Stuart #1 Reverse Drawings

[John PurdyParticipant @johnpurdy78347]

Just add a 1/4" or so to the 1/2"dia. x1 3/4" long steel supplied for the reverse lever anchor screw and nut.

John

[John PurdyParticipant @johnpurdy78347]

Just out of curiosity I got out the plans for the #5A and its reverse gear, and added up the dimensions to see if the reverse gear expansion link and valve rod line up on it. No problem with this one, everything lines up.

John

[JasonBModerator @jasonb]

Sounds like they use the same castings and drawings for both but should have altered the drawings for the No1. If they did not want to do a whole new drawing adding a detail for the No1 lever would not be hard to do or use an errata sheet as they do with other models though that can get lost!

J

PS I was thinking of square or rect bar to make a whole lever from, infact it could all be cut from solid and unlikely on full size engines to have been cast. Bracket would be the exception but even that is not hard to cut from solid and I'd probably change the width of the part that goes against the chest as I don't like how it partly overlaps the cover.

[David SeniorParticipant @davidsenior29320]

I've followed this thread with interest – I'm working on a 5A with reversing gear at the moment, and if I've got it right the eccentrics foul the step in the crankshaft. On nominal dimensions the eccentrics will rub on the flange of the crank bearing, but the crank change in diameter is a further 1/16" out. The additional drawing for the reversing gear shows a clearance of about 1/16" between the eccentrics and the bearing flange. (My drawings are dated 1954 and issued in 1965 – the engine was started by my grandfather who died in 1966 and I feel it is about time it was finished!)

Dave

[John PurdyParticipant @johnpurdy78347]

Dave
     My #5A was also acquired part built but by an unknown person and I have been working on it off and on, but whoever had started it has butchered the bed plate casting and bearing caps. It really needs new castings but the current price is putting me off. I'm trying to find a way to salvage them.

     Back to your problem; my plans are dated the same as yours and I have added up the relative dimensions and this is what I have come up with:
Cyl.centre line to valve rod centre line: 1 15/16"+5/8"= 2 9/16"
Bed plate centre line to Bearing outer face: 1 1/8"+3/4"+3/16"= 2 1/16"
Therefore valve rod centre line to bearing face = 1/2"
Eccentric face to valve rod centre line (in eccentric rod ): 1/64"+1/8"+7/64"+9/64" = 25/64" (for the reverse gear )
This then gives a gap of 7/64" (.109 ) between the eccentric sheave and the bearing face to clear the 1/16" extended dia. on the crank.
    Or am I missing something?
John

Edited By John Purdy on 19/02/2022 19:27:47

[JasonBModerator @jasonb]

If all else fails it should not be hard to fabricate abase that looks like a casting, this is one I drew up for someone who was missing it from some 10V parts they had

Built up in a similar way to this one of mine

Who's to know what's under the paint

[John PurdyParticipant @johnpurdy78347]

Jason

When I said in my previous post "just add 1/4" to the 1/2" dia. – – – – " I was thinking you were talking about the spacer not the whole lever but making the whole reverse lever out of the solid would certainly be a possible solution. Wouldn't actually be much harder as the casting (which is malleable iron and machines pretty much like steel anyway ) needs to be machined all over.

As far as fabricating the bed plate for the 5A, that's definitely possible but where I live it is next to impossible to get raw materials.

John

[David SeniorParticipant @davidsenior29320]

John

Thanks for taking the trouble to check your drawings

My belief is that the bearings need to be fitted with the thin flange inwards, and the thick one outwards (crank width across webs = 1 7/8", Gap in bed plate = 2 1/4" leaving space for bearing flanges of 3/8" i.e. 2 at 3/16"

So my calculation for bed plate centreline to bearing outer face is 1 1/8" + 3/4" + 5/16" = 2 3/16"

I agree with the 2 9/16" to the centreline of the valve rod

The eccentrics are a total of 3/4" wide, so half of that (3/8&quot inboard of the valve rod gives 2 9/16" – 3/8" = 2 3/16" so nominally touching the bearing face.

The crank bearing diameter extends to 15/16" + 1 5/16" from the centreline (2 1/4&quot (i.e. protruding from the bearing by 1/16&quot

If I am correct I will need to either shorten the bearing diameter on that side of the crank or (more likely) counterbore the eccentric pair to clear the step on the shaft. Skimming a small amount off the main bearing on that side to give a small clearance should be straightforward.

