Ring Gaps

[cl350rr]

what should the uncompressed ring gap be on a 1" bore cast iron sleve IC engine with 2 cast iron .050 width rings?

thanks
R

 

[b.lindsey]

cl,

Not a direct answer to your question but here is how I did it in the link below. All I can say is that the gap is minimal, once its put onto the piston and into the cylinder sleeve I can't measure it anyway.




http://www.homemodelenginemachinist.com/index.php?topic=6014.msg103347#msg103347

Bill

 

[cl350rr]

Thanks for the replies.

the rings are already made.

the gap when they are not compressed does not look large enough. I saw on a few sites that heat treating the rings with a peg between the end gaps will open the ring to an expanded shape.

I am trying to figure out what size peg to put between the ends to put enough spring in the rings to seal the cylinder.

If I'm reading your response right, .125 is what I am looking for.

Randel

 

[Maryak]

Guys,

Attached is an Excel file which gives the method I use to calculate piston rings. Based on work by Paul Chernokeef, Tubal Cain and Prof Craddock.

I don't use heat to form my rings but I do use spun cast iron as the material.

Hope this helps

Best Regards
Bob

View attachment Pistoncalc.xls

 

[Artie]

what should the uncompressed ring gap be on a 1" bore cast iron sleve IC engine with 2 cast iron .050 width rings?

thanks
R

G'day R, the uncompressed gap isnt too critical, the compressed gap is. The tension is required to give a machanical seal under cranking conditions, once the engine fires its the combustion pressures which press the ring onto the bore. Id go just a smallish gap as too much tension will increase the friction drag, small engine produce small power, drag is your enemy.... 8)

Using full sized engine theory, its 4 thou gap per inch of bore size.. thats 'UP TO' ... so a 1" bore could have a 4 thou end gap and be expected to work, a little less would be better with very thin rings.

Dont forget that the problem is that the ring will expand as it heats and the gap will close as it does.... so a 'correct' minimum gap will stop seizures and too much gap will not allow start because of low compression...... Ive had a Triumph seize up on me due to insufficient ring gap, not fun....

To check end gap in bore, place the ring in the bore and use the piston to square it up, then feeler gauges are used, as has been stated.

Be aware that the 4 thou quoted IS full sized engine stuff with thick rings and therefore more expansion when hot... might be worth turing up a test cyclinder the same size as the bore and putting a ring into it and heat to operating temp to see how close it gets.... maybe not....

Good luck

Rob

 

[Artie]

Looks about right, not forgetting that this looks to be for a steam engine. An IC engine will have much hotter combustion temps and therefore more expansion of the ring, Id therefore go a little on the looser side, perhaps 3 thou ??

 

[Artie]

With regards the side clearance in the piston ........ the piston (having more mass) will expand more than the ring in this direction and will become looser as it gets hotter... just a nice slide fit when cold id good.

 

[cl350rr]

thanks again for all of the help and info.

for the guys in the states, where do you buy cast iron for rings?

Randel

 

[Maryak]

Pat,

In the chart

Row1 Ring ID = 0.920
Row17 Piston Dia = 0.980
Row 18 Ring Groove depth = 0.033

Hence Ring Groove Dia = 0.980-0.066 = 0.914

Clearance = Ring ID - Groove Dia = 0.920-0.914 = 0.006

The axial groove clearance is 0.003.

Hope this helps

Best Regards
Bob

 

[Metal Butcher]

thanks again for all of the help and info.

for the guys in the states, where do you buy cast iron for rings?

Randel

I got the cast iron for my rings from Enco. The stuff they carry is called gray iron. I made quite a few rings from it and they all turned out well.

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=891-6528&PMPXNO=3906062

There are also many other on line metal sources that carry cast iron bar stock.

http://www.speedymetals.com/c-8388-round.aspx

-MB

 

[cl350rr]

MB,
Thank you, order going out today.

karma for you

Randel

 

[picclock]

I'm looking into the design of an engine to run off compressed air. As I would like the engine to have a long life I'm planning on using Cast Iron rings and bore.

Is there any reason why two rings, rotated 180 degrees should not be placed in the same slot as this would eliminate leakage through the ring gap as the surfaces of the rings would be in contact ?

Apologies for potential thread hijack.

Best Regards

picclock

 

[stevehuckss396]

I'm looking into the design of an engine to run off compressed air. As I would like the engine to have a long life I'm planning on using Cast Iron rings and bore.

Most compressed air engines do not need rings. I have 6 or 7 of them around here and none of them use rings. They would cause friction and put more of a load on the crank and bearings than is needed. Make a nice slip fit piston without the ring and concentrate on reducing friction and it will run well.

 

[picclock]

@ stevehucks
The engine I am considering making is not for show and would have a peak output of around 1KW. As I want to have good unattended life I intend to ballrace the mains and ends, but I foresee possible problems with cylinder lubrication. I am considering all options at the moment. I initially considered O'Rings but am not convinced about there longevity. Misting the air supply seems the simplest approach.

The engine design is twin cylinder, double acting, boxster style with the two pistons directly opposite one another to reduce vibration. I am intending to use an idea I found on the internet to facilitate this - see piccy.

Best Regards

picclock

(Have a good Xmas)

 

[compspecial]

Randel,
the old rule of thumb for IC engines was 3thou per inch of bore diameter, but turning to compressors the "puregas" co. of USA made compressors with PTFE rings and teflon coated parts which required no lubrication, the idea being that NO OIL was to be carried over into the receiver tank.This was for pressurising telephone cables.

 

[Maryak]

Is there any reason why two rings, rotated 180 degrees should not be placed in the same slot?

No, many steam pumps and air compressors use this configuration.

Hope this helps.

Best Regards
Bob

 

[Jasonb]

Seems like I saw two rings in one slot one time but I cannot remember where.Pat J

Could be that you were looking at a Clupet ring, quite a few of teh model traction engine boys overhere favour them together will an alloy piston to get a smoother running engine.

http://steamautomobile.com/phorum5214/file.php?1,file=261

Jason