The great O ring discussion

[chrsbrbnk]

OTTO GAS ENGINE WORKS 2167 Blue Ball Rd Elkton Maryland 21921-3330

phone: 410-398-7340

E-mail address: [email protected]

Home Page on the web: OTTO GAS ENGINE WORKS

Just about any size and the ones I have work well

 

[dsage]

Try running a small mail-order business for a while -- then report back on why shipping should always be free.

I didn't say anything about free shipping. Only reasonable shipping. If it's $20 then so be it. BUT
The fact is whether the order says two or one for pistons rings, it takes the same amount of time and effort to process the order. Except maybe a few tenths of a second to pull two from the drawer instead of one. Shipping is / should be based on package size and weight. There is no need to DOUBLE the shipping based on two piston rings. Maybe so for some other heavy items. That's fine.
In the US there is a flat rate package with US postal service. Put anything you want, any amount and any weight in a certain sized box and it's not a high as $40 (last time I checked). A bubble envelope is all that's required to send a couple of pistons rings. Charge the going rate, but don't double it for two in this case.

 

[Brian Rupnow]

You may have misinterpreted my post. Each ring costs $10 American. The shipping is a total of $20 American to ship both rings in one package. That total of $40 American translates to $52 Canadian because of the differential in the value of a dollar between Canada and USA.

 

[dsage]

Ok. My bad math / interpretation. $20 was enough though. Enough said.

 

[ajoeiam]

Possibly to to bring it up to $0, even.

Orders take time to fulfill. Someone has to read them, pack them, make an address label, etc. Unless you're doing it yourself -- and don't value your time -- someone has to be paid to do the work. $20 to send you an empty box, from a one-man business, means that someone is paying themselves around $15 an hour, or possibly less.

To a certain extent, big operations (like Amazon) can refine the shipping process to bring that minimum down, but even then "free" shipping is just a come-on, that results in more expensive orders subsidizing the less expensive orders, to reduce competition and lock in your business.

Try running a small mail-order business for a while -- then report back on why shipping should always be free.

I would counter that if it takes even a one man shop an hour to fulfill a purchase order - - - - - well - - - - he/she needs to stir their stumps at the minimum or devise better systems. In fact if you're taking more than 20 minutes do the same. (I'm not sure but I think markups have also increased but am not so sure of that!)

I think we have far too many people who go to work for a paycheck and precious few who go to 'work'.

(I'm looking at a local retirement residence expansion. They've already been at it for 8 months and their expected completion isn't for another year. When I worked in construction in the late 70's that size of project would have been done in some 8 to 10 months. Remember - - - -work expands to fill available space (I think most people today are allergic to work - - - they think they will die if they're faced with such!).)

I just love Amazon's shipping.
First they demand an urban address (sorta tough for us rural folks! but I spend money every month for such).
Second they complained when there was no one available on Easter Sunday morning at 09.15.
Somehow they haven't ever heard of business hours.
That kind of delivery really isn't enhancing service at all.
I wonder what Mr Jeff would do if I showed up at his house with an order say on a Tuesday at 06.00 - - - - and my working day starts before that.

 

[doc1955]

When making 2 or 3 rings I use the method from the book "The Shop Wisdom Of Philip Duclos" This method has not failed me. When I make a larger quantity then I make a fixture for heat treating. Once you have made rings a few times you will say "that was easy" LOL

 

[Dragons_fire]

Question relating to the o-ring debate... How small can CI rings reliably work? For example, Kelly's Tiny Inline 4 engine uses o-rings, but it's only a 3/8" bore. He recommends vinton o-rings, and that was my plan, mostly cause I'm having issues finding CI under 2" diameter and I'm not spending my life savings on that to turn it down to 3/8".

 

[Tim Wescott]

If you're in the US (or Canada, and want to spend money on postage) McMaster-Carr has cast iron rods down to 5/8" -- and pretty reasonable on price for the smaller dimensions.

