Desperate for help with 450 EX Cam mod!


20 replies to this topic
  • Nanotech9

Posted January 14, 2008 - 02:56 PM

#1

short and sweet:

Bike is a 2000 model YZ426, steel valves.
WR426 heavy flywheel and stator (for lights).

bought the '03 YZ450 auto decomp cam new from the dealer a year ago, never installed it.

Rebuilt my motor 4 months ago myself, all new bearings (all new everything).

Tried installing the 450 cam then, following the "PDF" etc, no luck. Dropped my 426 cam in, fired off 3rd kick from a fresh rebuild. Rode it like that for 4 months.

Tore bike down to install another shock, decided to give the 450cam another shot.

Removed valve cover, set piston to TDC.
Ziptied IN cam at the 12 mark to the chain. Verified Timing again.
Used a scribe to mark the angle of the tops of the cam lobes on the right side of the cam caps (with the CCT still installed).
Counted 12 PINS between stock 12:00 marks on IN and EX cams.

[COLOR="Red"]= Try 1=========[/COLOR]
Installed 450 cam with 12 pins between 12:00 marks, installed tensioner (CCT).
Checked scribed marks. EX lobe sits point at a HIGHER angle on top.
EX valves with 450cam have .033mm and .035mm of gap. Stock range is between .025 and .030. I'm too loose by .003 and .005mm respectively.
Buttoned it all up, no go, as expected.

[COLOR="Red"]= Try 2=========[/COLOR]
Installed 450 cam with 13 pins between 12:00 marks, installed CCT.
Checked Scribed marks. 450 EX lobe sits DEAD ON to the marks from the stock EX lobe.
Same valve gaps.
Buttoned it all up, no go. SUPRISED.

[COLOR="Red"]= Try 3=========[/COLOR]
Installed 450 cam with 14 pins between 12:00 marks, as called for by "THE PDF", installed CCT.
Checked Scribed marks. 450 EX lobe sits LOWER than the stock EX lobe at TDC.
Same valve gaps.
Buttoned all up, no go, as expected.

[COLOR="Red"]= Try 4=========[/COLOR]
Same as above. 14 pins between 12 marks.
Re-gapped the valves to be .029 and .030mm tolerance, within factory spec.
NO GO.

[COLOR="DarkRed"]= Try 5=========[/COLOR]
Haven't tried it yet. Very frustrated.
Gaps set within factory specs, going to go back to 13pins between 12" marks.

=============================


Cylinder reads 426 c3.
back of cylinder or cases (can't remember) says Y - Z (assuming this indicates that indeed it IS a YZ motor not a WR).
I've both timed this bike a half dozen times with the stock cams and its run perfectly every time, same with the valve clearances.
I've built this motor from the ground up, head and bearings and everything. There was not ONE part left in the cases during this process. Although i feel like a complete idiot trying to do this mod, i just can't accept that I am, but believe more that i'm missing some key piece of information.

Is it possible that i have a WR head and WR cams?
or maybe this is a stock 400 head and 400 cams?

Would i not have found problems while ordering all new valves, springs, keepers, cam chain, etc for the head when i rebuilt it?

What other possibilities are there that I'm ignorant of?

PLEASE HELP. I"M PULLING MY HAIR OUT!

  • grayracer513

Posted January 14, 2008 - 03:30 PM

#2

First, it doesn't matter whether it's a WR or a YZ, so forget that. It will basically be a YZ when you get done here, no matter which one it was.

Next, if the exhaust cam is a Yamaha OEM YZ450 exhaust cam (5TA-12180-00-00), the timing marks on the cam cannot be followed as originally intended, so it must be done this way:

Roll the engine forward to TDC, with the lobes angling out and up. Check the intake timing using the original "I" mark on the cam vs. the head surface, just as the book shows you. Be sure when you do this that the chain is pulled tight on the front side between the exhaust cam and the crank, and between the two cams.

Then, you position the exhaust cam by counting 14 pins between the "12:00 o'clock" marks on the two cams. If you get an incorrect count, move the exhaust cam only to correct it.

When you think you're done, double check the timing again:
>Back everything up a couple of degrees
>Turn the engine slowly forward to TDC
>Check the intake timing marks
>Count 14 pins between the two 12:00 marks

That's the way they go in. It should go without saying that you need to check the valve clearances.

