The great O ring discussion

[Brian Rupnow]

I have made piston rings in the past, but they were failures. It's been a while, but as I remember I turned the o.d of the rings to some pre-established diameter based on the cylinder diameter, turned the i.d. to a diameter based on some calculated formula, then split the rings by holding one side in the vice and pushing on the ring with my fingers. After "splitting" the rings were wedged open around a piece of bar stock and then heated until they fell off. The sides of the rings were then cleaned up by rubbing on a piece of glass with some 600 grit compound to remove any scale that had formed. When pushed into the cylinder and held up to a light, I could see visible gaps between the outside diameter of the ring and the inside of the cylinder. It seemed to me at the time that if I could have refixtured the rings and turned the outside diameter to be truly round, they would have worked for me. I remember that some time after making these rings that I seen a good write up on the Trimble method of making rings, which did include using a fixture to turn the outer diameter of the rings to be perfectly round, but by that time I had moved on and didn't pursue any more ring making. I have spent the morning Googling and watching Youtube videos about ring making using the Trimble method, and I can't find the article that I seen eight or ten years ago. Trimble wrote a 16 page paper on "Design and Fabrication of Piston Rings" but I haven't been able to find it anywhere.

 

[Tim Wescott]

That link that I posted for you links to two or three different methods of making rings, at least one (and I think two) of which have you compressing the split rings, clamping them into an arbor, then turning (and maybe lapping -- it's what I recall, but I'm too lazy to go read the articles) the rings to size.

Also in the framing article, Ron mentions that the easier methods do end up with rings that don't have the world's greatest fit at first, but will eventually run in. Personally, I think I'll start with one of the methods that makes round rings that fit the bore...

 

[kuhncw]

Hi Brian,

Terry Mayhugh's posts, detailing how he makes rings may help you. He uses the Trimble method.
Here are two links:

See the May 8 post.
Another Knucklehead Build

See Aug 4 post
https://www.homemodelenginemachinis...s-time-18-cylinders.21601/page-11#post-252230
Regards,
Chuck

 

[Brian Rupnow]

Chuck and Terry---Thank you for the links. I have read thru them and tried to comprehend everything I read.---Brian

 

[Brian Rupnow]

I'm getting old and kinda dumb---but Damn, I thought I had seen a method of making rings where there were two fixtures involved. One fit inside the stack of rings and clamped them before heat-treat with a torch, and one that fit inside the rings and clamped them for turning the outer diameter to a perfect roundness. I can not find that method anywhere. I distrust my own memory now.---Brian

 

[Brian Rupnow]

Hah!!--I'm not crazy after all. The method I remember seeing was work by Chaddock and Warsaw. One fixture was used to heat multiple rings at one time for heat treat, and the second fixture was used to turn the ring outside diameter to a perfect roundness, one ring at a time. The only catch is that in that second step, the depth of cut is 0.001" or less to achieve perfect roundness. That is a cut far more suitable to a toolpost grinder than any kind of cutting tool, and I don't have a toolpost grinder.
http://www.model-engine-plans.com/engineeringtips/pistonrings.htm

 

[Tim Wescott]

I wonder if you could achieve that second cut by lapping the outside of the rings. The tool would just be bog-standard outside lap, which you could whip up in an hour.

 

[mayhugh1]

If you use the Trimble method, the rings come out perfectly round without having to re-turn them in a second fixture after heat treatment. Trimble published two lengthy articles in Strictly IC containing the math he used to develop his method. He did his analysis on a programmable pocket calculator long before home computers were available. His heat treatment fixture is actually a precision device that according to his analysis creates a proper balance of radial forces to insure the rings end up perfectly round after heat treatment. The problem is, many people didn't read the original articles and if they did, don't understand and appreciate the math involved. Many have taken shortcuts with the dimensions, the cleaving, and the machining of the fixture and have been disappointed with the results. Some started combining a look-alike Trimble fixture with yet another method for making rings such as the one requiring a second final turning operation. Jerry Howell in fact recommended a similar technique in the plans for his V-twin, and I successfully used it to make my very first set of rings.

Unfortunately, Trimble also recommended a much higher normalization temperature than many 'experts' felt should be used. This cast some doubt on the credibility of his method in some builders eyes and may be one of the reasons it wasn't strictly adopted.

