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Discussion Starter · #1 ·
Hello,
I’m new to this website and am having trouble with my Rebel. A while back, we got the motorcycle and after an oil change and a quick tune-up it was good as new. My dad took it on rides daily, and one day the engine cut out. We checked the spark plugs, and there was the problem. One of the ends was dented because of debris in the engine. We rented a bore scope, checked in the engine, but couldn’t see far down enough. Not sure what to do now, any suggestions? Open to anything.
Thanks
 

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Welcome to the forum. What year and model Rebel do you have? Did you check the oil level with the bike level (not on side stand) dipstick unscrewed and just resting on the threads?
 

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I would most certainly verify that the plugs are correct type, that they appear physically the same, and that a crush washer was used on the offending plug on the offending side.

Following that I'd inspect the threads in the head for a previous repair. There could be a Time-sert (thread repair method, Google it)
That may have threaded in too far allowing the plug electrode to contact the piston.

If everything seems normal, just put 2 crush washers on that plug (to raise it up) and take it for a ride.
 

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you sai ddebris in engine, couldn't see far enough down, I personally would NOT start that engine until I was sure there was no debris in the cylinder, to do so could score the cylinder walls , piston, etc and the engine is now ready for MAJOR work, or scrap, there should be a way to cycle the engine and bring the piston to the top for a better inspection,
We will need year and model to help you do that
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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2005 would only be a 250 if it is a Rebel.
 
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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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On a few occasions throughout my life, I've either experienced or helped someone fix something that was deliberately done to cause a problem with a vehicle. IE: spark wires moved/disconnected so vehicle wouldn't start.
Was he parked in a public place, slightly out of the way of normal foot traffic when this problem cropped up?
 

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Discussion Starter · #9 ·
On a few occasions throughout my life, I've either experienced or helped someone fix something that was deliberately done to cause a problem with a vehicle. IE: spark wires moved/disconnected so vehicle wouldn't start.
Was he parked in a public place, slightly out of the way of normal foot traffic when this problem cropped up?
It’s a manual, and no it wasn’t. It’s been kept in my garage so I could work on it whenever
 

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Good! I'm trying to figure out what could cause this. Can you lift the rear wheel off the ground, then pull the left side plug on alternator side the engine. Carefully, slowly & gently, turn the engine over with the spark plugs out & see if you feel it impacting on something. DO NOT CONTINUE if any resistance is felt. Then more testing can be done afterwards.
 

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I agree. Turn the engine over with a socket and ratchet from the left side, and bring each piston up to top dead center. If you still have the bore scope you should be able to clearly see the top of the piston at TDC. Look for debris on top of the piston where you had the bent plug, and also for damage to the top of the piston. I don't see how any foreign debris could get into the cylinder. It could be something that was already in there, like a broken valve, but since you said you just gave it a tune up, I suspect that the plug on the cylinder with the bent plug may have been the wrong one, and too long. Is it just the side electrode that's bent, or did it also break the insulator around the center electrode? If the engine will turn over with the starter with the plugs out, I'd do a compression test, and compare the reading of both cylinders.
 

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something that was already in there, like a broken valve, but since you said you just gave it a tune up, I suspect that the plug on the cylinder with the bent plug may have been the wrong one, and too long.
My thoughts too on the valve. But, did you have the tune up done, or did you do it yourself? If the plugs were replaced, are they the same as the previous ones?
 

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Discussion Starter · #13 ·
My thoughts too on the valve. But, did you have the tune up done, or did you do it yourself? If the plugs were replaced, are they the same as the previous ones?
Only the electrode was damaged. It looked like it was hit with something because there was a gash about a centimeter in the top of the electrode
 

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What's the code number on the side of the spark plug? We're trying to figure out if they are the right ones.
 

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Only the electrode was damaged. It looked like it was hit with something because there was a gash about a centimeter in the top of the electrode
Can you please post a picture of the damaged spark plug?
 

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Only the electrode was damaged. It looked like it was hit with something because there was a gash about a centimeter in the top of the electrode
Did you inspect the plug prior, like cleaning them ? Could have been damaged before and installed that way.
 

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The top of the piston would not leave a gash in the electrode. It would have just smashed it flat. If the plug stuck too fan in, it could have made a hole in the top of the piston. But I went back and read your original post, and apparently it was running fine for some after you replaced the plugs before this happened. So that pretty much rules out the plugs being too long. If a plug was too long, it would have hit the piston as soon as you tried to start it. The only way a foreign object could have gotten into the cylinder would have been through the spark plug hole, while you had the plug out. And even if that had happened, the damage would likely have occurred right away. Besides the piston, the only other things in the cylinder are the valves. I've never had a Rebel engine head off, and don't know how close the valves come to the plug. One thing I thought of is, did you adjust the valves during the tune up? If you did, is there a possibility that you didn't tighten all the locknuts down good, and one of them could have come loose, allowing the valve adjustment to change and the valve to stick down too far into the cylinder? It might be a good idea to remove the cam cover and check the valves. Just grasping at straws here, but if the end of the plug was smashed it had to have been hit by a physical object, and there just aren't that many of those in the cylinder, and none of them could have hit the plug if they were all in their proper places.
 
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