Mrs. Robinson, Revisited.......

[Rob.Wilson]

Looks stunning David 

I like how its all self contained on one base 


Rob 

[vtsteam]

It's a beauty, all finished and ready to run. You will be very proud of that one when you demonstrate hot air engine principles to young and old. I'm sure everyone will love it. First rate!   

[sbwhart]

Looking great Dave excellent job, 

One ?:- what is Mrs Drilling going to use for a bread board now you are using it for the engine base.

 

Stew

[Stilldrillin]

Ralph, Rob, Steve(?). Thank You all! 

Stew. Thanks! Re- Mrs. Drillin......... As long as we keep on buying Warburtons sliced, she'll never know! 



So.........

Yesterday, I fired up, at the start of a full heat test run. Away she went, running nicely, as usual. 

Time to fill the cooling system. Using a 5% mix of Shell Supercut-Plus, instead of the previous Bluecol top up mix.......





A couple of minutes later, the well remembered water boiling sounds started. And she stopped. 
This proves, once again. Stirling Principle engines will not run on steam! 

Removing the thumbscrew, and extracting the stainless steel air tube, revealed smears of coolant.
The fluid must be leaking up the outside, and into the power cylinder. 

I machined 3off, 5thou deep recesses, into the tube's o/d. To hold the Hylomar, and seal between air tube and brass tube's bore.

Then I fired up the burner several times, spinning the engine to allow it to breath, and dry out.
Left the system open, and this morning all was well, and dry.   

Generous application of Hylomar sealed it, as hoped.


Set up, in the kitchen. Not a particularly good idea, so I was informed....... 

But all went well, during a half hour run.......




Observations.
The burner system is too on/ off. Also, needs a smaller diameter, more concentrated flame.

Smoke from under the feet, indicated things were getting much too hot. Couldn't touch the underside of the base wood! 

The copper chimney got a bit warm, too.......




I'm going to try this choke ring, next. Failing that, it's a new rose, with a smaller drilled area.......




Must look for a No 3 jet......

David D

[vtsteam]

David, would it be of help to line the cast base with a thin sheet of insulation on the inside? You might need less heat for the displacer cylinder that way, as well as keeping the base legs cooler. The stack could also be insulated on the inside to keep it cooler. Not sure what to use in place of a sheet of asbestos paper these days, but there might be something healthier out there.

[Stilldrillin]

VT.
Thanks for the insulation thoughts. 
I'll see if I can first, reduce the burner's power somewhat. 


Had another test run today. Just over 1/2 hour.

The burner is better, with the choke ring. But, there's still a lot of heat, where it's not wanted. Some lovely colours on the copper chimney!

Have started to make another rose. Probably, with 1.5mm holes, over a 3/4" diameter area.

Also, ordered a couple of No 3 jets. (One for the Huxtable).......

David D

[Stilldrillin]

Here's a little conundrum....... 

The new crankshaft bearings I'd made had too much clearance, on the 6mm silver steel shaft. 
So, I bought some 10mm o/d needle roller bearings. Mounted the pedestal on a mandrel, and recessed each end of the casting bore, to suit.

The needle rollers had a bigger wobbability factor than my original bushes!!   

Can't work that out. Am I missing something?   


Managed to locate four ball races. 6 x 10 x 3mm.




And these fitted perfectly, in pairs, at either end of the pedestal........




Job's a good un. But, I still can't work out why the rollers seem to be oversize, on the 6mm shaft....... 

David D

[vtsteam]

Are they quarter inch?

[Bluechip]

Dave
 
Some needle rollers need to have a specified interference fit to make 'em the right size.
 
As do IIRC Glacier bushes.
 
Also, but I'm not sure about this, some ball-races have polished rings on them. I think this is a similar thing.
 
ie. Interference fit outer, push fit inner etc. etc. etc.
 
Dave BC

[lordedmond]

As Dave BC says the needle roller bearing need to be pressed in to a a sized hole and must run on a hardened shaft

as to the hole size you need the manufactures spec sheet as to the correct hole size for the outer they are designed to shrink down to the correct size.

as a side note my dad was a foreman fitter at Stanton central workshops  they had made a large ball race made by SKF  it was about 36 inch bore , when it arrived a. the bore was to small and b. you could move the inner race inside the outer axially by about 1/8 inch.

So on the blower get the rep down here fast this is a load of junk ect.  So the rep arrives no the race it to specs , he then had them make up some go logo test bars to his figures , ok get them over the gas heaters until the gauges fitted the bore , pick them up with the crane the slid on the shaft like a well oiled jack boot , when cooled down there was no play and every one was happy and then retired to the Severn Oaks

That was the old works pub as the furnace side workers as part of their wages had 8 pint of beer per shift supplied 

Stuart

Good work with the engine

[Stilldrillin]

VT.
Nomate....... Not that big. Seems around 5 thou clearance.

Dave, Stuart.
Thanks for that. Not the sort of thing I get up to these days. Or, even previously! 

Popped the packet of 5, into a tub marked BEARINGS. Along with the previous freebies, from yourself, and Deco. 

David D

[Stilldrillin]

I said it was too getting hot, under her skirt. Didn't I? 

Even with the choke ring, the present burner is too enthusiastic....... 




Some mica insulation, under the feet........




Fitted a No3 jet, and made a smaller rose.......




Good. But still too much........




So, I reduced the burner area even more........




And, I reckon it could still work well, even smaller........




Start up from cold, is now "instant". 10secs is all she needs to begin to run.

Here's a little vid, during a 1hr test run. Mounted on a plastic turntable. Should give a smile.......

That was when I realised the flywheel balance weight was out of sync. After fitting the new bearings! 

Just got to find why she clonks, when hot. But not when cold........

David D

[vtsteam]

David, displacer grows when hot, contacts end?

[Stilldrillin]

David, displacer grows when hot, contacts end?

It has to be something similar....... 

Though it seems to be in sync with the power piston. At tdc. During the changeover between suck/ blow.

The Huxtable engine does the same thing. But, not as noticeable.

Strange things, hot air engines. Love 'em! 

David D

[vtsteam]

David Is the bore bell shaped? Can't remember if you did (or needed) a re-bore and oversize piston in the re-build....

I can imagine clack at TDC happening on a hot air power piston if the piston crown wasn't parallel with the wrist pin, or if the piston skirt wasn't long enough compared with the distance from wrist pin to crown -- assuming a little play in the bore at TDC.

As a guess, piston would tend to ride slightly skewed, and change the skew angle when the pressure changes sign. Clack would happen then.

Loose wrist pin would also do it .... though at both ends of the stroke

[Stilldrillin]

As an addendum to the burner development.......


Gas power is usually used, to get as much heat as possible, under a boiler. 
The problem is. I need a gentle, controllable, flame.

It finally dawned on me, what's needed, is lower gas velocity. Provided by larger holes!

As an experiment, I removed the rose insert. But it then insisted on burning, down inside the body.

Made a rose, with 3.5mm holes. (And 2mm central hole, which was already in the piece of bar).

The old, and new roses.......




No. 3 jet, giving a full flame. Which doesn't blow itself out when full on.......




But will turn down, sufficient for the engine to stop, with the burner still lit.......




Heading the right way, now. I think!

David D

[Ross]

Getting there David, Lovely engine!

[Stilldrillin]

Getting there David, Lovely engine!

Hi Ross.

Thanks Mate! 

David D

[vtsteam]

That looks really good, David!