A Simple Uniflow Engine

[gary.a.ayres]

Great idea on the viton ring, Jason. Thanks. Not sure how much work it will do, but I'd like it to do some I think. One step at a time as you suggest sounds sensible.

I have already drilled the exhaust holes on opposite sides of the cylinder with the possibility of a third one on top. I'm ok with that though as I have a half-formed picture in my mind of a funky-looking manifold that could be quite a visual feature if I get it right.

Any advice from anyone on depth, width, number, spacing and profile of oil grooves in the piston would be welcome.

[Jasonb]

I usually do 3 @ about 0.5mm deep equally spaced along the piston

[gary.a.ayres]

Ok ta.

Maybe with a parting off tool?

[john mills]

hi Gary

i would make the grooves a little deeper ,they will work to reduce leakage and the engine will run.I have an engine running with a larger bore has been running with out rings just the grooves and it runs 0k.you can always try running and add rings latter  .    I would use a grooving tool you have that will let you fit number of grooves across the piston if it is a parting tool that would do.
             John

[MJM460]

Hi Gary, another vote for no rings, just plain grooves.  I have done this on each of my engines and they all run quite well.

In large compressors, there is one at least one brand of oil free reciprocating compressors which has no rings even for high pressure hydrogen.  They have a series of square grooves with no rings or packing.  Admittedly more rings than you would want, but the principle is called a labyrinth compressor.

Basically, the gas or steam passing between the piston and cylinder reaches a groove, it expands into the groove, with a consequent pressure loss.  It then has to accelerate into the passage again.  So generally more resistance, and consequently less bypass than a plain piston.

I tend to use about 1.5 mm wide and deep, as I have a suitable tool for those.  And two or three depending on the length of your piston and what will fit.  Whether it is really the labyrinth effect, or the effect on the oil film, or even if a plain piston would be just as good, I don’t really know.  It would probably be necessary to rig up some sort of flow test, but it would need quite accurate instrumentation.

I always have it in mind to add some graphite’s yarn some time to see if this makes a difference, but my observation so far is that the engines run well without it. 

The same principle where the piston rod passes through the gland, though there, I generally return and add theming of graphited yarn, which definitely reduces the leakage.  Just the annulus between the piston and cylinder has a larger cross sectional area for flow than the gap around the piston rod.

With your nicely fitting piston, I would just cut the grooves and not worry further.

MJM460

[Jasonb]

For smaller engines I use vee grooves, same as found on thousands of Stuart 10 series engines so proven to work.


Most of the 24mm ones I have been designing over the last few years have a single O ring groove cut but have not found the need to fit the actual rings ( do on the IC engines)

[gary.a.ayres]

Thank you guys - that gives me plenty to go on.

 

[gary.a.ayres]

Meanwhile, still on the cylinder.

Eight holes for the bolt circle were drilled and tapped M5, and transfer screws were used to mark out their positions on the inside of the cap:



The edges of the cap were milled to size in situ on the cylinder body:





I think (hope!) that the cylinder would be functional in its present state with the addition of the valve, but there is still a fair bit of work of a cosmetic nature to be done on the outside of the cylinder block.

[gary.a.ayres]

A corner-rounding endmill was used to...er... round the corners:



Sorry about the grainy picture quality there.

This was done with the cap in situ. Some sanding was then carried out using 180 grit wet and dry paper with cutting oil on the surface plate. This made a difference quite quickly:



There is stilll more sanding to go to achieve the finish I want.

Now, once again, I seek your advice. I do not wish to paint this engine. How realistic is it to leave the cylinder  (cast iron as it is) untreated and just given an occasional light smear of oil to keep it from rusting? If that's not a good idea, I wouldn't mind blackening it with the chemical product called 'Black-it', though that's quite an expensive option. Do any of you know of any other ways to treat cast iron? I would be happy to hear of anything innovative to give it an interesting surface patina or colour...

[Admiral_dk]

You are doing good so far 

Have a look at how Chris Nickle plate iron - simple and without any problematic chemicals.

Best wishes

Per

[crueby]

I have electroplated nickel onto steel, never tried it on cast iron, seems like that would work too. It would not give the black color you want, though.

[Johnmcc69]

Over at the "other place" (HMEM)  there is a fellow building G. Britnell 's beautiful Holt model. He has been using some gun bluing solutions from "Brownells" with some really stunning results....
 Not sure how those solutions work with CI, or cost, but it adds an aged patina that looks great on that engine.

 Additionally, bead/sand blasting adds a nice "as cast" appearance.

 Nice work on that cylinder Gary!

 John

[gary.a.ayres]

Many thanks Gentlemen.

@Chris - would you mind telling me which thread of your prolific output contains the nickel plating? I'm not necessarily seeking a black finish.

@John - beadblasting... now that has some appeal, for sure.

Will think about the options...

gary

 

[crueby]

It was over on the Marion Valve Engine build thread, here:
Started here, with link to the instructions I followed:
https://www.instructables.com/id/High-Quality-and-safe-Nickel-Plating/
http://www.modelenginemaker.com/index.php/topic,9312.msg210244.html#msg210244
More a few posts after that one, and here too
http://www.modelenginemaker.com/index.php/topic,9312.msg210244.html#msg210244
Its quite easy to do, I recommend getting a variable power supply if possible so you can adjust the voltage - higher is quicker, but rougher finish, around 6 volts is good. The distance to the part changes it too, the closer the faster/rougher. Distilled water, non-iodized salt, a Nickel rod/plate for a source, and a plastic container are the only other parts you need. No nasty acids involved, and you can re-use the solution so a lidded container is handy to store it in. I've since done a bunchof knobs for the Lombards up at the museum, as well as parts for several models. After plating, you can buff the plating to shine it up.

[gary.a.ayres]

Over at the "other place" (HMEM)  there is a fellow building G. Britnell 's beautiful Holt model. He has been using some gun bluing solutions from "Brownells" with some really stunning results....
 Not sure how those solutions work with CI, or cost, but it adds an aged patina that looks great on that engine.

 John

John - I had a look and I think I found it - about half way down this page (by Mark T, or 'dnalot'):

https://www.homemodelenginemachinist.com/threads/marks-holt-75.31650/page-11

Very handsome it certainly is. Might well be worth  investigating gun bluing solution...