Old Bill

Fortunately for me, Norman, you can't see the bore very clearly. It chattered like mad on the very last cut!

Steve

I assume these joints are filled with a thick oil, but how are they sealed, the end caps look like they are in 2 halves for a start? Were conventional Hooke joints not in favour at the time?

Hi Mike.

Yes, they seem just to have a thick oil poured in and rely on centrifugal force to keep it there. The end plates are split but are cunningly made as a single piece and broken in two across the centre so there is no gap between them. I doubt that they will be oil tight though. One thing about the se old lorries, if they are not dripping, you haven't got enough oil in them!

Dennis had some funny ideas about flexible joints. Many of their early vehicles had 'box' joints where the end of the shaft had a large square lump machined on it with curved faces. This ran in a square hole on the end of the next shaft and had bronze wear pads in between. They are horrible things and gave endless problems to the Royal College of Science students fire engine. I expect Barry might make some comment about them in a moment, as used on his fire engine.

Steve

That is a very good explanation Steve, thank you!

 

So actually it is a homokinetic joint which has the same properties as a propshaft with two universal joints.

Hi Marcel.

I had to look up 'homokinetic'! I think that means 'constant velocity' so that the output shaft is always at exactly the same speed as the input throughout its whole revolution. Looking at it, I don't think these joints are. They appear to me to have the same action as a Hooks joint but to include some telescoping ability as well. If the engine and gearbox are correctly aligned, then there is no articulation of the joint at all and the constant velocity issue does not arise. Our shaft will not be perfectly in line but close enough not to cause a problem. Also, as the pins are directly in line with each other, the gearbox won't see any vibration anyway.

Gosh, we are getting technical tonight! I think we may just have set some questions for the clubhouse Christmas Quiz!

Steve

Hi on the drawings does it specify the type of material strength or if case hardened ( if they did that sort of treatment ? ) I know you've used other materials for some jobs for the better just wondered what detail is on the drawings

 

Would an angle grinder spanner do this job ?

Yes, the drawings do quote materials but this is before the days of En numbers and standardised specifications. The clutch bearing housing is described as 'Steel V.7 (HT) Brinell 217/269'. There is another specification which has been crossed out and I can't read it. It finishes up saying 'Harden and Grind'. The clutch bearing nut says 'V.4 H&T Steel' which I take to be 'Harden and temper' and again finshes up with a Brinell hardness specification. I must admit that we have not hardened any of this but I think we will get away with it. The sockets for the flexible joints use '40 ton mild steel' which we took to be something like En24. We have no drawings for the short prop shaft so I sketched it from the GA drawing and used En 24 again as we could get it and it is good tough stuff. Time will tell!

An angle grinder spanner is the right sort of idea but I think I will need to make one exactly the right angle and with pins both sides to get it to work on the pump gland. Access is very tight indeed as we will find out very shortly!

Steve

Sorry to ask what might be a silly question, but this is my first post!

 

What, in simple terms, is the constant velocity issue?

 

Hello Damian.

Good question and one that took me a while to convince myself I understood! Here goes:

The classic universal joint is a Hooks Joint with two forks facing each other at 90° and a block between them. A pin goes crossways through each fork and through the block as well. The forks can therefore move around the block. If each fork has a shaft connected to it, then if one shaft is turned, the other must follow and you can take the drive around a corner. This arrangement is commonly seen at both ends of a prop shaft. (see picture below). So far so good.

The point that is often missed is that the output shaft does not turn at exactly the same speed as the input shaft throughout the revolution. If the input shaft is running at a smooth constant speed, then through one revolution, the output shaft goes a little quicker, then a little slower, a little quicker and then a little slower until the revolution is complete and the shafts are in exactly the same position as when they started. Thiis effect gets worse the greater the angle of the joint. Now if you have two joints and the first (input) shaft is parallel to the third (output shaft) the joints can be arranged such that they cancel each other out. In that case, both pins in the middle shaft must be in line and the output shaft runs smoothly even if the centre shaft keeps speeding up and slowing down. If the pins are arranged at 90° then the effect of the two joints is added and the output shaft will be very rough. If the pins are worn, then the centre shaft will rattle and you will hear this in a vehicle, particularly when you ease off the power and coast.

Does that help? To convince yourself that it happens, take a prop shaft and put a bit of tape both sides of the joint exactly in line. Then bend the joint as far as it will go and turn it slowly in your hands looking along the joint. You will see that the second piece of tape moves first one side and then to the other of the first. I had to use meccano to prove it to myself!

Steve

No, I never have seen one or even a picture in the parts book. I was planning to make a sort of 'C' spanner with two buttons riveted on to engage in opposite slots. Even with that, looking after the gland will be difficult as the only access is through the hole in the side of the mounting casting. I think that re-packing will require the pump to be removed and partially stripped each time which will be quite a pain. With a bit of luck, the long bearing and pressure lubrication will extend this process to long intervals.

Steve

Thanks for the suggestion Norman. What sort of radius could they cope with? The pictures below show the rear of the headboard on the original Thornycroft J which are, I think, about 8-10" radius and what we want to achieve. The other pic shows the rear of the IWM, FWD model B. You can see that the angles on the sides are bent very tightly indeed and I am sure that must have been a blacksmithing job. Of course, I could just cut and weld them but that would be giving in!

The FWD pic also shows a lot of other ironwork around the tailboard quite a bit of which has been hot worked. I think these items are going to keep me amused for quite a while!

