Cam chain tensioner failure

[ZooR1]

Hey, anyone see one of these fail. Took a little ride this morning, noticed the motor ticking at idle. Tensioner felt weird. Decided to pull it apart. Note that top part of tensioner is pulled up into shaft and bottom part is broken off. Part is called tensioner setting bar. 

[Old School Al]

Yep, sure have................what year?  Pull the spark plug and have someone crank it over slowly while watching the end of the crank to see if it runs true or has some run out (wobbles).

Old School Al 

[ZooR1]

Good to see you’re still around. I have found much wisdom in your posts. Helped me to resurrect two of these 200s. One is a 1995, the one in the pic is a 2000. Both are mostly stock except for 80s suspension. Will do on the cranking, but not till my clutch parts come. Got the other side apart too. Btw did you see my other Q about the clutch basket?

[S.O.A.N.Z]

Good news is you can still get that part   ?  14520-969-010

[ZooR1]

Already have that and the tensioner on order. 

[woodsryder]

Yep, lost one too. When I checked my spares I found another tensioner with a crack in the same place. I have 5 parts engines and they all have extreme wear on the aluminum boss directly above the crank sprocket. That means all motors had seriously loose chains at one point.

Now that I know the sound, I know to shut the bike down. Bad idea to try limping it home as the motor digests itself.

[ZooR1]

I recently pulled the motor off my other 200. To go over the top end. It had a slight tick that I couldn’t get rid of. I thought it might be some wear on the lower cam sprocket. But I wanted to check the valves too. When I pulled the flywheel off I noticed that there was a little slack in the chain so I loosened the adjuster to check it out. Looks like the spring on the adjuster had gotten a little weak over the years and wouldn’t push all the way up. I did make a 3mm thread tool to be able to pull up on the adjuster for future use. That’s actually how I figured out that this one broke. I could engage the threads and the adjuster would just pull up and down with no tension. Hope pic below helps explain the tool. I just threaded a nail and made a handle since I couldn’t find a 3mm screw long enough. 

[NaCltK9]

12 hours ago, woodsryder said:

Yep, lost one too. When I checked my spares I found another tensioner with a crack in the same place. I have 5 parts engines and they all have extreme wear on the aluminum boss directly above the crank sprocket. That means all motors had seriously loose chains at one point.

Now that I know the sound, I know to shut the bike down. Bad idea to try limping it home as the motor digests itself.

Last year my 99 motor plastic chain tensioner broke while on the trail. It started running weird and making all kinds of noise. Tried to limp it back to the truck and blammo! Died on the spot. Got it home and tore into it only to find that the timing had gotten so far off i bent both valves, cracked the piston and shaved some aluminum off the inside of the case.

[woodsryder]

I forgot to mention that I also use the 3mm screw trick to lift up on the plunger. The springs are never strong enough and even with the screw it takes a firm pull to quiet things down. With the engine running I'll first push the screw down slightly until it just starts to rattle, then lift until it just gets quiet, then lock the nut. I do it every other ride. I have become sensitive to the noise so I am anal about keeping it tensioned.

long 3mm screws can be found holding vintage turn signal lenses on Hondas and many other bikes. Otherwise its a common screw size at most hobby shops. You won't find them in any hardware stores.

If you look at the center case right above the crank sprocket you will see a small aluminum boss cast into the cases. Every engine I have has the boss worn way down and sometimes missing. Imagine how much movement the chain must have to be able to do that? 

I think sprocket wear is another result of loose chains whipping around. Cam chains are seldom a wear point in other engines. 

Its just a weak system and the breakages are probably due to the constant beating from a loose chains so as long as you keep it tight you should be good. The CRF230 has a more robust system (won't fit the 200) but they also suffer from spring breakages and many use an aftermarket manual tensioner

[ZooR1]

I picked up both my 200s about a year ago. Both not running. And both needed lower cam sprockets and had worn out cam chains. One bike was neglected and looked like it spent time at the bottom of a river and the other one looked like it had been seriously “tested”. Lol. 

[Tbahr]

I didn't know there was a 3mm threaded hole in the end of the tensioner shaft. My cam chain spring seems a little weak. What's the procedure for using the tool to lift the tensioner shaft?

[woodsryder]

23 minutes ago, Tbahr said:

I didn't know there was a 3mm threaded hole in the end of the tensioner shaft. My cam chain spring seems a little weak. What's the procedure for using the tool to lift the tensioner shaft?

Refer to post #9 for adjustment procedure

[Doogee57]

   I use an old wheel spoke with the correct threads. Never had one break on me (I've owned several 200's since the late 80's and now have an 88) but I've always kept mine properly tensioned. I use the same technique that Woodsryder does to set the tension.

[Doogee57]

  I'd better check my spares for cracks too. Maybe just make up some new, beefier ones out of solid bar stock (4144 'pre-hard'). That would probably bullet proof it if the tension is kept correct.

[woodsryder]

I don't know how to address the cracking,.. it seems the part is hardened and the crack occurs where it was bent like you would expect. I think its the loose chain that beats it to death

A stronger spring would help it function as designed, otherwise it will never work properly. I would rather see it converted to manual. Maybe drill and tap the shaft for a 5-6mm bolt which would stay in place with a locknut to hold up the plunger. Don't rely on the silly spring to apply tension.

If you watch the flexible tensioner strip as you pull up on the screw its easy to over stress it. I do think sound is the best indicator but don't give it an extra tug after its quiet. Use just enough to take out the rattle.

I compared a half dozen tensioner strips and some were more firm than others too. Maybe aging,.. maybe aftermarket?? I used the stiffest one I had.

[Erik Marquez]

20 minutes ago, woodsryder said:

I don't know how to address the cracking,.. it seems the part is hardened and the crack occurs where it was bent like you would expect. I think its the loose chain that beats it to death

Likely not intentionally hardened, just stamped steel part, and work hardened at the bends creating a weak point and fracture more likely. 
That part at the bend will continue to work harden at the bend as vibrations and flexing takes place while in use. best bet is not use a used one, but a new one, which will still fracture some day, but give a lot longer  service life than one that has been in use for some time. 

[ZooR1]

I don’t want to screw around so I got new factory parts. I was able to replace the tensioner through the flywheel opening btw. It’s a tight fit wiggle but can be removed/replaced all from below.