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Post  Cribbs74 on Mon Feb 18, 2013 3:45 pm

Have any of you ever done this using stuff lying around? I know Rusty has removed skirt material to bring back SPI. I want to build a Venom clone (for myself not to sell) and was thinking about how to go about doing this.

Ron
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Post  tubebass on Mon Feb 18, 2013 4:21 pm

Here's how Milton Dickey does it. Spins the piston in a 1/2" drill, protected by a sleeve of brass tubing. He then carves out the inside of the piston skirt with an x-acto blade.Lightening a piston using common tools 70562_7026
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Post  Cribbs74 on Mon Feb 18, 2013 4:26 pm

That's more or less what I was thinking. However, How does one keep the connecting rod from flailing about?

Thanks Tubebass
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Post  tubebass on Mon Feb 18, 2013 4:34 pm

I believe he holds it to one side with a piece of 3/32 music wire inserted in the brass tube glued into the wooden base. It's visible near the con rod.
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Post  Cribbs74 on Mon Feb 18, 2013 4:39 pm

Ahhh, ok then. Thanks for the help!

Ron
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Post  andrew on Mon Feb 18, 2013 4:51 pm

cribbs74 wrote:Have any of you ever done this using stuff lying around? I know Rusty has removed skirt material to bring back SPI. I want to build a Venom clone (for myself not to sell) and was thinking about how to go about doing this.
Ron

There is a poster, Combatpigg, over in RCU who has done this. However, he has a lathe which makes things much easier. I think it would take at least a drill press to lighten the piston. His approach is to chuck the piston in the lathe, to use a wire to hold the rod up out of the way (as the lathe spins, the rod is held at an angle and is stationary), then use an Xacto blade to remove some of the material from the inside of the piston wall. It takes a steady hand and a light touch.

I don't think it would be possible to use a hand drill unless the drill was mounted in a fixed position. The drill press gives you a solid mount, variable speed and a platform to hold the rod out of the way. Removal of material from the piston wall would be by feel unless you could use a mirror to let you view the inside of the piston while shaving away some of the material.

You probably would want to wrap the piston with thin brass shim stock or turn a holder to keep the chuck from leaving any marks whatsoever on the piston surface.

andrew

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Last edited by andrew on Mon Feb 18, 2013 5:03 pm; edited 2 times in total
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Post  dckrsn on Mon Feb 18, 2013 4:54 pm

Ron, Milton Dickey(Dickeybird) called it the "poor man's lathe".
Scroll down to post #12 here.
http://www.rcuniverse.com/forum/m_688342/anchors_688342/mpage_1/key_poor%252Cmans%252Clathe/anchor/tm.htm#688342
Bob
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Post  Cribbs74 on Mon Feb 18, 2013 6:25 pm

Thanks for the visual Andrew, that's a little more than I have to work with though. At least I can see how it's done. I am surprised the hobby knife blade is hard enough to remove the material.

I will probably have to go the poor man's route as Tubebass and Bob show. The tricky part will be rigging the drill to run while I have both hands free. I guess I need to find some brass tubing to make a sleeve!

Ron
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Post  RknRusty on Mon Feb 18, 2013 9:19 pm

When I did it in my drill press, I wrapped the skirt with a couple of turns of electrical tape and chucked it lightly. I just held the con rod in my fingers while the piston spun. Like you mentioned, I only shortened it, I didn't shave the inner wall. I might try it though.

What are you up too, Dr Evil, Devil working on Tach Race 2014 already?

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Post  Cribbs74 on Mon Feb 18, 2013 9:26 pm

RknRusty wrote:When I did it in my drill press, I wrapped the skirt with a couple of turns of electrical tape and chucked it lightly. I just held the con rod in my fingers while the piston spun. Like you mentioned, I only shortened it, I didn't shave the inner wall. I might try it though.

What are you up too, Dr Evil, Devil working on Tach Race 2014 already?

Pssssh! I already got that in the bag!

Lol, totally kidding, I got lucky, plain and simple.

I am making a venom clone.....that's all.
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Post  getback on Wed Feb 26, 2014 7:09 pm

dckrsn wrote:Ron, Milton Dickey(Dickeybird) called it the "poor man's lathe".
Scroll down to post #12 here.
http://www.rcuniverse.com/forum/m_688342/anchors_688342/mpage_1/key_poor%252Cmans%252Clathe/anchor/tm.htm#688342
Bob
BOB I have looked at this a couple times and cant get the page to open says it don't exists I was wanting to know how much would you shorten as Rusty was saying . ERIC
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Post  dckrsn on Wed Feb 26, 2014 8:02 pm

Good question Eric.
I found this old post from Jason. Hope it helps.
Bob

Re: shortening and lightening a piston
Jason_WI on Tue Sep 04, 2012 8:18 pm
Dimentions from my shortned and lightned piston from Bernie:
Piston length: .3565"
Piston wall thickness: .015"
Depth of lightning: .150"
This is for use in a surestart cylinder with twin slit exhaust.
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Post  getback on Wed Feb 26, 2014 8:36 pm

Thanks Bob that helps for sure , but now will it work with a td set up dual ports twin bypass? anyone?  Babe Bee .049 
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Post  Cribbs74 on Wed Feb 26, 2014 8:44 pm

A TD may benefit from lightening the piston, but to be honest they spin up pretty good as is.