 

[Brian Rupnow]

I'm right in the middle of doing a bunch of research on making my own cast iron rings. What I am seeing is that for cylinders under 5/8" diameter, it is better to go for a lapped fit between piston and cylinder with no rings at all, or one Viton o-ring. That's not to say iron o-rings would be impossible, but at such a small size it would be very difficult.---Brian

 

[Nerd1000]

I think at 3/8" your rings would be devilishly thin. Rings for my Webster worked out to 0.8mm thick, and while I found making them to be easier than expected (I thought I'd goof up for sure) that's still a little thinner than i feel comfortable making. Plus the engine is far from finished so I can't speak to whether they'll actually work. 3/8" is a little under half the bore diameter of the Webster, so you'd want something like a 0.4mm ring? Crazy.

I think for such small rings I might try making them from bronze. Much easier to get in small sizes, and it works in steam engines so why not IC? Would need a larger gap to compensate for lower stiffness of the bronze.

 

[Steamchick]

I think Brian is right. I have owned a bought 1/2"bore Compression ignition engine that had no piston rings. - Just 2 grooves, because the gas dynamics resist blow-by. The clearance of piston to bore was incredibly small - which helped get the compression high enough for auto-ignition.
But a model I made, only ran for a couple of minutes, before the clearance was too big to get enough compression. With cylinder head changed to glow-plug type, I got another couple of minutes running before the piston to bore leaked too much so I had no compression.
However: It may be possible to make wire rings = wind a coil onto a shaft and select middle coils, after slitting. Hold coils tight on the shaft while slitting. I have not made any, but that's what the factory does. There is an "end effect" for the tangential load of the ring within about 30 degrees of the split, where the ring, when compressed in the bore, is trying to straighten more at the "ends", so this is compensated by bending-in the coil maybe 1 wire diameter at the ends. Of course, it may not be significant with wire rings in tiny bores? Also, dress ends so there are no sharp edges to score bores. Don't chamfer, just remove burrs and "sharpness" at the cut.
Modern cars have wire rings, not cast iron, (Mostly, as some have Lithium Batteries!).
Enjoy!
K2

 

[Nerd1000]

Would you have to straighten the slightly helical shape of a wire ring so it sits flat? Stands to reason you would.

 

[Steamchick]

HMMM... Assume I am thick, but why does it stand to reason? The ends (gap) don't have to align perfectly, because there is a gap anyway, and as long as the ring contacts all the way around it should be OK if "close", - with my reasoning? The ring groove does that anyway. With 0.5mm wire it only has a pitch of 0.5mm. as wound. The ring clearance will be only 0.025~0.05mm anyway, - which at max is only 1/10th of the wire diameter, so "I Guess" it will be OK? the slight axial force from the "twist" would probably just form a slight contact on one end on the top, and on the other at the bottom. If this prevented rotation then it would be an issue, but if the ends are suitably fettled they should slide, allowing rotation. I don't remember a "flattening" process on Production rings in H & G's factory. - But my not remembering doesn't mean there wasn't one. I can only suggest "try it and see".

K2

 

[awake]

I think at 3/8" your rings would be devilishly thin. Rings for my Webster worked out to 0.8mm thick, and while I found making them to be easier than expected (I thought I'd goof up for sure) that's still a little thinner than i feel comfortable making. Plus the engine is far from finished so I can't speak to whether they'll actually work. 3/8" is a little under half the bore diameter of the Webster, so you'd want something like a 0.4mm ring? Crazy.

I think for such small rings I might try making them from bronze. Much easier to get in small sizes, and it works in steam engines so why not IC? Would need a larger gap to compensate for lower stiffness of the bronze.

That's mighty thin, but possibly doable. However, keep in mind that when working with models, sometimes the math has to be thrown out in favor of what is practical - most people making the Webster use thicker rings, more like 1.5mm. In my case, I used a Viton o-ring, 1.5mm, and it has worked and continues to work perfectly.

 

[Nerd1000]

HMMM... Assume I am thick, but why does it stand to reason? The ends (gap) don't have to align perfectly, because there is a gap anyway, and as long as the ring contacts all the way around it should be OK if "close", - with my reasoning? The ring groove does that anyway. With 0.5mm wire it only has a pitch of 0.5mm. as wound. The ring clearance will be only 0.025~0.05mm anyway, - which at max is only 1/10th of the wire diameter, so "I Guess" it will be OK? the slight axial force from the "twist" would probably just form a slight contact on one end on the top, and on the other at the bottom. If this prevented rotation then it would be an issue, but if the ends are suitably fettled they should slide, allowing rotation. I don't remember a "flattening" process on Production rings in H & G's factory. - But my not remembering doesn't mean there wasn't one. I can only suggest "try it and see".

