This theme doesn't seem to have been dabated before too much, and knowledge and how to avoid engine problems are good to all of us.
Personally my sled has problems, and the problems came when I drove with faulty plugs. When I eventually changed new plugs the sled didn't become good again as before, so I am somewhat in the blue. But suspect the plugs had something to do with it.
After some diagnosis with trying differnt plugs++, I think it really is not a sparkplug problem, but engine damage, not what I hoped for.
When I run the engine on high rpm, then turn the key to off position, the engine still runs hard.
Sounds like the valve are unbalanced or some needle beerings are damaged? It sure is more vibrations there than what is good. It sounds harsh, metallic, sounds like there are some misfires..
And for information,, its a 90hp AC 440 motor, not the most rigid motors I have heard.
I have now demounted the jug and checked jugs and pistons. Here is how the jugs looked like in top:
The first two pics are from jug that was changed last year while the last pic is from the old jug.
Looks like fissures? Caused by what?
The pistons are some scuff on intake and exhaust, but not severe.
Also the engine has rare vibration, and some rattling...?
Even the smallest pieces of metal not cleaned out from the bottom of the engine can do this(after a major engine failure). I have heard some sled mechanics say that shaving away the head after its been bashed to pieces like this is the best way. If there is peices lodged in there, they could vibrate loose and run up and down with the piston again and re-pit it all.
The metal could be coming from anywhere, specially if you have a 'rare vibration'. Crank bearings, piston damage, wall damage, piston bearings at the top of the rod etc. Unless you tear it down, its hard to say. The piston bearings may have over heated and turned the rod into an oval shape at the top. My uncle's mx470 is like that, he needs new rods but didnt want to replace the crank, so we put it back together like that, and as i described it, it sounds like 'death' (but he still drives it locally, he needs the casings(all scored at the valve) and new pistons and bearings for it anyways, hehe)
its pretty obvious that there has been metal from somewhere has beating the crap outta it...
Last winter when I had the piston ring locating pin "disappear" causing the ring to rotate & snag the exhaust port, the head, cylinder & piston were trashed. I could've just replaced these parts. Instead I replaced the whole motor as it was 3 years old, had 7500 miles on it & I was planning on keeping the sled for @ least a couple more seasons.
However like steve6 has said w/o making sure the case was "clean", you don't know what is down there.
If the plug was just fouled, I can't see how that could cause engine damage. But if the insulator started to break up & bits of it were getting between the piston & head, yes that could cause damage.
Is the piston ring & or land intact? Anything embedded in the top of the piston?
Last week my buddy's '01 SRX w/ 24,000 klicks on it had the mag side ring break making a mess of the piston. Motor had never been apart. Mind you IMO, that's wayyyyyy too long to run a 2 stroke w/o freshening up things.
I'm just curious... why would you think metallic particles throughout everything would be caused by plugs? New plugs at that... faulty plugs simply don't run right. Something has to give to cause metallic particles throughout. I've experienced faulty plugs, new plugs always solve the problem... no metal particles.
Last year I had a plug burn up on me. Was WOT across farmfield and all off a sudden engine bogs. I let off the gas, nailed it again WOT full power then bogs again. The bog got worse and as I rolled to the end of the field i figured my engine was toasted. But sled idles on both cylinders! My buddy on MXZ is far ahead by now so I figure who cares this is an old sled I'l keep goin. From this point on anytime I give it more than half throttle it bogs, less than half it runs seemingly fine. I somehow make it over the hills to the next field where my friend is waiting for me. I wave him down and tell him I think I toasted a cylinder or something. We pull the plugs and one has nothing but the normal looking electrode left, the metal part at bottom that receives the spark from the electrode is completely gone. So we shine flashlight down both plug holes and from what we can see the pistons look just fine? I put brand new set of NGKs that I was carrying in and the sled runs great. I have had the same set of plugs in until last weekend before one fouled and i replaced them. I don't want to bash Champion but that was the brand I was running when this happened and I will not use them again. Maybe I got a bad plug. Maybe my sled doesn't like Champions. I don't know. It was a warm night about 34F and bare spots on the trails maybe thats why. I did quite a few more miles after I replaced them that night with no problems though.I was really worried about the metal from the plug that was missing seizing my cylinder but the sled runs great to this day. I guess it burned right up. Guess I am lucky. Weird huh.
I wish I saved that plug so I could get some pics of it but I threw it in disgust
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