A Robinson in the making. The conclusion.

[Alyn Foundry]

Thanks to both Ray and Jason. 

I wasn’t quite correct about the Robinson engine in question.  I thought it was my son’s but it’s video of an engine that came back to the “ works “ earlier this year for some tweaking….

<a href="https://www.youtube.com/watch?v=q2eOvxOJb_Q" target="_blank">http://www.youtube.com/watch?v=q2eOvxOJb_Q</a>

Just hit the “ slow “ setting.

   Graham.

[Jasonb]

I don't do much on Facebook but it has it's uses and you can be selective about what you look at.

Currently following Wayne Grennings latest restoration project, What Graham and other Alyn owners get upto and only last week on the Stuart Models group learnt of a Stuart engine that I had never heard of before which you could say is a bad thing as I've now drawn up my rendition and started cutting metal.

It's also been the source of size sand information that have enable dme to make a couple of other engines so can't all be bad.

[Alyn Foundry]

Cylinder and liner.

As with most of my previous scale models, the Robinson use’s a glued in liner. There’s a few good reasons for using this method.
1.  Ease of water jacket provision.
2. Being a blind cylinder, the liner can be bored and more easily honed.
3. Well, that’s about it really….

The cylinder casting was first fettled and put on the milling machine to flat off the base, using the flange top side as a datum. Once down to the correct thickness the casting was then transferred over to the 4 jaw chuck on the lathe. Before that the other flanges were also flatted, one for water the next for the pedestal fuel tank and the last for the sight feed lubricator. Just a couple more, the underside water flange and the face for the exhaust valve chest mounting pad.

We tend to first machine the liner to its outside diameter then bore the cylinder jacket to a slight oversize. This allows the Loctite high strength retainer to do its job properly. These days I leave the outside diameter of the liner in its rough, as cast state. Using a 4 jaw I get the cored hole running as truthfully as possible.  Cores can run off in all directions during casting so using this method can reduce the risk of not cleaning up properly. I then bore out the liner using as large a bar as possible to reduce the “ waft “ and so reduce the risk of a tapered bore. Some tapering is inevitable but you can minimise the effect by a couple of very light finishing cuts. The bored casting is then removed from the chuck and placed on an expanding mandrel. The Robinson didn’t allow much for the use of a separate liner so it has ended up being quite thin. Once on the mandrel the outside is cleaned and trued up, ready for honing.

My last set of stones for my Delapena honing machine disintegrated. The only other person who I knew used this type was Jo, here on the forum. I emailed her to ask if she had any spare stones I could buy. No joy. I tried eBay, a vendor in the USA was offering some but not overseas. What was I to do? Further trawling on t internet I discovered that Delapena were still trading. A very nice man discovered that the company’s website had failed to list the particular stones that I was looking for then proceeded to get them to me the following day. I was back in business. It’s amazing the difference the “ right “ set of stones make! I could spend hours in the past just getting parallel. It took just a couple of minutes. So now all nicely shiny I got back to finishing the cylinder jacket.
Several passes later the cylinder jacket was bored to size. It was then turned end on to make a face for both the cylinder head and exhaust valve cover mounts. Before I could glue in the liner there was one more important job to do, drill the top and bottom waterways. A long series drill was used to pass through the hole where the liner would go and down onto the ledge formed by the core. The holes were drilled to the correct depth and nicely picked up the ones drilled from either side of the water flanges. Before the gluing ceremony began I tentatively drilled the hole for the exhaust tract. Amazingly I managed to centrally pick up the cored hole from the combustion chamber and cleared out the remaining core sand.

The two machined castings were then thoroughly cleaned with Acetone before being liberally coated with glue. They were then put in the airing cupboard overnight to cure.

Since the Delapena incident I have bought a cylinder hone off eBay. I can certainly recommend those that come from India. The engineering is quite good and they certainly do a really good job. ( they are Delapena inspired ) My only complaint is the glue that they use to bond the stones to the metal frame is quite poor. I have used some Epoxy resin to good effect. I don’t use the three legged ones because they can have a tendency to get wider at the openings.

   Graham.

[Jasonb]

Graham, what size was the hone you bought? 34-60mm sounds about right for our uses though it would be nice if it went down to 32mm (1.5")

I was wasting time the other day on Youtube, this guy has a bigger tool but interesting to see how he used the different stones to take the bore out to size and then finish. I quite like his videos though it's bigger stuff than we tend to deal with. Video should start at the honing bit

<a href="https://www.youtube.com/watch?v=u1q2TC3UiX8" target="_blank">http://www.youtube.com/watch?v=u1q2TC3UiX8</a>

[Alyn Foundry]

Hi Jason.