I haven't checked with Stuart Models as to whether the drawings have been changed, so I don't know whether this is a recognised problem (or whether I am somewhere mistaken)

I am impressed with the look and finish of your No1 – I can only hope that my 5A will be somewhere near and that my grandfather would have been proud of it.

Dave

[John PurdyParticipant @johnpurdy78347]

Dave

You are right, the bearings have to be mounted with the 3/16 flange inboard. I was using the bearings with the 3/16 flange out as that what it looked like on the reverse drawings. Should have checked the crank/ bearing/bed opening, duh!

With the bearings the right way I get the clearances as:

Bed plate centre line to bearing outer face now 2 3/16"

Therefore valve rod centre line to bearing face now 3/8"

The way I calculated the valve rod centre line on the eccentric rod to the sheave face was: the ears on eccentric rod fork are (1/2"-9/32" )/2 = 7/64" wide, therefore centre line of fork is 7/64+9/64 from face of rod in slot in the strap, the edge of the slot is 1/8" from the face of the strap, the sheave is 3/8" wide, but the strap is 11/32" wide therefore the sheave extends out beyond the strap by 1/64", for a total distance fork centre line to sheave face of 7/64 +9/64+1/8+1/64 = 25/64 (.390 ) resulting in the sheave face being .015" into the bearing for things to line up. This doesn't take into consideration the 1/16" extension of the crank dia beyond the bearing face.

So it sounds like to make things line up the bearing face will have to be skimmed and the sheave counterbored for the crank unless we're both missing something!

So as you had initially found there seems to be a problem. Sorry for me confusing things.

Interesting that both the #1 and the #5 reverse gear have problems

Thanks for the kind comments on my engine.

John

[David SeniorParticipant @davidsenior29320]

John

I think you have missed the fact that the strap is not symmetrical about the locating groove. By my calculation (and as shown visually on the reverse gear drawing – not that that should be taken as gospel!) the straps align with the outer faces of the eccentrics, leaving a gap between the straps.

This doesn't change your conclusion, except that the skimming of the bearing face will only be to give working clearance, rather than to correct a foul. The eccentric pair will definitely need counterboring to clear the crankshaft bearing diameter.

I have yet to attempt to master the joys of tapered gib keys. Clearly here it is going to be important that the key doesn't protrude beyond the eccentrics.

I think we are there now!

Dave

[John PurdyParticipant @johnpurdy78347]

Dave

Your right again! I missed the groove in the eccentric strap being offset so the face is flush with the sheave. So ignore the extra 1/64" in my previous.

Is there any reason why the larger dia. on the crank has to extend out beyond the bearing?

I'd be curious to know how you machined the eccentric pair. I've looked at it a couple of times and tried to visualize how to machine it but haven't had much success.

John

[David SeniorParticipant @davidsenior29320]

John

There is no reason that I can think of for having the shaft longer, apart from not wanting it to be shorter than the bearing so that it can't wear a groove in the bearing. So I guess equal or just slightly longer would be best.

I haven't got to making the eccentrics yet, but I am thinking of doing the bore and keyway first, then mounting on a mandrel with both centres in the ends so that I can set between centres to machine. I intend to machine them to the same width as the straps, so there will be a section between them that looks like a woodworking biscuit joint piece, if that makes sense. That way it is not so critical about getting the 'joint' in the middle.

Not sure when I will get round to it. Technically I retired at the end of Jan, which is why I have started on this project. However retirement for me will be going to work everyday as normal (all my equipment is there) and hopefully not having to do any 'proper' work so that I can concentrate on the models. Right now I am still choosing to run cnc machines until a new employee starts in a fortnight, so I am not able to concentrate fully on this.

Dave

[John PurdyParticipant @johnpurdy78347]

Dave

If you have access to it, I just remembered that there was a series in Engineering in Miniature by Andrew Smith on building the ST Cygnet (basically a #5A ). I have dug it out and it ran from May '81 to Dec '83. In one of the installments he details a method of machining of the double eccentric, also an alternative.

On a totally different note, I don't know if you are aware, but you can prevent the "smlies" showing up at the end of a bracketed statement by putting a space before the final bracket.

John

Edited By John Purdy on 20/02/2022 20:10:48

Edited By John Purdy on 20/02/2022 20:16:30

[John PurdyParticipant @johnpurdy78347]

Dave

I've sent you a PM.

John

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