2001 Yamaha YZ426F project

The next piece of the puzzle arrived today! I picked up a brand new OEM cylinder for a really good deal. I'm pretty excited that I'll be able to finally start putting this thing back together soon!

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My piston kit came in today! I'm only a gasket kit and cam chain away from being able to throw this thing together!

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My valve springs came in today! I finally have all brand new parts to get this cylinder head back together.

 

 

Looks like Aftermarket SS valves and Ti OEM springs.

 

You cannot use that combination together.

 

Someone correct me if I am wrong

These springs are for a 2000 model which came factory with stainless valves so I should be good.

These springs are for a 2000 model which came factory with stainless valves so I should be good.

 

Gotcha I see now.

 

If I were you I would have that crank rebuilt while it is out now. It is hard to tell how many hours is on the big end bearing. Cheap insurance as you usually can get them built/balanced for ~$200 including all parts. Also new main bearings.

 

Would hate for you to have to tear down a "new engine" a few hours later because you skipped this step. Ask me how I know  :banghead:

I had to double check... Thank you for heads up! After doing a little research I found I do in fact have the correct springs. The first picture is a 2000 model with stainless valves which use these springs: (5BE-12113-00 // 5GR-12114-00). The springs for the 2001-2002 model with Ti valves have the prefix of (5JG) in the part number.

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Sweet deal!

 

Also cross check with partzilla dot com too. They are mostly 5-10% cheaper than other OEM distributors 

I was planning on rebuilding the crank. In its current state WR crank has no vertical play what so ever and only a normal amount straight lateral movement. I'm going to rebuild the original YZ crank as well to have a spare ready to go in case I have another failure.

That is where I picked these springs up actually.

 In its current state WR crank has no vertical play what so ever

 

It's seized then?  Of course it has vertical play.  It was built with between ~0.0005-0.0015" or thereabouts (the internal clearance of the roller bearing).  The correct way to measure it is to fix a dial gauge at 90 degrees to the side of the small end and rock the rod left and right without allowing it to slide along the crank pin.  See "F" in the illustration from the manual:

 

Note that this does not give you a direct reading of the actual clearance at the big end, but is a calculated value that will increase beyond the specification as the rod bearing wears.

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It is not seized, it just doesn't have any slop. It's very smooth and seems to be in perfect shape.

If you don't measure the clearance, you don't know what it is, and you're taking your chances.

The 01 YZ and 02 WR have different part numbers on the crank, though I don't know what, is any changes

I'll measure the amount with a dial gauge and let you know what I find out.

As far as I know the WR and YZ are the same motors with the WR having wider gear ratio transmission, heavier fly wheel, different stator with a lighting coil, and a little different timing.

As far as I know the WR and YZ are the same motors with the WR having wider gear ratio transmission, heavier fly wheel, different stator with a lighting coil, and a little different timing.

 

I understand that much, I own both bikes. But the 01 YZ and 02 WR CRANK have different part numbers, though I don't know what, if anything changes

I'll have to do a little research and find what the difference is. I know sometimes th manufacturers will change part numbers to supersede the previous numbers. Nobody really knows why this happens, sometimes it's seems it is just to keep us guessing. I'll let you know what I find out.

The two cranks interchange perfectly well.  The connecting rod in the '02 version of both the YZ and WR was revised for better strength, but they both use the same crank.  I would use the '02 if it's in good enough shape. 

 

 

I'll measure the amount with a dial gauge and let you know what I find out.

 

I don't need to know, you do. ;)

One of the things I want to try to improve for extended trail riding is the cooling system. I started by ordering a coolant overflow bottle off of a WR426 which arrived today. I like the idea of having a place for the coolant to go when it expands from heat. At least with the tank installed I won't spit all my coolant on the ground on hot slow trails.

I have seen larger three core radiators for about $80 online. Are these worth the money to help keep engine temps down?

Would a cooling fan be beneficial (after I install the WR stator/fly wheel of course)?

I don't have the plastic radiator shrouds (plastic louver things). Do these actually direct air to the core or were they an added "look cool" feature?

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Great thread and nice build! I always love seeing another 426 being rebuilt.

I've rebuilt mine twice and ironically bought mine from a buddy for $400 too with a blown top end lol.

The first rebuild was minimal and to get it running again and out of boxes, the second was a few years later when I had the means to really tear it down and go trough her.

Go for the boyesen super water pump kit, made a huge difference in keeping my yz cool, also I picked up those over sized radiators from eBay and have no issue, they really big and have been running great :) (blue radiator lines are nice too)

I recommend getting a 2007 - 2009 carburetor for the bike since you can rebuild the middle body as well as lower end. Made a WORLD of difference ditching my 02 carb. Hot cams is another great mod!

Keep wrenching away man can't wait to see what you do next.

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Thanks for the feedback! My bike is slowly coming together. Yours looks great! I'm just building up my parts and tool stash now but will start wrenching soon!

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