Quantcast
Jump to content

  • Join Today, It's Simple and FREE!

    As a member, you can post in our forums, upload your photos and videos, use and contribute to our downloads, create your own member page, add your ATV events, and even start your own ATV club to host your own club forum and gallery.  Registration is fast and you can even login with social network accounts to sync your profiles and content.

mfallavol

What could cause the timing chain to snap - Twice?

Recommended Posts

I picked up a 2003 KLF-250 for my son's first ATV a few months ago.  It had no compression and overall needed a lot of work.

To make a long story shorter, the major problems were in the head; mostly a bent valve.  We got it back and working and he was enjoying it until it just died.  Started back in to it only to find a broken timing chain.  I figured it had gotten stressed due to whatever caused the bent valve so no big deal...so I thought.  The problem is he was back riding it this weekend; probably has less than 4 hours on it since the timing chain was replaced and the same thing happened.  He'd been riding it down the trail very gingerly, we stopped to chat and he went to give it gas and it gave a little 'pop' and died.  When he hit the starter it was obvious it needed to be towed back.

Got it home to find the timing chain is broken again.  I really have no idea why.  It runs fine when running but now I'm gun shy.

Any thoughts and ideas would be appreciated.  He's getting pretty bummed so I'd like to get this figured out.  Just ordered another timing chain so we'll get back into it this weekend.

Share this post


Link to post
Share on other sites


That's interesting and the first thing that comes to mind is that it's too tight and stressed. Bad tensioner? Check out the service manual below and look at page 75 to inspect that tensioner. Also make sure you timing is correct:

 

Share this post


Link to post
Share on other sites
On 1/31/2017 at 9:17 PM, mfallavol said:

I picked up a 2003 KLF-250 for my son's first ATV a few months ago.  It had no compression and overall needed a lot of work.

To make a long story shorter, the major problems were in the head; mostly a bent valve.  We got it back and working and he was enjoying it until it just died.  Started back in to it only to find a broken timing chain.  I figured it had gotten stressed due to whatever caused the bent valve so no big deal...so I thought.  The problem is he was back riding it this weekend; probably has less than 4 hours on it since the timing chain was replaced and the same thing happened.  He'd been riding it down the trail very gingerly, we stopped to chat and he went to give it gas and it gave a little 'pop' and died.  When he hit the starter it was obvious it needed to be towed back.

Got it home to find the timing chain is broken again.  I really have no idea why.  It runs fine when running but now I'm gun shy.

Any thoughts and ideas would be appreciated.  He's getting pretty bummed so I'd like to get this figured out.  Just ordered another timing chain so we'll get back into it this weekend.

also check the gears to make sure they aren't worn to a point that the chain will jump over the teeth causing excessive stress and snapping the chain.  Pay particular attention to the gear on the crankend.  Make sure it's not slipping on the crank.  Good luck

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Forum Topics

    • By joninak
      Well, it overheated then started blowing white smoke!!
      I have it torn down & the cylinder appears to be warped. Going to have the head checked out next but in the meanwhile... Does anyone have the torque sequence/specs for the head bolts??
      TIA
       
       
    • By joninak
      I'm working on a 2018 Sportsman 570 and found in the service manual that there are two different torque methods for the head bolts depending on whether the bolts are silver or black. Well, silver bolts came out of my engine and I'm going to be replacing them with new bolts, however the parts fiche doesn't specify bolt color or that there is even an option!?! 
      Has anyone on here been through this before and can offer insight??
       
      TIA
       
    • By PolarisRich
      I've never done this before but after reading a few thread I decided to check my valves for the first time and to my surprise it was much easier than I thought.
      My bike is a 2005 Sp 500 HO.
      I first pulled the seat and the right side panel off, and that's it! It wasn't too bad to get at.
      Next I pulled the spark plug out and removed both the head cover ( 8-8mm bolts)
      [ATTACH]1021[/ATTACH]
      then the side cam cover (5-8mm bolts).
      [ATTACH]1023[/ATTACH]
      Also remove the plug in the recoil cover (14mm bolt) to see the timming marks.
      [ATTACH]1022[/ATTACH]
      Next I turned the engine over with the pull cord untill it was at TDC of the compression stroke.
      The best was to tell that your at TDC of the compression stroke is to rotate the engine until the
      timing marks are parallel to rocker cover gasket surface.
      The cam sprocket locating pin will be facing upward directly in line with the crankshaft to camshaft center line.
      Now fine adjust by looking into the timing hole in the recoil cover and line up the upside down "T" on
      the flywheel into the center of the hole.
      [ATTACH]1023[/ATTACH]
      Now using a feeler gauge, slide the .006" (.15mm)blade between the top of the valve and the bottom of the adjuster and adjust accordingly
      [ATTACH]1024[/ATTACH]
      [ATTACH]1025[/ATTACH]
      To adjust, Loosen the locknut (10mm) and check clearance with a feeler guage. Clearance should be .006" (.15mm) for both, intake and exhaust valves. Turn the adjuster with a stubby flat blade screwdriver untill the proper clearance is achieved then tighten the locknut (5.8-7.2 ft. lbs) while holding the adjuster in place with the screwdriver. Re-check the clearance with the feeler guage one last time and re-assemble the covers (72 in.lbs) and plugs.
      The only thing that i noticed was that I had to clean and silicone the side cam cover other than that I found the whole process rather simple.
      I'd give it a 4 out of 10 on the skill level scale.
      I hope this helps!
      Thanks Rich





    • By JacobSlabach
      in this thread, I want to discuss how 4-cycle atv engines work- what the different types are...  how they are set up and which you prefer.  To start off, are the cams on ALL atv 4-strokes powered by a cam chain?  I know that on say a lawn mower or logsplitter engine, the cam is turned by the tappet, pushrods, and valve rockers.  Which is better and why?  Chain-driven cams or pushrod-driven cams?  Are the pushrods just an old version and everything is transforming to chains or the other way around...or not at all?  Just looking for some explanation, history, and downsides/upsides...
    • By chem3233
      I have a 1998 yamaha grizzly 600 4x4 I have put back to life but as soon as I had all the bugs out it blew the special "L" plug out. What causes this? Is there something special I have to do to replace this?
  • Recently Browsing   0 members

    No registered users viewing this page.


×