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1985 Xr100 randomly died....

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I rode it around the yard for a little bit today to take a break from working on my car and it just died out of nowhere!

Right before it died it made this grinding sorta noise and then a "pop" like a backfire and just instantly quit. I can still kick it over fine, compression doesn't feel any different and it started first kick when I first brought it out of the barn. It was a pretty high RPMs when it died.

About 2 hours on fresh 20w50 and it was running fantastic until it died. Now it doesn't even try to start anymore. Still shifts fine and rolls easily in neutral. Haven't drained the oil yet, though.

Does this sound like a cam chain failure? I highly doubt it's ignition or carb related since I just went through the carb and it wasn't running funny at all.

This is my first 4-stroke, so don't be too harsh on me please! I have no idea what I'm doing with this thing haha. If it was a two stroke I'd know what happened the instant it died.

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That's like THE easiest bike in the world to check the cam chain and the valves. Just pull the tank and the two bolts, if it's a cam chain issue it's gonna be pretty obvious. It's a lot harder to take a shot in the dark then to pull that bikes valve cover..

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That's like THE easiest bike in the world to check the cam chain and the valves. Just pull the tank and the two bolts, if it's a cam chain issue it's gonna be pretty obvious. It's a lot harder to take a shot in the dark then to pull that bikes valve cover..

Thanks for the reply! Any good online tutorials that you know of? I'll pull the tank and start digging around after dinner if theres still any light outside. I'm hoping its an easy fix.

I snagged this thing for $350 about a month ago and beat the tar out of it at a party. So I guess I shouldn't be surprised it broke haha.

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Thanks for the reply! Any good online tutorials that you know of? I'll pull the tank and start digging around after dinner if theres still any light outside. I'm hoping its an easy fix.

I snagged this thing for $350 about a month ago and beat the tar out of it at a party. So I guess I shouldn't be surprised it broke haha.

This should show how to do it once it's opened up, but it's honestly really easy, I've done a valve change on it in 2.5 hours. That was the thing completely together, to apart, and using a piece of PVC to get the valve spring compressed, to fully together and running. It's that easy.

But, to get down to the cover, pull the tank(2 bolts on the front bottom left and right) and pull the seat to get to the rubber thing to pull the tank all the way. Then, just the two bolts on top. Don't bother with the side cover as this video shows www.youtube.com/watch?v=ga_apq9qDCI&app=desktop just do the top. Until you verify where the issue is or isn't at least. I'm wondering if it's possible your flywheel came loose and scraped on the stator and killed spark and made that grinding noise. But check the top first.

I just watched the beginning of that video. Honestly I watched a video on it like 5 years ago at least and haven't seen one since.

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This should show how to do it once it's opened up, but it's honestly really easy, I've done a valve change on it in 2.5 hours. That was the thing completely together, to apart, and using a piece of PVC to get the valve spring compressed, to fully together and running. It's that easy.

But, to get down to the cover, pull the tank(2 bolts on the front bottom left and right) and pull the seat to get to the rubber thing to pull the tank all the way. Then, just the two bolts on top. Don't bother with the side cover as this video shows www.youtube.com/watch?v=ga_apq9qDCI&app=desktop just do the top. Until you verify where the issue is or isn't at least. I'm wondering if it's possible your flywheel came loose and scraped on the stator and killed spark and made that grinding noise. But check the top first.

I just watched the beginning of that video. Honestly I watched a video on it like 5 years ago at least and haven't seen one since.

Thank you very much! I'll bring my feeler gauges home from work just in case one of the valves went out of whack for some reason and that's all that is causing this. It was making some extra noises at the party when it got super hot, so maybe that was a precursor to this happening.

That's very possible that the flywheel came loose, but it didn't appear so when I changed out the main drive sprocket (at least that I can remember). I guess that'd be a good excuse to change it over to a CDI setup from points haha. It seems that cam chain problems are pretty common with these engines, so I'm hoping it's just easy as putting a new one + sprockets in.

If it's looking like a serious issue I guess I'll be searching for a manual. Are there any free service manuals online for PDF download?

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Thank you very much! I'll bring my feeler gauges home from work just in case one of the valves went out of whack for some reason and that's all that is causing this. It was making some extra noises at the party when it got super hot, so maybe that was a precursor to this happening.

That's very possible that the flywheel came loose, but it didn't appear so when I changed out the main drive sprocket (at least that I can remember). I guess that'd be a good excuse to change it over to a CDI setup from points haha. It seems that cam chain problems are pretty common with these engines, so I'm hoping it's just easy as putting a new one + sprockets in.

If it's looking like a serious issue I guess I'll be searching for a manual. Are there any free service manuals online for PDF download?

No idea about the manual. I have one for the 03 style, really is the same for all years minus the body part stuff though. I have not opened it over the last 2 I have owned though. Last one someone put a drywall screw in instead of a idle screw.. Who knows why.

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Aluminum dust is covering the dipstick... I'm fairly confident that the cam chain tensioner gave up the ghost and the chain was smacking the engine case. Engine tear down this weekend after I get my big bike ready to hit the dunes next weekend.

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