Piston ring boor?

[Antay]

Hello guys,

First of all, excuse me if my english is a little bad!

The last couple of days I have been reading about how to make piston rings, and I have now decided to make some on my own.

I took a part an old nitro engine (OS MAX 60 H blackhead) some years ago because of bad compression. I remember that I took the piston ring of, but now I can't find it..

I have red about different methods on the forum which describes the
thickness, OD and gap. But what I can't find is the ID (boor) of the ring. I do belive that there should be some "back clearance" so the gasses can force the ring outwards.

What should that clearance be? (mm/inch)




Some info about the piston and sleeve.

Sleeve ID (bore) = 24mm
Piston is OD = 23.95mm (ish)
The ring slot diameter is 21.8mm


For the non-metric guys :

Sleeve ID (bore) = 0.944''
Piston is OD = 0.942'' (ish)
The ring slot diameter is 0.858''



Andy

 

[portlandron]

Not an expert on the subject but have made a few rings.

Think of the ring as a spring pushing against the sides of the cylinder. That is what makes the seal not so much "back pressure".

The grove in the piston need to be just slightly deeper then the width of the rings and the gape in the end of the ring needs to be sized so that the ring can be compressed to fit the cylinder.

The following are dimensions of two sizes of rings that I purchased.

For a one inch cylinder the ring is .0615 wide and .0401 deep and at rest the O.D. is 1.0225 and for a 3/4 inch cylinder the ring is .060 wide and .027 deep and at rest the O.D. is .7665

Hope this helps you.

 

[Antay]

Not an expert on the subject but have made a few rings.

Think of the ring as a spring pushing against the sides of the cylinder. That is what makes the seal not so much "back pressure".

The grove in the piston need to be just slightly deeper then the width of the rings and the gape in the end of the ring needs to be sized so that the ring can be compressed to fit the cylinder.

The following are dimensions of two sizes of rings that I purchased.

For a one inch cylinder the ring is .0615 wide and .0401 deep and at rest the O.D. is 1.0225 and for a 3/4 inch cylinder the ring is .060 wide and .027 deep and at rest the O.D. is .7665

Hope this helps you.

Yes, Thank you! This makes perfect sence. So if I just have a little gap behind the ring it should be ok I guess. I will try it

 

[gbritnell]

For a piston and ring this size I would allow .003 behind the ring (.006 on the diameter) As far as the end gap it should be a minimum of .0015 and no more than .0025.
Use a material like Ductile iron. Turn the I.D. and O.D. to size. Cut off leaving .002-.003 on the thickness. Make up a fixture to hold the ring. ( A cylindrical piece of steel with a counterbore equal to the ring diameter. The counterbore depth should be slightly less than the finished thickness of the ring.) Using a fine emery paper rub the ring on both sides until the thickness is obtained.
Split the ring. Make up a circular fixture with a round post on the edge of the diameter. This is to hold the ring open while heat treating it. For a ring this size I would use a post of about .094 diameter. The ring and fixture should be coated with a anti-scaling powder or encased in stainless foil while heating to prevent oxidization. Heat to a dull red color and let cool naturally. Once cooled the end gap will need to be adjusted for the bore.
gbritnell
http://www.modelenginenews.org/techniques/piston_rings.html

 

[Antay]

For a piston and ring this size I would allow .003 behind the ring (.006 on the diameter) As far as the end gap it should be a minimum of .0015 and no more than .0025.
Use a material like Ductile iron. Turn the I.D. and O.D. to size. Cut off leaving .002-.003 on the thickness. Make up a fixture to hold the ring. ( A cylindrical piece of steel with a counterbore equal to the ring diameter. The counterbore depth should be slightly less than the finished thickness of the ring.) Using a fine emery paper rub the ring on both sides until the thickness is obtained.
Split the ring. Make up a circular fixture with a round post on the edge of the diameter. This is to hold the ring open while heat treating it. For a ring this size I would use a post of about .094 diameter. The ring and fixture should be coated with a anti-scaling powder or encased in stainless foil while heating to prevent oxidization. Heat to a dull red color and let cool naturally. Once cooled the end gap will need to be adjusted for the bore.
gbritnell
http://www.modelenginenews.org/techniques/piston_rings.html

Wow! Thanks for the details. Really helpful. I will try it out and see how it works

again, thanks!