I am needing the specs for my 98 express 300 two stroke. I need the piston to bore clearance, ring gap. Anyone help? I need some SOLID specs here, not I think it should be this or that. If anyone could help I would be GREATLY appreciative. Thanks!

 

. 002 MAX piston to cyl clearance after honing! Ring end gap should be .010 to .012
Be sure to add oil to gas tank for break-in (about 50-1 ratio) to amount of gas.
Just rebored a 300 Explorer (.0015) at the shop,topped off gas,added oil (runs very
good) Others will give their recommendations, but mine is from boring a lot of jugs!
boring 2 and 4 strokes for 22 years. Clearance more than .002 on the old 300 just looses
length of time on the top end since max service limit is .005 clearance(shirt breakage
usually happens between .006-.008,that is IF it makes it that far! OPT

 

Thank you sir, I do greatly appreciate it. The oil pump has been deleted while I had the bottom end apart as I could not get it to stop leaking oil everywhere, so after the initial 50:1 break in what ya think I out to mix it at? Thanks again

 

Keep it at 50-1 if riding NORMAL or 40-1 ratio if running hard. OPT
We only premix higher (around 36-1) on hi performance machines such as our KTM 2-strokes.

 

Once again I do greatly appreciate your input. I have done alot of reading in this polaris section and your a great asset to this forum!

 

I just rebuilt my 300 with a WSM piston. It ran great for two weekends and then seized up. This was pretty rough, extreme riding though! I don't know what the bore clearance was, but I premix without an oilpump as well due to previous owner removing. I was running it 50:1, but this go around I am planning to mix 32:1 and get the jet a little larger by a few thousandths. I read somewhere that if premixing, the jet needs to be a little larger so I'm going to try it. Any truth to that OPT? Thanks

 

WSM is a good piston,but like you say what was the clearance? If larger could have caused problems,PLUS slow to medium break-in if bored tight to make it last is crucial!!!. 2 weeks a little lame! Plus a lot of variables too:crank seals,lower end rod bearing or worn crank bearings? They can take a new top end out!
You could go up one jet size,BUT not critical if every thing else ok! Check for air leaks,rough feeling crank,knotchy rod play or play up and down on rod,EVEN minimal play etc.If seizure on exhaust side,usually lean condition (air leak,crank seals,jetting etc)if on intake side usually a lubrication problem. Since I'm not there I have to guess!!! OPT

 

OTP,

The seizure did happen on the exhaust side. I think I'm going to jet up a little .155 to .160 to fatten up the mixture a little. The needle valve in the carb was in the next to lowest position on the valve, so could that lean the mixture out as well? The crank seals are new and the bottom bearings seem pretty tight.

This was my first polaris so I just thought it was slow, but when I pulled the engine back out I noticed the drive clutch was stuck! One of the ramp buttons came loose (broke screw) and was stuck, so I assume that was my power problem. Like it was kinda bogging down, with pretty good drag. Could this have contributed to the failure?

What should I do for breaking the engine in, instead of breaking it? This was my first 2 stroke build and I was listening to the local folks that used to race 2 strokes, "crank it and blast it". I don' think that worked to well on the polaris!

Thanks for the help! John

 

If you are talking about the rear clutch ramp buttons,then yes it could affect power,even front clutch can too.Dont think this could have affected seizure, number of problems for seizure to happen,BUT if rebuilding trust someone who knows what they are doing.Like I posted earlier .002 MAX on bore and hone finish!! This fairly tight and has to be broken in properly,bring engine to operating temp then shut off!! Let cool,then ride machine moderately,NO wide open long runs,you can "blip" the throttle every now and then in breaking in,you dont have to baby it,but you have to take it easy for about the first 2 hours. Try one size larger main jet,needle clip 3rd down from top. OPT

 

Cool, thanks for the help!