Yep, 34-60 mm. However the stones are carried in little Steel channels and are held to the expanding Brass portions by a couple of screw clamps. I’m sure we could develop a method that used shallower stones to get 32 mm.

Back when working at the motorcycle shop, before I joined them they were using Delapena kit to rebore the cylinders. They used ridiculously coarse stones to start and then moved on to finer grades to finish. Thanks to my background I persuaded the boss to buy a second hand Van Norman boring bar and stand. Within weeks the money saved on the cutting stones paid for the cylinder borer!! The properly bored cylinders only needed a light cross hone to finish.

The beauty of the 4 stone arrangement is that it keeps things concentric once the stones are properly trued up.

   Graham.

[Alyn Foundry]

The piston.

A very essential part of almost all reciprocating engines. Aluminium was just becoming available at the turn of the 19th century. Such an expensive metal that a number of manufacturers actually used it for their name plates and badges rather than Brass! ( 19th century bling ! ) That being the case it wasn’t widely used for early piston engines. The Robinson has a cast Iron piston with the now common gudgeon pin bosses cast into the side walls. There were still many manufacturers that didn’t trust this method and were still using the older yoke and pin fixing . At full scale the engine has quite a large bore and stroke
( 5-1/4” by 6” ) so we were at 1/3rd. 1.750”

The first casting back from the foundry was an absolute nightmare. I had to resort to Diamond technology to knock off some hard spots. I managed the gudgeon pin hole with solid Carbide but I just couldn’t get it properly round. It got a little softer at the crown end for the single Viton “ O “ ring but on testing the engine under power, it burned it out. There was nothing more I could do with this casting so I needed a replacement. I ended up using a Retlas piston casting, thankfully being 1.750” when machined. All went beautifully, partly due to the extra thickness I’d given the pattern. Thus making the casting a little thicker in section than that of the Robinson one.

Now with over 40 years of experience we come to piston rings. I’ve made hundreds of them, broken nearly as many, but not anymore. Back in the day Martin came up with a formula that worked for us. We used the same Iron as the piston, or liner and made the ring to bore diameter. The inside diameter was made to 0.180” smaller. This gives a thickness of 0.090”. We made them 0.090” wide as well, a square section. These rings were then “ cracked “ apart on a suitable mandrel and a very sharp blade, placed at right angles to the ring. A sharp rap with a hammer was all that was needed to crack them apart.

The next operation was to anneal them. Our standard was 0.125” and a group of rings would be placed in the forge on the metal “ gapping “ tool and heated, uniformly until bright Orange. At this temperature the rings would suddenly loose their hold on the tool and fall sideways. They were then allowed to cool naturally.

Are you getting bored yet? There’s more!

The next stage was lapping. On a sharp, flat Oilstone. Martin was a joiner by trade and had a thing for a particular stone from the USA. Washeter if my memory serves me correctly? This grit made short work of getting the edges sharp and crisp. You would constantly be checking the width of the ring with the groove ( the depth was made to 0.095” ) until they fitted snugly.
Nearly there now…. The rings were then correctly gapped to the Heppolite piston ring manual for water cooled cylinders.

Now, if you were lucky, it was time to successfully fit them to the piston. This required a really steady hand, invariably one would break, hence the batch making. And that’s the end of the process. Phew, thank goodness for modern technology.

I discovered Viton “ O “ rings several years ago now and all the previous text goes right out of the window. Measure the finished bore diameter, obtain a 2 mm section ring based upon the inside diameter ( so that’s ID + 4 mm ) make a single 2 mm wide groove in the piston at a depth of roughly 0.002” shy of 2 mm and fit the O ring. As that Meerkat Alexander would say, “ simples “

I have been using Viton rings for several years now even refitting my much tired rally engines with them. They work exceptionally well and don’t require any special lubrication either.

   Graham.

Robinson Oil engine with single Viton ring.

[Jo]

Are these the India honing sets you mentioned Graham : https://www.ebay.co.uk/itm/393155824129

They seem to have a good range (but are not as cheap as the 3 legged hones)

Jo

[Alyn Foundry]

Morning Jo.

Yes, that’s the type but they have jumped up in price hugely since April. I got mine at around the 30/40 pound mark with £10.00 express shipping. I got it within 4 days of ordering. With both the Robinson and Little Otto having a 44 mm bore diameter this was beyond the scope of my Delapena machine’s capability.

I know you’re familiar with honing as you have the same machine as me. The tool carries a pair of adjustable stones on a special, parallel mandrel. Opposite the stones are the “ Brass or Aluminium shoes “ that contact the bore. With this method of contact it ensures that the stones cut to the bore because they’re mechanically held. The 3 legged types are spring loaded and pivoted on the stone centre. This can cause a couple of problems. Any hard spots will push the stones away from cutting. And, if you’re over zealous on the stroke the ends can become “ Bell mouthed “ because of the pivot.

Now before I start a war, there’s nothing wrong with the latter mentioned hones. If used correctly they do their job. However for doing commercial work you go with tried and tested equipment. For us folks that build engines over and over again the little extra price is well worth it in the long run.

  Graham.

[Alyn Foundry]

The Crankshaft.

As Per put it “ there’s many a way to skin the proverbial feline “ indeed there is, particularly with the crankshaft.

Being lazy, my method is the “ composite “ build. I use ground stock/drill stock for the shafts and pin. The main shaft is centre spotted to aid any warp correction later. Separately cut Steel billet for the webs. Having recently ruined an expensive horizontal cutter trying to cut the keyway after Silver soldering I now cut the keyways before soldering.
With this method you need to accurately drill and ream the webs as a pair then place them on a perfectly flat firebrick with a decent flux covering the joints to be soldered. Having tried many fluxes over the years only one has stood the test consistently. Tenacity No 5. Specifically designed for long heated ferrous metals. With plenty of firebricks placed around the shaft I start playing the heat from end to end. This gets the main shaft expanding outwards before you concentrate the heat on the 4 joints being soldered. I tend to cut the Silver solder into little pieces and place them on the fluxed joint transitions. Experience has shown that a 1/8” diameter cut to 3/16” long will adequately fill each joint. This doesn’t stop me from hovering around with stick in hand as a “ just in case “ moment might occur. The shaft is then allowed to cool naturally before being “ pickled “ for 24 hours in an Acetic acid bath. This removes any unwanted flux residues. Once pickled and cleaned the crankshaft can have the main shaft metal removed from between the webs to form the nearly completed crankshaft. Now put in the lathe, the crankshaft can be checked for truth. I have a very accurate chuck for this task but obviously known for truth collets work just as well. A DTI is placed on the far end of the shaft and any runout noted. By having a centre spot the shaft can be nudged using a solid centre from the tailstock. Once trued, and a packer placed between the gap you can now machine the big end radius and clean up any excess solder at the main bearing sides. To true up the crankpin I have a special jig that’s held in the 4 jaw chuck that carries the shaft and puts the crankpin on lathe centre. You can now clean up the pin and do the other radius on the webs. All that remains is to carefully clean and polish the webs and shafts with fine grade Emery cloth. The method described above can be partially used for cast crankshaft’s too.

As a footnote and totally my own opinion, I don’t believe that pinning is a good idea where composite crankshaft’s are concerned. Particularly on larger, slow running and with heavy flywheel’d engines. Rather than aiding the joints they have a tendency to weaken and actually reduce the overall strength that a good soldered joint can provide. We are talking about some quite dynamic forces here. This comment is based upon years of experience and having tried just about everything.

If you’ve got plenty of time and patience, I have neither, the ultimate crankshaft is cut from suitable billet Steel in the form of an elongated “ E “ shape. One end spotted for both shaft centre line and pin centre line. With the aid of a 4 jaw chuck you can then hack your way down to form the shafts and webs before turning it around to form the crankpin and inside webs. You will see that Dave welded on the extensions to the casting for the full size replacement.

Being a purist the only good keyway is a horizontally cut keyway. My old Denbigh mill makes an excellent job of this task. I just centralise the shaft in the vice, set a 0.065” cut and then go do something else whilst it gets on with the work. All that’s required is a light lick with a Diamond file to clean up the cut edges. They’re really sharp and have caused more leaks of the “ Claret “ than anything else that I can think of !

It’s very probable that the original engine had its crankshaft made, down the road at Gardner’s machine shop. Having had the pleasure of speaking to an early apprentice he told me that one of his first jobs was drilling the through holes in Steel plate billet ready for the slotting machine. The rough shape would be slotted out before moving over to one of the “ in house “ designed crankshaft lathes. I believe designed by Charles Gardner. Luckily one or two of these machines survive and are kept at the Anson engine museum.

  Graham.

[Alyn Foundry]

Number 2 son making his scale Gardner crankshaft.

You might notice that one of the little pieces of Silver solder slipped away needing a little help from dad.

<a href="https://www.youtube.com/watch?v=QwlmaAIzUMU" target="_blank">http://www.youtube.com/watch?v=QwlmaAIzUMU</a>

  Graham.

[Admiral_dk]

Thank you for a very imformative Video 

I first noticed that he brought the colour up to Red-Orange and thought that this would have Flunked my Test back in time - we where Told in no Uncertain Manner, that if you Ever got it that Hot - you have Ruined the whole Solder Process (should be Golden-Straw) -> take it all apart, Rinse, Clean and Start over again ....

.... hmm - it probably has everything to do with the Flux & Solder Combo used here - compared to what we where taught, to use back then (1979) 

Next I noticed that the Flux started to go 'Liquid' - followed by the Solder doing the same - so that kind of confirmed that it is a very different Solder to back then ....

That begs the question - what Solder do you use in the Video (the Flux has been told) ?

Per

[Alyn Foundry]

Hi Per.

You are most definitely correct about the heat. Back in the day the Ferrous material would have oxidised, preventing the joint to be made.

Thanks to the Tenacity number 5 formulation this allows for much higher and prolonged heat without oxidisation of Ferrous material.

The Silver solder is Oerlikon brand and costed over £9.00 per rod over 10 years ago. I bought a whole pack, way over £100.00’s worth. I can’t imagine what the cost would be today! 

  Graham.

[Jo]

Let me teach you a little trick Graham to save your fingers getting burnt 

Find yourself an old bit of copper tube say 6mm O/D about 30cm long. About 50mm from the end bend it a bit so that when you poke a length of silver solder into the tube it holds the silver solder in place. When you want to apply silver solder to a job hold onto the copper tube and stick 20 or 30mm out of the end of the tube. Worth lightly heating the silver solder and sticking it into the flux before applying it to the job 

Jo

[Alyn Foundry]

Thanks Jo, that’s a very useful tip for one and all. 

Typically things go bosoms up when you’re filming. Non of us expected the solder to fall off the joint but it does happen. My brand new side cutters got a serious baptism of fire as they were the closest thing to hand.

The Sievert burner is massive @ 30 mm bore and was a snip @ 50 pence, brand new, at a car boot sale many years ago. They didn’t know what it was. I also got a full bottle of Tinmans solder paste for a quid. Lucky me….

  Graham.

[Alyn Foundry]

The conrod.

Or connecting, rod is made from ordinary mild Steel. A suitable length of mild steel is marked out with the big end and small end  centre spotted. Before cutting through the big end centre line a pair of holes are drilled and tapped, end on to allow for the conrod to be fitted with its bearings and then bolted onto the crankshaft. Once the cut ends are properly cleaned up the cap can be bolted back ready for drilling and reaming. This can be done on the milling machine or even an accurate pillar drill. The only critical point is that both holes need to be parallel with each other. The model is trying out some, off the shelf Glacier bushes for the small end bearing and a pair, of well tried Zinc alloy shells for the big end.

Once the holes are finished the surplus metal was removed by using an angle grinder fitted with a thin cutting disc. I hadn’t tried this method before mainly because I didn’t know about their existence until number 2 son brought some home for me to try. With a steady hand the amount of metal you can remove is amazing. You can even dig down, between cross cuts if you’re careful. The roughed out rod was then placed on my little used Harrison L 5 that has a taper turning attachment and a traditional looking conrod emerged from the swarf.

The top slide was used to radius both big and little end eyes to finish. All that remains will be to drill through the big end cap holes and replace the bolts with the correct looking fixings.

I have used Zinc alloy for many engine parts over the years, I refitted my Gardner with both big end and mains. The full size engine had Babbitt but at half scale it’s a difficult material to work with. I chose Bronze at the time. Now fitted with Zinc they have done hours of display time and haven’t worn either themselves or, in the case of Bronze, the crankshaft. Pictured is the half mould and ejector and the castings. The extra length serves two purposes, head for the casting and the chucking stub for machining.

   Graham.