Please help me out with which pistons to buy? Tight budget!

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Yamaha99MM700

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Jan 23, 2014
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So I had two piston skirts break a long while back and am just now about to buy new parts. The skirts broke after I went flying pretty high landing on hard packed snow/ice while still throttling.. this is my first sled so I was oblivious to this thump noise. Seemed to be running on 2 cylinders but I rode it home.. Compression was actually good on two of the cylinders even though 2 piston's skirts broke. Had to buy a new case due to a crack on the bottom. I also was pre-mixing and not using the oil pump (maybe that had something to do with it? It had a lot of miles on it. Cleaned the crank and it seems good.

I'm on a very low budget and there's not much winter left so I have a dilemma on what piston kits to buy.. I also have SLP triple pipes I wish to install as well.
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Here are my options:
OEM pistons with rings, pins, bearings, circlips:
Total = $330/ with gasket kit = $420
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Do I need to get new pins and bearings or can I keep the old ones?

OEM without pins or bearings = $250. $340 w/gasket kit

SPI piston kit w/gaskets = $227.00......w/ OEM piston ring set = $300

Wiseco piston kit w/gaskets = $327

Winderosa gasket kit = $90



I've actually heard really good things about SPI on other forums with people getting thousands of miles on them with no problems on high powered sleds. Too many cold seize stories about wiseco. I've also read somewhere here to run OEM rings on SPI. I read that for some of these brands you need to get your cylinders fitted to the piston.. I just can't afford that right now, I'd like to bolt them on and be good. Any and all help would be much appreciated! This is giving a newbie a headache! Thanks! I'm on an extremely tight budget..
 
Just a opinion a while back I bought some parts unlimited teflon coated pistons from dennis kirk never had any issues with them as far as gasket set I would bite for the cometic brand ones I think they are better quality. If your sled has a lot of miles I would get new bearings the new piston kits should come with pins
 
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I'd rather buy OEM, but I think I'm just gonna order the SPI.. And maybe OEM rings, maybe not. These are some expensive little things! I think these aftermarket pistons should do me good for at least the rest of this winter.. If I do buy OEM pistons, I need to buy everything separately, and am curious as to whether or not I need to buy new pins, and piston bearings (those alone like 80 bucks more) and is it absolutely necessary to replace my gaskets?
 
Don't cut corners with old gaskets, I think you'll regret it. As far as reusing pins and bearings, I personally don't think its a good idea. If you've already removed pistons and the wrist pins have zero sign of grooving, maybe you can get away with it, but the bearings could be worn though. You don't want piston wobble; there's a spec for rod side-to-side freeplay (0.8mm-1.0mm); I've not seen a spec for piston pin though. If you see signs of wear, best to replace. I just bought new pins/bearings/clips/piston/rings/gaskets for my XTC since I found a cracked skirt during top end inspection. My pins indeed grooved and I'm north of 4000 miles.
 
Don't throw in the towel just yet. See what some of the more senior member on here have to say. As what MrSled said, refer to MrViper. He knows his stuff. I know you're on a budget, but it's important to not look past seemingly obscure issues that could be problematic later.
 
Installing pipes aswell? Go Oem with new everything, if you do go another route make sure that sled is warmed up real good. Save a dollar now but, how many times do you want to take it apart?
 
Debating on just not putting the pipes in this season with these pistons, but I'm tempted to! From what I've gathered on non yamaha forums at least, SPI pistons seem to work out great for a lot of people, even in piped beasts getting thousands of miles with them. Maybe I will pipe it, and change to OEM next season as I would hope they would at least last me the rest of this winter haha. Still need to clean my carbs and various parts as this sled has been sitting almost two years. Change fluids, grease, etc. hopefully I can get some sledding in soon. Just that worry in the back of my head telling me something might go bad.. Getting snow dumped over here as I type this! Aargh
 
Snow here too man! Got most of my parts but pistons are still in the mail! Aaahhhh!!
 
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I ordered SPI pistons and Winderosa gasket kit, I had everything in 3 days and was back on the snow 5 days after losing a piston.

SPI appeared to be a good quality piston no issues yet- but only 175 miles on them.
 
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