the machine shop i talked to said i should start with a piston 10 over. they said i should ask for the finished size as a reference point and wanted the piston so they could make a proper fit. they said something about if the cylinder was made out of a nickel alloy that it can't be bored just cleaned up and new piston put in. is a 1988 250 engine from a trail boss able to be bored. i believe it is but need to confirm it before i order new parts.

thank you

 

i forgot to add in my previous post that when i removed the cylinder i found that the tube that runs from the oil pump to the carb intake manifold was broken. this tells me that the oil was not mixing with the gas. i've been told that a 2 cycle will seize up quickly if there isn't any oil in the gas. the cylinder wall looked good and the piston wasn't scared , just a few scratches. i haven't pull off the recoil or the clutch cover yet but i ordered new seals and will change them while i'm working on it.

 

Well I can`t tell you what the cylinder walls are made of but I can tell you I have had in the past a jug bored 20 thou or .5mm over sized to reround the cylinder and the ports chamfered. also had the jug honed on a different one. I had a 90 trail boss 250 as well as a 92. the machine shop I dealt with had no problems doing the job. These jugs are sleeved if you want to go that route order a sleeve and have it put in

 

i ordered a top end rebuilt kit for my Polaris from mfgsupply.com early last week, they took my order and the next day set me an e mail saying the part was on back order and should be there in 3 to 5 work days. yesterday they called and said the manufacturer said they didn't know when they could ship and they had it on back order since July. why they couldn't tell me this when i ordered is beyond me. i ended up ordering it from bike bandit and they are supposed to ship it today. my cylinder was out of round 7 one thousands so i'm going 20 over. how do you tork the cylinder to the crank case with the limited amount of space? i'm trying to do this without removing the motor from the bike, but will if i have too.

 

What I do is use the torque wrench on the 2 nuts that I`m able to reach. lets say my wrenches are 6" long, I set the torque wrench at specified LBS and hold it about the same distance as my wrenches are long making a mental picture the amount of torque required to set the nut in the required steps. Then with an open ended wrench I use it on the 2 nuts refocusing on the mental picture I had from the pressure from the torque wrench. Once the jug is torqued to the crank I use the wrench on the nuts that had the torque wrench on and compare there tightness. While doing this I try my best not to move the properly set nuts but to be able to compare you will a little bit and make sure the wrenched nut are set the same.
Its easy to do just follow the steps if the job ends up within a pound or 2 I don`t think that will hurt anything just try to focus on setting them the same.

 

Min torque on the cyl base bolts is 25 ft-lbs. I had 6" wrenches also. What I did was borrow one of those weight scales that you can hang things from that went to 50 lbs. (I don't have it with me now to describe better).

Hooked that to the end of the wrench, pulled it through to just over 50 lbs. (because the wrench is 1/2 foot)

Kept it around for a few days as the initial part of break in procedure wants you to re-torque after running the engine a bit.

 

OK now for a depressing update. i replaced the piston with one over 20. had the cylinder bored and honed to fit the piston. rebuilt the carb. replaced the crank seals on both sides. new filter and lines. made sure the gas cap was vented and clear checked the pitcock on the tank to make sure it's operable. put 3 gallons of gas in it mixed with 2 cycle oil for 40 to 1. checked the spark and compression (120 lbs). i torqued the cylinder base to 49 pounds and the head to 25 lbs. it fired up and dies. a couple more tries only produced a couple of back fires. what am i doing wrong? it's behaving just like it was before i started.

 

Could it be possible that the exhaust is full of gas? sounds like you done everything correctly. Long shot here but unhook the exhaust and see if it will start and run Now i`m thinking it can`t breath.

 

in addition to what Randy suggests, re-check the basics, such as the carb settings. And make sure the carb is positioned properly and mechanically working right.

Also, even though you replaced the seals, might want to doublecheck that the crankcase is in fact sealed and not leaking -- and also check other sources of leaking, eg the intake boot.

 

pulled the carb and cleaned again. found nothing to suggest the carb isn't working correctly. with the throttle open and my hand over the carb intake it is sucking air in. pulled the spark plug, finger over the spark plug hole throttle open it pushes my finger off. checked the pit **** and the gas line they are working. put the spark plug wire on the spark plug and layed it against the cylinder and turned it over the spark appeared strong and steady. the plug was just slightly damp (NGK BR8ES). i looked the case over real close and didn't find any cracks or damage. checked the head also. i took the carb boot off and cleaned it and didn't find any damage to it. don't have a way to do a leak down test but that will be my next consideration i guess.

one of my problems may be that i don't know how to correctly adjust the pilot valve. i tried to get it all the way closed and without much slack in the cable have it open as much as possible. the throttle is closed with just a little slack at the thumb lever. i left it closed and opened the pilot when trying to start.