How to Check Squish on a Two Stroke Engine

This guide is a general instruction on how to check squish on a Two Stroke Engine.

First step is to determine what the squish is supposed to be.  If you are using a SwedeTech Engine, we supply this number to our customers.  If you are not using a SwedeTech engine, contact your engine builder for the proper squish measurement.

Squish = The measurement between the piston and combustion chamber with the piston at TDC ( Top Dead Center ).  This measurement is taken at the edge of the piston.

For this example, let’s assume the desired squish measurement is 0.040″.  In this example, you will use 0.050″ solder.  For SwedeTech Engines, we prefer to use solder that is approximately 0.010″ – 0.012″ thicker than  the desired squish measurement.    Note – Some rules such as Rotax call out in the technical specifications the required solder thickness.  Always check your rules to make sure you are in compliance.

Rotate crank so the piston is resting about 1/2″ down from TDC.  This will give you room to insert the solder as well as clearance to run the piston to TDC to squish the solder.

  • Cut two pieces of solder a minimum of 4″ in length – length of solder must be long enough to reach edge of cylinder and maintain control of solder ends from the spark plug hole.
  • When cutting solder, use a sharp razor blade and cut perpendicular to the solder.  This will leave the end of solder square.  Wire cutters will leave the solder edge tapered, and this may affect your measurement.
  • Bend the solder so the you can feed the solder through the spark plug hole, to the edge of the cylinder / piston.  Now insert the second piece of solder in the opposite direction of the first.
  • You will always want to check the squish directly above the wrist pin.
  • With the solder butted up against the cylinder wall, rotate the crank back and forth so the piston “squishes” the solder 4-5 times.  Go past TDC 0.020″ -0.040″ , then rotate opposite back to TDC.
  • Remove solder from cylinder and measure the thinnest part of the solder with a set of calipers that have been zeroed out.  This can be a few 1/1000ths from the end of the solder.
  • Using base gaskets or head gaskets, move the cylinder or head in the direction of desired squish measurement.  Repeat above steps until desired squish is found.
  • Note – If squish measurement from left solder to right solder differ, you may need to move the head around to achieve equal squish on both sides.  Make sure the nuts or bolts for the cylinder and head are torqued evenly to the proper specifications.

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