A new attempt at making piston rings

[doc1955]

Hi doc1955: I didn't know bore gauges gave larger bores than measured... I thought they had small radius ball ends to accommodate the bore curvature? - Or maybe I misunderstood your info? - I use inside callipers myself, although I bought some "spring-loaded lockable" bore gauges, I still just use the inside callipers.... set to the bore, then compared to a mic. - Never had a problem that I know about.
Cheers.
K2

I think its the spring pressure and vers size of bore not the curvature of ends of the snap gauge. checking for out of roundness using a lathe is quite simple though. I have inside mic for small bores I use occasionally.

 

[Brian Rupnow]

Snap gauges are only as good as the "feel" the user develops from using them. I don't have any other device here for gauging bores. I have just checked out some bore gauges on Ebay that will have the range to measure a 1" diameter hole, and the cheapest is about $75 USA money which translates to $100 Canadian money plus shipping. I've blown my budget on the heat treat oven and controller and toolpost grinder.

 

[Steamchick]

With care you can get a bore within 0.001" of the target diameter using only the boring bar, no lapping required. But that's not a big deal on a single cylinder, you just get within 0.005" and make the piston and rings to match. Boring bars naturally cut a true circular bore (taper is another matter, make sure your lathe is in good condition and well aligned) subject to the circularity of your headstock bearings. My lathe uses wheel bearings from a truck, which should have at most 0.0002" deviation from circularity. Far better than I can measure.

Not sure about your comment on taper... but maybe you have the work-piece in the chuck and the boring bar in the tail-stock or something?
GEOMETRICALLY - and professionally in all the factories and machine shops I have seen... the correct way (that everyone uses) is to fix the cylinder, and traverse the rotating boring bar through the bore, along the axis required. In fact I use a boring bar in my mill-drill, and NOT the lathe for boring. I bore vertically down through the cylinder... Then fit a hone and hone on the same centre.
But when I have needed a proper bore on the lathe, the work-piece is mounted on a fixture on the saddle, then the boring bar (between centres) rotates and the work-piece traversed past the rotating tool. That way guarantees a round bore - and no taper... And I can still fit a hone instead of the boring bar, so I hone on the same centre. Remember - Geometrically: you should "Describe a circle with the tool then traverse axially".
But maybe not everyone knows this?
Incidentally, the lapping/honing is necessary (in the professional world) to get the correct surface finish for durability, longlevity, lubrication and low friction while providing a suitable surface for good gas tight sealing.

N.B. If there are any professional machinists or toolmakers (which I am NOT!) who can correct my errors, I seriously would appreciate your advice. I may have been doing it the wrong way all my life? - I am human, not a machine. Toolmakers taught me a lot in my work....
Cheers!
K2

 

[minh-thanh]

I truly am at the point where I don't know what to do next.----Brian

Hi Brian !
Put it aside, don't think about it, 1-2 days later, check everything again !

 

[L98fiero]

Use of a reamer, or so I was taught, would make a multi-faceted hole, with the number of facets equal to the number of cutting edges plus 1. Although I can't recall anyone else ever saying this, I believe it is true "mathematically". So don't use a reamer.

That used to be true but at least better quality reamers don't have evenly spaced flutes and that eliminates the problem.

 

[L98fiero]

Brian, check your messages

 

[mayhugh1]

Mayhugh1-You said that you make your cylinders out of steel. What material do you make your rings and pistons from? Hot rolled steel is about 1/4 the price of cast iron, but I have never used it for a cylinder. I have always used cast iron, but would gladly change to hot rolled steel is it does a good job and there are no unusual friction or wear problems.---Brian Rupnow

Brian,
I made the cylinders for my radials out of 12L14 and then had them hot-blued. The rest of my cylinders were usually made from Stressproof (1144). I usually make my pistons from 6061 but sometimes from 7075 depending upon what I have laying around.
Be careful, don't head down another rabbit hole on advice from others who don't have actual hands-on experience with ring making for model IC engines. Terry

 

[Brian Rupnow]

Terry--That is the biggest problem with taking advice from the internet. It's not that people deliberately mislead you, It's just that there is too much advice on how to do something from people who have never done it themselves.---Brian

 

[werowance]

Snap gauges are only as good as the "feel" the user develops from using them. I don't have any other device here for gauging bores. I have just checked out some bore gauges on Ebay that will have the range to measure a 1" diameter hole, and the cheapest is about $75 USA money which translates to $100 Canadian money plus shipping. I've blown my budget on the heat treat oven and controller and toolpost grinder.

