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Cox Engine of The Month
shortening and lightening a piston
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shortening and lightening a piston
i have the means todo this and want to give this a second shot, i saw second because i tried shortening a .049 piston today in my machining class at a local community college and accidently snapp the con-rod in half
is there a better way to keep the con rod out of the way like using a piece of tooth floss tied to the open end of the connecting rod? and how should i go about lightening it?
thanks
is there a better way to keep the con rod out of the way like using a piece of tooth floss tied to the open end of the connecting rod? and how should i go about lightening it?
thanks
mitchg95- Diamond Member
- Posts : 2103
Join date : 2011-12-19
Age : 28
Location : Geneva, mn, USA
Re: shortening and lightening a piston
To bore out a piston you will need to grind a HHS blank tool to make a small boring tool.
I was thinking about using a magnetic base and a piece of elastic band with enough tension to keep it out of the way.
I was thinking about using a magnetic base and a piece of elastic band with enough tension to keep it out of the way.
Jason_WI- Top Poster
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Posts : 3123
Join date : 2011-10-09
Age : 48
Location : Neenah, WI
Re: shortening and lightening a piston
Yes, a custom boring bar will be necessary. I usually use a piece of music wire to hold the con-rod while machining.
Matt
Matt
Re: shortening and lightening a piston
EXModelEngines wrote:Yes, a custom boring bar will be necessary. I usually use a piece of music wire to hold the con-rod while machining.
Matt
ill try that thanks
mitchg95- Diamond Member
- Posts : 2103
Join date : 2011-12-19
Age : 28
Location : Geneva, mn, USA
Re: shortening and lightening a piston
Here's why I'm not a machinist.
My first thought would be to stick the piston down to a table with double faced tape and then fill the skirt with hot melt glue or even candle wax.
Then you could chuck it up and cut away - until you stick a tool in and popped out the plug.
I'm a wood guy by trade. Does it show?
My first thought would be to stick the piston down to a table with double faced tape and then fill the skirt with hot melt glue or even candle wax.
Then you could chuck it up and cut away - until you stick a tool in and popped out the plug.
I'm a wood guy by trade. Does it show?
lousyflyer- Gold Member
- Posts : 342
Join date : 2012-06-25
Age : 64
Location : Garden City Ga
Re: shortening and lightening a piston
Also, I have had better results shortening the piston first. A lot of time if you lighten first the material is so thin it will sort of buckle when trying to shorten it later.
Matt
Matt
Re: shortening and lightening a piston
EXModelEngines wrote:Also, I have had better results shortening the piston first. A lot of time if you lighten first the material is so thin it will sort of buckle when trying to shorten it later.
Matt
Just curious -
Are you thinning your piston skirts by dimensions or are you using the TLAR method? (That Looks About Right)
lousyflyer- Gold Member
- Posts : 342
Join date : 2012-06-25
Age : 64
Location : Garden City Ga
Re: shortening and lightening a piston
Here's a link Matt.
Lots of info on shortening and lightening pistons.
Bob
http://www.rcuniverse.com/forum/m_8088423/anchors_8255167/mpage_1/key_/anchor/tm.htm#8255167
DICKEYBIRD'S Poor Man's Lathe.
Lots of info on shortening and lightening pistons.
Bob
http://www.rcuniverse.com/forum/m_8088423/anchors_8255167/mpage_1/key_/anchor/tm.htm#8255167
DICKEYBIRD'S Poor Man's Lathe.
dckrsn- Diamond Member
- Posts : 2750
Join date : 2010-10-21
Age : 71
Location : Long Island, New York
Re: shortening and lightening a piston
lousyflyer wrote:EXModelEngines wrote:Also, I have had better results shortening the piston first. A lot of time if you lighten first the material is so thin it will sort of buckle when trying to shorten it later.
Matt
Just curious -
Are you thinning your piston skirts by dimensions or are you using the TLAR method? (That Looks About Right)
Tlar, i dont have any dimensions
mitchg95- Diamond Member
- Posts : 2103
Join date : 2011-12-19
Age : 28
Location : Geneva, mn, USA
Re: shortening and lightening a piston
lousyflyer wrote:EXModelEngines wrote:Also, I have had better results shortening the piston first. A lot of time if you lighten first the material is so thin it will sort of buckle when trying to shorten it later.
Matt
Just curious -
Are you thinning your piston skirts by dimensions or are you using the TLAR method? (That Looks About Right)
Yes and no. When we build custom engines for customers who want a lightened piston I usually go to about a .015" wall thickness which is around what the OEM Killer Bee had. Even that is a bit thin for structural integrity and will have a short life as compared to a regular piston. I have tried to go as thin as I could and it ended up about .005"-.007" which, needless to say, will run great but longevity of the piston is rather short
Matt
Re: shortening and lightening a piston
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.
Piston length: .3565"
Piston wall thickness: .015"
Depth of lightning: .150"
This is for use in a surestart cylinder with twin slit exhaust.
Jason_WI- Top Poster
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Posts : 3123
Join date : 2011-10-09
Age : 48
Location : Neenah, WI
Re: shortening and lightening a piston
Jason_WI wrote: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.
will that work in my cylinder? has no # is modified and has 2 boost and bypass ports?
mitchg95- Diamond Member
- Posts : 2103
Join date : 2011-12-19
Age : 28
Location : Geneva, mn, USA
Re: shortening and lightening a piston
does this cylinder have SPI with a standard piston? If it does then no it will be too short and have too much SPI.
Jason_WI- Top Poster
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Posts : 3123
Join date : 2011-10-09
Age : 48
Location : Neenah, WI
Re: shortening and lightening a piston
Jason_WI wrote:does this cylinder have SPI with a standard piston? If it does then no it will be too short and have too much SPI.
Correct, do not further shorten a piston that already has SPI in its current cylinder setup.
If a setup does not have SPI, there are 2 ways to induce such.
#1) Shorten the piston (we shorten by aprx 1,500ยต)
#2) Lower the exhaust port cutouts by the same amount as #1
Either way is fine, depending if one prefers torque over mass/inertia or vice-versa.
Re: shortening and lightening a piston
Jason_WI wrote:does this cylinder have SPI with a standard piston? If it does then no it will be too short and have too much SPI.
it did not have spi, but now it does
mitchg95- Diamond Member
- Posts : 2103
Join date : 2011-12-19
Age : 28
Location : Geneva, mn, USA
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