Beta Evo Top End Rebuild Kit - 300cc
Top end rebuild kit including the piston, gaskets and O-rings
For the Beta Evo 300 trials bikes from 2011 to 2025.
Please select the piston letter size and base gasket size required to suit your bike, each bike is different, the base gasket thickness is used to set the squish clearance correctly (the gap between the head and the top of piston).
Piston Sizes
| Letter | Size | Part number |
|---|---|---|
| A | 78.95mm | |
| B | 78.96mm | 007.02.045.80.0A |
| C | 78.97mm | 007.02.045.80.0B |
These S3 piston are very slightly different to the original Beta piston but all the critical measurements are the same, they are both even made in the same factory (Vertex). The only differences are:
The Beta piston is 0.01mm bigger in diameter i.e. a size B Beta piston is the same as a size C S3 piston (78.97mm).
The Beta piston has a chamfer on all 4 corners of the bottom edge of the skirt.
The Beta piston has a small machined groove to help fit and remove the c-clips.
The anti friction coating has radius corners on the Beta, rather than square.
The skirt support lugs are little bit bigger on the Beta, so it's about 8 grams heavier then the S3 version.
None of the above will affect the way the bike runs so I'm more than happy to recommend this S3 piston for use in the Beta Evo 300.
The factory recommended piston to cylinder tolerance for the Beta Evo 300 is 0.04mm, if you are considering putting the next size up piston in please be aware that your original piston will have worn down and any wear in the cylinder is unlikely to be uniform down the bore so please check the bore size all the way down the cylinder and from left to right as well as front to back, measure the piston and cylinders at 20 degrees C. The piston is measured front to back and 19mm up from the bottom of the skirt, be aware that the pistons are manufacture tapered (larger at the bottom) and oval (larger front to back) to allow for unequal expansion of the piston in use.
18mm Gudgeon Pin by 56mm long
Centre of the gudgeon pin to the top edge of the piston 28.8mm
Overall height 66mm
Weight including rings, gudgeon pin and C-clips 280 grams
The base gaskets are available in different thicknesses to allow the correct squish clearance to be achieved.
Beta doesn't state the squish clearance (the gap between the top edge of the piston and the cylinder head), instead they use a go/no go guage.
| Manufacturer | Beta |
|---|