Question on pistons

[kvom]

I managed to overbore the cylinder on my current build by .02" (.774 vs .752). So I can remake the cylinder or the piston. Since it takes 4+ hours to make the cylinder and 45 minutes for the piston, you can guess my preference.

The current piston is CRS, as is its twin. I don't have any round stock that's larger then .75", so to remake it in steel I need to wait a week or so to find some at school. OTOH, I have some 1" brass rod that can be turned down.

Is there any reason that a brass piston in an aluminum cylinder would be a bad idea?

 

[Brian Rupnow]

You should be all right running the brass in an aluminum cylinder. These small engines are ran only for demonstration purposes, and always kept lightly oiled, so I don't see a problem. On the other hand, why not use the piston you have already---just machine an o-ring groove in it and run a viton o-ring slipped over it. They seal excellent, cost next to nothing, are low friction, and will last forever.

 

[Philjoe5]

I have used brass or bronze pistons in aluminum cylinder blocks and haven't had a failure with over 100 hours of running time. As Brian said these compressed air driven engines aren't subjected to a lot of stress. If you want some experience machining a piston for an O ring, here's your opportunity. Otherwise, go with brass and enjoy lots of run time with your engine.

Cheers,
Phil

 

[deere_x475guy]

Kvom, my avatar pic has brass pistons running in aluminum and I have over several hundred hours on it...

 

[Jasonb]

You will have a job finding a plus .020 O ring, its not a good idea to try and stretch a 0.750 one.

I'd just make it again in brass.

Jason

 

[Brian Rupnow]

You will have a job finding a plus .020 O ring, its not a good idea to try and stretch a 0.750 one.

I'd just make it again in brass.

Jason

Jason---Not to belabour a point, but an 0.020 diametral stretch on an o-ring is nothing, and can be easily achieved.

 

[deere_x475guy]

Brian, what kind of O ring should I use for steam/air and where can I find the specs on bore size to match an O ring with?

 

[Brian Rupnow]

Just a standard urethane o-ring should do the trick---for higher temperatures, use Viton. For engineering specifications and sourcing, I would try any industrial pneumatic or hydraulic service/sales outlet.

 

[Tin Falcon]

MSC Big book page 4260 has a pretty complete guide to O-Rings and of course they have a large selection most in packs of 100
O-ring guide
or McMaster Carr
http://www.mcmaster.com/param/html//Oringsize/9452kac.pdf
Tin

 

[Brian Rupnow]

deere_x475guy ---I see from your profile that you are in Michigan. In Ontario, where I am, there is a company called Hercules O-Ring---they are a distributor for just about every kind of o-ring known to man. I have been in there different times and told the counter guy what I was trying to do, and a couple of times I took one of my model steam engines in and ran it for him on the plants compressed air system. He was so impressed that he just gives me whatever o-ring I need, and asks for "A dollar for the coffee fund" whnever I try and pay for an o-ring.

 

[deere_x475guy]

MSC Big book page 4260 has a pretty complete guide to O-Rings and of course they have a large selection most in packs of 100
O-ring guide
or McMaster Carr
http://www.mcmaster.com/param/html//Oringsize/9452kac.pdf
Tin

Tin thanks I have these bookmarked now for future ref.

 

[deere_x475guy]

deere_x475guy ---I see from your profile that you are in Michigan. In Ontario, where I am, there is a company called Hercules O-Ring---they are a distributor for just about every kind of o-ring known to man. I have been in there different times and told the counter guy what I was trying to do, and a couple of times I took one of my model steam engines in and ran it for him on the plants compressed air system. He was so impressed that he just gives me whatever o-ring I need, and asks for "A dollar for the coffee fund" whnever I try and pay for an o-ring.

Yea Brian I am just south of Lansing in a little town called Eaton Rapids. Very nice quiet little community. Wife and I love it here. I have had a similar situation with the Car Quest auto store here. I was looking for a cylinder hon to use on the Webster I have started and I took it in with me. Those guys bent over backwards to find me one that went small enough and once I finally get it finished I have to take it back in. One of the counter guys took a real interest in what I was doing and I have had him in the shop several times now and took some time to teach some basic things. I have a feeling he will be looking for a small lathe and mill real soon here.

Thanks for your input and I also will be sending you a pm about your beam engine plans. Take care.

 

[ken4570]

http://www.oringsusa.com/