I would be cautious if you lighten it as it may be more than it can handle.

SPI shouldn't be an issue with a TD cylinder unless there was a really bad machine job at the factory or someone reset the ball socket to harshly.
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Post  getback on Wed Feb 26, 2014 9:20 pm

It want actually be atd only the piston / cyl. I have been reading this old post 28,000 sounds crazy  
http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/8088423-subinduction-piston.html#post8088423


Last edited by RknRusty on Wed Feb 26, 2014 9:29 pm; edited 1 time in total (Reason for editing : FIXED LINK)
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Post  Cribbs74 on Wed Feb 26, 2014 9:55 pm

Keep in mind that was a 4.2x3 prop so that is where most of the RPM gain was. Heck I would do it if I felt the need. Right now I am more into stunt so I try and find ways to tame engines.  lol! 
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Post  Mark Boesen on Wed Feb 26, 2014 10:33 pm

Guys, I gotta read that R/C article with my short pants on....as I think its pretty deep!

I've always felt and still do that SPI is way overrated in the hunt for RPM. It reminds me of people back in my gearhead days talking about "fuelie heads" like it was some magical silver bullet, same goes for lightening pistons.

Lightening the piston will not give you 28K RPM, nor will SPI...maybe running a .020 prop would give you higher readings, but your planes not going anywhere.

Here's how you go fast: https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program
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Post  Jason_WI on Thu Feb 27, 2014 12:10 am

The piston on the right is lightned and on the left is standard. Not sure if this even helped my mouse engine at all.

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Post  John Goddard on Thu Feb 27, 2014 6:55 am

Easy does it Ron.
IMO even the Killer Bee pistons (I seem to remember these being the
lightest standard piston) can be on the 'delicate' side.
If my memory serves when I was doing the speedy speedy stuff
in 2011/12 a very fast engine that got slower over a couple runs
often indicated wrong timing/compression which if not rectified
V quickly ie another 1/2 gaskets added. A Holy/shattered piston
resulted particularly using the KB's.
 lol!
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Post  RknRusty on Thu Feb 27, 2014 9:40 am

Mark Boesen wrote:Guys, I gotta read that R/C article with my short pants on....as I think its pretty deep!

I've always felt and still do that SPI is way overrated in the hunt for RPM. It reminds me of people back in my gearhead days talking about "fuelie heads" like it was some magical silver bullet, same goes for lightening pistons.

Lightening the piston will not give you 28K RPM, nor will SPI...maybe running a .020 prop would give you higher readings, but your planes not going anywhere.

Here's how you go fast: https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program
Mark, thanks for tossing in the lifesaver of sensibility. A certain amount of SPI, not too much or too little, can certainly bolster the F/A charge in the combustion chamber and help the power of a reedie, but not so much in a rotary. Thinning a piston skirt seems to me like something that might sound cool to advertise and talk about, but it's hard to believe it actually increases power. If you want to reduce the mass of the rotating assembly you could just as easily shave it off the counterweight and put the heavy blade of the prop on that side to more than make up for it. I wouldn't recommend either.
Rusty

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Post  crankbndr on Thu Feb 27, 2014 2:56 pm

I've found good performance using the shortened, lightened piston and Sure Start cylinder combo from Cox International.
They have been in my Tach Race engines for the last three races. I tested many piston, cylinder combos always with 25%N and 5/3 prop as a baseline and keep coming back
If and engine won't spin up over 18K on normal compression I set it aside and move on. Tried TD with four boost flutes, TD with two boost flutes and Killer Bee combo and
none did as well as the Sure Start. That said, I keep losing so I'll have to try something else next, I'm going to look at the older #1 Black Widow set, the fit seems to be better than the newer sets. Two Cents  You sure would not want to shorten a piston cly. set that comes with SPI. All my tests were done on reedies,  could you spin a TD up to 28K with less prop and more nitro? Hot  Hot 



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Post  Mark Boesen on Thu Feb 27, 2014 4:17 pm

I really doubt it, I wouldn't wanna even try. A) The socket would likely fail and ruin a good piston/cylinder match, or B) That small a prop you're not going to go very fast.

I flew 1/2A R/C pylon years ago and it was common practice to lap piston/cylinder to reduce friction and heat, but never lightened piston or crank. We used about the same size prop as C/L Mousers do, 4.75x4. If I recall about 22-23k was about all they'd do on ground and they'd unload and turn more in air.
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Post  getback on Thu Feb 27, 2014 5:33 pm

hea Crankbedr is that one u cut down? it lokes good and seems in the pic the piston still has a lot of meat at the skirt end ,  Huh... well thanks for the replys guys ,Mark I have been using and have printed the Paul Gibeault article I am sure they would know the tricks that will last the longest and perform the best. Thanks Am going to still put my hand to it just to see what I can do with it, have a drill press and old blades ..tubing / tape ??  Laughing 
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Post  crankbndr on Thu Feb 27, 2014 5:57 pm

I don't have the skills to do this, that piston came as a set from Cox International


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Post  getback on Thu Feb 27, 2014 8:49 pm

crankbndr wrote:I don't have the skills to do this, that piston came as a set from Cox International


Lightening a piston using common tools Ci_tif10
WOW I am sure that cant be gotten anymore, never seed that before.  Very Happy 
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