few pic's of the bike's first rebuil at 140 hours, could have easily gone another 60 without touching the engine, one ring (top) was just out of spec, and the gouging pin had a very very slight groove on it (only just notesable with my fingernail), piston still in spec with very minimal blow by and little carbon build up on the piston and none on the head, just cleaned the cylinder with a scotch brite pad and installed the new piston, rings, gouging pin and wrist pin bearing.

40:1 oil mix with motorex cross power 2t





there are some minor scratches an what not on the piston which were done after i removed it and had it floating around the shed.







next rebuild will be at 350 hours looking at this.

nice! same situation i experienced with my 05 300, so i plan on getting a lot out of the 09 before needing a top end.
Joe

Thanx for the info!I've been wondering about life for a top end.

your piston looks very very rich.huge piston wash there.that is also why your head is so clean,rich jetting.

a little jetting work and there are some ponies to be found in that motor.

cj

not rich jetting, the bikes jetting very cleanly, no load up when idleing, no spluttering, no 4 strokeing, no spooge and little smoke, gone from a 165 to a 160 main, 40 to a 38 pilot, lowered the needle two clips and opened the air screw 3/4 of a turn from the stock jetting.

my best guess for the carbon on the piston is a lot of single track along with KTM's poor squish band.

ttoks, good pics and info. After doing my 2008 200 rings at 50 hours ( both rings out of spec) and doing the piston and rings at 100hours (both just a touch out of spec) I would have guessed the 300s would be due rings at least at 100 hours. It just goes to show the larger bore KTMs 2strokes really do have good longevity.

Your piston does look well washed which indicates rich jetting but you do have a crisply jetted 300 (Ive ridden it) Your comments about standard squish and ST is probably right.

I have reduced my squish to .9mm (.035) and run my 200 jetting on the leanish side, I run 40:1 Motul 710. As a comparison, this is how my piston top looked at 100 hours

when are you and your boy gonna head up here again? got some good track's for ya's to try.

That's crazy how many hours these 300's go on a top end. What does the manual recommend?

With the amount of riding I do (did) 140hrs would be 3 seasons of riding.

Great pics , good info i was wondering how long my 09 300 would go before i need to put in top end. Only have 20 hrs on her , got a long way to go. Thanks

Dirty Sanchez said:

that was 5 months worth for me :ride:

What piston did you go with for the rebuild? and what did it cost you for the complete top end kit in AUD?

riles said:

While semi-true riding style has a lot more to do with it. I know of several guys that I race with that ride 300's and they can't get even 60 hours out of their top ends.

Well my hour meter says 64 hours, and I probley have 20-30 hours before I bought the meter.

My pipe cracked on me near the cyclinder yesterday, I took it off to bring to a friends house to get welded back up, I looked at the piston in the cyclinder and
it looks good. nice and clean on the side, no scratches, rings look well... like rings, they arn't stuck or anything, and theres no blow by passing the rings yet, I.E. the side of the piston looks clean.

Cyclinder looks good, no marks, top of the piston looks a little black but nothing much. so I am wondering if I should be thinking about changing the piston and rings soon or not.

90 hours on it and it looks fine. still starts nice and idles well, decent power still.

Plug looks black with a hint of brown on it (I know. rich, lots of oil) and I do alot of trail riding in a tall gear bogging it along as I go. (I have never fouled a plug yet)

Thinking wait till I have 150 hours on it before I replace the piston.. What do you guys think?

mtman said:

the only way i see riding style causing such short top end life on a 300 is if the guys riding them are pro and reving the buggery out of them everywhere, they're ridden flat out on wide open fire trails everywhere, or as soon as the piston is a thou bigger then the tock size these guys are replacing them, i do a lot of differant riding, fair share of MX, wide open fire trails, and long (as in 2 miles long) sandy hill climbs with single track mixed in between, she see';s her fair share of rev's and high load and still has plenty left in it.

that or they've been running to little or poor quality oil.

my 09 300 has 75hrs and 1300 miles. it is reading only 135 psi. according to the shop it needs a new top end. sounds early from the other 300 rebuild stories im hearing.

I'm thinking for under a couple hundred bucks for a new OEM piston, rings, C clips, wrist pin, and gaskets it probably best to just bite the bullet and do the whole job at so many hours whether it "needs it" or not. I might change my mind since the hours seem to be adding up pretty fast. If I did a rebuild at 80 hours it would probably be 3 or 4 times a year:ride::bonk::lol: