Piston Rings 1.1/2″ diameter.

[ChinkoaParticipant @chinkoa]

[ChinkoaParticipant @chinkoa]

I am in the process of making Piston rings for my 5" Gauge Mrchant Navy Class Loco. The rings are made and I am about to heat treat them according to all the inforamtion out there from Cain/ Trimble. I have made rings before and got good results but this is a big loco and I do not want too high a wall pressure as I want o be able to turn it over. My problem is wall pressure. Cain recommends 8 to 12 Lbs/Sq." My question is what is the initial gap I start with in the Piston ring in the heat treatment jig that will put me in the ball park for the 8 to 12 Lbs./Sq." Reading further suggests that a lower figure is perhaps better. I have made enough Rings to have several attempts/failures. Measuring the wall pressure according to Tubal Cain in ME.Issue 172/1994 is fairly straightforward.

[Paul LousickParticipant @paullousick59116]

The bore on my traction engine is 2 3/4" dia and I made the rings with a clearance fit on the bore using a formula of 0.001" per inch of diameter. (Some builders recommend making them 0.001" oversize on the bore which allows for them to wear down slightly when beding in and be an exact fit). Mine are very wide rings compared to that used in an IC engine and the piston is made in 2 parts so that the ring does not have to be stretched over the piston head.

The ring was split with a 1mm thick Dremel cutting disc. This does leave a small gap when assembled in the bore but the 2 rings are fitted in the same groove with the gaps spaced 180 degrees apart. The theory being that there is no gap as one ring is sealed by the adjacent ring.

The spring in the rings was set by holding the gap apart with a piece of 6mm bar and heating the ring all over untill it fell off the bar. The gap in the rings was left expanded to about 3-4mm and a ring compression tool was required to squash the rings for insertion into the bore. It seems to work OK with very little sliding resistance.

Paul.

 

Edited By Paul Lousick on 31/03/2020 12:52:41

[not done it yetParticipant @notdoneityet]

You should not need too many rings for further attempts – just heat again with a wider spacer if too slack, or heat inside a ring of steel to go back to original before the next attempt.

[ChinkoaParticipant @chinkoa]

Just had a dummy run with a 0.150" spacer and got 5lbs/sq" I am aiming for 6/7 so back to the propane burner.

Colin

[duncan webster 1Participant @duncanwebster1]

I seem to remember there were quite a few typos in the ME article. There bis some info in Model Engineers Handbook (Tubal Cain), I could scan it if you don't have a copy.

I made my rings to TC instructions, 0.045" square for a 1.5" bore loco, they seem to work a treat, although it hasn't done much running. Design it, make it, prove it works, get on with the next project.

[Author]

Posts