Piston Change

Which clearance do I need when changing the piston ?

If you change your piston please notice that piston rings are all the same size … so normally you need to shorten the ring to get the right piston ring gap
we recommend a gap of
85/100 0.3mm
125/144 0.3mm
250/300 0.5-0.6mm
an „A“ piston will have a clearance of
0.07mm on the 85/100 – 47.87
0.06mm on the 125/144 – 53.94 / 55.94
0.07mm on the 250/300 – 66.33 / 71.93
we recommend the 2 ring pistons for performance improvements
85/100 (not available as 2 ring piston – use the OEM one)
125 (OEM has a 2 ring Vertex piston 53.94 – 53.98)
144 (OEM has a 2 ring Vertex piston)
250 (OEM has a 2 ring Vertex piston) 
300 (OEM has a 2 ring Vertex piston)
The pictures below are for the 250/300cc to show you how to measure the piston rings and fit them. (it works the same for other bikes only the ring gap is different)

Piston Remounting


Which squish do I need to run on my 2 stroke bikes ?

The squish is the distance between the cylinder head and the piston (messured at the cylinder sides at the postion of the piston pin)
TM offers different cylinder gaskets, so you can adjust the squish for your personal preferences
we recommend a squish of
1mm 85/100cc
1.2mm 125/144cc
1.4mm 250c
1.9mm 300cc
to improve your performance you can get the VHM heads with special squish and head volumes
those parts really work and are available in our webshop
VHM has a nice video about how to measure the Squish: https://www.youtube.com/watch?v=bMDro5MFKFg
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