Steve

Thanks Andrea. A sympathetic blacksmith is a very good find. I also see that he does short introductory courses which seem like an excellent idea. There is nothing like learning a new skill!

Steve

Last weekend, we had a family get-together, not only to work on the lorry but to celebrate Tims and my birthdays. A good time was had by all and look what I got!

Aren't I lucky! :-D

Steve

This is the early pattern body from a Dennis publication which explained how the 'Subsidy' scheme worked. Ours will be of the later pattern with solid sides and much squarer hoops but you get the general idea.

Steve

The body will be the later pattern 'Subvention' body with steel hoops and a canvas top. It is quite straightforward and various drawings and diagrams have been published over the years. I think we have an original Dennis drawing in stock too (I must go and look it out!) so I don't anticipate too many problems. It does, however, have quite a few forged iron brackets which I would like to make. To that end, I am in the process of setting myself up with an anvil and hearth and reading up on blacksmithing so I can do it. The most difficult bit will be in bending the steel angles to form the hoops and side brackets. Nowhere can I see how to do it so if there are any experienced blacksmiths out there who can explain how it is done, I should be very glad to hear from you!

The body will be of some nice quality pine planks on an ash frame and we are budgeting about £1000 for it. A joiner friend will procure and prepare the timber for us and Tim has been busily importing square nuts from the USA to go on the bolts and hold it all together.

As far as the seat box is concerned, we have only overall dimensions. However, an original exists on the Thornycroft J at the East Anglian Transport Museum and I have measured that up and drawn it in detail. It will need tweaking to get the shape right for the Dennis but we will use the same methods of construction. We just need to find the time to do it all!

Steve

Just to prove that I am doing something too, here are a couple of oil cups to which I have given the treatment. Tim and Dad rescued them from part of the brake mechanism on one of the gearboxes. The box we have used does't seem to have a place for them but I spotted that they would be ideal for the pedals. They were both seized and thoroughly encrusted with what appeared to be limescale so I started off by pickling them in sulphuric acid overnight. They certainly fizzed and fumed quite well when I put them in! Unusually, I didn't take a 'before' picture but the first here shows them after removal from the acid. I then attacked them with a mini rotary wire brush mounted in a 'Dremel' which polished them up nicely. Finally, here they are in the pedals. The thread of one is pretty poor but it still has enough bite so I am pleased with the results. Two more parts on the road to completion!

Steve

Well, yes. I didn't like the idea much either. However the surface of the axle casing is so poor that a simple paper gasket wouldn't have done much although we might have used both together I guess. Alternatively, I could have filled the surface and rubbed it back. A bit late now! Will have to wait and see how it performs.

Steve

You are quite right Barry. This pump is enormous compared with later pumps. I wonder whether it was just a rough estimate as to how big it should be and they made them smaller as experience showed what they needed. I have seen it written that the subsidy engine didn't need a pump at all and would survive quite happily relying only on a thermo-syphon. Mind you, at what speed does yours run? Is it camshaft speed or crank speed? Doubling the rotational speed would allow you to reduce the diameter by a half and still maintain the tip speed.

Steve

I must admit that I hadn't thought of balancing at all! It runs at camshaft speed, say 500rpm peaking at 750 so I am not really too concerned. However, I will roll it across the surface plate and see how it looks. If it is drastically out, I shall have to attack it with a file!

Steve

Wonderful! I knew it existed but had never seen photgraphs before. Thank you!

Steve :thumbsup:

Tremendous clip!

Steve

Part of the 'subvention' scheme requirements were that the radiator be mounted entirely above the chassis which is where ours is. However, the pump we copied came from a lorry that was just post war and the radiator would very likely have been mounted much lower with the starting handle through it. Therefore the elbow I originally copied pointed much more downwards. Obvious now!

Steve

Hi Gordon.

Yes, hopefully, it will be a straightforward draw. I have made a couple of compromises to allow this though. The 'lump' around the flange bolt hole hidden behind the elbow has extra material running tangential to it and perpendicular to the split line so there is no re-entrant shape which would drag through the sand. I have also added an extra bit to the small flange as well. Hang on a minute, I will take some pics. Worth a thousand words as they say!

Steve

I like the way how Steve has drilled the flange holes. No rotary table was used here, just an old fashioned set of dividers.

 

 

Barry.

Not I ! That's Father's work!

Steve

Wouldn't the double coilspring washers be nearer replacements for thackray washers?

 

http://www.fabory.com/pages/categories.html?catId=fabory_0000092195_0000092684_0000092712_0000092736

 

They would need a very close look to spot the difference when fastened up.

Yes, you are quite right. I will get some to try.

Cheers!

Steve

The lorries came from Guinness but were sent to Inchicore railway workshops where they used whatever was to hand to make them. The main shape is formed of four locomotive smokeboxes from main line railway locomotives which were 5'3" gauge. The reinforcement over the lorry cab is a locomotive cab roof. I haven't been able to work out the class of locomotives used, however!

Steve

I agree that they look like different vehicles but David Fletcher states that the brewery had three Daimler lorries which were converted so this is very likely.

Steve

When I pick up the blocks for final machining, I will take the pins as well, and bore the blocks to fit. I don't think my lathe could cope with a 7/8" reamer in bronze!

I am actually more concerned about the fit in the ends of the prop shaft as we have now placed the order for that as well. I hope that the pins will be a firm push fit with no rattle. We could cope with 0.001" clearance by using Loctite but if there is much rattle, we might have a problem. Fingers are crossed!

Steve

What a glorious motor car! I am so looking forward to seeing it out and about!

Steve