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Tomo.T

Another J Type on the way !

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David Rossington has been in touch. He was the guy who found and recovered this engine near Tumut, NSW in 1996. He researched the history with the Thornycroft register and found the following details;

Engine M4/ 7328 fitted to 'X' Type 8586. Erection commenced 28 Sept 1920 and delivered to A. Hatrick, ( NZ.) 29 Oct. 1920. ( Hatricks' were Thornycroft agents for NZ and Aus. before 1921, when Thornycroft Australia was created to handle Aus. exports.)

David has kindly sent pics of the remains of this vehicle as found in 1996 and I will attempt to post them here. There are some mysteries with this engine which we will explore later.

 

 

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This engine is quite intriguing., it still bears the number 7328 (1920) on the attached plate, but is clearly an earlier model than the number would suggest .

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Early features include;

1/ Cast iron inlet manifold, produced in aluminium by late war.

2/ High level oil pump with priming tank. This was superseded by a bevel drive gearbox and extension shaft to mount the oil pump lower and remove the need to manually  prime the pump before starting. Introduced about 1918.

3/ No baffle plate fitted to prevent over oiling of bores. Later models had extended main bearing bolts for this purpose.

These features point to a an actual wartime build date before 1917. 

Is it possible that there was a deliberate policy of fitting war stock engines to export models in the 1920's ? This would make perfect sense from the manufacturers point of view, who would have had plenty of these engines suddenly surplus to requirements. Re-numbering this stock would have concealed this from all but the most astute customers. ( It is also likely that stock was only numbered when assigned to a chassis in order to keep it fresh.)

It is certainly true that stocks of WD plate type wheels were used up on export models until about 1925 and the evidence for this is still visible on the many abandoned trailers, still to be found in Australia and NZ.

One more mystery concerns the major refurbishment of this engine which included oversize pistons and also possibly a new crankshaft. 

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The part number 69320 is clearly stamped into the flywheel end, but looking up this number in a 1919 parts book gets you nowhere, in fact the part numbers top out at 65421 at this time. Next to this number is another stamp which looks suspiciously like a date.  1. 27. Could this have been a late replacement crank ? This might explain the extraordinarily good condition of crank and bearings and might also explain the replacement engine rumour. Not replaced, but rebuilt perhaps.

From a personal perspective, I am very pleased to have an early engine pretty much exactly as fitted to 2393in 1915.

Tomo

 

 

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Posted (edited)

Moving on. I paid a visit to F.J. Paynes at Evesham. They will be taking on the re lining work to the cylinder bores. The pistons are in remarkable order and it has been decided to re line the cylinders to suit the pistons.  Paynes are now in charge of proceedings and I came away happy that the kit is in safe and experienced hands.

Edited by Tomo.T

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Going through Steve's Thorny thread for the upteenth time, I was suddenly struck by the difference in our pistons. I have pinched a pic to illustrate this.

DSCN6128.thumb.jpg.f38e1bd1db27d76878f5c689c324d4e1.jpg

20190609_181500.thumb.jpg.a2e5414665558b8c010d56238371a3fc.jpgThere are obvious differences in the much larger 3 compression rings and the oil scraper ring which bears no resemblance to Steve's. I think these pistons were fitted quite late in Australia, but they could have been old stock of course. Incidentally they have been turned down from +30 oversize in a slight taper and the skirts are slightly wider than the tops, presumably allowing for expansion. Does anyone have any wisdom to impart on these please ?

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Don't forget, Tomo, that I made the pistons to suit the rings I could buy!

Steve  :)

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44 minutes ago, Tomo.T said:

Going through Steve's Thorny thread for the upteenth time, I was suddenly struck by the difference in our pistons. I have pinched a pic to illustrate this.

There are obvious differences in the much larger 3 compression rings and the oil scraper ring which bears no resemblance to Steve's. I think these pistons were fitted quite late in Australia, but they could have been old stock of course. Incidentally they have been turned down from +30 oversize in a slight taper and the skirts are slightly wider than the tops, presumably allowing for expansion. Does anyone have any wisdom to impart on these please ?

I only found this drawing after Steve had problems with his. 1920 piston design for M type engines

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All the old cast iron piston drawings I have seen show the top of the piston a few thousandths smaller to allow for the thermal expansion.

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Ah, some confusion on my part I'm sure. Reference to the 1919 parts book shows this. There doesn't seem to be an oil scraper ring ! Also of note is the stepped piston ring where mine is the earlier type.

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54 minutes ago, Tomo.T said:

Incidentally they have been turned down from +30 oversize in a slight taper and the skirts are slightly wider than the tops, presumably allowing for expansion. Does anyone have any wisdom to impart on these please ?

I think that it is normal for the ring lands to taper a few thou (in steps). The area above the top ring runs a lot hotter than the skirt. 

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2 minutes ago, Tomo.T said:

Ah, some confusion on my part I'm sure. Reference to the 1919 parts book shows this. There doesn't seem to be an oil scraper ring ! Also of note is the stepped piston ring where mine is the earlier type.

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Hi Tomo,

The bottom ring is an oil scraper, it has the 'step cut' ends to keep the oil from passing the ring gap and the reduced diameter and oil holes under the ring allow the oil to pass down inside the skirt.

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Posted (edited)

Thanks for that Richard, all my rings are diagonal cut which makes me think I have an early version. Also there are three plain rings with no oil control ring and no drain holes.

