Every activity, it seems, whether it is a sport, a hobby or something in between, has its share of odd terms. Baseball has frozen ropes and there’s some nutmegging going on in soccer, and how could we not mention running’s infamous “fartlek.”
PWC is no exception, and today, we’re gonna take a look at your squish … no, seriously.
To paraphrase half a dozen reputable resources, the “squish” on a 2-stroke engine is the measured space between the highest part, or crown, of the engine’s piston and the perimeter of the combustion chamber, or head deck, when the piston is at Top Dead Center, or TDC ( and yes, the term top-dead-center will always be said in Mona Lisa Vito’s voice in my head).
This is also known as squish clearance, or “quench.”
There are a multitude of reasons that setting this gap correctly is crucial, and equally as many schools of thought on how to properly adjust the “squish” for optimal performance – with the ultimate goal being more chamber turbulence, better atomization of fuel, more complete combustion, more power, better fuel economy and better resistance to pre-ignition detonation (knocking).
However, that discussion is beyond the scope of this article. Here, we will simply look at the process of measuring that squish to give you the information you need to proceed into those more advanced considerations. Most shops will also ask for this measurement when you send your heads in for work.
The term Squish is also appropriate for this measurement process, which is accomplished, in simplistic terms, by inserting a piece of solderwire through the spark plug hole and squishing said solderwire between the piston head and the chamber perimeter by rotating the crankshaft. The squished section of the solderwire is then measured to provide the “squish” clearance.
There are a number of key aspects to this process that were noted in each of the numerous tutorials on this process that we noticed:
- Do not use acid core solderwire
- Solderwire should have a diameter of more than 1.5 mm, with 1.8 mm being the most-often referenced diameter for a stock 85 or 125, and 2.5 or 3 mm thickness on a stock 250 or 300.
- Always position the solderwire parallel to the piston rod, (or left to right, not front to back) in line with the wrist pin, to minimize the impact of piston rocking on the measurement.
- Always insert the solderwire all the way to the edge of the bore.
Following is an informative and easy-to-follow video tutorial on squish clearance measurement from John Zigler of Watcon/Watercraft Talk
