Aprilia closed their big end pins with conical plugs, but that wouldn't solve the aux/transfer short circuiting either.
Past experience tends to point into the opposite direction: circlips can be very good at
causing disaster.
And what about that 3 piece pin? Well, what about acceleration values of 5000 g around BDC and 7850 g around TDC (Aprilia RSA at its 14500 maximum rpm)?
Do you think any built-up contraption would stay together long enough under that kind of stress? You're right about that, providing you use circlips at all. That is why I did away with them and click my plugs straight into the circlip grooves.
The issue is not the volume of the remaining space, but the cross flow area of the leakage path between auxiliary exhaust ports and transfer ports.
Turning to the simplest solution I could think of: leave the circlips out (saves weight) and click the plugs directly into the circlip grooves. They will work fine in combination with a normal piston pin (saves a
huge amount of money compared to a Pankl pin) and it reduces the aux/transfer leak path better then even the latest domed Pankl pin, shown in the picture below-left. Right is my simple, very light plug.
There were never any lubrication problems, only a problem when someone used plugs, designed for a Simson piston, in a Kreidler piston which has different circlip goove dimensions. One plug came out, passing through the engine without doing any harm, but then the piston pin started wandering sideways, scraping the cylinder bore.
Most of the research went into finding the proper plug material. And since I don't expect I'll ever get rich from selling plugs, I'll let the cat out of the bag:
the plugs are made of
Torlon. The stuff ain't cheap, but you'll get about 20 re-usable(!) plugs for the price of one Pankl pin.
Attachment 326134 Attachment 326135

Originally Posted by
Frits Overmars

Originally Posted by
F5 Dave
Yep, that's the stuff. Like I said, it ain't cheap.
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