XR250 BAD ticking. Timing chain or Decomp?

My 1989 xlr250 (same motor as 91-94 xr250L, etc) recently developed a bad ticking. Initially attributed it to valve clearance, and planned to adjust at next oil change. Anyway, It got progressively worse the last time I rode to the point of power loss on the last few miles home (I live up a ~2000 v. ft hill). Felt like 50% less torque. Barely made it back.

It wasnt SUPER loud at that point, but after I shut if off, looked over a few things and restarted I had to shut it down immediately because the noise was VERY VERY bad.

I put in a 280 kit last year, and noted that the timing chain was worn (wedge in tensioner was very low). I've ridden about 500-1000 or so miles since then.

I understand that sometimes these things can be caused by the decomp hitting/wearing out or w/e.

Perhaps the spring on the cam chain tensioner broke?

I should also note that I recently over heated the bike (left it idleing unattended for 20-30 mins, to the point of smoking from engine). I dont remember if it initially started ticking before or after that, but do remember it running just fine (or "normal" ie. how it ran before it over-heated) afterwards.

I have not pulled the valve cover off, but noticed some awfully metallic looking oil around the decomp (it has a light leak there).

I also heard that the chain/cam can rub the valve cover. What causes this?

Anyway, I am just looking for what I could possibly expect once I pull the cover off. Best way to describe the noise would be pulling a bicycle chain over a right-angle metal surface, but I may be biased since I'm leaning towards the timing chain being the problem.

Should I expect both of the plastic tensioners (i think they are plastic, right?) be totally trashed?

Anyway, thanks for any insight you can offer and I'll likely pull the valve cover soon.

My cam chain is also worn.first thought it was the tappets.but tappets were fine when i checked.on idle or very low revs sounded like a old tractor(like unadjusted tappets)but if you ride,the noise is not present on revs above idle.same power loss as you mentioned but not as drastic as yours.also ruled out oil not getting to head.checked cam chain worn out.you will have to replace cam chain,tensioner and guide together.while you have opened top cover.check cam bearing condition.change if worn.check rocker arms for wear and camshaft.

Also check head for warpage

If it over heated.

But ideally you bike doesnt have to overheat so quickly.

Could be faulty oil pump.

So i took it apart today. The main issue was due to the cam holder cylinder things (you know on either end) popping out, allowing the cam to literally come free from both its bearings. VERY HEAVY damage to the cam journal resulted. However, I got everything back together and it runs great, except for the still present moderate metallic click (Not the super bad one I was concerned with, but the initial noise that its been making for 1-2 hundred miles now). The cam chain was at some point, or perhaps currently is, rubbing the rocker box cover. The chain isnt super streched, and the tensioner appears to be mostly working as it should.

Any ideas why the chain would rub, if thats whats actually currently going on?

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