Sizing Piston Rings

[318J]

Hi all,

I'm getting ready to order cast iron piston rings. I think these will need to be custom sized, as the cylinder bore is nominally 2.908". Nearest "stock" rings I can find are for a 2.875" bore, and next size up is for 2.999".

Is there any other information I should give when getting a quote? Shooting for a ring width of 0.125" and the diameter for the groove (ID of the ring) isn't as critical as I'll be cutting those to suit in the piston which is soon to be made.

How much play should there be when the ring is sitting in the groove? And how much gap should there be between the ends of the ring to account for a couple thousands variation in the cylinder bore?

And does anyone have a particular vendor they've liked ordering rings from in the past?

[gwrdriver]

Be sure to mention these are for steam, not internal combustion, because the wall pressures are considerably different. This may not have an effect on what they are able make, but it might.

[hoppercar]

There's a good article in the book....so you want to build a live steam locomotive....by Mr. Nelson......on how to make your own cast iron rings ....I've used his tables, to make my own rings for years....

[Bill Shields]

So have I..used Nelson's description

but I also purchase rings from Otto who is practically a neighbor.

He has rings that are practically the same calculated dimensions as I get from Nelson's numbers.....and they work just fine.

[ALCOSTEAM]

I have always made my own rings and will likely be making a few this weekend for some air brake cylinders of about 2.100". If you can make a piston the rings should be no problem. One bit of advise I make my own parting tool for cutting rings apart from a piece of HSS ground down to a pretty narrow width as most parting blades are so wide you eat up a good bit of material just to get a few rings. Like others have mentioned follow Joe Nelsons book for making rings and you will be fine,,, you do have a copy?

[318J]

I don't have a copy. Was more interested in sourcing these over machining them in the interest of time (I'm not an experienced machinist).

[Mike Walsh]

Sam...

Does 300 have liners?

If you're that concerned, I'd make new liners to the proper fractional dimension, then order appropriate rings. Take the time to do it right now. Ordering custom rings will just cause headache down the road... Ask us how we know. Do it right the first time.

See you around,
Mike

[Bill Shields]

are the cylinders worn to that size or were they made that size?

how SURE are you of your diameter measurement...and don't tell us that you measured it with a caliper...

[318J]

Cylinders were machined out professionally to remove existing scoring, and as little material was removed as possible.... there isn't much play room to remove more material than that without putting in liners- which I don't want to do either. Having some rings made and keeping extras in stock will make sure we have what we need until the cylinders are worn out again wayyy down the road.... at which time liners may be the solution.

I'm sure of the measurements I took. While I don't do much machining I know how to take measurements and use telescoping gauges and micrometers properly.

[Bob D.]

With the cylinders freshly bored I question why there is several thou variations in the bore…. Have they been honed?
Instead of iron rings have you considered graphite packing yarn? Works just fine, can accommodate any odd bore size. Easily refreshed when needed and very cost effective. (Cheap). Don't make them too tight.

[Bob D.]

These guys made 5-1/16” rings for me that I used in a steam stoker engine (full size) rebuild. They were very nice. A bit of a lead time and were not cheap. Maybe much cheaper for a small size…. The setup fee was more than the cost of the rings. They can give you all the clearance requirements for the ring groove.
https://adpistonring.com/step-cut-piston-ring.html

[Bill Shields]

They are good, but as you say, cost of setup exceeds cost of individual rings.

A dozen rings probably will not cost more than 4.

In reality, step cut are nice, but not needed for our application.