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Old 11-22-2012, 03:39 AM   #161
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Chris,

If I may ... would give me the dimensions of the Piston and what O-ring are you using... maybe a 012?


Thanks

Pat H


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Old 11-22-2012, 04:02 AM   #162
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Question to mods can the name of this thread be changed to team build 8 without deleting the info in it?

Dave

Name changed -- Gail in NM



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Old 11-22-2012, 11:56 AM   #163
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Path the piston is .490 on the outer edges and
I believe I went to .435 on the oring grove ( I will have to double chech when I get home)
I'll check on the oring but I am pretty sure it is a #11 the 12 would be too big on the outer diameter I think anyway.
I will get a rough measurement on the oring when installed for you too.
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Old 11-22-2012, 07:12 PM   #164
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Thanks ... also the grove dimension for the O-ring (drawing has it as .067") which is too small for this O-ring.

Thanks,

Pat H
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Old 11-22-2012, 10:45 PM   #165
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That will be fine . I will bore as close to .500 as I can . The name change is a good Idea . If it can be done , Thanks Dale
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Old 11-23-2012, 12:32 AM   #166
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Ok the ring grove is .420 the piston is .490 and.070wide
With the ring installed it is about .530 when it makes contact. The ring is a #011
Finished piston will still be the same .187 so as to not have to worry about any Interference issues.

Chris
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Old 11-23-2012, 06:56 PM   #167
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I'm working on cutting material today.Can I use stainless for the connecting rod keeper plate? I havs quite a bit in 1/16 stock. At least I'm guessing it's stainless. It's not aluminum but it's also non magnetic.

Chuck
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Old 11-23-2012, 08:09 PM   #168
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Chuck,

Yes, SS would be great.


Pat H.
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Old 11-23-2012, 10:11 PM   #169
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Quote:
Originally Posted by chrispare View Post
Ok the ring grove is .420 the piston is .490 and.070wide
With the ring installed it is about .530 when it makes contact. The ring is a #011
Finished piston will still be the same .187 so as to not have to worry about any Interference issues.

Chris
Thanks for the measurements.

After reviewing the data I suggest that a design change is in order for the piston. Not a big change.

The sizing for the piston was based on a Cast Iron Ring or Delrin or Teflon.
Since we are using an O-ring (a good choice) the gland area needs to be changed so that O-ring will provide a good seal but not too tight.

Since the cylinder has a bore of .500" the correct O-ring size is the 012. It is designed for that bore, the .011 is for a 7/16" bore. If the 011 is used with the diameter .420" (inside diameter for the .011 is .301") it will be stretched over 25%. The manufactured suggested stretch is 0-5% with typical at 1-2%, the excessive stretch can overstress the material.
The next issue is the squeeze. For reciprocating applications 10-20% is generally acceptable. The squeeze using the current the piston / O-ring is over 43% ...very tight and unnecessary. Aiming for 15% would allow some variation the Bore and gland diameter.

Finally the gland width , typically in this application 15% is usually the norm. Due to the squeeze, heat expansion etc the O-ring will need that extra room.

So in summary:
Use a AS568-012 O-ring.
Inside groove diameter should be .375-.380" .
Grove width should be .081 to .085

The cylinder should be as close as possible to .500 and smooth (a little honing may be needed). All corner and holes should have a smooth radius to prevent damaged during insertion and using.

The Piston Rod Gland (item #23) and Valve Gland (item #21) needs to be reviewed to insure that it will not be too tight.

Pat H.
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Old 11-23-2012, 11:42 PM   #170
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Quote:
Originally Posted by chucketn View Post
I'm working on cutting material today.Can I use stainless for the connecting rod keeper plate? I havs quite a bit in 1/16 stock. At least I'm guessing it's stainless. It's not aluminum but it's also non magnetic.

Chuck
I found some more of this material (inhereted from my Dad, over 10 years ago) and found markings indicating it was 304 SS. Woohoo! It machines nice! Dad was a maintenance electrician in a factory that made electrical contacts for aircraft and military applications. That same factory produced the magnitos used on the Spirit of St. Lewis. He used to bring home all kinds of scrap and cutoffs from work. My brother works there today and I get brass bar ends from him.


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