YZ426F

vet323
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vet323
Edited Date/Time 11/2/2014 5:16pm
I was given a blown-up 2001 YZ426 yesterday. It has been sitting for over a year since the engine quit. The guy I got it from took it to a mechanic I trust who told me that it will need a piston and rod (apparently rod failures are not uncommon on these). The head looked serviceable to him.

I have no problem rebuilding the crank and top end and freshening up the bike, but who here has experience with this bike? What should I do as far as mods while I'm in there? I understand they have some starting issues, what can be done to help with those problems?

Any feedback appreciated.
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APLMAN99
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APLMAN99 11/1/2014 1:51pm
11/1/2014 1:51pm
The starting trick is to swap in a 450 cam. I think the 2003 model year? Did it to my 400 and it was a huge difference. Should be able to find more info and detailed instructions online.
vet323
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vet323 11/1/2014 2:09pm
11/1/2014 2:09pm
That looks like it should be easy enough. I should be able to find a 450 cam on ebay,, I'm sure.
Highsider
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Highsider 11/1/2014 2:32pm
11/1/2014 2:32pm Edited Date/Time 11/1/2014 2:41pm
Up to 2007 450 cams were pretty spicy.
In 2009 the cams were de-tuned.

My 426 was pretty lively, for its time.
I never had reliability issues with the six big YZ bikes I have owned and raced.

98 YZ400F
01 YZ426F
03 YZ450F
05 YZ450F
07 YZ450F
09 YZ450F(11)

The Shop

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kevin204
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kevin204 11/1/2014 3:40pm
11/1/2014 3:40pm
Yeah, I'm not so sure about rod failures being an issue on these things, every YZ4 1998-2010i I've ever heard of has been Honda XR-like in reliability.
Paw Paw 271
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Paw Paw 271 11/1/2014 3:51pm
11/1/2014 3:51pm
From what I have seen, the cam from the 2003 will not last in the earlier units as the cam gear pitch changed which caused quick wear. I found the best way to do this was to install an updated HOT Cam they made for this switch and it comes with the auto decompression built in to it. They may be hard to fine as I believe they stopped production some time back.
Just verify what I am telling you , please look at Thumper Talk and do a search there for this swap as I think it was covered in detail.

Paw Paw
Maddeh
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Maddeh 11/1/2014 6:06pm
11/1/2014 6:06pm
I did the cam swap in my WR426 and did not like it. Although there was a procedure to starting it before, it was 1st or 2nd kick if you did the procedure right. Once the cam was in it was always kind of a crap shoot. There was a noticeable difference in power though (not sure it would have the same impact on the YZ that it did on the WR).

I still have the bike, been meaning to part it out forever but its just been sitting in the garage. Feel free to message me if you need anything.
JW381
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JW381 11/1/2014 6:51pm
11/1/2014 6:51pm
Highsider wrote:
Up to 2007 450 cams were pretty spicy. In 2009 the cams were de-tuned. My 426 was pretty lively, for its time. I never had reliability...
Up to 2007 450 cams were pretty spicy.
In 2009 the cams were de-tuned.

My 426 was pretty lively, for its time.
I never had reliability issues with the six big YZ bikes I have owned and raced.

98 YZ400F
01 YZ426F
03 YZ450F
05 YZ450F
07 YZ450F
09 YZ450F(11)

My dad had an '03 450 and I couldn't believe how hard that 4 speed Woukd pull. Makes sense about thr cams because I've rode newer 450s since that weren't as "spicy".
RandyS
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RandyS 11/1/2014 7:38pm
11/1/2014 7:38pm
The starting issues were overblown, if you just kick them through with a smooth motion they'll start. If you try to kick the shit out of them like a two stroke you'll be there all day. I would love to have a 99 400 again for a play bike, they were pigs compared to today but for just playing around in the woods they were more fun than modern 450s.
markit
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markit 11/1/2014 7:53pm
11/1/2014 7:53pm
I guess im glad i never did the cam on my 99 PC 400.
Forza
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Forza 11/1/2014 8:25pm
11/1/2014 8:25pm
Highsider wrote:
Up to 2007 450 cams were pretty spicy. In 2009 the cams were de-tuned. My 426 was pretty lively, for its time. I never had reliability...
Up to 2007 450 cams were pretty spicy.
In 2009 the cams were de-tuned.

My 426 was pretty lively, for its time.
I never had reliability issues with the six big YZ bikes I have owned and raced.

98 YZ400F
01 YZ426F
03 YZ450F
05 YZ450F
07 YZ450F
09 YZ450F(11)

Lies 4strokes blow up every other ride! J/k.
Enjoy the bike.
Crash82
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Crash82 11/1/2014 9:21pm
11/1/2014 9:21pm
vet323 wrote:
I was given a blown-up 2001 YZ426 yesterday. It has been sitting for over a year since the engine quit. The guy I got it from...
I was given a blown-up 2001 YZ426 yesterday. It has been sitting for over a year since the engine quit. The guy I got it from took it to a mechanic I trust who told me that it will need a piston and rod (apparently rod failures are not uncommon on these). The head looked serviceable to him.

