Author Topic: Twin marine oscillator (Read 6406 times)

Team ricky · « **on:** November 18, 2025, 02:50:14 PM »

Hi Chaps,

I’ve wanted to build from scrap stock for a while now !

I thought I would base the engine around the original puffin twin and use some different materials and style , Not sure if it will just be a display or fitted just yet .

The materials used are :

Standard : Cast iron
Flywheel : Cast iron
Shafts. : 316 stainless
Cylinders: Cast GM (purchased)
Pistons. : Bronze 11x5
Base. : 316 stainless
Bearing block : GM
Crank discs: Silver steel

Bore 11mm stroke 11mm

It should make good power and efficiency

Jobs to still do are :

Calculate the piston rod lengths
Calculate and make the big ends
Make GM throttle arm
Make steam fittings

Not too much more to go !

crueby · « **Reply #1 on:** November 18, 2025, 03:45:26 PM »

An excellent start!

Sanjay F · « **Reply #2 on:** November 18, 2025, 05:44:33 PM »

Well, that's impressive you look like you're well on the way with it, should hear that rumble into life soon!

CI · « **Reply #3 on:** November 18, 2025, 11:31:17 PM »

Looks nice !
.

Michael S. · « **Reply #4 on:** November 19, 2025, 04:38:09 AM »

The motor looks good. A good, robust design. I have a similar motor in my model steamship, and it's very reliable.

Michael

Team ricky · « **Reply #5 on:** April 06, 2026, 05:00:46 PM »

Hi Chaps….

It’s been a little while since I have made time on this project!

The engine is now running well and close to final finishing

Without gaskets it runs at 3-5 psi which is encouraging to say the least
I did run the engine partially in on the lathe with the correct shims so to not damage the bearings
All went well so I went straight onto compressed air to keep running in

Now seems well sealed cylinder wise , a little work needed to polish the top of the standard to better seal the throttle arm and I think it’s good to go

So just a throttle arm to make as I’ve robbed one from another model lol 😂 and some gaskets …

I have recently found a lovely little o ring internal booring bar that just fits in an 1/8” hole that allows me to insert o rings on the piston rod to bottom cover, this is a bit of a game changer in terms of leaks and friction, It works so much better than graphite yarn !

Team ricky · « **Reply #6 on:** April 06, 2026, 05:03:38 PM »

Some pics

Team ricky · « **Reply #7 on:** April 06, 2026, 05:04:42 PM »

Team ricky · « **Reply #8 on:** April 06, 2026, 05:08:36 PM »

Ooh ,

Just forgot to mention the cylinder security to the standard needs a bit of thought…. Currently cable ties holding them in place for testing !

I have ordered a tension spring to go all the way around both cylinder and I was going to mill a slot in the standard to accommodate the spring and hide it somewhat , alternatively a bracket could be used or peg the cylinders and use two springs between each cylinder…..

Not sure yet but that’s the joy I guess

Jasonb · « **Reply #9 on:** April 06, 2026, 05:30:44 PM »

Looking good. A stretched O ring is another option for holding the cylinders.

Sanjay F · « **Reply #10 on:** April 06, 2026, 05:34:52 PM »

Nice engine - looking forward to seeing it running

PaulR · « **Reply #11 on:** April 07, 2026, 11:04:11 AM »

Very nice.

I've looked at building this sort of configuration before but was never keen on the methods used to hold the cylinders in place, brackets of some sort being the least worst in appearance to my eye. Another possibility would be uprights at each end of the crankshaft with screws and pads pushing on the outside of the cylinders but I'm sure that wouldn't be everyone's cup of tea!

Team ricky · « **Reply #12 on:** April 07, 2026, 05:34:49 PM »

Today I milled the slot each side of the standard to accommodate the spring/oring and made the throttle arm/disk on the rotary table, All went well and I installed an oring for testing

Runs a treat just the right amount of pressure on the cylinders

https://youtube.com/shorts/YuYA7sgmCJo?si=Ct-G4ew-7IOn1jne

Charles Lamont · « **Reply #13 on:** April 07, 2026, 06:12:13 PM »

This has made me think about how some means of retaining the cylinders might be built in to the column. Is the porting like this?:

Jasonb · « **Reply #14 on:** April 07, 2026, 07:45:39 PM »

Tension spring down the pivot with pins to hook over set into a pivot stub on the cylinders

Team ricky · « **Reply #15 on:** April 08, 2026, 01:36:28 PM »

Hi Charles,

Yes that’s the port layout I used ….

