Model Engine Maker

Help! => Specific Engine Help => Topic started by: PJW on April 02, 2014, 03:44:03 PM

Title: fitting small piston rings
Post by: PJW on April 02, 2014, 03:44:03 PM
I have to fit two piston rings on a 7/8 in piston, I am a bit timid & frightened to just prize them on as they look like they will snap like a carrot! has any members got any tips before I have a go.
If I do brake them I have to send to the States for replacements. I am building a Webster IC engine which is just the second engine I have attempted, I have had to purchase the piston rings & the two gears but I have done the rest & will post pictures & if I can get it to run, a vidio clip!!!
Title: Re: fitting small piston rings
Post by: cfellows on April 02, 2014, 04:45:26 PM
I can't recommend any way to make it easier or less likely to break the rings, but if you do happen to break one or both of them, try substituting simple O-rings.  In my experience they work better and I've never had to replace one yet.  Some folks recommend Viton or Buna, but I've used simple black plumbing O-rings which are probably made from neoprene or nitrile.

Chuck
Title: Re: fitting small piston rings
Post by: philjoe5 on April 02, 2014, 05:25:51 PM
If you want to use cast iron rings I would suggest you learn to make them.  I'm no expert and I was intimidated by the prospect of making them but the advantages make it a worthwhile learning experience.  You can make a lot of them with a simple fixture and a small lump of CI.  When I make mine I adjust the widths by a few thou and experiment to see which fit the best.

(http://i250.photobucket.com/albums/gg261/philjoe5/Bonza/pistonandunfinishedrings_zpscc81d79a.jpg) (http://s250.photobucket.com/user/philjoe5/media/Bonza/pistonandunfinishedrings_zpscc81d79a.jpg.html)

The rings shown here are approximately 0.054" x 0.060" x 1.20" ID.  I haven't broken any putting them on yet, but I've broken a few prying them off. 

Good luck

Cheers,
Phil

Title: Re: fitting small piston rings
Post by: Graham Meek on April 02, 2014, 06:55:18 PM
I use a method advocated by the late Professor D H Chaddock who used to write in the Model Engineer. In an article on "Piston Rings and Compression Ratios", ME July 2nd 1976 he advocates putting the two split ends of the ring into the desired groove and then pushing the back of the ring over the piston crown, to quote Prof's words "It is Brutal, but it works every time" I have since used this method when fitting piston rings and have never suffered a breakage. One thing I might add is that the diameter to thickness ratio is the key to a good ring, the recommendations in the article is D/25 to D/30, and despite the D/30 giving a thinner ring it is in actual fact a stronger ring according to the Professor.

My best regards
Gray,
Title: Re: fitting small piston rings
Post by: ian cable on April 02, 2014, 08:47:59 PM
I ll second what gray has said prof chaddocks articles are spot on ian c
Title: Re: fitting small piston rings
Post by: Mosey on April 02, 2014, 09:03:06 PM
Now, if it gives you more confidence, I speak for the novices here to say make your own. Cast iron is lovely stuff, and making them is a joy. Make a few extra, and pop them on. So, if you break one, just put another one on.
Mosey   :pinkelephant:
Title: Re: fitting small piston rings
Post by: PJW on April 02, 2014, 09:27:12 PM
Hi Graham, I read your piece, but I cant quite see how this works :hammerbash:
but i will read all the input before I try to fit them, Thanks
Title: Re: fitting small piston rings
Post by: Zephyrin on April 03, 2014, 08:14:03 AM
rings are easy to do once you have the proper cast iron stuff. just making a tube and parting rings, a few experiments on the size are unavoidable...and yes, thickness between D/25 and D/30 is a large part of the success.
To insert the ring in its grove and not scratching the surface of the piston, I use pieces of shim copper foil put under the cut ends of the ring as in the picture.
I have put "o ring" on my new engine, not yet finished and tested...
Title: Re: fitting small piston rings
Post by: steamer on April 03, 2014, 09:23:04 AM
Great thread guys!.....nicely done....taking notes!

Dave
Title: Re: fitting small piston rings
Post by: Graham Meek on April 03, 2014, 09:37:42 AM
The attached photograph shows the piston rings I made and fitted to Professor Chaddock's recommendations and method of fitting. I also make these rings with no gap and the broken ends are left untouched that is I do not square them up with a file. The engine that these pistons are fitted to has now clocked up nearly 80 hours of running.