Edited by Tomo.T

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Posted (edited)
7 hours ago, BenHawkins said:

I only found this drawing after Steve had problems with his. 1920 piston design for M type engines

1555475971_MPistonCropped.thumb.jpg.02137cf06d1ee00ef21ccaf820acb2e1.jpg

All the old cast iron piston drawings I have seen show the top of the piston a few thousandths smaller to allow for the thermal expansion.

Now that is a nice useful drawing and timely too.( for me at least.) I note the top corners are rounded which I thought was a modification on mine. Clearances are marked 5-7  thou until the top ring lands and then 12-14 thou ! Thanks very much for posting Ben.

Edited by Tomo.T

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It does seem that piston design was improving rapidly at this time. "Auriga" notes that all piston rings were changed from diagonal cut to stepped from June 1917 on WD vehicles and that this was done to increase efficiency. Earlier in Feb. 1915, 6 x 9/16" oil drain holes were to be added below the gudgeon pin. It looks like oil scraper rings were added to the skirts in 1920 and later moved up to take up the third ring position. All this suggests my pistons are early and I might be wise to investigate the possibility of fitting oil scraper rings and drain holes retrospectively. Very interesting session, thanks to all.

Tomo.

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11 hours ago, Tomo.T said:

 All this suggests my pistons are early and I might be wise to investigate the possibility of fitting oil scraper rings and drain holes retrospectively. Very interesting session, thanks to all.

My own opinion (and it is worth exactly what you paid for it) would be that if you have the early pistons then they should be kept precisely because of that. 

I doubt that oil consumption is a significant expense in the context in which you will be operating the vehicle. 

 

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15 minutes ago, andypugh said:

My own opinion (and it is worth exactly what you paid for it) would be that if you have the early pistons then they should be kept precisely because of that. 

I doubt that oil consumption is a significant expense in the context in which you will be operating the vehicle. 

 

Hi Andy, 

It's not the consumption that bothers me, but the tendency to over oiling the bores, making for a smoky exhaust , oily plugs and rapid carbon build up. They had a few goes at this, with piston drain holes and a rather crude baffle plate in the crankcase but I think what sorted the job was oil scraper rings. It's a minor improvement that will never be seen and worth investigating at least, in my opinion.

Tomo

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43 minutes ago, Tomo.T said:

It's not the consumption that bothers me, but the tendency to over oiling the bores, making for a smoky exhaust , oily plugs and rapid carbon build up.

All authentic features of a WW1 truck 🙂

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Posted (edited)

No thanks ! If I want to drive something smokey I'll light up the steam roller. The pistons are a disposable item on their last regrind back to standard "A" If I can make a big improvement to the running of this old girl by a small modification which was taken up anway in 1920, I feel inclined to give it a go and I'm  afraid I don't see your problem. 😏20190610_165358.thumb.jpg.75a7f72f268867486841b66bd263b07f.jpg

Edited by Tomo.T
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With machining now in progress, I have transferred my attentions to the steering box, which has come to bits fairly easily, except for the inner screw thread and its white metal counterpart. Heat is not an option here for obvious reasons, although boiling water was tried without success. The offending item has been put back into soak to consider its position and I will return to it with steering arm to hand which will give me better leverage. Both main ball bearings have been revived from a solid state. One of them might go again, the other is rough.

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Edited by Tomo.T
Box not column.
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The weather has brought unexpected oportunities to get on with the J type. First up was the sump which has been treated to two coats of Eastwoods Glyptal sealer, over the internal surfaces.

This celulose based American Brushing paint is specifically aimed at sealing porous sumps and gearboxes. So following the belt and braces principal I have added an extra defensive layer.  I like the rich oxide colour a lot, the price, not so much !

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Next up for attention were the cam followers which having been winkled out of  the crankcase were dismantled and thoroughly cleaned. I was delighted to find what little rust was present responded to a manual seeing to and the result was very pleasing. All followers are free and fit for further service. A day well spent. 

 

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Edited by Tomo.T

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Then off to Stan's today to prepare pistons for grinding to standard 'A' clearance sizes. They were decarbonized, roughly cleaned up and checked for cracks etc. Mike Lewenden is IC Grinding and says he is looking forward to the challenge. Photos by Stan, very sore thumbs by me.

 

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Edited by Tomo.T
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Dropped into the paint shop today, prepped the surfaces and brought the steering box halves into service colour.

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Whilst I had the brush out I gave a final coat to an early fire extinguisher bracket which was a previous ebay find.

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I couldn't wait to get the thing home and see if my 1918 London badged Pyrene extinguisher fitted ok. I have been searching for one of these for years and was very pleased and surprised to find one recently for sale on this very forum. 

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A perfect match.

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All these Pyrene extinguishers were made in America, but those supplied to the ASC for use in MT vehicles were channelled through a distribution centre at Great Queens St. in London. They were badged up accordingly and are now very hard to find.

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Edited by Tomo.T
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These extinguishers were filled with Carbon Tetrachloride and were widely used for many years. They acted by denying oxygen and thus extinguished small fires very successfully. Unfortunately it was discovered that this chemical when heated ( like in a fire ) produced poisonous Chlorine gas to the detriment of the operator ! 

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Edited by Tomo.T
Ad pic.
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11 hours ago, Tomo.T said:

 Unfortunately it was discovered that this chemical when heated ( like in a fire ) produced poisonous Chlorine gas to the detriment of the operator ! 

I think it's worse than that, the gas created is Phosgene. 

Though Wikipedia suggests that the direct toxicity (to the liver) is just as bad, and it's an ozone-depleting gas too. 

 

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