wr450 jumping timing


10 replies to this topic
  • topp38

Posted June 14, 2013 - 01:40 AM

#1

hi all my wr wasnt running right,,so i checked valves and re shimed them,,took it out and it died on me,,took apart and checked clearances again,,which was ok,,checked cam chain tensioner and it seem fine,,thought the cam chain was a bit loose,why i thought it was jumping timing,,got new one in and chain chain is bang on the same size as old one,,so it iant that,,any ideas whats causing the problem,,chain guides look ok too,,am puzzeld..

any help would be great thanks

  • Do I Care?

Posted June 14, 2013 - 03:02 AM

#2

hi all my wr wasnt running right,,so i checked valves and re shimed them,,took it out and it died on me,,took apart and checked clearances again,,which was ok,,checked cam chain tensioner and it seem fine,,thought the cam chain was a bit loose,why i thought it was jumping timing,,got new one in and chain chain is bang on the same size as old one,,so it iant that,,any ideas whats causing the problem,,chain guides look ok too,,am puzzeld..

any help would be great thanks

Replace the tensioner.

  • topp38

Posted June 14, 2013 - 03:46 AM

#3

thanks for the reply,,i check the tensioner a few times and it seems to be working fine

  • Do I Care?

Posted June 14, 2013 - 03:57 AM

#4

thanks for the reply,,i check the tensioner a few times and it seems to be working fine

You obviously didn't check it properly if you say ''it seems to be working fine''.
You must measure the specifications as in your manual. he only other thing it can be as you said that the guides are fine, is the cam chain sprockets or damaged drive gear.

  • topp38

Posted June 14, 2013 - 04:14 AM

#5

to me it is working fine,,u cant push it in when its right out,,all the gearing is fine,,chain guides look just as they should with no visable sighns of heavy wear

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  • Krannie McKranface

Posted June 14, 2013 - 05:24 AM

#6

You have made no mention if it has actually jumped a tooth, by how much, and what your timing tooth count is once corrected.....

  • grayracer513

Posted June 14, 2013 - 07:26 AM

#7

The most common cause of skipping timing is neither an overlong chain nor a failed or failing tensioner, it's when the chain develops stiff, binding links. The tensioner can be "fooled" into thinking it has taken out the available slack by the presence of a stiff link or two running down the back run of the chain. If ever the engine kicks back, or bounces back off of the compression stroke when stalling, the drive tension on the chain is reversed, the stiff links rolling down off the intake cam are pulled out straight, and there's all of a sudden a whole bunch of slack on the front side of the chain, allowing it to skip.

The cause of the chain getting into this condition is most probably a matter of running the engine oil too far between changes, based on observations of those I have seen apart. Replace both parts anyway. Neither one is expensive enough to risk an engine on.

You must measure the specifications (for the tensioner) as in your manual.


And apart from the torque specs, those are located on which page, please?

  • Do I Care?

Posted June 14, 2013 - 01:39 PM

#8

The most common cause of skipping timing is neither an overlong chain nor a failed or failing tensioner, it's when the chain develops stiff, binding links. The tensioner can be "fooled" into thinking it has taken out the available slack by the presence of a stiff link or two running down the back run of the chain. If ever the engine kicks back, or bounces back off of the compression stroke when stalling, the drive tension on the chain is reversed, the stiff links rolling down off the intake cam are pulled out straight, and there's all of a sudden a whole bunch of slack on the front side of the chain, allowing it to skip.

The cause of the chain getting into this condition is most probably a matter of running the engine oil too far between changes, based on observations of those I have seen apart. Replace both parts anyway. Neither one is expensive enough to risk an engine on.






And apart from the torque specs, those are located on which page, please?

I'm not trying to argue with you Grey as you are much more experienced than myself but...
If you read the post (it is hard to read I know) but I am pretty sure the OP said that he replaced the cam chain.

Your right about the tensioner limit not being specified, wonder why that is???

The new chain and good 2nd hand tensioner are fitted and now the engine turns over perfectly. I had the 2 chains laid out on the bench and the old one does appear to be a couple of mm longer than the new one.


Here is a pic of the difference in the tensioners :
Posted Image

Edited by Barra8, June 14, 2013 - 02:05 PM.


  • grayracer513

Posted June 14, 2013 - 02:19 PM

#9

Neither of those shown look as if they are tensioners used in a 2000 or newer YZF. There's no extension limit specified (if that's the spec you were talking about) because the tensioner extends well beyond the range that the chain might possibly grow to from wear and still actually work. The only considerations in checking them is that they move smoothly and freely as the screw is turned, and that they can't be pushed back.

It would be helpful if a torque spec were published to check the force applied by the spring, but they don't give that.

  • Do I Care?

Posted June 14, 2013 - 02:25 PM

#10

Neither of those shown look as if they are tensioners used in a 2000 or newer YZF. There's no extension limit specified (if that's the spec you were talking about) because the tensioner extends well beyond the range that the chain might possibly grow to from wear and still actually work. The only considerations in checking them is that they move smoothly and freely as the screw is turned, and that they can't be pushed back.

It would be helpful if a torque spec were published to check the force applied by the spring, but they don't give that.

Thank you for the explanation and yes I was talking about how it extends and the spring rate.

The tensioners were not from WR (good observation) but it was an example.

Looks like it still comes down to replacing the tensioner though.

  • topp38

Posted June 14, 2013 - 10:59 PM

#11

thats great help guys,,there is about 2mm in difference on old and new chain on futher enspection,,ill go ahead and order new tensioner aswell to be on the safe side then




 
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