250-500cc How many hours on a WR 300 piston?

I was counting on how many hours i have on my standard piston, and i came up to around 70 hours. My question is if anyone has cracked a piston caused by long running time. I also wonder where i can see on the cylinder which size my piston should have. Is there a stamp somewhere? I have great compression and the engine sounds perfect, but it would be intresting to know how many hours you guys have on your pistons!

Johnny:sweden:

I rode my 200xcw all summer, so my 300 only has 110 hrs on it (bought new in april). I'm planning to go 200 hrs before I worry about the top end. That has been fine for riding style and conditions on ktm 200 and 250 and 300's so far.

not sure bout hours, but ive been told bout 2500klms for the average rider. R n D husky even seen up to 3500klms

I changed mine after 75 hours, I cant really say how worn out the piston was but in my opinion it look like it was time for a change.
I very seldom rev my bike to the top but I´m not afraid to let the bike do the hard work in races if you understand what I mean.

I have 98 hours on mine. Great compression, run perfect.
I have checked it at 70 hours an it look like new. I will change it this winter for preventive. I think this engine is bulletproofs

At 55hrs mine had a lot of ware on the intake side of the piston from the intake port. I put it back in for now but had I had a new piston on the shelf I would have replaced it. I plan on changing it when things get really cold here probably Jan Feb. I just started riding racing in the woods but for mx on my yz's 40 hrs was the go to #. That was a lot of wide open stuff that you just don't see in the woods. But the ware at that amount of hrs does not seem that much different. Having said that when inspecting the piston that comes in the 300 if you look at the underside it has very strong webbing that supports the skirts. Because of that I'm sure you could extend the service interval due to the fact that it can probably handle more piston slap as the skirts ware. My opinion anyway.

Mine was wasted at 70hrs (I think it was 70hrs, anyway), but I believe the stock Mikuni was passing dirt. I put on a 7602 racing carb filter (and then transferred that to the Keihin I bought) and haven't noticed anything since.

FWIW, I wouldn't run a cast piston beyond one set of rings. Cast pistons like to shatter skirts without warning. I'll run a forged piston through 2-3 sets of rings before swapping it.

Here's what my OEM piston looked like


Rings were holding good still, but the intake window wore deep grooves into the piston. No way was I going to reinstall that.

PC that is the same as mine looked but I had a little more blowby showing. 55hrs about 10hrs mx the rest in the woods motule 800 50 to 1. Plenty of oil coverage when I took it apart. No signs of dirt I just think with that large an intake port its gonna ware like that.

I think the WR250 ports make the pistons not last a long time either. It's funny that the 125 can have 70 hours and look almost like new, at least mine did.

Ok,
So where are you getting your pistons?
I haven't found an aftermarket source for the 300 piston so I am assuming your going through your local dealer?

If so, what is the approximate cost for one of these?

Not trying to change the direction of the thread just trying to figure what and where I'll need to go when I need to replace mine.

It definitely looks like PC's new piston was not stock - ring pins are in different positions and the top is domed. Also the cutout for the wrist pin is different.

Got my new piston from Motosportz. Cant remember exactly how much it was...

That pic above shows my OEM WR300 piston on the left and a Gas Gas 300 piston on the right.

My Ex 02 250 CR never had a piston\ring change in over 6 yrs riding with many hrs in GPNF ... Not sure on the hours but it has to be well over 300 ... U should be well with in any tolerances changing it under 100 ...

These engines are not a 4T ...

I'm glad you posted that picture Brandon, when I had my reed valve off, the piston in my 250 looked like that, which I thought was eccessive for its hours. Guess I'll be getting some filters. I have them on the 450, but somehow forgot the WR.

Are you pretty well healed up?

Filter your fuel, keep a clean air filter is key. A nice warm up is very important. I laugh when guys start their bikes and rev the crap out if them. Watched a guy squeek his motor one morning. I just chuckled. Personally I like cast pistons and never had a problem getting 200+ hours. Fresh rings every 30 hours or so. Run good premix and proper jetting is very very important.

30 hrs? That would be weekly 4 me ..lol ...I wear my underwear longer than that ... U must be a contender? ...

I've always thought the same thing on starting a bike and I never REV mine much after starting but I went to a SX race once and guess what... the PRO guys would crank a bike a REV it hard ..these were the 4t machines ... I would never do my 4t like that either ...

Rings at 30 to error on the side of caution.
The pro guys also aren't paying for rebuilds. Lol

Also depends on how you ride. If your a lugger then you can go longer

HRC 630 here at the forum has done 100 hours on his 300 which is tuned to over 50bhp on the standard piston, and comp is unchanged=). And he rides it hard!

Yep that's what I was saying I change pistons at 200 and rings at about 30. I was trying to say your good at 200 ( with checks if course) unless you are constantly in the pipe and just beating the snot out if it.