150cc Piston Compression Height By frmrwiseguy (Read 523 times)

[frmrwiseguy]

If anyone has a old or new 150cc Piston laying around can you please measure the Pin Height/Compression distance?
This is measured from the top of the pin bore to the leading or top edge of the piston.
I can come up with the accurate measurement by dividing the pin bore by 2 and adding half of that. 15mm pin in this case. 7.5mm or .591 inch.
mm or inch is fine.

Thanks in advance

[Alleyoop]

Why are you bothering with that measurement?? A piston can be domed and or a crank with a longer arm will change the stroke.
Alleyoop

[frmrwiseguy]

You do not measure to the top of the dome.
Think in terms of a two stroke. This would be to the timing edge.
A crank with a longer rod only effects the Rod to Stroke ratio not the displacement. This would also mandate a change in wrist pin location.
Longer rod= shorter piston, Short rod=long/tall piston.
A longer rod in a engine straitens out harsh rod angles, Longer piston dwell time at TDC and BDC, easier on cylinder walls, Piston skirts.
Helps keep the rings more square to the bore once the piston changes direction.
For instance a SBC with 3.480 stroke and stock 5.7 rod has a stock pin height of 1.550 with a 9.025 deck height
A SBC with a 3.480 stroke with a 6.125 rod has a 1.125 pin height.
No change in displacement.
Can someone measure me a piston Please
Thanks in advance.

[Alleyoop]

I know you do not measure the top of the DOME, I said why bother with your measurement SINCE A PISTON CAN BE DOMED. Explain the timing Edge when I can change where in the cylinder I want it to fire by advancing or retarding the timing without changing piston and or crank.
Alleyoop

[frmrwiseguy]

On a two stroke the leading or timing edge controls the opening and closing of the ports. In a four stroke it just the flat outer edge of the piston.
With the wrist pin divided by two i get the Compression distance or Compression height.
I am trying to match this up with some high end light weight forgings already on the market without have to have customs made.
Trying to find strutted forging with short pin boss for a stronger light weight package.
I have found Dazon had some customs built several years ago, but they are all gone. the forging and prints are available to make more.
May solicit a group buy if enough are interested.

[Alleyoop]

A lot of messing for a mm here and there and cost for not much benefit in return.
Alleyoop

[frmrwiseguy]

ok I'll jus pony up and buy a OE piston and measure it myself.
I'm trying to match it up with a Strutted high end light weight Forging already in production thus is why i need this measurement.
My goal is reliability and performance.

[Alleyoop]

I think your overthinking this Frmwiseguy, If you do not over rev these motors they will last a long time. You can setup the scoot to get good top end at low rpms with good low end torque. I have mine setup that it never goes over 7K and the redline starts at 8K.

I have it setup that it will cruise at 50mph at 5100 rpms and at 60mph at 6100 rpms way below the 7500 rpms that the motor makes it's max hp. But it has good strong pull up to speed and It
pulls away from a stop light right behind the cars, cars behind me do not have to wait for me to get up to speed. Of course I had it bored out from 149.6 to 182ccs with taller gears but I did not want a screaming motor on me to cruise around at 50-60.

I haven't had to do anything to it but change the oils every 1000 miles and grease the differential. I have over 10k miles on it.
Alleyoop

[frmrwiseguy]

With the spec. requested I can match up with std or larger bore, low tension oii ring, TiN comp ring.Liight weight taper bore DLC coated wrist pin.
And if I can match it up it wont cost me anything but my time.
Since I will be inside this thing this winter I would like to make this upgrade.
I enjoy Hot Roding everthing.
My 1976 Hot rod Cub Cade on Alky.
Restored Eric Sorby Factory KX250 56 rwhp.
91 385 ci sbc Silverado. pushing 500hp. 12.62 @ 107.92 mph first time out.
2012 CBR1000RR 156rwhp.
Just a Tim Allen type a guy.

[frmrwiseguy]

Dug deep into my archives and resources.
Top of pin bore to timing edge. .491 or 12.47mm
Compression distance or Compression height=center of pin bore to timing edge of piston. .78622 or 19.97mm
Valve angle 21 degrees.
Made some special for a customer several years ago.
57.5mm bore with a .044 dome rise=11.1-1 compression ratio.
15mm taper wall pin weight=35.5 grams.
Nice ring pckg. 1.mm or .039 top ring Alloy Steel Ferrox coated Chrome Faced, Second ring 1.2mm or .047 Cast iron Phosphate coated taper ring. Oil ring low tension 2.5mm or .098 Stainless spacer with Chrome faced rails.
Thinking of making a dozen of these in 59mm bore.
Piston weight would be in the 109.1 gram area.
Bore out stock cast iron sleeve and replace with Forged Aluminum and have Millennium plate it. I can run a much tighter piston to cylinder clearance this way.
The best place for Cast Iron is on the back yard grill
Cast iron has terrible heat dissipation and Thermal expansion qualities.