Last night i took my carbs off the ski-doo to look for piston scuffing and sure enough i found it. I went out and bought myself a compression tester to only find out i only have a 100lbs of compresions in each cylinder. The machine is a 2003 mxz 380 with 1700miles on it I am not happy with the idea of already having to replace the pistons but i have no choice. I was thinking about putting wiseco pistons in my machine because they are forged pistons but one mechanic told me he installed 4 different machines and 2 come back with problems and 2 are still working fine. Can any one tell me if they are good.
if you have scores on the intake, you most likely did not have good enough filtration and dusted it, or got a little too hot. I used to always see scoring on the exaust side of my dirtbike piston. Never the intake side. But i always hear of it on snowmachines, not dirtbikes, so it may be something to do with the cold too.
I like using Wiseco, they mke good pistons. The clearance between the cylinder and piston must be a little larger for forged pistons becasue they expand to a larger size than cast pistons. New pistons in a good used cylinder usually do great, casue you get athat little bit of clearance without haveing to resleeve of bore.
The nikasil sleeves cant be bored, so re-sleeving is the only option for a new cylinder , or a whole new cylinder head with stock piston diameter.
Your pistons would probably last a lot more miles. A new set of rings with a little crossahatch effect on the cylinder wall would mostl ikely bring your compression up. Rings create compression. If you get your stock or higher compression back, im sure you WILL notice an increase in power from where you are now.
If your pistons are scored, then your cylinder is probably just as bad. So either go and buy all new parts, or throw a set of wiseco's and rings with a little cylinder preparation and youll be good to go. Check main and rod bearing while your at it too. Might as well.
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97 MXZ 670 outfitted with a 136", 2" track, 8 tooth finals, and aluminum tunnel extension.
Just a little info for you. The nickasil bores can be bored and re- plated. I have done this on my 03 REV 800 so I could replace the stock pistons with some two ring Pro-X pistons as this seems to be the fix for this model. I had mine re-plated by Langcourt and would NOT use them again as I had problems with their plating/clearence caused the engine to seize again, they did not clearence them right (they were to have made the clearence .006 and when checked after the fact it was only .004). I guess it was my fault for not checking it more careful. They then repaired the cylinder and were told to set the clearence at .0065 and when we checked it the clearence varied from .006 to .010. Enough said.
unclemd, I had the same 368cc in my 2000formula S and the compression is never over 140, so yours is marginal. The scoring in these motors comes from too short warmup time in my experience.. I let mine run 1/4 throttle for about 10 minutes on trail before hammering it in the ditch or drag.. The ring job is a good idea, and stock pistons (cast) will save you some bucks and in a small carb engine like ours we don't need forged pistons. The Forging process dissipates heat more evenly in high compression and big slug engines, which we don't have. Save your $, I say and ride the thing hard!
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