Stretched timing chain?


7 replies to this topic
  • manther

Posted March 15, 2008 - 10:43 PM

#1

Do timing chains stretch much? I put a 450 cam with autodecomp in my wr400. I was soo certain I had the timing correct and the valve shims correct. But after I ran the bike for a little while I could noticeably hear my valves clicking. I have a new timing chain I haven't installe yet. When I was setting the timing the marks seemd to be half a tooth off from TDC. I was thingking that if I installed the fresh timing chain it might help lining up the timing marks easier. Is changing the chain easy? Do you have to remove the flywheel? Does this flywheel require a flywheel puller? Sorry for the 20 questions.

  • Speedracer747-400

Posted March 16, 2008 - 02:44 AM

#2

A timing chain will stretch over time. A good change interval would be around 100 hrs. Better to be on the safe side than have your motor grenade. Here's a pic of a timing chain after 9 months of use.
http://www.thumperta...ht=timing chain

You will need to remove the flywheel to replace the timing chain. A flywheel puller is required.
http://motionpro.com...ywheel_pullers/

If you don't have a service manual for your bike you can download it here.
http://www.yamaha-mo...ice/manuals.jsp

Here's good instructions for changing the timing chain written by Grayracer in the YZ400/426/450 forum.

Takes about an hour if you don't throw in any valve adjustments.

Start and run the bike for just long enough to clear the sump of oil. Remove the cam cover, ignition cover (no significant oil will be lost), flywheel (puller required, don't cheat), and stator plate (#27 Torx bit required). Remove the tensioner (see manual for unloading instructions) and the two bolts holding the bottom of the rear chain guide shoe. Rotate the bottom end of this part outward and remove it by pulling it down. (If it gets stubborn, you can just let it sit in there out of the way.)

Remove at least one cam (probably both will be required) and rotate the chain off the crank as you did the rear guide.

In reassembling, you have a couple of options:
a) place to the chain over the crank and bolt the rear guide back in place. Reinstall the stator and flywheel, and depend on the front and rear guides to keep the chain from looping off the bottom of the crank sprocket as they are designed to while you time and assemble the top. Probably safe, but you always find yourself wondering if the chain is really on right.

:confused: Remove the spark plug and use a screwdriver to find TDC, or eyeball it by lining up the flywheel key with the bore centerline and time and assemble the chain and cams with the whole run of chain visible. Foolproof, but be sure to double check the timing by pushing the flywheel and cover on by hand and using the real marks just before torquing everything all the way up. You don't want to have to take any more apart than necessary if you screw up.

I use option b myself.

Two mistakes commonly made are failing to torque the cam caps right, and timing the cams wrong because the cams weren't rolled back. Back the engine up to a few degrees before TDC, and then roll each cam back until the front run of chain is tight, and the slack is on the back side. Now, hold pressure against the rear guide shoe by pushing your finger through the tensioner hole and rotate the engine forward back to TDC. Then check the timing. Note that there's no point in worrying too much about the timing marks lining up perfectly. The marks simply are never going to be perfect. What you do is imagine the timing marks on in the same position on the next tooth, and see how that would look. If it makes it closer, move it. If not, it's OK.

Always carefully torque up the cam caps in three successively tighter steps. I use 75 in/lb instead of 86. 86 just seems too tight to me, and I believe Yamaha has reduced that value for the later models.

It's a pretty simple job. Remember to check your valve clearances before removing the cams in case any of them need correcting, as this will be the perfect time for that.



  • dirtysouth

Posted March 16, 2008 - 06:28 AM

#3

Timing chains stretch...this is the reason for the tensioner. Are you sure that your valves are tapping or are you hearing things now that you replaced your cam and have a nervous feeling since you have never done this before. Take a piece of water hose about 3 ft long, hold one end to your ear and the other end to various places around your motor i.e. clutch cover, carb, valve covers, exhaust head connection. You can narrow down the source of the sounds that you "think" are the valves tapping. My recommendation is based on the fact that when I did my first valve adjustment I swore that the valves were tapping but turned out that the slide on my carb was the source of the tapping that I assumed to be valves.

  • manther

Posted March 16, 2008 - 10:09 AM

#4

Thanks guys for the help. Since I have a new timing chain in my possesion, I guess I should use it huh... Nice instructions. And dirty, no I'm not sure it's the valves tapping. I went out to the trails and easily started the motor with my new 450 cam and reshimmed vales and here goes this clicking sound that was so noticable all my friends said whats that noise... But I will try the hose trick. (or something like it). It annoys me that when I find TDC the timing marks are about 10 degrees (half a tooth) off in either direction making it impossible to precisly set the timing... And I know I'm finding TDC acurately because I'm putting a thin rod in the spark plug hole and watching for it's highest point right before it begins to go back down. But here is a question, lets just pretend for a second that it definatly was my valves clicking... Would one tooth off in either direction cause that? Also would going down in shim size cause that? Also when I first finished the job and started it for a minute it was not clicking. It didn't start until I rode it around the block... I'm wondering if it is the valves then what can change after running it for a bit? Is that the shims settling into place? Is that the chain getting tighter? And last question if in fact it is my vales clicking then must they now be bent because they are hitting the piston? Or can they click as thay snap back up into their seats? Again sorry for all the numerous questions. -J

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  • ncampion

Posted March 16, 2008 - 10:54 AM

#5

Timing chains do not actually "stretch" however they do elongate due to slight amounts of wear at each pin thereby making the overall length of the chain slightly longer. As was said earlier, that is what the chain tensioner is for - up to a point. It does affect the cam timming slightly but probably not to the extent that you can notice it. If the clicking was due to bent valves, the bike would not run. My guess is that one or more of the valve clearance is way off. this would make a clicking noise, but still allow the bike to run, probably at reduced power depending on how far off it was. I would just pull the cover and re-check all the valves, it can be kinda tricky to get a feeler guage in there correctly because of the tight space. Be extra creful with the one exhaust valve that is "decompressed" on the 03 cam so you don't get the feeler guage under the decompress button. Good luck, let us all know what you find.

  • manther

Posted March 16, 2008 - 12:52 PM

#6

Just for my personal understanding... If valve clearances were off enough to cause clicking / ticking what would be actually causing the noise? The reason I ask is because as I understand it, valves need to be re-shimmed because they get tighter. In other words the valve constantly hitting the seat in the head slowly causes it to seat higher and higher, making the top of the vavle stem get closer to the cam lobes. So most people upon re schimming need to goto a smaller shim size. So if you get your valve clearances wrong, chances are they will be too far from the lobe. Which means the lobe will push the valve down not quite as far as it used to. So under that premiss it can not be the valve hitting the piston because now the valve doesn't go down as far as it used too. So is it the valve snapping back up into it's seat? Is it the lobe slapping against the top of the valve stem? What exactly causes the clicking when it's due to improper valve clearance. Sorry for being picky I just want to understand it better.

  • manther

Posted March 16, 2008 - 06:09 PM

#7

Maybe no one knows the answers to my questions in my previous post, but how bout this one... Using a feeler gauge. I can always force one more feeler guage in is that the one to record as the measurement? Or do I record the last feeler that slid in without resistance?

  • maxtherat

Posted March 16, 2008 - 07:48 PM

#8

sounds like the lobes are slapping the buckets. You may need to recheck your clearances. Some guys use a "fit, does not fit method" This means that you record the last feeler gauge that actually fit vs the next one that does not fit at all. If you find yourself pushing on the feeler gauge fairly hard then it's to thick and you need the lesser reading. I, also, had to reshim a second time after installing new cams.




 
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