450 cam in a 426


21 replies to this topic
  • nugie

Posted August 19, 2010 - 08:10 AM

#1

So Ive read about putting a 450 ex cam in the yz 426 so you can have the auto decomp. So I picked up a new hot cams from e bay and when I opened up the box it says on a small piece of paper all the specs and what not and then it says that the cam will not work on a 426 due to sprocket differences. Can anyone confirm this ?

  • grayracer513

Posted August 19, 2010 - 08:22 AM

#2

If you browse through the whole original 450 DCM thread, you'll see that this question was an issue early on with using OEM YZ450 cams in the 426. The sprockets ARE slightly different in that the tooth profile of the chain and sprockets of the two engines are different. The pitch is exactly the same, however, and no one I know of has ever had a problem that resulted from using an OEM Yamaha 450 cam in any 426.

One would think, then, that an aftermarket cam that was made to fit a 450 properly would work as well, but I cannot vouch for that. Normally, anyone buying a HotCams cam for a 426 would have just bought one actually made for the 426 with the auto-decompression feature included and avoided the whole question along with the odd timing procedure required to use the 450 cam. My guess is that it should work as well as the OEM 450 cam, but there may be some problem come up, too. I have no way of knowing for certain.

Remember that you cannot use the timing marks on the exhaust cam as you would with the stock cams or a 426 HotCam.

Read Both:
http://www.thumperta...078#post3706078
http://www.thumperta...040#post5378040

  • Codeman69

Posted August 19, 2010 - 10:02 PM

#3

I just installed a Hotcam for the 450 into my 426 same as they one you have and everything worked flawless, you have no worries.

  • nugie

Posted August 20, 2010 - 12:37 PM

#4

Ok thanks guys much appreciated :bonk:

  • nugie

Posted August 21, 2010 - 08:48 AM

#5

I just installed a Hotcam for the 450 into my 426 same as they one you have and everything worked flawless, you have no worries.


I just installed it but never tried to start it yet. It does not look like it fits as nice over the sprocket, did yours look like that ?

  • grayracer513

Posted August 21, 2010 - 12:08 PM

#6

It will appear to ride slightly high. It's OK, though.

  • nugie

Posted August 21, 2010 - 12:29 PM

#7

Ok thats good because I just put it back together and said screw it I gotta see if it runs and I gave it a couple of twists of gas pulled out the choke and first kick she started right up:). Damn was I glad. I hear a little bit of valve noise that was not there before so I guess im gonna have to adjust the valves. Something I never done before yet. But other than that she seems to pull strong and run great. I know you can put a 18mm frost plug in were the decomp was but I could not get one, Is it ok to leave the decomp thing in the motor or is that not a good idea ?

  • nugie

Posted August 21, 2010 - 04:16 PM

#8

anyone....? can I leave the decomp mechanism in there or is this not a good idea

  • grayracer513

Posted August 21, 2010 - 07:59 PM

#9

You can leave it there IF you leave the coiled return spring on the lever.

  • Codeman69

Posted August 22, 2010 - 07:45 AM

#10

MIne appeared to ride slightly higher, but has ran flawlessly. That valve noise you could be hearing is the auto decompression on the new cam, makes a slight ticking sound. Perfectly normal as my buddy bikes makes the same noise and has many hours and seasons of riding on it. ON the decompression mechanism I took the cable off and than cut the slide that went into the motor. I cut it so I 1/8" sticking out the front of the bike and flush on the inside, so the screw can still hold it in its place. Seems to be fine and I have a day of riding on it.

