Cam Chain Tensioner Fix
I recently brought home a 2003 400EX and bought it cheap because it sounded like it was gonna splode. I posted here the other day about it and got confirmation to check valves and cam chain tensioner.
After setting the valves to spec, I fired it up and it was still bad sounding. I loosened the pipe and silencer so I could get to the tensioner and pulled it out. There was no spring action to it and it was completely collapsed. Not knowing how it really works, I put it back in and turned the screw to push the tensioner rod out. Then tried it again and it still sounded bad.
Took it off and realized it was missing the spring action needed to twist itself out and apply pressure to the chain guides. I tried looking up how to rebuild it and could not find any info. I decided to have a look inside. First I popped off that tiny retaining circlip and carefully pulled out the plunger assy. Mine had quit working because the tensioner spring winding had snapped at slot in the bottom of the plunger. This kind of spring is similar to what you would find in a lawnmower pull start. I pulled the rest of the wound spring assy out and using needlenose pliers reformed a new end to slide into the plunger assy.
It got kinda tricky trying to put it all back together. I coiled up the spring really tight and once it had a very small diameter, then grabbed it with the needlenose pliers and pushed it down to the very bottom of the housing. I then pushed the slotted end of the plunger assy down into the housing so it slipped over that reformed end of the spring...make sure it gets into the plunger assy slot or it will not work.
You do not need to preload the spring at all, it is pretty much impossible due to the direction the plunger assy unscrews anyway. So I set it in there and wiggled it around back and forth a bit until it all fit down in there. Then the hardest part was holding it all together and putting that little circlip back on. A second pair of hands would be nice but not necessary.
I decided to give this a try because I went on ebay earlier and everyone wants $50+ for a new tensioner and I would have to wait a week to get it. Anyway, it worked and now this EX is no longer a ticking time bomb. I wish I could have taken pix but I did not have any help and most of the time I didn't think I was gonna come out on top of it. Anyway, it is a pretty simple fix once you tear into it and may save you some $$$ if you give it a try.
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