Author Topic: fitting small piston rings  (Read 7852 times)

Offline PJW

  • Full Member
  • ****
  • Posts: 375
fitting small piston rings
« 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!!!
Old Guys Rule the Dark Side of the Shed!

Offline cfellows

  • Full Member
  • ****
  • Posts: 1700
Re: fitting small piston rings
« Reply #1 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
So many projects, so little time...

Offline philjoe5

  • Full Member
  • ****
  • Posts: 1011
Re: fitting small piston rings
« Reply #2 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.



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

If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Graham Meek

  • Full Member
  • ****
  • Posts: 309
Re: fitting small piston rings
« Reply #3 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,

Offline ian cable

  • Full Member
  • ****
  • Posts: 76
Re: fitting small piston rings
« Reply #4 on: April 02, 2014, 08:47:59 PM »
I ll second what gray has said prof chaddocks articles are spot on ian c

Offline Mosey

  • Full Member
  • ****
  • Posts: 1584
  • Rosemont, New Jersey, USA
Re: fitting small piston rings
« Reply #5 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:

Offline PJW

  • Full Member
  • ****
  • Posts: 375
Re: fitting small piston rings
« Reply #6 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
Old Guys Rule the Dark Side of the Shed!

Offline Zephyrin

  • Full Member
  • ****
  • Posts: 378
  • near Paris, France
Re: fitting small piston rings
« Reply #7 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...

Online steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10271
  • Central Massachusetts, USA
Re: fitting small piston rings
« Reply #8 on: April 03, 2014, 09:23:04 AM »
Great thread guys!.....nicely done....taking notes!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Graham Meek

  • Full Member
  • ****
  • Posts: 309
Re: fitting small piston rings
« Reply #9 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,

Offline PJW

  • Full Member
  • ****
  • Posts: 375
Re: fitting small piston rings
« Reply #10 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:
Old Guys Rule the Dark Side of the Shed!

Offline PJW

  • Full Member
  • ****
  • Posts: 375
Re: fitting small piston rings
« Reply #11 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:
Old Guys Rule the Dark Side of the Shed!

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12552
  • Hampshire, england.
Re: fitting small piston rings
« Reply #12 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
Usus est optimum magister

Offline Graham Meek

  • Full Member
  • ****
  • Posts: 309
Re: fitting small piston rings
« Reply #13 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,

Offline Steam Haulage

  • Full Member
  • ****
  • Posts: 218
  • Notts UK
Re: fitting small piston rings
« Reply #14 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
Dogs look up to you, cats look down on you, pigs treat you as equal.