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XR600 cam chain tensioner failure - why lack of compression?

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My 96 XR600R (with a 630 kit if that matters) started running rough as guts, acting like a fouled plug or something, then quit and wouldn't restart. Kickstart jammed after about 20 kicks so I pulled the motor and the head and found the cam chain had jammed a couple of links super hard. So obviously the tensioner has failed but my real question is why had it dropped compression? By that I mean before I pulled the engine I could push the bike forward in gear. Could it have skipped a gear and the valve timing be out?

I found a piece of cast metal sitting on top of the pistion, which itself was in pretty bad shape. There's some fairly nasty scoring of the bore but nothing that could have let the piece of metal through, likewise bottom of valves are pretty chunked up but not broken as such.

I'll upload some photos tomorrow when I get to work.

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Bent valves are a good possibility.

A very good possibility if not a certainty.

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Thanks for the replies all. It's definitely steel - I finally got around to getting the photos off my camera. Although it looks like the piece in question has gouged the piston crown there, I'd just put it back down to take the photo. You can see what it's done to the valve recesses in the piston.

The thing that's messing with my head is it looks like no other metal I can see anywhere. My next guess is that it was foreign matter that got in at the last valve adjustment and managed to jam open a valve? That'd explain the lack of compression, and maybe even why the cam chain jammed.

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How do the CamchainTensioner guides look..Last time I had a chain looking like that was because one of the holding tabs had given way allowing too much slack,,thus,,jammed chain.,,,Pretty solid looking bit of metal to have come from the Choke butterfly,,Plug looks hell lean as well.,maybe that's a trick of the light.

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When did you notice the easy push symtom? Before or after you kicked the crap out of it and jammed the starter? I cant think of any reason why that would break something between the clutch and gears, but you may want to crack it open and look. Not just because of that, but there may be other mystery metal pieces below the piston.

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Brian, you were spot on mate.

IMG_1755.jpg

So the piece of choke flap has broken off and jammed one of the intake valves open causing lack of compression. I'm guessing that also caused the cam chain to tension and jam. Oh well, at least it's mystery solved. Should I replace it with an OE choke flap?

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:bonk:

NOW ...who said i was wrong and that piece was NOT from the choke..:lol::lol::lol:

I say this to him

:smirk:

:lol:

Well anyway.........poor design..cast metal is not good for this piece,,it`s destroyed many top ends.....i`ve seen this numorous times..

B

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Brian, you were spot on mate.

Should I replace it with an OE choke flap?

Oh.........big NO on OE choke plate...get an aftermarket one or risk a repeat.....XR`s Only has a billet replacement...somebody else prob makes them too.........

Cast metal is brittle,will not take vibrations well,,,,

B

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:bonk:

NOW ...who said i was wrong and that piece was NOT from the choke..:lol::lol::lol:

I say this to him

:smirk:

:lol:

Well anyway.........poor design..cast metal is not good for this piece,,it`s destroyed many top ends.....i`ve seen this numorous times..

B

Yes Yes you were correct,,,I thought it was the small alloy flap that generally gave way,,photo says otherwise..,Suppose I'd better do something about mine before the same thing happens ,,Might remove it entirely as I don't need choke to start my bike.,.

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Yes Yes you were correct,,,Suppose I'd better do something about mine before the same thing happens ,,Might remove it entirely as I don't need choke to start my bike.,.

:bonk::smirk::lol:

yup,removing it is the other alternative,,,but putting a billet one in is fairly cheap,,nice to have in cooler weather..

B

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:bonk::smirk::lol:

yup,removing it is the other alternative,,,but putting a billet one in is fairly cheap,,nice to have in cooler weather..

B

Few people make there own ,,seen a few threads around here or somewhere else about making one,,I'll consider options..

http://www.thumpertalk.com/forum/showthread.php?t=848857&highlight=choke+plate

Similar deal but 650r I think,,whoops,,,600 and 650.,

Edited by Horri

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Beauty, thanks for that info. Makes a lot of sense to go with an aftermarket billet one. Anyone reading this, REPLACE YOURS NOW NOT LATER!! I miss having my XR on the road and due to $$$ it'll probably sit in the garage for a couple of months.

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Few people make there own ,,seen a few threads around here or somewhere else about making one,,I'll consider options..

http://www.thumpertalk.com/forum/showthread.php?t=848857&highlight=choke+plate

Similar deal but 650r I think,,whoops,,,600 and 650.,

Wouldn`t be a big deal to make your own Horri....you chicken wire everything together anyway,,,this should be easy:lol::bonk:

:smirk:

B

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Beauty, thanks for that info. Makes a lot of sense to go with an aftermarket billet one. Anyone reading this, REPLACE YOURS NOW NOT LATER!! I miss having my XR on the road and due to $$$ it'll probably sit in the garage for a couple of months.

That sucks,,sucks big time......i`d be a little pissed if it caused me to have downtime...oh well.do what i used to when i needed something when i had no money,,sell off some crap i wasn`t using....then fix the bike,,and buy new stuff that you sold off later when you can afford it.....more important to ride than eat for me when i was younger:smirk:

B

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I've been running for the last few years with no choke at all. Yes, if the bike is cold soaked down to freezing it can be a bit of a challenge to get going.

On a different subject I'm not sure how the debris in the combustion chamber could cause issues with the cam chain. Not saying that it couldn't happen, but I just have a difficult time visualizing how it could happen. You might have had a worn out tensioner at the time the choke plate decided to let go.

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I just let XRs Only soak me for the plate and 10 dollars shipping. But, i have put things off and suffered in the past. A while back i was reading a thread about proper tire pressure and on the next ride i got a flat becuase it was too low. I was reading one this past week about clutches and mine started slipping. Now choke plates!?!?!

So, i better play it safe and get it in the mail.

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