MX TUNER / ANYONE : SOS : TIMING CHAIN TENSION

I think I may have screwed up royally. Reading the YZ thread I came across the below from MX Tuner.....

start quote "Yes, I've seen this (particular type of cam and valve damage) a couple times. Only on bikes that the tensioner was installed without being retracted. This puts a huge amount of tension on the chain and stretches it. I had to replace the chain and 3 intake valves on a '99 400 due to this. You may be able to tell how stretched the chain is by how far the tensioner plunger has to extend to take up the slack in the chain." end quote

When I changed my WR to and from YZ timing (see thread There and Back Again) I couldn't figure out how to 'cock' the chain tensioner. I just took it out and reinstalled it, it seemed right however, I did notice that the timing chain appears to be REALLY TIGHT.

However, bike runs real smothly, I went for an hours ride with it like this. Have I screwed up ?

How the hell do I adjust/cock the timing chain tension ?

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The Missile

'99 WR400F

Airbox Lid - gone

Throttle Stop - shorty!

Plastics/Tank/Seat - One Industries

Street Legal

tensioner is spring loaded...???

How does it work ??? I read of a 'screw' to turn but couldnt see one to turn !!!

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The Missile

'99 WR400F

Airbox Lid - gone

Throttle Stop - shorty!

Plastics/Tank/Seat - One Industries

Street Legal

It is a simple spring loaded tensioner. It takes a small regular screwdriver.

If you want to be sure, just check it.

Take the bolt off the end of the tensioner while still mounted to motor.

insert the screwdriver and turn the tensioner so it loosens the chain.

If done properly when backed out all the way it will lock in place and the tensioner can be removed.

Once re-installed, Turn screw in opposite direction to release and you will feel the srewdriver want to turn in your hand. Let it go and the chain will be automatically tensioned.

If you do this with the valve cover off, you will be able to feel the chain tensioner release and get tight.

It is self tensioning. This has been my experience with it.

Mike

I just replaced my cam chain and tensioner guides in my 98 WR400. After 6700 miles with only regular oil changes and two valve adjustments I think it's holding up pretty good. My bike had no valve damage and the clearance was in spec. at teardown.

The symptom my bike had was an excessive engine rattle that got worse as the bike heats up.

Replaced the piston and rings just because I was working in the neighborhood.

It runs like new again.

Zaknavage,

Old guy and GPS Geek

I did the same thing when I changed my 01 to YZ timing. I pulled the complete tensioner off without retracting the center screw. As I pulled it off the center extended fully. Not knowing what just transpired I reinstalled the tensioner later. The bolts are long enough to install the tensioner fully extended. It was not until I tried to kick the bike over that I realized something was wrong. It was extremely hard to turn over. I stopped and took it off discovering what I had done.

The tensioner is only spring loaded in the sense that it uses a spring to extend the threaded center piston. There is no give to the piston that presses against the shoe. I called a local engine builder and explained what had happened. He said that I probably would have done some damage if I had started the bike. He also told me that this is not the first time someone called with this problem.

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