May need/want to specify a little. Otherwise I will be writing a book.
Engine Trouble Top Dead Center?
- Thread starter CrispyLeaves98
- Start date
Chainlube
Well-Known Member
Just give it to him in tiny chapters.
Chainlube
Well-Known Member
But first he should make sure the piston is clearing the intake and exhaust ports at both the top and bottom.
Just make sure it's small in size, can be read in short order, ya know, a real "page turner" like Leo Tolstoy's War and Peace...lol...lol.
Sidewinder Jerry
Well-Known Member
A 2-stroke only has one top dead center. A 4-stoke has two top dead centers. You're correct in that on a 4-stroke the combustion stroke top dead center is the one to use for making adjustments.
Sidewinder Jerry
Well-Known Member
CrispyLeaves98
Well-Known Member
So would I measure squish gap as the distance between the piston at tdc and tdc of the cylinder? I read some forums saying .5mm or .6mm is optimal
The Squish gap is the smallest measured distance between the crown of the piston when at top dead center and the surface of the combustion chamber. Ideally, the tightest point would be at the far edges of the bore closest to the cylinder wall.
If you have good accurate measuring equipment you can measure and calculate the squish gap using the deck height of the block and cylinder, thickness of the base and head gaskets after being compressed, compression height of the piston, rod length, and the surface of the combustion chamber (which may or may not require some geometry and/or trigonometry to calculate depending on the shape).
There is no such thing as "tdc of the cylinder" so please stop saying that phrase, because it is incorrect.
A simply way to get a decent approximation of the squish gap is to use a piece of solder or other soft material that will hold it's shape after being crushed, and cycle the engine over with everything installed and torqued to specification with that material in the chamber, usually fed through the spark plug hole, and to then measure the thinnest sqashed piece. The drawback to this method is that the piston moves in the bore, so no measurement you take will ever be 100% exact. A way to work around this is to take an average of multiple points, which is usually what I do.
