Cam Chain Tensioner


18 replies to this topic
  • dcleball

Posted October 07, 2009 - 09:10 AM

#1

Has anyone had any problems with their chain tensioner. The reason I asked is because I had a problem with my kx450f not starting. I needed some other work needed to be done other than the starting problem so I took the bike to a local mechanic. The mechanic said the bike jumped time. I assume it was for a stretched cam chain. He replaced the chain. He also adjusted my valves.

Since the mechanic worked on my bike, I didn't check the valves (work was done in August). Recently the bike was getting hard to start so I thought the valves needed adjusted. When I was checking the valves, I noticed the timing chain was one tooth off. Also, the left exhaust was .016 and should be around .008.

I have two possible conclusions. One is the bike still started one tooth off because it was hard to start since getting the bike back from the mechanic and has gotten harder to start recently due to the weather OR the bike jumped time again which I would have to say could be caused by a weak chain tensioner.

Any thoughts?

  • aka_tinman

Posted October 08, 2009 - 04:08 PM

#2

I had the same problem. I replaced the tensioner ...cheaper than breaking the motor

  • dcleball

Posted October 08, 2009 - 05:35 PM

#3

Did you also replace the cam chain when you replaced the tensioner? My chain is about 3 months old with 40 hours on the chain.

  • adynes

Posted October 24, 2009 - 01:50 PM

#4

I just had the same thing happen on my 06. A few weeks ago, I reset the clearance on the intake valves and noticed the intake cam was one tooth retarded. Reset cams back to spec., ran great for two practices. At this point I just assumed the previous owner had assembled it wrong.

Next weekend, I went to open practice at Redbud. On first startup (cold) the topend sounded excessivly noisy for a few seconds, then went away. The bike seemed down on power for the first session. When I tried to start it for the next session, it did the same thing and died. It was now very hard to kick over and would barely start. Removed the spark plug and it kicked over fine, so no valve conctact. I opened the bike up and found the cams were now WAY off. I didn't count an exact number of teeth, but the exhaust cam was advanced(auto decomp no longer in contact), and the intake was again retarded. Lobe separation was almost 180 deg.! Reset the cam timing and ran fine the rest of the day.

I've been doing a lot of searching on this problem the past few days. It seems to happen on all brands of bikes (both dirt and street) with auto cam chain tensioners. I've always had a chain slapping/chattering noise at low rpm lugging conditions that I previously attributed to the drive chain. Now I realized its the cam chain making this noise, and this seems consistent with what I've read elsewhere. The tensioner seemed to function properly "on the bench", but maybe it looses its grip under a certain load oscillation and frequency. I am going to remove it and do some investigating.

I'm thinking at this point that it would be in my best interest to go to a manual tensioner. I don't want to take the chance of a catastrophic failure, and this seems like a common fix for this problem. I'm sure a new auto-tensioner would fix it for the time being, but for how long?

How many of you have found your timing to be off? How many of you have this cam chain chatter? How many of you run a manual tensioner?

  • adynes

Posted October 24, 2009 - 03:45 PM

#5

I just disassembled my auto tensioner. I can't find anything visually wrong with it. Maybe the springs have relaxed? I'd have to compare it to a new one. I can't seem to put any amount of force on it that will cause it to retract (fail) once the screw is released. I think I'll make a manual tensioner to help find the root cause to this problem. If the chatter sound (and skipping) goes away, then I'll know the ACCT is at fault.

  • adynes

Posted October 24, 2009 - 04:55 PM

#6

Well, I think I found part (or all) of the problem with my bike. The front chain guide is not engaged in its pocket! Hopefully the chatter goes away once this is fixed:

Posted Image

dcleball, have you ever heard chatter sound coming from the cam chain area? If so, maybe check to see if your guides are installed correctly?

  • kwalhood

Posted November 08, 2009 - 01:41 AM

#7

I've just had the same thing happen to my '06 KX250F.When I was inspecting it I noticed that the rod locking mechanism was nearly completely froze up I literally had to pry it back and forth with a screwdriver just to get it to lock and unlock.The spring was useless it didn't have enough pressure to keep it in the locked position.The only thing I could come up with is that maybe the pin that keeps it on there somehow got distorted or bent,because I can't even knock it out with a pin punch or anything else.I've tried almost everything to remove it and have exhausted all my resources,but one and that would probably destroy the whole darn thing.LOL Adynes You mentioned that you were gonna make a manual tension adjuster.That sounds like the route to go.Would you mind filling me in on how to "make"one or would this be an aftermarket part?Thanks.

  • dand450

Posted November 09, 2009 - 10:25 AM

#8

Sorry to hijack your thread but, I am planning on putting in a new piston rings ect. this winter I was also going to replace the timing chain. Do you guys think I should replace the tensioner too? bike has 120h on it, 07 kx450. This will be the third piston but never had a new chain. Thanks

Edited by dand450, November 09, 2009 - 10:41 AM.
hijack


  • numroe

Posted November 09, 2009 - 03:45 PM

#9

Well, I think I found part (or all) of the problem with my bike. The front chain guide is not engaged in its pocket! Hopefully the chatter goes away once this is fixed

Interesting story. So the guide was installed the wrong way - like not seated correctly? You said it ran OK one weekend, then bad on the next weekend at cold start. So do you think the cool down had something to do with? Sounds like you put it in wrong before those two practises but got away with OK running. Sounds like you are pretty lucky you did not mince your valves and head.