I have no problem rebuilding the crank and top end and freshening up the bike, but who here has experience with this bike? What should I do as far as mods while I'm in there? I understand they have some starting issues, what can be done to help with those problems?

Any feedback appreciated.
My 2000 429 started first kick when it was hot. I got a 2002 416 rear shock almost brand new, I guy used the motor from a new bike in a 4 wheeler and parted out the rest. I got a stock triple clamp with bearings, I will never use them and will let them go cheap!
Crash82
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Crash82 11/1/2014 9:25pm
11/1/2014 9:25pm


My old bike Cornwall, wish I would have never sold him.

bvm111
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bvm111 11/1/2014 10:03pm
11/1/2014 10:03pm
I rode my buddies 426 back in the day... Wouldn't turn worth a shit but in straight line hold onto your shorts that things was fast!!!!
scottydogmx 11/2/2014 12:15am
11/2/2014 12:15am
Best way to start one of them beasts is to park it on a hill and bump it with the decompressor lever in!! Started first time every time for me!
APLMAN99
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APLMAN99 11/2/2014 6:51am
11/2/2014 6:51am
Paw Paw 271 wrote:
From what I have seen, the cam from the 2003 will not last in the earlier units as the cam gear pitch changed which caused quick...
From what I have seen, the cam from the 2003 will not last in the earlier units as the cam gear pitch changed which caused quick wear. I found the best way to do this was to install an updated HOT Cam they made for this switch and it comes with the auto decompression built in to it. They may be hard to fine as I believe they stopped production some time back.
Just verify what I am telling you , please look at Thumper Talk and do a search there for this swap as I think it was covered in detail.

Paw Paw
I didn't put a lot of hours on after I did mine, so can't personally vouch for the durability issue, but mine was definitely easier to start afterwards! As for power, I never came close to needing more in the first place and never came all that close to finding the limits either before or after the swap. It had plenty of power for me either way and the overall rideability of the bike was so much easier than a 2 stroke that it felt like when parabolic skis first came out. So much easier to do nearly every terrain on.
vet323
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vet323 11/2/2014 10:00am
11/2/2014 10:00am
You guys are giving me just the kind of info I was hoping for, thanks. Keep it coming.
fulltime wrench 11/2/2014 10:45am
11/2/2014 10:45am
I have a 2002. I bought it in rough shape with intentions of rebuilding it completely. The bike had no mods except for PT handlebars, so what I saw while rebuilding is a good indicator of what a high hour bike would look like.

-Water pump shaft was grooved up bad.
-RH balance shaft bearing was loose/notchy. Replaced both.
-one camshaft journal in the head had "mushroomed" over into the adjacent tappet bores. Used a Dremel to grind it away so I could remove the bucket. Ended up buying another head when I found a crack in the little spark plug tunnel drain hole. Also had the same mushrooming.
-all the transmission bearings were good but replaced them anyway
-cam chain sprocket on crankshaft was hooked to the point it wouldn't pass through the bearing. Used a Dremel again. Replaced the crank which was the plan anyway.
-clutch had OEM plates, no notches in basket. Inner fiber plate has a larger ID to accept a jutter(sp) spring and seat ring. Tossed that junk, replaced with a Barnett plate with the same ID as the other plates. The jutter had worn into the inner steel plate so I replaced it as well. Not sure if the 01 had this same setup.
-cracked front wheel.
-clunky shock bearings.

Some stuff I'm sure I'm forgetting. I will add to this post if/when I remember.

I'm thinking the 01 and later (could be 2000) had a primary gear that was keyed to the crank. This was a problematic area, it was changed to a splined shaft and gear the next year.

Pit Row

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Highsider
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Highsider 11/2/2014 2:15pm
11/2/2014 2:15pm
Good stuff, wrench. You are covering all the bases!
KMC440
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KMC440 11/2/2014 2:19pm
11/2/2014 2:19pm
So my 98 that had the topend done in 01 is due ? Wink

Highsider
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Highsider 11/2/2014 2:34pm
11/2/2014 2:34pm
KMC440 wrote:
So my 98 that had the topend done in 01 is due ? Wink

Only if you ride.Cool
KMC440
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KMC440 11/2/2014 2:46pm
11/2/2014 2:46pm
Awwwwwwww ya caught me .... no races in the past month and it'll be spring before life gets back to normal around here..... you know the drill ... I'll look for you next July at Millville. I'll have a topend done by then as well as the trans checked.
plowboy
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plowboy 11/2/2014 5:16pm
11/2/2014 5:16pm
I was still racing HS with my 88 XR when the 400 and 426 came out. Actually not that great an advantage in the handling dept but that 4 speed gearbox just ate me alive. What great weapons. Vastly better brakes didn't hurt either.

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