DRP: Night Rider
Posted: Fri May 13, 2016 3:39 am
A Replica Racer forum for Derbi GPRs, Aprilia RS50s, and similar motorcycles
https://gprcamp.com/foro/
The ones on the RS4 look even prettier. But I don't think either of them will fit on the Derbi tank with this bike.Rj_666 wrote:Tora - for your tank issues, you might consider a part from an Aprilia RS50.
It might require a 'massage since your stock bolt is M5. From the parts diagram at AF1:
15 AP8150202 Hex socket screw M6x50 1
16 AP8121819 Washer 6,5x12,5* 1
Thanks Randy I'll check it out.Rj_666; wrote:I've had pretty good luck with automotive stuff from Painless Performance:
http://www.painlessperformance.com/webcatalog/copi
I've never read or heard a good explanation... so I can only share what I've learned over the years. If you understand what "piston wash" is, then it's pretty easy to know what to look for and what to look out for.
The first thing you need to realize is that the top of the piston is not a uniform temperature. The area in front of the exhaust port that is exposed to all of the hot gases exiting the cylinder is naturally the hottest. The area in front of the transfer ports that is cooled by the fresh air and fuel entering the cylinder is obviously going to be the coolest. And, the center of the piston will be somewhere in between.
The second important thing is that there is some small range of temperatures where the piston is hot enough to char the oil that comes in contact with it, but cool enough not to melt the piston.
Putting those together, you have "piston wash".
When the engine is jetted very rich, most of the piston (except near the exhaust port) is too cool to char the oil; and you will have large areas spreading out from the transfer ports that appear to have been "washed" clean of carbon by the air and fuel entering the cylinder... that is "piston wash".
If you jet down leaner, the temperature of the whole piston will increase... and more areas will be hot enough to char the oil. The "washed" areas will be large circular areas, located just in front of the transfer ports. At this point, the center of the piston is quite hot; and is actually charring the oil on the underside of the dome, right in the center.
Jetting down further will cause the whole piston to get still hotter. Now, nearly the entire piston is hot enough to char the oil... and the "wash" will be just a small area about the size of a half of a dime, right in front of each transfer port. The bottom side of the piston will be charring the oil over a large area by now also. At this point, the area near the exhaust port is getting almost hot enough to melt. This would be considered (at least by me) to be jetted correctly... but near the "edge".
If you go leaner yet, the whole piston will be hot enough to char the oil on top of it and there will be no "washed" areas left. The entire piston will be covered with carbon, and the aluminum at the edge of the piston, right in front of the exhaust port will actually be slowly melting away and smearing onto the rings... more than a few seconds of this and it's time for new pistons.
That, for whatever it's worth, is my own twisted look at piston wash.
Some things to keep in mind include the fact that the size of the "washed" area depends somewhat on the upward angle of the transfer port. If the port is angled flat across the top of the piston, there will be more cooling and more wash... in spite of the fact that the area in front of the exhaust port might be just as hot as it would be on a motor with upward angled transfers that shows much less wash. The upward angled transfers don't cool as much of the piston top.
Also, the size of the "washed" area has to be somewhat proportional to the size of the piston. A "half a dime" sized wash area on a 600 triple (very small piston) means the piston is a lot cooler than a "half a dime" sized wash area on an 800 twin (with coffee cans for pistons)! What you're really interested in is how much of the piston isn't clean, because that tells you how much of the piston is hot enough to char the oil... and you know the exhaust area is hotter yet.
All this really means is that you can't just say, "Every motor should have a half-dime sized wash area." You have to correlate the size of the wash area to other indicators and engine specs... and use it as just one of your tools for jetting.
Rj_666 wrote:Looking GREAT, Tora!!
Hey ESP! I've been wondering where you've been lately and how your project is coming along—post some updates! I hope you'll have a running bike in time to bring it to GPR Camp. It's now less than a month a way. It's all very exciting.Espresso4Blood wrote:This bike is just amazing!
RJ, the way I remember the story he did!Rj_666 wrote:If Hiro Protagonist rode a GPR.