One mistake some new auto decomp users make is to believe it necessary to go past the detected compression point (the "hard spot" you feel when you turn the engine over) before kicking. This is incorrect. With AD, you kick from the hard spot. That is, you push down until you hit compression, reset the lever, and kick. You can in fact kick the engine over from virtually any where without regard from where it is positioned, but kicking from just past TDC on the power stroke puts you a bit far away from the next compression stroke in terms of engine rotation. Try it this way first.

You might want to drop the original cam back in it just to be sure it still behaves the way it used to so you aren't fighting an unknown issue, but a new plug might be in order, too. Also, cold temps in your area may be contributing to a hard start problem.

  • todds924

Posted January 14, 2008 - 03:31 PM

#3

short and sweet:

Bike is a 2000 model YZ426, steel valves.
WR426 heavy flywheel and stator (for lights).

bought the '03 YZ450 auto decomp cam new from the dealer a year ago, never installed it.

Rebuilt my motor 4 months ago myself, all new bearings (all new everything).

Tried installing the 450 cam then, following the "PDF" etc, no luck. Dropped my 426 cam in, fired off 3rd kick from a fresh rebuild. Rode it like that for 4 months.

Tore bike down to install another shock, decided to give the 450cam another shot.

Removed valve cover, set piston to TDC.
Ziptied IN cam at the 12 mark to the chain. Verified Timing again.
Used a scribe to mark the angle of the tops of the cam lobes on the right side of the cam caps (with the CCT still installed).
Counted 12 PINS between stock 12:00 marks on IN and EX cams.

[COLOR="Red"]= Try 1=========[/COLOR]
Installed 450 cam with 12 pins between 12:00 marks, installed tensioner (CCT).
Checked scribed marks. EX lobe sits point at a HIGHER angle on top.
EX valves with 450cam have .033mm and .035mm of gap. Stock range is between .025 and .030. I'm too loose by .003 and .005mm respectively.
Buttoned it all up, no go, as expected.

[COLOR="Red"]= Try 2=========[/COLOR]
Installed 450 cam with 13 pins between 12:00 marks, installed CCT.
Checked Scribed marks. 450 EX lobe sits DEAD ON to the marks from the stock EX lobe.
Same valve gaps.
Buttoned it all up, no go. SUPRISED.

[COLOR="Red"]= Try 3=========[/COLOR]
Installed 450 cam with 14 pins between 12:00 marks, as called for by "THE PDF", installed CCT.
Checked Scribed marks. 450 EX lobe sits LOWER than the stock EX lobe at TDC.
Same valve gaps.
Buttoned all up, no go, as expected.

[COLOR="Red"]= Try 4=========[/COLOR]
Same as above. 14 pins between 12 marks.
Re-gapped the valves to be .029 and .030mm tolerance, within factory spec.
NO GO.

[COLOR="DarkRed"]= Try 5=========[/COLOR]
Haven't tried it yet. Very frustrated.
Gaps set within factory specs, going to go back to 13pins between 12" marks.

=============================


Cylinder reads 426 c3.
back of cylinder or cases (can't remember) says Y - Z (assuming this indicates that indeed it IS a YZ motor not a WR).
I've both timed this bike a half dozen times with the stock cams and its run perfectly every time, same with the valve clearances.
I've built this motor from the ground up, head and bearings and everything. There was not ONE part left in the cases during this process. Although i feel like a complete idiot trying to do this mod, i just can't accept that I am, but believe more that i'm missing some key piece of information.

Is it possible that i have a WR head and WR cams?
or maybe this is a stock 400 head and 400 cams?

Would i not have found problems while ordering all new valves, springs, keepers, cam chain, etc for the head when i rebuilt it?

What other possibilities are there that I'm ignorant of?

PLEASE HELP. I"M PULLING MY HAIR OUT!


Try this. Take both cams out. Run it up to TDC. Install the exhaust cam FIRST!!!! Dot aligned with the valve cover mating surface. Install the intake cam so the dot aligns with the mating surface...don't worry about "counting pins" What your after is both of those marks aligning with the mating surface when you have tension on the cam chain. This is the proper procedure for the newer yz's. Its been awhile since i have even seen, let alone worked on one of the older 400/426. You might wan't to also ask Grayracer...he can definitely point you in the right direction. OOOPS!!! sorry gray! you posted while i was typing!!!!:banghead:

  • grayracer513

Posted January 14, 2008 - 03:43 PM

#4

Run it up to TDC. Install the exhaust cam FIRST!!!! Dot aligned with the valve cover mating surface. ...

