary drive gears).

The OEM parts can be had at Thumper Talk OEM for deeply discounted prices.

is the 426 crank stroked over what a 400 is? I'm lookin at the Lukes 420 big bore kit. If I mix that with a 426 crank, what do I end up with? Since I need a crank, rod, piston, cylinder, I like the idea of going to the 426 rod with the bigger bearing, and if I have to buy a crank I might as well get the 426 crank if it's stroked stock......am I confused?

did you have that thing in las vegas a while ago. possibly for the us open?

Not for US open, but I was there for the SEMA auto show around halloween with this bike.

Ok here's another question. Can I just replace the crank, rod, piston, cylinder all with 2000 YZ426f OEM parts and have a stock 426? It seems like I can, but I wanna make sure I have everything straight here.

is the 426 crank stroked over what a 400 is? I'm lookin at the Lukes 420 big bore kit. If I mix that with a 426 crank, what do I end up with? Since I need a crank, rod, piston, cylinder, I like the idea of going to the 426 rod with the bigger bearing, and if I have to buy a crank I might as well get the 426 crank if it's stroked stock......am I confused?

The 400 and 426 share the same stroke, but the bore is bigger on the 426. In order to utilize the pistons for the 426 or overbore kits made for it, you need to use the 426 rod, which has a larger small end than the 400, and of course, the 426 cylinder. Both engines use the same crank pin and main bearings, but the 426 big end bearing is a little beefier.

The 400 and 426 share the same stroke, but the bore is bigger on the 426. In order to utilize the pistons for the 426 or overbore kits made for it, you need to use the 426 rod, which has a larger small end than the 400, and of course, the 426 cylinder. Both engines use the same crank pin and main bearings, but the 426 big end bearing is a little beefier.

One more thing - if you go with the 426 hardware, you will also have to buy the gear that's mounted to the crank that drives the counter-balancer. This gear is aligned with a Woodruff key on the 400 crankshaft, whereas the 426 crank/gear combo is splined.

One more thing - if you go with the 426 hardware, you will also have to buy the gear that's mounted to the crank that drives the counter-balancer. This gear is aligned with a Woodruff key on the 400 crankshaft, whereas the 426 crank/gear combo is splined.
That's only true if you use a crank for an '01-'02, and you'll need to do more than that, as I mentioned. The 2000 426 crank uses the same balancer drive gear as the 400 does, and so needs no parts to convert it, other than the 426 piston and jug.

so if I'm understanding this right, I can get a stock 400 crank/rod, and the big bore kit from lukes and end up with a 420.

OR

I can get a 426 crank/rod, cylinder, piston, etc and have a 426?

The OEM parts can be had at Thumper Talk OEM for deeply discounted prices.

Ok, I understand supporting the site and all, but it really bugs me that you have to pay to see the prices. What bugs me more is that I paid the $9.95 or what ever, to find out that the prices aren't any better than what I can get from other places online (like ronayers) that do not require a membership.

In fact for the long list of parts I just put together the TT store is roughly $8 more expensive than Ron Ayers, and when you add in the membership and shipping the difference is closer to $40. This may not seem much compared to the nearly $900 order, but I'd still rather spend that money on something else.

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