Fomula To Determine Stroke Of An Engine

[motosierra]

Does anyone know the formula to determine stroke of an engine…knowing the diameter of the piston and distance from top of piston to centerline of wrist pin opening?

 

[Lakeside53]

All you have to do is measure the min and max distance the piston travels in the bore, and subtract them. The diameter of the piston has nothing to do with the stroke length.

Am I missing something?

 

[fishhuntcutwood]

Andy, he may be wanting to work backwards from total displacement, knowing bore, because measuring the travel would be my recommedation as well.

 

[motosierra]

Andy, he may be wanting to work backwards from total displacement, knowing bore, because measuring the travel would be my recommedation as well.

...I do not have the cylinder but I do have the piston and therefore all of its dimensions...I am trying to determine stroke distance to help identify piston.

 

[fishhuntcutwood]

...I do not have the cylinder but I do have the piston and therefore all of its dimensions...I am trying to determine stroke distance to help identify piston.

What model saw is it? Or is it even a saw? You could determine stroke without the cylinder, but it'll be tougher to ensure it travels in a straight line, as it would within a cylinder. I guess I've never thought to ID a piston by stroke, I've always just done it by model. Meaning, I'll buy a cylinder for an 056 Mag, not a 38 mm stroke cylinder.

 

[BlueRidgeMark]

...I do not have the cylinder but I do have the piston and therefore all of its dimensions...I am trying to determine stroke distance to help identify piston.

That isn't going to work. There are an infinite number of possibilities. If you have the rod as well, you could probably figure it out pretty closely. The maximum angle that the rod can swing would tell you how far down the piston could go.

But just from the diameter, or the distance from the top to the wrist pin? Nope. Those are not related to the stroke. There is no formula.


If you had a LIST of possible pistons, then you might be able to COMPARE measurement and find one that matches. Post the numbers you've got and someone might recognize them...

 

[motosierra]

That isn't going to work. There are an infinite number of possibilities. If you have the rod as well, you could probably figure it out pretty closely. The maximum angle that the rod can swing would tell you how far down the piston could go.

But just from the diameter, or the distance from the top to the wrist pin? Nope. Those are not related to the stroke. There is no formula.


If you had a LIST of possible pistons, then you might be able to COMPARE measurement and find one that matches. Post the numbers you've got and someone might recognize them...

This is what I am trying to do. Using Clymer's "Chain Saw" Manual"... one of the piston's I have a is 1.968 in. or 50mm in dia..... but there are 2 Jonsered saws (I think it is Jonsered piston because of the shape) that have that dia. size piston....the 70E and the 75 but one has a 35mm stroke and the other is 38mm..... so without knowing the stroke.... it is a 50/50 chance.

Maybe I will post a picture of the mystery pistons with the numbers I have and someone can identify them.

I appreciate eveyone's input on this thread...thanks