You're right, that's the textbook way of doing it. The trouble is that here, we are trying to use a cam from a 450 head in a 426 head. The heads are different enough that the timing marks on the 450 cam don't align with the 426 head the way that they are supposed to, thus the weird timing procedure.

You have to get the intake timed first, so you have a known reference to the crank, then time the 450 e-cam to that.

  • Nanotech9

Posted January 14, 2008 - 03:57 PM

#5

problem is, i'm honest to god following al the "rules" to installing these.

I'm happy to check the plug and check that it runs with the stock cams - that should take me about 10min.... (might put that off till tomorrow - i have a splitting headache).

With stock cams, the bike starts, FIRST kick, or if its been sitting over a week, then sometimes it takes 3 kicks. Never more, never fouls, always runs good.

Something else i did not mention earlier.

with the STOCK CAMS, at TDC, the IN cam lobe is lying nearly flat on the top, and the EX cam is pointing up maybe 5deg. They are not equally level at TDC.

This seems to be the ONLY oddity in comparison to everyones else's experiences.

maybe my Stock IN cam isnt really stock? Any markings i should check for on the IN cam to verify stock or not?

  • 642MX

Posted January 14, 2008 - 05:54 PM

#6

The easiest way to time a 426 with the 450 cam is.....

Find TDC, install the intake cam, install the exhaust cam. Make sure everything lines up, and then rotate the exhaust cam one tooth counter-clockwise.....and your done. Count your 14 pins to verify. Be sure to recheck your valves....typically the shims need to be increased by 2 shim sizes (for example, if has a 180 shim, it may need a 190 to be in spec).

I just did one last week. I think that makes 6 or 8 bikes I've done. :banghead:

  • todds924

Posted January 14, 2008 - 08:44 PM

#7

You're right, that's the textbook way of doing it. The trouble is that here, we are trying to use a cam from a 450 head in a 426 head. The heads are different enough that the timing marks on the 450 cam don't align with the 426 head the way that they are supposed to, thus the weird timing procedure.

You have to get the intake timed first, so you have a known reference to the crank, then time the 450 e-cam to that.


Ahhh!!!! I get the picture now. Never had the opportunity to do one of those mods on the older gen. bikes. Pretty much everything i see is 05 or newer. Thanks for clearing that up for me Gray, you learn something everyday. 642MX sounds like he has it down!!!!!!!! Good stuff!!!!

  • grayracer513

Posted January 14, 2008 - 10:25 PM

#8

642 is right, but the reason that having an exhaust cam in place first (not necessarily timed) is important is that it simply gives you something to run the chain over so that the full run of chain leading from the front side of the crank sprocket all the way to the intake cam can be drawn up tight. That way, it's easier to be sure the intake cam is correctly placed. Otherwise, he's got it exactly right.

Something else i did not mention earlier.

with the STOCK CAMS, at TDC, the IN cam lobe is lying nearly flat on the top, and the EX cam is pointing up maybe 5deg. They are not equally level at TDC.

This seems to be the ONLY oddity in comparison to everyones else's experiences.

maybe my Stock IN cam isnt really stock? Any markings i should check for on the IN cam to verify stock or not?

There isn't a certain way to tell for certain from the cam itself that I know of. But when the "I" mark is aligned with the head, the lobes of the intake cam should look quite a bit like the picture in the posted instructions. If it "lays nearly flat", that raises the possibility that the sprocket may have slipped at some point.

  • Nanotech9

Posted January 18, 2008 - 05:47 PM

#9

ok... finally have some pics.....

Checked the plug - good spark (pulled plug, kicked it over and watched it spark)

Look at these pictures, and tell me if my stock cam isnt pointing just a little "low".....? I wonder if i need to rotate it one tooth counter clockwise after setting everything at 14 pins?

Flywheel at TDC.
Posted Image


450 Cam with 14pins between 12 O'clock marks as called for in the PDF
Posted Image

Posted Image



450 Cam with 13 pins between 12 O'clock marks which actually aligns with stock cam lobe marks.
Posted Image

Posted Image


Doesnt start on either....

Unless i just can't figure out how to check the valve lash properly and am still way out....

