CAM Chain Slipped

14 replies to this topic
  • rholbrook

Posted July 26, 2011 - 04:06 PM


So my friend and I was swapping out the exhaust cam on his WR450 for a YZ450 exhaust cam and he accidentially let the chain slide on the cam. I don't know which direction it slid and how many teeth.

I have set it at TDC based on the "I" mark on the flywheel, set the dot on the intake cam level to the head, put in the exhaust cam with 13 chain pins between exhaust and intake cam, put it all back together and nothing. I have done this so many times now that I am frustrated and pissed and it takes me a lot to get to that point.

The exhaust cam marks seem to be a little clockwise, not even a full tooth and if I rotated it, it would be at 12 teeth.

It wont start, occassionally it will back fire if when I hit the E Start button but it will mostly just turn over with nothing.

It has spark and it has fuel. Am I overlooking anything?

  • William1

Posted July 26, 2011 - 04:43 PM


You have the wrong mark at the flywheel, check it again. Be sure the cam chain is under tension when you check it.

  • rholbrook

Posted July 26, 2011 - 05:01 PM


I go off the "l" mark correct? I have tried like 10 times to make it tight when I put the chain on the cam. I will try again.

  • rholbrook

Posted July 26, 2011 - 11:20 PM


I took it apart and set the flywheel at the "l" mark set the intake cam where it needed to be with the punch mark at the top of the case and set the top punch mark on the exhaust cam at 13 pins in between the upper punch mark on the intake upper mark.

This is all according to several threads on TT plus my manual. Buttoned it up and tried starting it with only a couple of back fires.

I rechecked my valve clearances and the intakes were at ,04 and should be between .1 and .15 and the exhaust valves were at .16 and should be between .20 and .25

If I turn it over by hand it seems to be lacking compression compared to my own WR. Could the clearances be so tight that the Valves are not closing all the way? The owner is headed to the dealer for some shims in the morning so we can get the valves within spec.

  • dgcars

Posted July 26, 2011 - 11:59 PM


TDC is the single line past the 'H' mark. At 13 pins, all the marks should line up with the chain tensioned.
At 0.04, your intakes are way tight. At 0.16, your exhaust is getting there too.

  • rholbrook

Posted July 27, 2011 - 07:09 AM


Would the valves being too tight give me those symptoms?

  • zlathim

Posted July 27, 2011 - 07:23 AM


I think it should still at least start, even with the valves as tight as they are. There is some clearance, which means the valves will fully close, at least until the engine reaches operating temperatures. Of course, I am assuming that the engine ran before you decided to swap the cam.

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  • dgcars

Posted July 27, 2011 - 07:33 AM


TDC is the single line past the 'H' mark. At 13 pins, all the marks should line up with the chain tensioned.
At 0.04, your intakes are way tight. At 0.16, your exhaust is getting there too.

The dot on the YZ exhaust cam should also line up.
If there is a measurable clearance, it should start.

  • rholbrook

Posted July 27, 2011 - 10:07 AM


Is there any reason that I should remove the intake cam to line it up. I have been removing the exhaust cam and cam tensioner to create the slack to move the intake cam the necessary teeth on the chain to get the punch mark to line up. Some instructions I have read said to remove the intake cam. Theoretically, that shouldn't matter right?

I have done this on my own bike and others litterally twenty times with no issues.

Posted Image
You can see that the marks are really pretty close.
Posted Image
I can't get a picture of the "l" mark of TDC but you can kind of see it here. It is a little to the right by just a nats ass. If I rotate it a smidge to line up perfectly the dots on the cams should be pretty close.

Does it look right to you? It does to me. It just wont fire for me. I hope by getting the valves adjusted properly it will work. Any thoughts?

  • dgcars

Posted July 27, 2011 - 10:29 AM


Timing looks good.

  • rholbrook

Posted July 27, 2011 - 03:06 PM


I think I found my problem.

I removed the exhaust caps, changed my shims and then bolted everything back together, removed the intake cam and found it difficult to get the cam cover off. Went to remove the little caps and couldn't get them off. Upon further inspection you can see where the cam journals got hot and reamed them out some. Long storey short is a new head, intake cam, etc., etc..

Anyone have a new head and WR intake cam and accessories for sale? Perfect time to go through the engine.

PM me what you have and how much.

  • L. Euler

Posted July 27, 2011 - 08:38 PM


Sorry for your luck on that one. I had exactly the same thing happen to my 03. Had to get a used 04 head from a YZ off of ebay after the dealer quoted me around $1800 for all the new OEM parts I needed. My problem started just as suspected may have been your problem. The valve clearance had gone slightly negative and the intakes were holding open.

I've heard that the journals can be repaired, but I haven't pursued it. I took the opportunity to go ahead and replace the piston and timing chain while I had it apart. My intent was to go ahead and sell it after I got it running again, but it runs so good now I can't part with it.

  • rholbrook

Posted July 28, 2011 - 06:28 AM


Does anyone know of a shop that can fix this head and repair these journals?


  • R_Little

Posted August 04, 2011 - 11:11 AM


That timing looks okay.

What year bike is it?

Keep in mind that when you change cams you HAVE to re-shim the valves.

Too tight valves will do nothing but backfire all day long!!

  • R_Little

Posted August 04, 2011 - 11:12 AM


Does anyone know of a shop that can fix this head and repair these journals?


Engine Dymanics in CA fixed my WR cam journals.

Call Mike Crowthers

Edited by R_Little, August 05, 2011 - 05:59 AM.


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