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  • nugie

Posted August 23, 2010 - 02:29 AM

#11

[quote name='Codeman69']MIne appeared to ride slightly higher, but has ran flawlessly. That valve noise you could be hearing is the auto decompression on the new cam, makes a slight ticking sound. Perfectly normal as my buddy bikes makes the same noise and has many hours and seasons of riding on it.
Can anyone else vouch for this

  • Ryan426

Posted August 23, 2010 - 02:49 AM

#12

:thumbsup:Long live the 426's!!!!!:bonk:

  • grayracer513

Posted August 23, 2010 - 08:34 AM

#13

[quote name='nugie'][quote name='Codeman69']
Can anyone else vouch for this[/QUOTE]The AD mechanism won't make a single sound with the engine running because it's pulled out of play at anything more than 700 RPM. The slight ticking, if in fact it really did show up as a result of the mod, and not something you are just hearing for the first time, is either a valve that you set too loose by mistake, or it could be that the HotCams doesn't have as gentle a lift ramp on the base of the lobe as the OEM cam does. Recheck the clearance if you're in doubt.

  • nugie

Posted August 23, 2010 - 10:10 AM

#14

[quote name='grayracer513'][quote name='nugie']The AD mechanism won't make a single sound with the engine running because it's pulled out of play at anything more than 700 RPM. The slight ticking, if in fact it really did show up as a result of the mod, and not something you are just hearing for the first time, is either a valve that you set too loose by mistake, or it could be that the HotCams doesn't have as gentle a lift ramp on the base of the lobe as the OEM cam does. Recheck the clearance if you're in doubt.[/QUOTE]

Ok checked my clearance and added new shims, I now have the right clearance and she sounds good as new. Thanks alot grey and whoever else may have helped me along the way.

  • nugie

Posted September 18, 2010 - 08:13 AM

#15

OK Ive used her for 3 or 4 hours without any issues accept for today. I began to hear a funny engine noise almost like exhaust escaping from the motor / funny ticking noise, so I shut her down and when I go to kick it over there is zero compression for a few kicks and then solid. I have left the decomp mechanism in the motor so I manually hold that up and then am able to kick it over again with zero compression. Is it possible that the decomp mechanism has screwed any thing up ? Or is there something going on with the new ex cam...... ex auto decomp sticking or something. Anyway she will not run now .

  • nugie

Posted September 19, 2010 - 06:52 AM

#16

OK Ive used her for 3 or 4 hours without any issues accept for today. I began to hear a funny engine noise almost like exhaust escaping from the motor / funny ticking noise, so I shut her down and when I go to kick it over there is zero compression for a few kicks and then solid. I have left the decomp mechanism in the motor so I manually hold that up and then am able to kick it over again with zero compression. Is it possible that the decomp mechanism has screwed any thing up ? Or is there something going on with the new ex cam...... ex auto decomp sticking or something. Anyway she will not run now .


Anyone?????????????

  • moto2000

Posted September 19, 2010 - 09:22 AM

#17

I would start with checking the cam timing.

  • nugie

Posted September 25, 2010 - 07:01 AM

#18

Ok I took the valve cover off and the timing chain was falling off, The chain adjuster kicked the bucket. Why or how IDK but I had another one off a old motor that I used. Now just to make sure I did this right I have a quick question. Before I bolted the tensioner on I screwed the screw in all the way and carefully put it in, then when I had it all snugged up I gave it a little tap and the chain tightened up , Is that all you have to do ? Because thats all I did last time and got 4 or 5 hours use before I ran into trouble.

  • grayracer513

Posted September 25, 2010 - 07:27 AM

#19

Yes, the only thing necessary is to rotate the center screw of the tensioner just far enough counterclockwise to let the spring take over and run it in against the chain.

You should, however, inspect the tensioner before installing it to see that it will retract and extend smoothly through its whole range and that it cannot be pushed back by any means other than retracting it with the screw.

  • nugie

Posted September 25, 2010 - 08:30 AM

#20

Yes, the only thing necessary is to rotate the center screw of the tensioner just far enough counterclockwise to let the spring take over and run it in against the chain.

You should, however, inspect the tensioner before installing it to see that it will retract and extend smoothly through its whole range and that it cannot be pushed back by any means other than retracting it with the screw.


The one I put in it seems to be fine. What would cause the other one to fail ? The end on the adjuster pushed right out past the c-clip which holds it all together .





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