064/056 mag11 build

[jmssaws]

With the taller crown you're adding 5mm worth of volume to the cylinder above the exhaust roof which is more cc's. How many exactly I do not know...I made a guess.

If the piston was a foot longer it still will be 98.5 cc's
Whatever you add to the top you take away from the bottom.

 

[jmssaws]

If he runs a spacer to raise the jug ,does this still apply ?

As long as the bore or stroke doesn't change then cc's don't change. Don't matter what piston you use the crank moves it the same amount.

 

[srcarr52]

If he runs a spacer to raise the jug ,does this still apply ?

Displacement = stroke * (bore/2)^2 * 3.14159

It has nothing to do with the volume left in the chamber at TDC or the trapped volume above the exhaust port. Those are used to calculate compression ratio and the 2 stroke corrected compression ratio.

 

[Chainsaw Jim]

Valve fed vs piston ported. Anything below the exhaust in a piston ported engine is basically part of the case volume.

 

[junkman]

As long as the bore or stroke doesn't change then cc's don't change. Don't matter what piston you use the crank moves it the same amount.

My 250r had a spacer under the jug so could run an 86 piston i think with the 89 rod .

 

[srcarr52]

Valve fed vs piston ported. Anything below the exhaust in a piston ported engine is basically part of the case volume.

Anything above the exhaust port is considered the swept volume. Still, the displacement of the engine is from BDC to TDC.

Anything after the intake closes is considered case volume.

 

[jmssaws]

My 250r had a spacer under the jug so could run an 86 piston i think with the 89 rod .

I have pressed many 250r cranks apart and put in offset pins to stroke them.
Had to have a spacer under the cylinder.

That does add cc because we're changing the stroke.

 

[jmssaws]

Were talking about displacement, fill it with water at bdc then turn it to tdc,the amount it displaces is the cc. Nothing can change that other than stroke or bore changes.

 

[Chainsaw Jim]

Dammit I was thinking the combustion chamber was part of the equation.
Sorry guys.

Oh well screw off it still feels right! Lol

EDIT:
The techs at the motorsports shop claim on a piston ported cylinder you add cc's when you use a taller crown height piston and grind the chamber to fit it even though you don't change the stroke.

 

[leadfarmer]

Well, I'll be jiggerd.............Weres the dagum vids at. Impatient here..[emoji3]

 

[jmssaws]

Dammit I was thinking the combustion chamber was part of the equation.
Sorry guys.

Oh well screw off it still feels right! Lol

EDIT:
The techs at the motorsports shop claim on a piston ported cylinder you add cc's when you use a taller crown height piston and grind the chamber to fit it even though you don't change the stroke.

You add cc's to the combustion chamber but it doesn't change displacement.
Regardless of piston height it still moves the same amount,whatever you add to the crown at tdc you take away at bdc.
Nothing will change displacement other than a different crankshaft or bigger bore.
Does reducing squish add cc's?
If squish is 010 or 100 feet displacement is the same.

 

[jmssaws]

Well, I'll be jiggerd.............Weres the dagum vids at. Impatient here..[emoji3]

I'm building a muffler and making sure the piston won't explode and ruin a unicorn cylinder. Lol

Hopefully by dark i can run it full bore

 

[Mastermind]

I've been playing with 3120s all day. I've got one that tries to go lean after it's good and hot. I finally tracked it down to the carb mods I did. I had the main jet too restrictive. Ended up going back to a stock main jet, now it's way too fat. That tells me it ain't getting enough fuel thru the circuit I made. Back to the drawing board......

 

[jmssaws]

I've been playing with 3120s all day. I've got one that tries to go lean after it's good and hot. I finally tracked it down to the carb mods I did. I had the main jet too restrictive. Ended up going back to a stock main jet, now it's way too fat. That tells me it ain't getting enough fuel thru the circuit I made. Back to the drawing board......

I have spent a lot of time changing jets in wj69's and can't tell any difference between the 62 and 74 so I don't bother anymore.
I'm fashioning a oem muffler on this saw.

 

[Mastermind]

I can't tell any difference in that either. The WJ has a high speed circuit that bypasses the main jet. So with a smaller main jet, the high speed needle would just be out a little more.

The carbs I'm messing with are WGs that don't have a high speed needle. So I add that circuit, and if I get it just right, I can block the main jet completely off.

 

[Redfin]

I can't tell any difference in that either. The WJ has a high speed circuit that bypasses the main jet. So with a smaller main jet, the high speed needle would just be out a little more.

The carbs I'm messing with are WGs that don't have a high speed needle. So I add that circuit, and if I get it just right, I can block the main jet completely off.

Wouldnt mind seeing this unless you have already posted Randy.

 

[cgraham1]

Wouldnt mind seeing this unless you have already posted Randy.

I remember a thread by randy about the 3120 carb mods over on AS...

 

[jmssaws]

661 piston measures .870" from the top of the pin bore to crown, intake side skirt width measures 1.377" at the narrowest exhasut side is 1.484" total piston height is 1.70" wrist pin is 12mm
395 piston measures .813" from the top of the pin bore to crown skirt measures 1.48" intake and exhaust side total piston height is 1.89" wrist pin is 13mm

That you Darren?

 

[Iron.and.bark]

The Partner K1200 piston is an interesting animal- 56mm and I believe it uses a 12mm pin. I bought a NOS one for potentially installing in a Solo 603. I can measure it if needed.

Try a 56mm big bore 066 piston here. Was going to use one till I got a nos 603 piston (cost to much, but prob more available).

 

[Redfin]

I remember a thread by randy about the 3120 carb mods over on AS...

Sooo how good at copy and pasting are you Mr Clint?