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  • adynes

Posted November 09, 2009 - 06:09 PM

#10

I've just had the same thing happen to my '06 KX250F.When I was inspecting it I noticed that the rod locking mechanism was nearly completely froze up I literally had to pry it back and forth with a screwdriver just to get it to lock and unlock.The spring was useless it didn't have enough pressure to keep it in the locked position.The only thing I could come up with is that maybe the pin that keeps it on there somehow got distorted or bent,because I can't even knock it out with a pin punch or anything else.I've tried almost everything to remove it and have exhausted all my resources,but one and that would probably destroy the whole darn thing.LOL Adynes You mentioned that you were gonna make a manual tension adjuster.That sounds like the route to go.Would you mind filling me in on how to "make"one or would this be an aftermarket part?Thanks.


It sounds like your bike uses a different style tensioner.
Tokyo Mods makes a manual tensioner, $200 for the 450 and $120 for the 250, not sure of any others out there. I didn't take the time to get pictures of my manual tensioner before I installed it, but here it is after. I made it using a lathe, drill press, and disc sander, a 10mm bolt and jam nut:

Posted Image

Interesting story. So the guide was installed the wrong way - like not seated correctly? You said it ran OK one weekend, then bad on the next weekend at cold start. So do you think the cool down had something to do with? Sounds like you put it in wrong before those two practises but got away with OK running. Sounds like you are pretty lucky you did not mince your valves and head.


I feel very confident I reinstalled the auto tensioner correctly the first time. I even made sure it had retracted fully with a small screwdriver, and the chain had no slack. I went ahead and made the manual tensioner, and installed it with no other changes. Same chain (probably original 06), and the guide is still not seated. I'll have to take the head off to fix that, so I'm going to wait till the snow flies.

While I had the bike apart for the MCCT install, I checked to see just how much chain play is required to jump a tooth. I had to retract the auto tensioner (ACCT) fully, and even then it was just barely enough. I did some playing around with the the ACCT and found that if I twisted the plunger back and forth while it was loaded, it would in fact retract. I think that the ACCT is probably marignally sufficient when everything is new, but once the chain/tensioner starts to wear out, vibrations increase and it will eventually retract. My chain does have some resistance when you flex the links from and outside radius to an inside radius. I'm going to replace that this winter too.

The bike has run flawlessly for 3 practices now, probably about 10 hrs worth. The valvetrain noise has been GREATLY reduced, especially when cold, and at idle. I'm really happy about that. There is still a bit of noise at low rpm lugging conditions though. I'll let you guys know if any thing changes. :smirk:

Here's a pic of the ACCT disassembled:

Posted Image
Posted Image

  • numroe

Posted November 09, 2009 - 09:53 PM

#11

Can you see any signs of wear on your ACCT?

Wondering if it looks fine, but works wrong (retracts all the way).

  • kwalhood

Posted November 10, 2009 - 09:17 PM

#12

adynes you are correct my tensioner is a completely different style than yours.By looking at your homemade one gives me an idea on how I can make one.I have access to a small machine shop to fabricate the part.looks to be fairly easy thanks.Just to make sure I'm doing this right...........I guess when you start hearing valve noise would be the time you would want to manually tighten the tensioner,or should it be done after a certain amount of time(after so many hours).

  • numroe

Posted November 11, 2009 - 05:17 AM

#13

Would you simply check the chain tension by feel, when doing the valve clearance check, and adjust the manual tensioner if reqd?

  • adynes

Posted November 11, 2009 - 03:24 PM

#14

Can you see any signs of wear on your ACCT?


No, not really.

adynes you are correct my tensioner is a completely different style than yours.By looking at your homemade one gives me an idea on how I can make one.I have access to a small machine shop to fabricate the part.looks to be fairly easy thanks.Just to make sure I'm doing this right...........I guess when you start hearing valve noise would be the time you would want to manually tighten the tensioner,or should it be done after a certain amount of time(after so many hours).


Hard to say what kind of interval would be required. I'm going to recheck mine soon to see if it has moved at all. One thing I was real carefull with was making sure the end of the M10 bolt had a flat and polished face, so that it would not wear into the chain guide.

Would you simply check the chain tension by feel, when doing the valve clearance check, and adjust the manual tensioner if reqd?


Yeah, that's what I plan on doing. When I set the tension with the MCCT, I basically just tried to duplicate how I remembered it feeling with the ACCT by pressing down on the chain between the cams. I tried to err on the loose side. Hopefully it works out ok; so far, so good.

I wonder it the 09s will have any issues down the road? I think I remember reading that they reduced the spring force on those.

  • adynes

Posted November 11, 2009 - 03:27 PM

#15

Does anyone know what the pro's bikes use for tensioners? I've been meaning to do some searching on that, but forgot untill just now.

  • jjm525

Posted March 23, 2010 - 02:11 PM

#16

Wwe've had our 06 do this twice now. I guess you guys are OK now with just a new chain & tensioner?

  • adynes

Posted March 23, 2010 - 09:00 PM

#17

Wwe've had our 06 do this twice now. I guess you guys are OK now with just a new chain & tensioner?


I haven't even put my new chain in yet. The swap to the manual tensioner fixed the problem for me.

  • ridintolive

Posted March 23, 2010 - 09:31 PM

#18

this problem seems to be bike dependent. I know of about 3 engines all various years that have had the problem. I have had a 06 kx450 and it has never jumped teeth or even needed a valve adjust till this last year, only 150hrs on it and my 09 kx450 hasn't skipped yet either and it is on it's second top end with a fresh bottom end. Both bikes are on stock cam chains and tensioners. Sounds like the springs in the ACCT's are inconsistent and causing a problem. Curious what the pros are using as well.

  • robfromga

Posted March 15, 2011 - 12:35 PM

#19

Im fighting the same problem now, ran across this thread doing a search. Tensioner will be here tomorrow, hope it cures my ills. The chain has 4-6 hours on it.





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