Beta 300 top end rebuild.

Top end rebuild on a 2018 Beta 300rr.

Hone. Do not hone the jug. Jeff doesn't recommend honing the cylinder. I never did. https://www.youtube.com/watch?v=vaFp8aYkHNA

I did do the reeds, as per instructions provided. Easy enough.
This kit fits the Beta with zero issues and is cheap.
Pick a 2014 KTM XCW 300
https://www.rockymountainatvmc.com/parts/v-force-4-replacement-reeds-p?s=1125738

Compression pre/post rebuild.
I couldn't find a pressure rating for the Beta anywhere. And for good reason.
https://www.mide.com/air-pressure-at-altitude-calculator
Turns out that you can take your compression ratio, and times it by air pressure at your altitude, i.e. a at sea level would get 175 PSI out of the same motor. I have to make do with 154 PSI.
The colder the temp the lower the compression. Logic would dictate that a warmer motor gets higher comp.

Beta is a 11.9:1 comp *12.96 gives an adjusted for pressure number of 154 PSI.

I'm still a bit off that number (147 PSI when checked after a short .2 hr run, on warm motor), as I'm using a tester that has half the thread of the actual spark plug (moar volume. less pressure).
The new piston and rings have only 1 hr of run time. I attempted a few heat cycles yesterday, but comp still sits at 147 PSI (cold). Bike does feel very good, and takes nothing to bring the wheel up.

When I got the Beta with 25hrs, I borrowed a friends good quality comp tester and got a reading of 157-159 PSI. The above are with my shitty tester from home, so that might be part of it.

Also recommended to check comp on the kick starter, and not the electrical starter. I'm SOL there.

Видео Beta 300 top end rebuild. канала One track muppet