K2

It's my understanding that the ring seals against the bottom of the ring groove (on the power stroke) so it must either be flat or get forced down into a flat shape by pressure in order to work. Otherwise the gas could go around it via the ring groove.

 

[Steamchick]

Good one. I guess you are right. I just don't remember seeing a flattening process in the factory 30 years ago.
K2.

 

[timo_gross]

Oh hell, not again. This hobby is dying. Why make the barrier to entry more difficult by criticizing how people make their engines? The whole "you're doing it wrong" does nothing but push people away. So what if someone wants to use sealing method over another? Give it up.

I am fairly new to all this trying to make a first sort of working steam model at some point. ( boiler beeing the problem ) Piston rings beeing an interseting question.
No ring at all works fine so far. ( not beeing combustion, not running on steam, not required to do more than just moving )

I did not read a "you*re doing it wrong" in the original post, rather than a "it is horribly difficult to make an engine anyway, so the rings are not the worst hurdle" and "just go for it, before you tell yourself it cannot be done!"

... continues reading ...

Greetings Timo

 

[Steamchick]

Timo. I agree with the "just go for it" sentiment. But please can I offer some advice (from my bucket of scrap knowlege from 50 years in Engineering).
Develop manufacturing methods, techniques and skills by following an existing design. (My first few engines were from drawings).
Try and understand the designs so you can appreciate critical sizes, fits, etc.
Then consider you own "freelance" ideas.
At each stage gain buckets of knowledge from "teachers" on this site, books, theory, calculations, etc.
Remember, a machining apprentice would take 4 or 5 years full-time work to become fully proficient. A professional Engineer would take 3 to 5 years of education plus a few years or decade of experience to become reasonably good at Design and Manufacturing.
Experts have even 50 years experience and are always learning and improving.
So you have picked a hobby that can occupy a long and happy life!
Enjoy!
K2 (just learning, after 50 years!)

 

[timo_gross]

Timo. I agree with the "just go for it" sentiment. But please can I offer some advice (from my bucket of scrap knowlege from 50 years in Engineering).
Develop manufacturing methods, techniques and skills by following an existing design. (My first few engines were from drawings).
Try and understand the designs so you can appreciate critical sizes, fits, etc.

Hello steamchick,

i think I am trying to follow that advice on the one hand and doing some things "freelance" in parallel. Trying to not get too much off topic from the piston rings . So far I started with a myfordboy "compressed air engine", then I found some Elmers engine design on the internet (it is a barstock engine), finally another bar stock one that is called "Gerry Dykstraa beam engine".
They are all somewhat running without any piston ring. The nuts that tighten the packing around the piston rod are also "missing" ( not all, but some ). All of them have a Brass cylinder with approx. 12 mm diameter and a rattlefitnesium piston.

My assumptions concerning the piston rings

• Low friction is better if the engine does not need to really work, but only move, so a little leak in the piston does not harm?
• A new piston with rings can still be "retrofitted" or a ring groove can be added at a later stage or is there a reason why it needs to be done right away?

Task at hand for me as beginner converting the "compressed air" engines into steam engines. The piston rings, may become one task during this endeavour.

Greetings Timo

 

[Steamchick]

There are 2 schools of thought:
1) - the best possible sealing is the most efficient.
2) - Steam engines usually run "wet" - I.E. condensate from the expanding (And cooling) steam condenses and the droplets lubricate the bore and help seal the piston anyway.
Unless you are running a locomotive or some serious load, then a few grooves acting as a labyrinth seal are usually adequate on most stationary models, that are idling rather than doing any serious work. The major advantage is the low friction of a labyrinth seal so the models run on a minimum of steam and the slow action looks more "real". Unless you have a high speed engine of course!
But making a working piston ring of whatever design is necessary for high compression engines - like infernal combustion engines. And some do it "because they can".... even if it takes hours of labour and experimenting to get it right.
Cheers!
K2