Wrist Pin Stuffing

[cannonball2]

While reading about raising crankcase compression in two strokes I found an article written years back covering the subject completely. One thing I havent seen mentioned here was the loss of compression into the wrist pin. Back in the day builders stuffed the pin with a portion of hardwood dowel . If you think about it there is some volume to the center of a wrist pin as well as the in the circlip area. Having my Zeda top end off I decided to try this. I drove a section of dowel(about 1/4") into each end of the pin. I am using a Sthil pin which is somewhat shorter than the stock pin and 1.8 grams lighter including the dowels. The shorter pin will allow me to make Teflon buttons to completely fill the circlip area and ditch the circlips. Found 10mm Teflon rod pretty cheap on ebay. This is a cheap and easy way to raise compression. Dont expect miracles from this but if one is stuffing the cases, dont over look this.

On a piston port engine it would seem that drilling holes in the piston to lighten it would not be the thing to do. Sorry about the pics but you get the idea.

 

[Dan]

Thank God you use your powers for good!

 

[cannonball2]

Thanks Dan!

Need to clarify the Teflon buttons are to keep the Stihl wrist pin centered as it is shorter. Not to replace the circlips. The buttons will be behind the circlips. Otherwise they would travel into the transfers and into the cylinder in short order.

 

[cannonball2]

Heres the object of the experimentation. I have to say this has been a killer success! Not really due to the stuffed wrist pin but to finding a better piston. While waiting for the teflon to get here I started weighing several pistons and wrist pins I had. The Zeda has been a fairly smooth engine however it vibed pretty well at max rpm. Its been known for a long time the 66cc CG pistons tend to be too heavy.

I found a new high pin piston I had never used I also found a super light wrist pin I had bought from Treatland years back. Super thin wall. This piston with this wrist pin weighed 10gms less than the stock Zeda! 98.7 vs. 88.5. So now the engine is super smooth and actually revs higher with basically no vibes. Nicest CG I have ridden thus far!

I wish parts sellers would weigh their replacement pistons since the weights are all over the place!