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I was riding my 2005 RM125 dirt bike the other day when it bogged down all of a sudden. I noticed the spark plug had backed out of the head, thus causing the stall. I pulled the spark plug all the way out and realized that the small bottom piece of the plug was missing. enter image description here

Evidently it had broken off inside the cylinder. I got the bike home and fished around in the spark plug hole with a magnet to try and retrieve the piece, but I couldn't find it. I even took the head off and fished around some more. I'm about to give up. Is it safe to crank the bike without making sure I find the little piece, or should I make sure and find it before riding again? I just don't want it to cause serious damage inside the engine.

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Either it's in there or it isn't. If you've taken the head off, you should see the top of the piston and know if it is there or not. You don't want to refire the thing without knowing if it is there or not. If it is in the cylinder it could rub on the side of the cylinder wall and cause damage. Scoring of the wall and damage to the piston are the two big issues here. I have seen a lot of times where small debris like this will get blown right out of the exhaust. Depending on whether the RM is a two stroke (they were when I was familiar with them) will probably make a difference.

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  • Yes it is a two stroke. I sure hope it was blown out the exhaust. So is there a way it could have slipped past the piston to lower parts of the engine? Bc I'm pretty sure it's not on top.
    – hgwhittle
    Dec 25, 2014 at 10:55
  • @hgwhittle ... It all depends on the shape of the piston and where the ports are for intake/exhaust. Don't be magnanimous about "if it's on top" or not. Either it is or it isn't. If you've taken the head off and the piece is not there, then it's not there. It most likely went out the exhaust. There is no way to my line of thinking it could get past the reed valve and into the crankcase, if that is your wondering. You could pull the exhaust pipe off and see if you can find it there. You can also drain your engine oil and see if it's there.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 25, 2014 at 12:04
  • Great tips, I'll check the exhaust and oil. Thanks for your help.
    – hgwhittle
    Dec 25, 2014 at 12:13
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    @hgwhittle ... Remember, too, if you took the head off, you'll need a new head gasket and possibly new head bolts (depending on whether these are torque to yield head bolts). Check on this with the dealer prior to assuming everything is peachie.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 25, 2014 at 12:15
  • The first thing I'd do is stick a magnet on a string or telescopic rod down the plug hole and see if it comes out with the missing piece attached. If it does, it saves you pulling the engine to pieces. If it doesn't, that doesn't mean it isn't in there but it could be a nice quick win if it works.
    – Steve Matthews
    Aug 16, 2016 at 10:44

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