lost the gap on the plug --700 twin mtmax

[CB Rob]

A friend called me for my advice on his 98 yami. It was running like crap so he took it to the shop for a checkup, shop says compression is down a little from being an old sled and says they see nothing wrong. It runs like crap after getting it back from the shop, so my friend checks the plugs. One of the plugs has no gap, and he hopes it was juct a case of the mechanic dropping a plug. He regaps the plug and gets the motor to run rough, then it dies again. Plug is ungapped again.
I'm guessing the only thing that is squishing the plug is the top of the piston. Is it possible that carbon could build up so thick that it hammers the spark plug? or is it a bad top or bottom rod bearing?......

 

[alrevedup]

Rob, I am no mechanic. Couldnt it just be the wrong plug in the machine. A plug that is too long could surely get hit by the piston.

Good luck

 

[CB Rob]

Rob, I am no mechanic. Couldnt it just be the wrong plug in the machine. A plug that is too long could surely get hit by the piston.

Good luck

I was hopeing that was the case, but its the same plug thats always been there, and same as the other cylinder. br9es I think

 

[ruffryder]

regap the plug then turn the motor over slowly using the primary and hear/feel for a slight impact. When in doubt it is probably best to pull the head and take a closer look at things.

 

[pgsledder]

You've got a bigger problem than the plug
The sled should be a triple, not a twin.
Your missing a cylinder. lol

 

[CB Rob]

You've got a bigger problem than the plug
The sled should be a triple, not a twin.
Your missing a cylinder. lol

hmmmm, maybe its a 600. its definately a twin

 

[pgsledder]

hmmmm, maybe its a 600. its definately a twin

Then why would it say 700 the title?

 

[Lt Rascal]

You've got a bigger problem than the plug
The sled should be a triple, not a twin.
Your missing a cylinder. lol

HaHaHaHa Good one.

I would check the connecting rod. The needle bearing or the crank bearing mite be gone allowing the piston to travel to high and hit the plug.

 

[CB Rob]

Then why would it say 700 the title?

I was just assuming it was a 700 because he used to out climb my polaris 700with it. He uses it for a daily short trip commuter sled, about a mile twice a day. thats what has me hoping its just carbon. I hear about outboard motors having carbon issues, and I think I've even seen decarbonizer for sale at marinas

 

[CB Rob]

I was picturing the head- dome -squish on my old polaris, and i dont think it would be possible for the piston dome to reach the plug, I think it would get stopped at the squish ban first. I think there has to be some carbon built up higher than the piston top for the piston to be able to reach the plug.

 

[CB Rob]

found a thread

I found this thread
http://snowest.com/forum/showthread.php?t=48883&highlight=bent+plug

It sounds like my friends case is either a piece of ring or skirt bouncing around, or some carbon chunks that came loose and bounced. I would be surprised if it was detonation due to being an old sled and at high altitude.

If he pulls the head and does not see any metallic looking damage he might be ok to just clean the pistons up.

 

[SRXtreme]

I was just assuming it was a 700 because he used to out climb my polaris 700with it

LOL now thats funny I don't care who you are. I have a twin with a tonne of mods, it's a great sled but that twin is a pice of junk!!! I mean JUNK!!!!. Like was said above it is probably a wrist pin bearing, rod bearing or the ring spun and broke off. Pull it apart and take a look see.................SRXtreme

 

[geno]

SRXtreme, junk by Yami standards, best motor ever, by BRP standards. lol, all how ya look at it.

 

[Linc]

HaHaHaHa Good one.

I would check the connecting rod. The needle bearing or the crank bearing mite be gone allowing the piston to travel to high and hit the plug.

That's it right there!!!

 

[Givemeaboost]

I would think that if the pin or rod bearing was the problem that it would be farther away from the head as it comes to the top because the compression woud be pushing it down against whatever is still holding it together. These second generation 600 twins did have their share of crank and piston failures.

 

[Linc]

It's bits and pieces of the main bearing cage or the thrust washer from the big end bearing.

 

[0007]

What you do on saturday night in the back yard is turn the motor over so the suspected cylinder goes just past TDC (use a screw driver) then if you can push the piston back down a smidge without the crank turning
You need a crank
If it's a 700 tripple then there is probably pieces of the cases in the bellypan already

 

[CB Rob]

it happened

Well, it took another 30 or 40 miles, but it happened. The crankshaft has come through the side of the motor. Keep your eyes out for a 700, no I mean 600 twin for sale.

 

[BOOST]

First if its a 98 700 it will be a triple. Anyway the piston shirt is breaking off and pieces are working there way on top the piston and flattening the gap. Ya theres not gonna be a cheap fix. If its at that point the pot will need to be redone and a set of pistons as well. Had the same thing happen, good luck.

 

[IDsledding]

Gap?

I had the same problem with my wifes 98 MM 600. The gap kept tapping closed. The piston skirt on the bottom of the piston had broken off and worked it's way through the transfer ports to the top. The pieces tapped the gap closed and then spit out through the exhaust port. When we would look in the motor, the wash looked good and didn't see any damage. We rode it for 3 weekends before one of the pieces wedged in the plug electrode so we could see what was going on. Look in the mod postings under "bad pistons". Someone else had the same problem.