I've closely followed Trimble's method (except for his excessively high normalization temperature) for well over a hundred rings and light testing showed them to be perfectly round after heat treatment with no further turning required. What I have found tough is that some care is required to turn the initial blanks from which the rings will be parted. Trimble's method assumes distortion-free starting blanks from which the rings will be parted. Even quality cast iron has pent-up stresses that will be unevenly relieved when the blanks are initially turned. Some of this distortion can show up days after the blanks are turned. I've tried different methods for creating blanks with minimum starting distortion during my various builds and was most successful with the one described in my last build - the 270 Offy. In any event, I think it's much easier to tackle the up front problem of creating distortion-free blanks that it is to take a .001" clean-up pass on a finished ring and hope its final circularity is within a tenth or so. - Just my two cents worth - Terry

 

[Brian Rupnow]

Thanks Terry. ---I've read your post, and I keep adding to my knowledge base.---Brian

 

[IC-man]

I too have used the Trimble method with good results, making 3-4 rings in a stack
Many seem to worry about the cleaving but I have found by griping the ring with 2 pairs of flat nose pliers (right next to each other) and just bending slightly i get a clean break every time. Clean and gap with needle file after heat treatment.

 

[Brian Rupnow]

I have spent the last week or so reading everything I can find about making piston rings. I would much rather buy them than make them, they only cost $4 each and I only need two.---But---the guy at Ringspacers.com seems to be very, very busy. I emailed him and got no response, and then after a few days I called him and he said he was so busy he couldn't spit, and it might take him a while to send me a quote. It's been another 3 or 4 days now, and I still haven't heard from him. I'm going to have to buy some grey cast iron and make a new piston to suit the rings. (I don't want to make the piston from aluminum this time, because grey cast iron has much better wear qualities when it's running in a cast iron cylinder.) I do have lots of short ends of grey cast iron laying around here, big enough to make rings from but not big enough to make a piston from. I used rings from Ringspacers in my vertical hit and miss engine, and they worked very well, and the bore on it was 1", same as my vertical engine-2021---So---I have all of the necessary dimensions to build another piston. I'm not under any time limitations except for my own impatience, so I'll give it another week and if I haven't heard from Ringspacers I may try making my own rings again.

 

[dsage]

I thought you bought some rings from DeBolt machine in the past and were satisfied?
Click Products below. 1" is $8
https://www.deboltmachine.com/collections/all

 

[Brian Rupnow]

Deboldt and Ringspacers are the same place. EDIT--EDIT---they are not the same place. i was mistaken.

 

[dsage]

Good to know. Thanks

 

[Brian Rupnow]

dsage--I may have been mistaken on that. Debolt has a nice new web page with good information and pricelist. Ringspacers has an old web page which seems to imply that it was once owned by Debolt but may now be owned/used by somebody else. I believe the mans name was Dave Reed, and his rings were $4 each. I contacted him by phone and by email over a week ago, and he said he was overwhelmed by work and would get back to me. I am tired of waiting for him, so will now try to order rings from the link you gave me. If anybody knows what is actually going on with them, please let me know.----Brian

 

[Brian Rupnow]

After a bit of sleuthing I have found the following. Two different companies. Debolt is out of Zanesville, Ohio. Ringspacers is out of Elkton, Maryland. I have dealt with both in the past and consider their products to be first class stuff.

 

[Tim Wescott]

You may also want to try this guy -- he caters to people keeping model airplane engines alive, but he says he makes stock and custom rings. https://rmjmachineworx.com/online-store

I think if it was me I'd call him with an approximate bore, and see if he's got something in stock that comes close, then machine my cylinder/piston to fit.

 

[Brian Rupnow]

Just placed an order with Debolt for two 1" rings. Rings are $10 each and shipping is $20 so $40 American---which is $52 Canadian. Ouch, ouch, and double ouch!!! Oh well, I've studied so much this week on how to make my own rings that my NEXT set will be made by myself.

 

[dsage]

What !!
Are you saying they charge $20 US PER RING for shipping?
Like it makes any difference if they put one or two (or a dozen) in the same shipping envelope. Robbery. (Sorry).
I've noticed this same approach from a lot of companies. Seems they are taking advantage of charging shipping to increase their profit. It will be interesting to see what the actual shipping charge was on the package. Keep us posted.
Of course there could be another explanation.

 

[Tim Wescott]

Seems they are taking advantage of charging shipping to increase their profit.

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.