  • 642MX

Posted January 18, 2008 - 05:57 PM

#10

The top picture with the 14 pins between the 12 o'clock positions is correct. Be sure that your valve clearance is correct.

If it still won't start, then check your plug, clean your carb, ect...

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  • jbrooks26

Posted January 18, 2008 - 06:58 PM

#11

Also remember that when you do this mod it is going to change your starting charactaristics and your normal routine may not make the bike happy any more. I installed a Hotcam in my 02 426 and it took me quite some time to find the magic combination but once I figured it out It starts right up for me now. I know that you have been warned against twisting the throttle before starting the bike, but try this once. Just turn the throttle wide open and hold it long enough to let the AP finish it's squirt. Then start like you normally would. If it doesn't fire then try two twists. I never got past 2, and I only give it that if it is really cold or the bike has been sitting for more than a week. I also had to do some jetting work, including a 72 starter jet which really helped with the cold start. Give this a try and let us know what you find. If you have fire and the timing is correct then you most likely have a fuel mixture issue. You may even want to try bump starting the first time so you can get a feel for what needs to be done in the carb. Hope this helps.

Josh

  • grayracer513

Posted January 18, 2008 - 09:55 PM

#12

The top picture with the 14 pins between the 12 o'clock positions is correct. Be sure that your valve clearance is correct.

If it still won't start, then check your plug, clean your carb, ect...

+1

You need to look at the lobe centers, not the angle of the face of the lobe.

  • King_Air

Posted January 19, 2008 - 04:09 AM

#13

The top picture with the 14 pins between the 12 o'clock positions is correct. Be sure that your valve clearance is correct.

If it still won't start, then check your plug, clean your carb, ect...


I am in agreement with 642. 14 pins and those positions are correct. At least in my hazy section of my memory banks.

  • jbrooks26

Posted January 19, 2008 - 07:43 AM

#14

Nano, are you near Tulsa? I would be willing to help you if you are close.

  • Nanotech9

Posted January 19, 2008 - 10:03 AM

#15

oklahoma city....

i spoke with a guy on the phone (local racer) that had installed several of these a while back...

we pretty much concurred that i was right on the money.

so, i threw the stock cam back in, and to my surprise it took over 20 kicks to get it to sputter and a few more to fire off...

I keep thinking i'm doing this all in a heated garage, but my heat is a combo of my dryer and a keroseen wick heater (big one) so the garage gets warm quick, but i noticed the motor is still freezing from overnight (down in the high 20s over night).

So, i let it run 30seconds with the stock cam to warm the cylinder up a bit and put the 450 cam back in at 13 pins...

suprisingly, now i'm getting some backfiring and poping and what seems like a half-assed attempt at starting.

So, i'm gonna try 14 pins in a bit. I'm winded from kicking that thing over about 4 dozen times in rapid succession.

I'll get back with you guys.

  • jbrooks26

Posted January 19, 2008 - 10:28 AM

#16

I suspected that the cold might be giving you fits. I was doing the same thing, and finally just waited for it to warm up. Sounds like you are getting it, good luck.

Josh

  • 642MX

Posted January 19, 2008 - 10:30 AM

#17

So, i let it run 30seconds with the stock cam to warm the cylinder up a bit



This is exactly how YZF foul plugs. You must completely warm up the bike before shutting it off.

and put the 450 cam back in at 13 pins...


This is incorrect.


So, i'm gonna try 14 pins in a bit.


14 pins is correct. Be sure to replace the plug before you wear your leg out.

  • King_Air

Posted January 19, 2008 - 10:43 AM

#18

Remember to prime a cold engine with the throttle. 2-3 twists [COLOR="Red"]before[/COLOR]kicking it over.

  • Nanotech9

Posted January 19, 2008 - 10:44 AM

#19

she fired off at 14!!!!!!!!!!!!


good grief this has been a long road.

I think the only thing keeping this from working was the cold. That really pisses me off lol.


Thanks for the help guys. I guess i had it right all along... just like everyone said.

Now i know... and maybe this will help anyone else having the same problems.


14 pins is the magic number just like everyone says.

and never try to mod and start a very cold motor. lol.

  • grayracer513

Posted January 20, 2008 - 06:49 PM

#20

This is exactly how YZF foul plugs. You must completely warm up the bike before shutting it off.

It's a totally off topic sidebar, but this is one of the things that the late model coils we were talking about will improve.





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