Brian, would a set of gauges like this picture work? i just googled for the image. i have a set like this that was given to me that i will never ever use. the wood chest they came in was pretty much destroyed when it was given to me, water damage and abuse. but the gauges must be stainless or something because they did not rust. and they were individually wraped. looked like most had never been used. at anyrate if you think something like this would help you can have them for the shipping cost. and ill send a picture first along with the guage sizes of course. there are more of them that this stock photo i googled for shows.

 

[Brian Rupnow]

Werowance--thanks for the kind offer, but those are go/no go gauges. They are used when trying to make a hole between specified lower and upper limits. My engines are all 1" bore, so I don't think you would have gauges that reach that range.---Brian

 

[Brian Rupnow]

--I thought that a ring .062" wide as purchased was too wide. Everything I have read about it (And I have read a lot) suggests making the ring 1/30 to 1/25 of the bore size. With a 1" diameter bore, that comes out to a ring 0.033" wide to 0.040" wide. My reading material also suggests that a ring which is square in cross-section is proportionally correct. I purchased these rings from Debolt and then machined a piston to match the rings, with a ring gap 0.063" wide x 0.055" deep. (The rings are 0.051" thick). I paid $50 for two rings, so I haven't been rushing to throw them away, but I think I've just about ran out of things to do to make them work. I'm more or less "lost in space" now. I could make another cylinder with an exact 1.000" bore and see if that worked with the existing piston and rings. I could make new rings and a new piston to suit my cylinder "as is". I know I could make a new oversize piston and lap it into the existing cylinder and not use any rings, but the whole point of this exercise is to make my own cast iron rings with my own equipment.---Brian

 

[Nerd1000]

Not sure about your comment on taper... but maybe you have the work-piece in the chuck and the boring bar in the tail-stock or something?
GEOMETRICALLY - and professionally in all the factories and machine shops I have seen... the correct way (that everyone uses) is to fix the cylinder, and traverse the rotating boring bar through the bore, along the axis required. In fact I use a boring bar in my mill-drill, and NOT the lathe for boring. I bore vertically down through the cylinder... Then fit a hone and hone on the same centre.
But when I have needed a proper bore on the lathe, the work-piece is mounted on a fixture on the saddle, then the boring bar (between centres) rotates and the work-piece traversed past the rotating tool. That way guarantees a round bore - and no taper... And I can still fit a hone instead of the boring bar, so I hone on the same centre. Remember - Geometrically: you should "Describe a circle with the tool then traverse axially".
But maybe not everyone knows this?
Incidentally, the lapping/honing is necessary (in the professional world) to get the correct surface finish for durability, longlevity, lubrication and low friction while providing a suitable surface for good gas tight sealing.

N.B. If there are any professional machinists or toolmakers (which I am NOT!) who can correct my errors, I seriously would appreciate your advice. I may have been doing it the wrong way all my life? - I am human, not a machine. Toolmakers taught me a lot in my work....
Cheers!
K2

I put the cylinder in the chuck and the boring bar is mounted to the lathe toolpost. To my knowledge this is the usual way of boring on a lathe? Anyway, it's 100% possible for my way to make a tapered bore:

Firstly too greedy of a cut can 'spring' the bar leading to a tapered bore. You can clean this up with spring passes but it is a trap for the unwary (such as me). Secondly, any twist or wear in the lathe bed will cause taper, just the same as when OD turning. This is a constant problem for me because my floor shifts whenever the temperature or humidity changes, I have to re-level the lathe every time I use it.

 

[Nerd1000]

--I thought that a ring .062" wide as purchased was too wide. Everything I have read about it (And I have read a lot) suggests making the ring 1/30 to 1/25 of the bore size. With a 1" diameter bore, that comes out to a ring 0.033" wide to 0.040" wide. My reading material also suggests that a ring which is square in cross-section is proportionally correct. I purchased these rings from Debolt and then machined a piston to match the rings, with a ring gap 0.063" wide x 0.055" deep. (The rings are 0.051" thick). I paid $50 for two rings, so I haven't been rushing to throw them away, but I think I've just about ran out of things to do to make them work. I'm more or less "lost in space" now. I could make another cylinder with an exact 1.000" bore and see if that worked with the existing piston and rings. I could make new rings and a new piston to suit my cylinder "as is". I know I could make a new oversize piston and lap it into the existing cylinder and not use any rings, but the whole point of this exercise is to make my own cast iron rings with my own equipment.---Brian

Given all your struggles, I think you should control as many variables as you can. Probably a good idea to make a new cylinder (bored rather than reamed), piston and rings. Then just change one thing at a time (be that your ring making technique, the ring dimensions, bore surface finish, etc) and keep track of what changes result.

