Piston Replacement

[jdaro356@gmail.com]

New to me last year 2018 300rr with 3,000 hrs, Piston has not been touched, original. The bike runs well and no unusual noises. I will perform a compression check and disassemble to see what it looks like. Question, I've been reading about OEM and Replica pistons and want to make sure I use the OEM type. How do I ensure I purchase the correct piston? Thanks, Jim.

[jdaro356@gmail.com]

300 hrs, not 3,000, sorry

[Dr Z]

I bought my 2018 300 with almost 60 hours on it and just got it back together last weekend. 179 hours on stock piston and it needed it, even though it ran fine. It runs like new now. Measure the cylinder and check the stamping inside the cover. Mine was an A cylinder and I put a B piston in based on the measurements. I used Pro-X just because Rocky Mountain had it in stock at a decent price. The directions said it should have .05 to .08mm clearance. The manual says .1mm is the upper limit. Get the squish tool also as you will need to set the base gasket thickness.

[JoeMaico]

On my 2016, I use Vertex Pistons. Pretty sure that is what comes stock on Beta's - 2018's as well. With 300 hours on it, you will need to go to the B size. You can also use KTM E-Z Clips on Vertex pistons to make installation easier. 2018 and later pistons are domed, not flat. So, I would agree getting an appropriate tool that follows the curvature of the piston crown makes setting the squish at lot easier. You can measure the thickness of the existing base gasket (or gaskets) and match them up as best as possible with what you get in the Beta gasket kit. But, measuring is always better.

joe

[Dr Z]

I used the same thickness base gasket as what came off it and had to pull it apart to go thicker. The vertex piston has a little round protruding flat spot on top. I had to move the gauge just off the edge of it to align it with the dome to measure. Definitely not exactly like the stock beta piston I pulled out. Would have had to stack all the gaskets to clear that spot under the measuring tool!

[JoeMaico]

I thought you used a Pro-X and not a Vertex?

joe

[Dr Z]

Oh crap, sorry. It was a Pro x. I mis-typed.

[jdaro356@gmail.com]

Thanks, great information