Why did the ring fail? This piston has an L shapes upper ring which seems strange. BB said he hasn’t seen those since the 70’s. Someone took a hack saw to the intake side of the piston to increase the duration will post a picture later.teazer said:That head should be a significant improvement. It should be possible to lose a little metal around the outside and maybe groove it to lose a few grams, but don't thin it too much and have it distort.
Did you determine why the ring snapped? It's hard to see from the video but with a wide port, it's important to have sufficient curvature of the roof and a suitable chamfer to ease ring back in after it bulges into the port. A square top makes a little more power by creating more time area and because the pressure wave is stronger but it kills rings. That higher pressure wave also creates a sharper exhaust note. So once again it's a case of finding the optimum. Raise the center of the port which will add even more exhaust time area and be easier on the rings.
14:1 CR sounds fine for an air cooled machine. If you go much higher, the combustion chamber gets to be too flat and that can hurt flame propagation, pressure rise and power. More optimization decisions.
Texasstar said:Why did the ring fail? This piston has an L shapes upper ring which seems strange.
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teazer said:Beautiful welds. Not at all like mine.....
Dykes rings are the bees knees but like most things in life have some issues. Check you exhaust port shape and chamfer when you get a chance.
Thanks BrodieBrodie said:Bike of the month nomination for this mate. Keep up the good work.
There is always nitrous....teazer said:If we had engines that revved to 12k with powervalves etc which made around 240hp/liter, we'd all need programmable ignitions. Unfortunately, our old clunkers are not so responsive to ignition timing - except when it's too advanced on the day that air is dense and we are jetted lean......
The higher teh state of tune, the more that we need to get timing spot on to get the most out of a motor. At low revs with zero to negative pipe effects, we can light the fire much earlier. On the pipe at higher revs compression and temperature are higher and we need less advance to get peak pressure at the right time (14-16 ATDC).
What's really nice with programmable ignition on our old bikes is that you can set timing quite late at startup to reduce the chance of kickback and reverse running. On a low state of tune drag bike that only runs at wide open throttle and in the powerband, there's probably not as much need for a complex ignition curve, but it all helps.
Sleds are interesting. Some Polaris 2 strokes had peak advance as low as 3000 and retarded slowly from there. Others don't reach peak advance until 6000 (19 degrees) and drops off to around 11 degrees at 8,000. What Sled guys spend a lot of time on is setting up the clutching to get the most out of what power it makes.
I see lots of dyno time in your future.
Parts on the wayteazer said:Now you're talking.....