 

[minh-thanh]

Brian !
If I remember correctly, you have an engine that runs with rings, right?
if correct, measure and compare between 2 cylinders, if the figures are the same with very little error: you can be confident that your cylinders are ok
And just focus on rings. I don't think the rings will bother you
The way I make the rings is based on the information on the forum
with my tests in comment 86 : With a slightly small piston - it's a piston that is too small and I wouldn't accept when making an engine and with a ring that is not in full contact with the cylinder - that ring I won't use - unless I only have one (I usually make more rings than I need : i need 8 , i will make 15 , 18... ) : and they're fine
About the ringless piston: it's just one way I test the cylinder before, if the engine runs well with the cylinder and ringless piston I can be confident it can run with the ring and I just focus on the ring - of course Of course that's just the way I think and do
I haven't made 1 inch large diameter rings yet, hope you don't mind my comments

 

[ranger]

Is it possible with your toolpost grinder setup, to internally grind the cylinder bore, avoiding the ‘spring’ of a boring bar, and producing a decent finish? Then maybe a few strokes with a hone to finish off.

 

[minh-thanh]

Hi All !
This is the tool I usually use
It helps to keep the temperature relatively uniform between the inside and outside of the ring when firing
That's just the way I usually do it , hope it helps , or just an idea for you to improve...

 

[johwen]

Hi Brian,
first of all a couple of thou in Bore variation won't matter at all in the sealing of the ring. As I see it from your photos it appears to me that the ring is too wide for a one inch bore and the other question how thick is the ring because if it is too thick it will not be flexible enough to seal with behind the ring pressure from compression or combustion. Now that you have the ring groove machined I would turn up two rings half the width but to the section as described by Trimble Turn the rings one thou oversize split on a tapered mandrel and gap to correct clearance and heat treat in enclosed cup as per Trimble using the correct gap spacer. Lap the edges of the ring to achieve correct side clearance don't lap the OD of the ring just use the fine turned surface for easy sealing in the bore. The important aspect of the ring is the ratio of the thickness to the width and bore diameter Put two rings in the wider groove with the gaps 180 degree apart.
The other important issue is in the heat treatment Take the time to make up the heating cup as per the Trimble and make a dozen rings fore one inch bore for your next engines But before closing the cup wrap some clean white pare around the rings filling the gap so when the whole unit is heated the paper burns using all the oxygen in the space so that the ring surfaces do not oxidize, the rings come out blue. It is important not to oxidize the metal as this could easily change the surface of the ring in reference to circularity Hope this helps Brian

 

[dsage]

The cylinder actually mikes at 1.003" to 1.004" inside diameter.

If your cylinder measurement is accurate at 1.004 and your rings are still meant for a 1" cylinder then that's your problem. A 1" ring will not be round when it has to expand to 1.004.
But who knows where you are now if you have also worn the rings.
As Mayhugh1 suggested - and now that you have the equipment - you need to start over.
Make a new test cylinder and follow the Trimble method exactly for the rings.
Make the test cylinder first to completion including a VERY LIGHT honing. Measure it a dozen times if you have to and then make the rings to suit it.

Do not use any of your existing pieces (including the purchased rings). At this point they are all suspect.

BTW. If you want to test your "feel" for snap gauges. Find yourself a large bearing and measure the inside diameter. They are dead accurate. Repeat the measurement of that until you get a feel for what it takes to get the right measurement.

 

[Brian Rupnow]

Today I will try a new trick. Conventional wisdom says that a cast iron piston should be 0.002" less than the cylinder bore. Conventional wisdom also says that the piston rings will take care of sealing that .002" diameter difference between the piston and cylinder. I am going to work from the assumption that my new piston, grooved for my purchased rings is perfect. I am going to assume that my purchased rings are perfect. I will make a new cast iron cylinder with a bored hole of 0.996" then use the new 0.998" diameter piston (with the rings removed) to lap the hole in the cylinder to as perfect an air-tight fit as I can get. Then I will put the rings back on the cylinder and fly with that. That is what I did on my vertical hit and miss engine, and it has wicked compression.

 

[Steamchick]

Terry--That is the biggest problem with taking advice from the internet. It's not that people deliberately mislead you, It's just that there is too much advice on how to do something from people who have never done it themselves.---Brian

I am one of those Brian, so please consider my advice with a "total lack of experience"!
Do you have a large bucket of salt to hand?
K2