You guys recommend OEM pistons?

oem quality and machining tolerances are always great you can count on them.

Nothing wrong with

oem
pro x (same as oem made in same oem factory in japan but to pro x specs)
wossner (best forged pistons in the world)
vertex great cast pistons fancy coatings but i think only come in one size A

i find wiseco is hit and miss in its sizing on 2 strokes and thats dangerous with forged pistons. when i buy forged i go wossner

I like oem and pro x because they are cast, inexpensive and come in ABCD sizes to match the wear of the cylinder as the hours go up.

Wossner are the best forged pistons on the planet, german made and made well, also come in ABCD sizes for proper fitment.


a hot setup in the yz250 is the 808 racers choice wiseco piston for the 2003+ yz250 its single ring and lighter it frees up the revs and makes more power. this is the same piston carmichael ran in his factory rm250 back in the day.

All said and done I would still go with a oem prox or wossner dual ring rm250 piston for the longer wear intervals

I agree with everything mentioned above. I would also like to add, that if for some reason you can't find a Wossner piston kit, Athena rebadges Wossners pistons and sells them under their name here in the US. The Athena pistons are the exact same as the Wossners in everyway.

http://www.partsgiant.com/p325816-athena-forged-piston?r=b-32184&r=c-23…

FWIW, I have done some comparisons between Pro-X and OEM parts, and I can't find any differences.

Date codes, Manufacture markings, everything is the same on both parts. I would bet Pro-X buys exactly the same part from the same OEM supplier and just packages it and sells it for cheaper.

JD sells a very nice kit for the guy that doesn't want to experiment. You will not get what is listed in the kit that you linked. you get 2 needles and I believe 2 pilots and 2 main jets. His blue needle you will more than likely not use anyway. For the $75 that you will spend on the kit I could list a bunch of needles and jetting combos that will be useful to you for less. The OEM Suzuki and Yamaha needles that I would recommend run between $11--$13 apiece. Aftermarket pilot and main jets are very cheap as well.

Jeffro, did you pick up another RM?

Good looking scooter, congrats!

Best mod for the 05 rm250 is a carb manifold and reed spacer from a yz250.

Fmf factory fatty with the stock silencer rips also.

I cant disagree with him, its the setup i ran LOL

05rm250,
yz intake setup
full varner motor,
fmf factory
stock silencer
applied clamps
hinson everything
arc axis perch (discontinued)

hands down fastest 250 2 stroke i ever owned. Im in the process of trying to make my yz250 anything close to what my rm250 was like

I'll throw in my two cents here. I have used plenty of Pro-X pistons in many top end services on both 2-stroke and 4-stroke engines with zero problems. I was told by the Pro-X guy many years ago at Loretta Lynns that their pistons are the exact parts that the OEMs supply, as they get their inventory from the same suppliers as the OEMs. I was working for an OEM at the time and literally took new parts to his display area to compare them and much to my surprise, they were identical to the OEM parts I took up there. As a result, I was brand loyal for many years.

A couple of years ago (February 2014), I did a complete engine rebuild on a customer's YZ85 and used a Pro-X piston. When I opened the box, I noticed that the piston I received was not the same as the OEM piston I was removing. The Pro-X piston was lighter and the skirts were thinner than the OEM piston. I also noticed that this particular piston had "PRO_X" molded into the inner wall of the piston rather that "ART". ART Metal Manufacturing Company manufactures many of the OEMs pistons. It was obvious that this was an entirely different part. I measured it to be sure that it wasn't a mispackaged part for another model of bike, but dimensionally it was fine. The bike ran for only a few hours and the exhaust skirt broke off. I took care of the repair for my customer and contacted my supplier who informed me that Pro-X was distributed by Wiseco here in the US. So, I contacted Wiseco looking for some allowance for the failed part. What I received was one excuse after another as to why it was not a part failure, but a problem that occurred resulting from incorrect engine build procedures. Everything he threw at me, I had the correct answer for. His solution was to sell me another piston. I wasn't happy with the end result, but that's where it ended. By the way, I've been working on off-road motorcycles professionally since 1983 and started working on my own stuff in 1973, so I have a clue. Also, and I'm not lying here, this was the first and to date only engine rebuild failure I have experienced in 40+ years of working on off-road motorcycles. With this experience, I lost a little respect for the Pro-X brand, as this was my first negative experience with the brand since I started using their products since opening my own business in 2009. I then contacted my buddy Chad Watts and asked what he used for top end service parts and he replied that he uses Vertex exclusively in 2-strokes and JE exclusively in 4-strokes unless the customer requests otherwise. He also stated , as I know too, that you can't really beat the reliability and quality of the OEM parts. Chad went on to tell me the story of how he was at Pro-Circuit when the decision was made to test and eventually use Vertex pistons in their race bikes. It was no "seat of the pants" process that directed that decision and Chad stated that once the decision was made, every one of Ricky Carmichael's 125s ran Vertex pistons in every race from that point forward with no issues. That was a good enough testimony for me. I ordered a Vertex kit for the YZ85 to re-do the job for my customer when the Pro-X shattered. I had to completely disassemble the engine to clean and inspect everything and luckily for me (extremely luckily for me!), there was no damage to any other parts in the engine. All I had to do was clean everything, and I mean clean, and prep and assemble the engine. I assembled the engine and installed it back in the frame and I apologized to my customer for the inconvenience. He kept that bike for another year and a half with no other issues.

About a week after I did the initial rebuild on the YZ85, I performed a top end service on a 2012 KX450F and had ordered a Pro-X piston kit for it also. When I received the kit, I also noticed that the piston was lighter and a different casting than the OEM one I was removing. Again, this KX450 piston had "PRO-X" cast into the skirt instead of "ART". I noticed also that the piston was lighter and also lacked the integrity of the OEM part it was replacing. I went ahead and installed it and kept my fingers crossed. It was probably a month or so before I heard from my YZ85 customer that he'd had a problem with his bike, so I was uncertain about the KX450F piston without evidence but just had a gut feel. I have waited since the installation of the KX450F to hear back from that customer that there has been a failure, but I never heard a thing, so it obviously held together.

Sorry for the long post, but I wanted to share my experiences. I have not purchased a Pro-X piston since the one I purchased for the KX450F back in 2014 and will probably not purchase from them again based on the arrogance and lack of support from the technical rep I dealt with at Wiseco during the issue with the YZ85 piston. Up until then, I was a loyal and committed customer. Since then, I go by the old saying "Screw me once, shame on you. Screw me twice, shame on me." In closing, since 2014 I have used either OEM or Vertex in 2-strokes with zero issues, and either OEM, JE, or Vertex in 4-strokes with zero issues.

Thank you for sharing your experience with pro x, im going to double check the pro x topend i have sitting at home for a yz250 build i am doing for a customer right now. i have always had great luck with their stuff, i hope they haven't gone down the road of wiseco with shitty chinese made pistons. I love vertex but i dont like the one size fits all pistons.



And the the intake boot for the rm250 we speak of, its the rubber intake boot between the carb and the reeds, not the reeds themselves. And the reed spacer off a yz250 goes between the reeds and the cylinder to increase crankcase volume. No this is not ESSENTIAL but it does help a bit.

and for the factory fatty you cant find one? i ran with with a factory silencer and it revved forever. I find myself becoming more of a PC guy.




holy crap i cant find one on ebay or fmf racing website, I suggest you call fmf this is very weird

I would suggest you give bills pipes a chance, they have roots in suzuki and run very very well on the rm250

http://www.ebay.ca/itm/MX2-Works-Exhaust-Expansion-Pipe-Bills-Pipes-S-2…