My best regards
Gray,
Title: Re: fitting small piston rings
Post by: PJW on April 03, 2014, 11:31:04 AM
thank you all, with all the help I have received I have now fitted the rings :pinkelephant: :cartwheel:
Title: Re: fitting small piston rings
Post by: PJW on April 03, 2014, 03:01:27 PM
I was very timid about this job as I thought cast iron rings would be quite brittle, I was surprised with the amount of spring in them, next time I might have a go at making my own. :help:
Title: Re: fitting small piston rings
Post by: Jo on April 03, 2014, 03:14:36 PM
Good for you Peter  :ThumbsUp:, You will find that they are actually very easy to make. The snapping, or as I do cutting is a bit nerve racking  ;)

Jo
Title: Re: fitting small piston rings
Post by: Graham Meek on April 03, 2014, 04:49:38 PM
I usually grip one side of the embryo piston ring in a small toolmakers vice, (vise) which I hold in my bench vice, then using a small toolmakers clamp I grip the ring adjacent the vice jaws. With a slight tweak of the toolmakers clamp the ring breaks cleanly and squarely adjacent the toolmakers vice.

My best regards
Gray,
Title: Re: fitting small piston rings
Post by: Steam Haulage on April 03, 2014, 07:17:39 PM
Hi all,

Just in case nobody is  of the pre 60s practice (1960s not 1860s) my dad did a lot of work on lots of types of engines, diesel and petrol from 800cc upwards and on motorbikes. He was an inveterate do-it-yourself-er as well as time served. We had a stack of CI rings in the shed, doubled as my boyhood workshop, these all had the splits at an angle, from memory about 60 degree angle. I have often wondered since why there were so many designs. Too late to ask him now.
Of course if I could read Prof. Chaddock's article again I might find this was common knowledge, so it provided for what it's worth.

Jerry
Title: Re: fitting small piston rings
Post by: PJW on April 04, 2014, 09:26:12 AM
Hi I might try to make some rings, is meehanite ( cast iron ) suitable?? as I have a bit of this :-\
Title: Re: fitting small piston rings
Post by: Jo on April 04, 2014, 09:49:27 AM
Meehanite ? That's a bit technical for me.. I buy the round sticks of CI from the usual suppliers, which I suspect is centrifugally cast Iron = no holes.

I was thinking of trying some of my heat treated (in the bonfire  :naughty:) sash weights. The only problem with sash weights is they can be full of holes but they came to me at the right price so nothing to lose  ;).

Jo
Title: Re: fitting small piston rings
Post by: Stuart on April 04, 2014, 11:24:26 AM
if you are buying cast  iron bar you are 90% sure its mehanite you can tell it cuts like butter and to confirm it makes wonderful rings

I just make them the same size of the bore on the OD the other measurement to suit the piston , snap them make up two washers to clamp the in a stack , wedge the rings open a couple of MM and cover the whole shebang with soap ( bar soap the boss uses green works ok ) get em red hot and keep them at that for ten mins and allow to cool on there own ,not in a draft

rum the faces up with a bit on emery paper on a face surface and your done

the soap just keeps the scale off when heating

other will have different method but thats how I do it , after heat treat the ring are remarkably springy