I’m pretty much decided on no bracket

Onto a boiler now I guess ! Here’s a pic of the internal grooving tool , this little tool is amazing and can just sneak into an 1/8” hole which is a common size of piston / valve rods on small engines

Team ricky · « **Reply #16 on:** April 13, 2026, 04:38:14 PM »

Hers a pic of a second hand not completed Scotch return boiler….

It looks to be wetback but I’ll have a look when it arrives to see if it is or not… most model ones I’ve seen are dry back single pass.

I’ve got a small boiler fully fitted but it’s spirit fired and I’m not too keen on it ! So I’ll take the new fittings I used on that one and build up the Scotch return

It was cheap and obviously comes with the risk the current build is not good but I’ll see , It’s silver soldered so far probably except the smoke box which looks to be soft soldered (no good) Easy fix to de solder that and re-silver solder

Team ricky · « **Reply #17 on:** April 17, 2026, 04:55:13 PM »

So the boiler arrived no problem 😉

As I expected from the pictures the front head has been tickled with a bit an obvious leaks along the seam, an attempt to braise was made unsuccessfully

I’ve cleaned off the braise, opened up any gaps and picked , soldered and fixed

Next there is a tiny leak in the combustion chamber rear, about the worst place pollution lol 😂

It is tiny and not structural, it actually stopped when a bit of contamination went over it tested on low compressor air, Because it’s dry back as expected I can use the loctite trick to draw a tiny bit into the void ! Bit of luck needed but I have very thin post application loctite which is perfectly suited to this type off job

I did just have another thought… it’s possible to fill the wet side of the back head with rosin flux and solder at the end of the job (post bushes) and heat it in place with the boiler up right… that will certainly caulk the problem too….

Team ricky · « **Reply #18 on:** April 17, 2026, 06:36:28 PM »

This arrangement seems best for the sight glass …

Nice and high and gets a little protection from the smoke box, I’m pretty sure I’ll have to make new holes to suit and blank bush some others I don’t need !

Team ricky · « **Reply #19 on:** April 17, 2026, 06:36:53 PM »

Team ricky · « **Reply #20 on:** April 20, 2026, 01:30:16 PM »

Here’s a pic of some progress

I’ve made a Scotch style steam dome and made some bushes ready to solder in place , I decided to go with the sight glass off to one side, pick up on all the existing holes in the side of the shell to feed the gauge, It will be mounted on 11x11 brasss square stock to help it not getting knocked…!

Team ricky · « **Reply #21 on:** April 21, 2026, 05:47:36 PM »

Now at the stage where the next silver solder session begins!

I’ll solder up all the bushes and sight glass manifold in one …

Just thinking on the back head leak as to whether opening up the dry back to have a good look and provide servicing access to the tubes …. I’m thinking a hole saw set up in the lathe and fixture the shell to the cross slide ! What could possibly go wrong lol 😂

Team ricky · « **Reply #22 on:** May 03, 2026, 01:11:24 PM »

Here’s a quick steam test

Weather is good so had a run !

Alls good , fairly well sealed and runs sweet in both directions and will run slow too , I think I will mount on a board just to display for now

https://youtube.com/shorts/ACl07So0OBM?si=hn89M-s6g4Xf5krT

PaulR · « **Reply #23 on:** May 03, 2026, 03:58:20 PM »

Nice

Weird visual effect near the start of the video makes it look like the left then right cylinder is stationary!

Sanjay F · « **Reply #24 on:** May 03, 2026, 04:04:23 PM »

Looking and running great, I had that weird visual effect on the Stuart oscillator I built where it looks like one cylinder stops too .......

Team ricky · « **Reply #25 on:** May 03, 2026, 09:31:55 PM »

Good spot

The frame rate of YT causes that lol 😂

Thanks for the kind remarks gents

I’ve enjoyed making this engine and glad it runs well

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Author Topic: Twin marine oscillator (Read 6406 times)