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WW1 Thornycroft restoration


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You are correct - However, many times you will find these old T-heads with bent rods. As you have probably discovered its very easy to have things jamb-up and the rods take the weight of the block if the pistons get a bit off kilter.

 

With the White and Poppe engine on the N-type we normally set the crank crosswise and leave the piston skirts sat on the crank webs as we lower the blocks into place. Then push them up into the bores and engage the big ends.

 

This only works with flat-sided crankshafts though.

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We seem to have been playing around with the front axle for some time when really it should have all been quick and straight forward. The axle arms that we finally chose have come from two different front axles – the bearing surface on one arm from the first axle was very rusted whilst its mate on the opposite side of that axle was sound. On the other axle, the equivalent of the heavily rusted axle was sound whilst its mate on the other side was very worn – it fact it had become tapered and oval so we had to take the pair that we wanted to finally use from the two axles – a bit of “mix and match”.

 

The tale of the removal of the King Pins has already been related and they are out – the bushes on the first arm came out very easily but the bushes on the other defied all of our efforts at home and it was a case of returning to the local Garage to use their 60 ton Press. A 5/8” diam draw-bar would not move the bushes at home – only bent a 1/2” steel plate which was worked against. At the Garage and at 40 tons, the bushes moved! Interestingly again, the bottom bush on one arm is made of bronze whilst the one on the other arm is of steel.

 

The top bushes have the lower part of a Thrust Bearing integral with it and we have been unable to find such an item in the modern world. So Steve has taken the top bush away with him to Leicester to scheme out and design a substitute bush to which we can marry up a modern Thrust Bearing.

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The Arms have now gone away for sand-blasting – we have tried to protect the bearing surfaces as far as possible by wrapping some blue rope around them very tightly. The Ball Joints will have to come out and be replaced.

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The top bushes have the lower part of a Thrust Bearing integral with it and we have been unable to find such an item in the modern world.

 

It's just machined and heat-treated steel. How hard can it be?

 

A lump of Silver Steel machined and heat-treated would almost certainly last well enough for a vehicle not actually driving two shifts all week.

 

(I could have a go if you want, but I suspect that Steve will spot the thrown gauntlet at this point :-)

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It's just machined and heat-treated steel. How hard can it be?

 

A lump of Silver Steel machined and heat-treated would almost certainly last well enough for a vehicle not actually driving two shifts all week.

 

(I could have a go if you want, but I suspect that Steve will spot the thrown gauntlet at this point :-)

depends on how much carbon was in there to start with...
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depends on how much carbon was in there to start with...

 

Why?

 

It doesn't really matter exactly what the original composition was as long as you can achieve the same, or nearly the same, mechanical properties. Silver Steel is just a readily-available oil-hardening tool steel, and probably has a better balance of properties than the steel that Thornycroft used. The fact you can buy it from Cromwell on a Saturday morning is just a bonus.

 

If one wanted to be really careful it would be possible to hardness-test the originals and temper the new ones to match.

 

Not that there is anything much wrong with pressing a sleeve into a standard bearing to recreate the same function.

 

I will point out for Steve's benefit that if you can get 120m/min (or more) on your lathe at the diameter in question then a CBN insert will machine bearing steel. In a rather spectacular way, and to a lovely finish. That DSG mentioned earlier would be a great candidate for that.

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I think that this is an example of a situation where it really doesn't matter what the exact spec of the original steel was. The question is what would be the most suitable choice now. We now have a vastly bigger choice than they did then and as Andy said we can machine the steel that ball races are made of in its hard state, which was unheard of 50 years ago. However we do need to understand the whole picture so that we don't just create new problems. I am sure Steve has it all in hand, and a bearing catalogue too !

 

David

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I ran into a similar type in a 1909 Jackson. The mains were simply machined Babbitt inserts with no backer. They were indexed in the crankcase and caps with steel dowels...I am assuming they did it this way because of the difficulty of bonding poured Babbitt to aluminium.

 

This seems to me typical of phosphor bronze bush / plain bearing design in industrial machinery. I've seen PB bearings done like this in machines built right up to the '60s. Is it likely that, given it was the very early days of IC engines when design fundamentals were still being sorted out, they simply drew a parallel with what they knew?

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The Arms have now gone away for sand-blasting – we have tried to protect the bearing surfaces as far as possible by wrapping some blue rope around them very tightly. The Ball Joints will have to come out and be replaced.

 

Of interest that tape we use in the military for everything, airframe tape, 100mph tape (100 mph was how fasted it was nicked) is useful to protect surfaces to be sandblasted. As the texture is rubbery the grit bounces off

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I have had a look through the catalogues and have ordered a pair of LT 1 7/8 thrust bearings. These are exactly the right OD and are big enough for a 1 1/2" bore bush to be pressed into them. Dad will turn up the bushes from bronze and just machine a shoulder to locate the bearing at the top. This should give us a good reliable solution with a minimal use of material which Father tells me he already has in stock from a lucky buy at some autojumble. The next step is to decide whether the king pin should be skimmed or is good enough to use as it is. This will determine the size of the bore.

 

Steve :-)

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Steve has been pattern making again. This time for the gearbox mount and the engine mount. The early J-types had the gearbox bolted to the sub frame at each corner. However, the wracking of the chassis caused cracks around the legs of the box so later versions were three-point mounted by bolting down in two places one side and supporting the other with a spigot in a plummer block. Our box has the spigot but no block. Fortunately, Steve measured up the one on the Portsmouth bus some years ago and was able to make a copy.

 

An old beech roller from a lawn mower formed the top of the block but the base was made from the usual MDF.

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He then cut a groove with a razor saw and chisel and glued the two together, using the vice as a clamp.

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Then hi filled it with Isopon and dressed it all back with glass paper and a Dremel pencil grinder.

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The second pattern is for the engine mount. To get over the wracking problem, the engine is bolted to two pieces of steel angle which Father has already made. The right hand angle is bolted up to the inside of the sub frame but the left hand swings on a centre pivot to avoid loading the crank case. This casting is for the centre pivot and bolts to the middle of the angle.

 

As usual, Steve started with pieces of MDF which were cut, sanded round and glued together before adding fillets with Isopon again.

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The filler was again dressed with glass paper.

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Both patterns were painted with two coats of Bondaprime, rubbed down after the first coat and then polished with wire wool after the second.

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. Father took them to the foundry and picked up the castings this week. All very satisfactory.

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They are ready for machining and can be fitted at any time.

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I know it must be just me (because nobody else has said anything) but I am unsure as to what is meant by 'chassis wracking'. I can guess, but it would be nice to have a definition from the 'Gosling English Dictionary of Automotive Terminolgy'!

 

Barry.

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Glad you are learning from the discussions. There is so much knowledge out there and it is a shame to waste it!

 

Your first lathe is a very exciting prospect. Very soon you will not be able to understand how you lived without one!

 

Good luck and have fun!

 

Steve :D

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  • 2 weeks later...

It has often been said that we couldn’t do this hobby without our friends and this has been shown once again.

 

When we started preparing the new front wheels that we had obtained from Shildon (page 130) we noticed that the bores had become noticeably bell-mouthed. The bores are the bearing surfaces so if we did nothing about them, then the wheels would wobble. The fix was quite simple in that they just needed skimming out oversize and new bronze bushes making to suit but they are 720mm dia and weigh a good hundredweight each so to find someone with a lathe of this capacity who was prepared to take the job on became quite a challenge. Steve was at the railway one day and mentioned the problem to our good friend Adrian who simply said

 

‘Come and use mine!’

 

Steve has just taken him up on this very generous offer and this is the result.

 

This is the lathe, a Schofield and Oldfield of 12 3/8” centre height with a gap bed and a faceplate with bolt-on jaws.

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It probably dates from the 1950-1960s era but Adrian knows nothing of its history. Steve reversed the jaws and then they rolled the wheel up onto the bed before manhandling it into the jaws and nipping them up.

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Then they checked it with a DTI and found that it was only 0.1” eccentric at the first try!

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. By adjusting the jaws, the full needle deflection was reduced to 0.01” Adrian then leaned on the jaws to make sure that the wheel really was secure as throwing the job out on a machine this size could be fatal. Steve set a nice new carbide tipped boring tool in the toolpost and off they went at 83rpm.

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I hope the next bit comes along soon, not sure if I can stand the suspense !

 

Does anyone know of a set of bolt on jaws like the ones that Steve was using. I have a faceplate for my big lathe but no four jaw and have been keeping my eyes open for a set of bolt on jaws for some time with no result. They seem to either get scrapped when businesses close or are suddenly made of gold. Same with big four jaw chucks - my lathe has a D1-11 Camlock fitting and can take up to 4' diameter in the gap so a chuck 30" diameter or over would be ideal if anyone has one in a corner somewhere.

 

Thought it was worth asking....

 

David

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Steve is inclined to treat this sort of thing very gingerly with the result that the tool chatters. Adrian said to wind it more quickly but it is very difficult to change the habit of a lifetime! Anyway, after fifteen minutes of machining, success was achieved. Interestingly, the casting has some porosity but this will cause no problems.

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On measuring, the bore proved to be 2.875”, exactly 2 7/8”, completely by luck!

 

The wheel was taken down and the second one put up following the same routine. Whilst the rim was true, on starting the lathe, it became obvious that they bore was eccentric. Investigation showed this to be about 0.050” off-centre which meant that one side had to have 0.1” removed before the tool would begin to touch the other side. Steve was concerned about the wall thickness of the casting until Adrian saved the day again with an ultrasonic thickness meter.

 

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This showed a thickness in excess of 14mm.

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Adrian re-set the tool to prevent the bottom edge from fouling the bore and Steve set to and bored the wheel out to 2.870”. As he was hand-feeding the lathe and it was a long overhang for the tool, he was not brave enough to try to remove the last 0.005” and left it at that. As you can see, it almost cleaned the bore out completely with only a tiny patch untouched so they left it at that and lifted the wheel down.

 

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That was by far the biggest machine Steve has ever used and it was nerve wracking to say the least. However, success was achieved and we are all very pleased thanks entirely to our good friend Adrian.

 

Thanks Adrian!

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Great work again on a lovely old lathe! Good thing that not all of these heavy old machines have been scrapped or exported. I missed out on a big facing late from the early 1900's a few months ago. Not that I have a lot of use for it but if I find one I will find a spot in the shed to install it.

 

Another way of boring wheels (if a lathe is not available) is to put them on a radial drill. I did this with a tractor wheel a few years ago, with a homemade tool holder.

 

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Marcel

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