Stuart
Title: Re: fitting small piston rings
Post by: Ian S C on April 04, 2014, 12:01:11 PM
      I'v got some cast iron that I think is Meehanite, it doesn't turn like ordinary cast iron, more like steel, I made some rings for an IC engine, they seem OK so far.
      For the Stuart Turner S9, I used the cast iron from a brake disc,  it turned well, very fine grained.
       I have not used sash weights for piston rings yet,  but I have used them for making pistons for hot air engines, I try to make the skirt of the pistons as thin as I can, I can usually get it down to 1 mm thick, although about 25% fail before they are out of the lathe, none have failed in use.  The only problem I'v had was with a weight that I dropped on the floor, and broke, the fracture was white crystalline. On trying it in the lathe, a carbide tool just bounced of it.      Ian S C
Title: Re: fitting small piston rings
Post by: Mosey on April 04, 2014, 01:19:11 PM
Meehanite is a brand name (trademark) for a large company producing all kinds of high quality cast iron. It is generally the good stuff. Have at it.
You could turn it into razor thin sections easily, and it is a pleasure to work with.
Mosey
Title: Re: fitting small piston rings
Post by: PJW on April 04, 2014, 03:35:03 PM
Thanks for the info, I made my cylinder & flywheel out of this & it was nice to work with. I have a nice piece left to have a go with 7 using the feedback I have had I am almost confident in tackling the job :headscratch:
Watch this space :Lol:
Title: Re: fitting small piston rings
Post by: PJW on April 06, 2014, 09:13:01 AM
I broke one of the piston rings I purchased trying to remove it, I had nothing to loose so I had a go at making a replacement, I followed all the advice I had received including the heat treatment and ended with a perfect piston ring. All the advice was spot on and my thanks for all the help. I have added a picture of the ring & in situ, its the bottom ring. the last pic shows the build so far!
Title: Re: fitting small piston rings
Post by: Jo on April 06, 2014, 09:31:43 AM
 8)

How difficult did you find making it?

Jo
Title: Re: fitting small piston rings
Post by: PJW on April 06, 2014, 09:54:22 AM
Morning Jo, I bored out the hole to the desired size, then turned the O/D to the same size as the bore, then just parted to off to width unfortunatly I only had enough material to make one or I would have made  one or two spares! I then snapped it as told ( my heart was in my mouth as I did this) but it was so easy. the next step was the heat treatment, I used an old broken 2mm drill to open up the gap, then clamped it between two penny washers after using soap, then heated it up red for 10 mins and let it cool slowly. a bit of a clean up & job done, what was I worried about. There is a lot of knowledge on this forum & people kind enough to share it,
thanks!
Title: Re: fitting small piston rings
Post by: Doc on April 06, 2014, 03:09:07 PM
 The cast iron you speak of should be nodular iron or ductile. The differences are that there are two basic types and granular shapes are different the ductile the molecules are spherical and the what is called gray iron they are like flakes. Nodular iron actually has a tensile strength rating while gray is usually not rated.


Hi I might try to make some rings, is meehanite ( cast iron ) suitable?? as I have a bit of this :-\
Jo I actually tried this with no luck the ones I had were obviously gray iron. They had little to no tensile strength and snapped very easy and was unsuccessful in getting them on a piston. 
Title: Re: fitting small piston rings
Post by: Graham Meek on April 06, 2014, 03:41:29 PM
As regards heat treating the rings I just use a wedge shaped piece of steel held vertically in my bench vice, (vise), the piston ring is then placed on the wedge such that the gap is the desired dimension and the ring is horizontal. I then start heating the ring with a small hand held Butane torch at one end adjacent the wedge. As the ring gets cherry red I make my way around the ring until I reach the other end, by which time the ring has fallen due to gravity and is now touching the side of the wedge.

The fact that the ring has fallen also indicates that it has taken on a permanent set. The small flame can be easily controlled and I get very little scale which is easily removed in a citric acid pickle for a few minutes, plus you do not use so much gas.

My best regards
Gray,
Title: Re: fitting small piston rings
Post by: Brian Rupnow on April 06, 2014, 04:29:30 PM
PJW--It appears in your picture that the gas tank is situated higher than the centerline of the carburetor. If so, it isn't going to work properly. There is no float and needle mechanism in that carb to stop the flow of gasoline, so you will experience constant flooding of the engine, and possibly a fire. The top of the gas tank should be 1/2" to 3/4" below the centerline of the carburetor. There is enough vacuum created by the venturi effect in the carb to pull the gasoline up from the tank.---Brian
Title: Re: fitting small piston rings
Post by: PJW on April 06, 2014, 04:39:12 PM
Thanks for that Brian, the tank is not fitted yet so it will be no problem dropping it, I looked at it this way with no fuel pump it would be gravity fed & the flow would be sorted with the fuel needle. I will shorted the legs to the suggested height,

Peter
Title: Re: fitting small piston rings
Post by: PJW on May 10, 2014, 06:57:43 PM
I ran my finished engine with the piston rings I made it ran well, & as an experiment I made another piston & used an O ring as suggested by Chuck, the one with the O ring had the better compression & even ran better!
Nice one Chuck :ThumbsUp: