Blown up 02 Mountain Max 700

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WhiskeyDoc

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Jan 12, 2015
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Montana
I just bought this 02 MM 700 from my buddy for $450 with 1009 miles on it. This is my first sled but I've been a motorcycle guy since I was 13.
I started tearing the motor apart and discovered the piston in cylinder 2 was completely obliterated. Any ideas on what caused this or has anyone seen this before? I don't want to rebuild it only to have it blow up again 2 weeks later. I'm also considering trying to delete the oil pump but am struggling to find a block off plate. Has anyone done this and do you have any advice? I'm used to pre mixing on dirt bikes anyway and feel that the extra effort could be worth the peace of mind. Feel free to chime in and any advice is greatly appreciated. Any suggestions for improvements while I have this thing all torn apart would also be awesome.
 

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the crank is junk in that one, I would bet when you get the engine out the crankcase will be cracked on the bottom as well, so about the only thing your gonna salvage from that engine is the other 2 good cylinders and pistons. Just find a good used engine and put in it.
 
Save what you can off that engine, pick up a used one, 98 plus but your going to want to swap over your ignition stuff for the later CDI box. Check you carbs, make sure their clean and just take it easy making sure jetting is good no air leaks then go flog it.
 
Agreed. That motor would cost more to fix, than the sled is worth. Find a good used one, and ask the guy if he has a seat, and whatever other parts have been Mickey Moused.
 
Could be broke a ring and seized the piston causing it to separate from the connecting rod thereby beating the poop out of that cyl. Cause? That is pretty unusual for a red head with 1000 mi. If it were me I would find a used motor.
 
Thanks for the input guys. I just ordered a used redhead on ebay. Has anyone done an oil pump delete on these and what are your opinions on switching to premixing? Feasible or no?
 
I would just leave it oil injected. From what I've heard....when the pump does go bad it just opens up and dumps alot of oil in. I've been running oil injected yamaha's for almost 30 years and never had a problem with the oil injection.
 
If you ask me removing oil injection is a huge step backwards on these sleds. Unless your racing or are going to be mixing your gas/oil externally it's more of a pain than it's worth with no reported record of problems with the system.


Go to the gas station and fill up then go $hit how much oil do I now add and it's not going to mix because it went in after the gas.
 
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I agree with previous posts. Yamaha oil injection has been around since the 60's. Problems are rare. It is true that 2 stroke oil is expensive, but you don't need to run powervalve oil. Any high quality oil would suffice and be economical in your 600 with the oil injection.
 
I would never mix it in the tank. I would measure it out and mix in a gas can. I just wanted to know if anyone had done this, if they had issues with the water pump getting lubricated, etc.
 
WhiskeyDoc said:
I would never mix it in the tank. I would measure it out and mix in a gas can. I just wanted to know if anyone had done this, if they had issues with the water pump getting lubricated, etc.
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Not sure about the redheads, but the SRX has oil fed to the bottom. Unless you're looking to shed every ounce of useless weight I'd leave the injection in place... it really is that reliable.
 
So I picked up a 98 redhead but the head doesn't have the extra nipple for the small coolant line and the small one on the water pump cover is missing as well. They appear to be minor updates, does anyone know is it worth swapping the head and water pump cover or is it not really that big of a deal?
 
Your going to want to swap those things over. Make sure your head is ok though.... The heated carbs was a great improvement. The heat prevents icing and adds stability to the intake system through temperature changes. Polaris and ski doo had heated carbs that you couldn't turn off, they were on all the time and most people didn't know it was there.
 
Is there anything else i need to swap over? The CDI has a different plug as well which I'll switch but other than the head and water pump cover should I be good?
 
WhiskeyDoc said:
So I picked up a 98 redhead but the head doesn't have the extra nipple for the small coolant line and the small one on the water pump cover is missing as well...
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Sounds like a 97, those ports were included on 98's.
 
So the 97 should still be good though right? The guy on ebay listed it as a 98. Can I just block off the heated carb lines and run them like traditional carbs with no issues? Or maybe reroute the coolant to run through them from somewhere beside the head? I don't want to get a new head just for the coolant port. I did switch the cdi though because the plugs were different.
 
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