WÖSSNER Piston Kit for TM RACING E 250, EN 250, MX 250 1999-2019

On TM RACING E 250, EN 250, MX 250 from 1999 to 2019, the WÖSSNER piston kit (Ø 66.33 to 66.35 mm depending on the size class) fits in place of the original part. At the heart of the top end, the piston soaks up the heat and pressure of every explosion. As it wears, the rings no longer seal against the cylinder: compression drops, power drops with it, and the risk of seizure goes up.

Key features

• Forged piston in T6 heat-treated 4032 alloy, designed using computer simulation (FEA).
• Permanent skirt coating that reduces friction.
• Very tight running clearance, for a quieter engine (according to Wössner).
• Complete kit: piston, rings, pin and circlips. Small-end needle bearing not included.

Specifications

• Brand: WÖSSNER
• Manufacturer part numbers: 8136DA, 8136DB, 8136DC
• Piston diameter: A = 66.33 mm, B = 66.34 mm, C = 66.35 mm
• Available versions: A: ref. 8136DA; B: ref. 8136DB; C: ref. 8136DC
• Engine: 2-stroke

Choosing the right size class

The letters A, B, C… are very close diameter grades, one hundredth of a millimetre apart. Measure the cylinder bore with a bore gauge (diameter, ovality and taper) and choose the grade that gives the piston-to-cylinder clearance specified by the manufacturer. As a rule, grade A goes into a new or reconditioned cylinder, grade B into a cylinder that has already been run in. A scored or out-of-spec cylinder has to be reconditioned: you don't make up for its wear with a bigger grade.

When to replace it?

• Loss of power, sluggish pick-up, harder starting: compression is dropping.
• Piston slap on a cold engine, getting more and more noticeable.
• On teardown: vertical scoring on the skirt, stuck or worn rings, thick carbon on the crown.

Replace the piston as set out in your bike's service manual, sooner if you race, and straight away as soon as these symptoms appear. As a Cross-Mania guideline, plan for a new piston every 20 to 40 hours of engine running depending on whether you race or ride for fun. Always measure the cylinder at the same time: a new piston in an oval cylinder won't last.

Fitting tips

1. Clean the cylinder and check it: diameter, ovality, taper and condition of the bore coating.
2. Check the end gap of each ring in the cylinder against the figures in the manual or the manufacturer's instructions.
3. Fit the rings with the mark facing up and each gap correctly located on its locating pin.
4. Check the small-end needle bearing and the pin: at the slightest play, tight spot or marked needle, replace the bearing.
5. Fit the piston with its arrow pointing to the exhaust side, oil the pin and the small end, then fit the circlips without distorting them, gap opposite the notch. A circlip that has been taken out is replaced with new piston pin circlips, never refitted.
6. Reassemble with a new top end gasket kit and tighten the cylinder head in a criss-cross pattern to the manufacturer's torque.
7. Refill the coolant and fit a new spark plug.
8. Break the engine in: warm it up gently, vary the revs and avoid sustained full throttle for the first hour.

Why WÖSSNER?

Wössner is a German family business based in Weil am Rhein and founded by Eckart Wössner, a former racer from the 1970s. It has been making its own forged pistons since 1994, from blanks produced in its own forge, and Wössner pistons are used in Supercross as well as in MXGP.

Spare parts and items to plan

• Piston rings : VERTEX 53010006640N8 · VERTEX 53010006640
• Top-end gasket kit : VHM SK33000.VITON · VHM SK33000
• Small end needle bearing : NTN
• Coolant : MOTUL 1 L · MOTUL 20 L
• 2-stroke oil : LIQUI MOLY 1 L · LIQUI MOLY 4 L

Frequently asked questions

Does the kit include the gaskets?
No: the kit contains the piston, rings, pin and circlips. Add a top end gasket kit, because a head or base gasket can never be reused.

Which size should I order?
Measure your cylinder: A, B, C correspond to different actual diameters (66.33 to 66.35 mm). Choose the class that gives the piston-to-cylinder clearance specified by the manufacturer.

Can I replace just the rings later?
Yes, as long as the piston and cylinder are still within tolerance. Replacement rings can be ordered on their own, as can the piston pin and the circlips.

Should I replace the small-end needle bearing?
It isn't included. Check it at every piston change and replace the needle bearing at the slightest play or tight spot.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
TM RACING E 250 2019
TM RACING E 250 2018
TM RACING E 250 2017
TM RACING E 250 2016
TM RACING E 250 2015
TM RACING E 250 2014
TM RACING E 250 2013
TM RACING E 250 2012
TM RACING E 250 2011
TM RACING E 250 2010
TM RACING E 250 2009
TM RACING E 250 2008
TM RACING E 250 2007
TM RACING E 250 2006
TM RACING E 250 2005
TM RACING E 250 2004
TM RACING E 250 2003
TM RACING E 250 2002
TM RACING E 250 2001
TM RACING E 250 2000
TM RACING E 250 1999
TM RACING EN 250 2019
TM RACING EN 250 2018
TM RACING EN 250 2017
TM RACING EN 250 2016
TM RACING EN 250 2015
TM RACING EN 250 2014
TM RACING EN 250 2013
TM RACING EN 250 2012
TM RACING EN 250 2011
TM RACING EN 250 2010
TM RACING EN 250 2009
TM RACING EN 250 2008
TM RACING EN 250 2007
TM RACING EN 250 2006
TM RACING EN 250 2005
TM RACING EN 250 2004
TM RACING EN 250 2003
TM RACING EN 250 2002
TM RACING EN 250 2001
TM RACING EN 250 2000
TM RACING EN 250 1999
TM RACING MX 250 2019
TM RACING MX 250 2018
TM RACING MX 250 2017
TM RACING MX 250 2016
TM RACING MX 250 2015
TM RACING MX 250 2014
TM RACING MX 250 2013
TM RACING MX 250 2012
TM RACING MX 250 2011
TM RACING MX 250 2010
TM RACING MX 250 2009
TM RACING MX 250 2008
TM RACING MX 250 2007
TM RACING MX 250 2006
TM RACING MX 250 2005
TM RACING MX 250 2004
TM RACING MX 250 2003
TM RACING MX 250 2002
TM RACING MX 250 2001
TM RACING MX 250 2000
TM RACING MX 250 1999