Experimenting With A 2stroke Trimmer Piston

Petros: 2 cycle engines are the product of many years of engineering and improvement. You can be fairly certain that the shape and size of the piston and ports has been carefully designed to produce maximum power and any changes in the configuration will affect the performance. Although I don't understand exactly why the piston is shaped as it is, I would wager that is where you need to copy the original as close as possible
Mark
 
markba633csi said:
Petros: 2 cycle engines are the product of many years of engineering and improvement. You can be fairly certain that the shape and size of the piston and ports has been carefully designed to produce maximum power and any changes in the configuration will affect the performance. Although I don't understand exactly why the piston is shaped as it is, I would wager that is where you need to copy the original as close as possible
Mark
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Words of wisdom!
Thank you Mark. I adopt this way of seen things... but on the other hand... if we do everything "by the book" we will miss all the joy hehehe

Petros
 
The development of 2 cycle engines is quite interesting, much of the pioneering work was done in Japan in the 60s
In my younger days I had two Kawasakis: a 250cc twin with rotary valves and a 500cc H1 triple cylinder. Crazy fast bikes.
It's a wonder I'm still alive.
Mark S.
 
Although I'm not young, (57) I have 3 Yamahas, a 2 stroke 50cc Bop II, a 110 cc (13HP) 2 stroke F1ZR and a 4 stroke single cylinder 660 cc XT to play with.
All my friends tell me that at my age "bones heal slowly" to stop riding and use my car... But I like riding, it makes me feel younger!
Petros
 
You could try drilling round holes in sides to see if it imptroves starting/running. Round holes would obviously need to be smaller but would 'weaken' the piston less. Unfortunately I haven't messed with two stoke piston modifications since the early 1980's
Oh, the main two stroke development was done in East Germany, the 'Schnurle'(sp?) design only came to 'western' notice after a defection by MZ works rider around 1965. Suzuki were probably first to use it?
 
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crazypj said:
You could try drilling round holes in sides to see if it imptroves starting/running. Round holes would obviously need to be smaller but would 'weaken' the piston less.
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As these engines run in high rev speeds I suspect that the piston needs all the material around wrist pins to have the strength needed to push and pull back itself thousant times a minute. Inertia is the enemy here.
To be honest I hesitate to drill or mill at this area. I would easily drill or mill enywhere else but there.
petros
 
Pretty sure holes at sides of pin away from main boss will be fine. I've been modifying engines since around 1974
 
Actually 2 Strokes go way back before the 60's and Japan.
I had a Lawnboy mower that was my grand fathers'.
I use to get $1.00 when I was 10 to cut his grass with it. (he wouldn't let you run the power mower until you were 10, if you were younger you used the push reel mowers - he had 2)
I'm 61 and the mower was also used by oldest brother who is 9 years older than me.
I'm only guessing but I would say this was an early to mid 50's model.

It had an open flywheel and you have to wrap the starter cord around an open pulley.
Once it started you tied the cord to the push handle. - No auto rewind that didn't come for many years.
Unfortunately the material around the coil give up and disintegrated into dust, and I was unable to find anything to replace it.
 
I'm only 60 :rolleyes:
'Playing with 'motybikes' at 18 monhts old but was 11 when I got 'more involved' with them
Fully aware two stroke motors were around a long time, Scott started in 1908 and was made until 1978 (as SILK)
Weird engine, 'overhung' crank, (only one flywheel each side for twin cylinder)) deflector pistons, etc.
Piston 'strength' with holes drilled shouldn't be affected, drilling holes would lighten it ever so slightly and it's 'apparent weight' would be substantially lower at 7~10,000 rpm (inertia makes an 'ordinary'1lb 85~90mm piston weigh around 5~7 tons at 7~9,000 rpm TDC when it has to 'stop dead' then reverse direction. As long as you don't remove material too close to pin things will be fine
 
WOW,just looked Scott up on Wiki. Seems Alfred Scott invented and patented the loop scavenge system and MZ copied it
 
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