Tomo.T

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 !

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.

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. 😏

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

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.

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. Nb. These clearance sizes are given as a total diameter . So 4.5 inches minus the figure in thous. The actual clearance will be half that stated. Tomo

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.

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.

Well ok, but I think the pic is of your old pistons ??

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 ?

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.

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 . 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. 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

Good to see your progress. I came upon some notes I made concerning these vehicles. There were Q types in military service in the Great War, they had an increased payload of 5 tons, but they all had the 40 bhp M4 engine, as fitted to the J type. BB4's became available from 1924 rated at 50 bhp. I dont know if they were ever taken up by the military. Good luck with the restoration. Tomo.

The HE colour for all munitions was BS 381 (c) 359 Middle Buff. A bright red 3/4 " band denoted live round and a mid green band below that showed that the explosive had been filled.

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.

Mike Lewenden has performed wonders with the oil pump and it has been bushed and all its excessive clearances dealt with, to such an extent that it was now slightly stiff to turn. Stan improved the situation with a little compound and I put my mind to creating a flexible drive 'whizzer' to complete the 'lapping in 'process. The pic is self explanatory and Stan even took a video of the machine in action. Needless to say the pump now turns over sweetly and is ready for some oily action. received_384400302176303.mp4

Apart from that I have been cleaning parts and surfaces and also gave the cylinder drain cocks a birthday. One of which is going to need a handle Interesting news has arrived from the Antipodes concerning this engine, which was apparently bought as a replacement unit via Thornycroft Australia. It has always seemed odd that it has a full set of early features but a post war (badge) number. My thoughts are, it may have been a factory refurbished engine from war stocks. Which would suit me very well of course. I look forward to hearing more details.

Worked out a method for storing my valves in a neat and orderly fashion. I tried various methods but this one actually worked. The valves are poked through a box from underneath with a 2 inch collar of wound up corrugated cardboard placed over the stems inside, which puts just sufficient tension on the springs to stop the pesky collets escaping. Details can then be written on the inside of the box. Hey presto, all my ducks in a line ! Probably wasting my time, as the stems seem quite worn ( no lubrication ?) and one is badly necked as shown. I can see a new set being ordered from G&S. The springs and collets seem fine though.

Generally speaking this engine is in remarkably good order. It has done some work, following an extensive rebuild, but never run short of oil or attention and was looked after well prior to being laid up. Many of the components look fit for further service, but there are some pockets of corrosion. This inlet valve had the misfortune to come to rest in the open position when the engine was last run, a little water ingress is all you need, plus sulphur and carbon deposits, et voila !

Part of the Pitmans range of motoring books, written by an ex ASC ( Sergeant ?) and full of useful information about the dawn of Mechanical Transport generally and Thornycrofts in particular. Originally 2/6 d ( arf a crown ) I bought mine at £80 (Ouch) but have found it invaluable and have read it cover to cover except for the hard sums ! Tomo

Plenty Meat Update. The ultrasonic gubbins has recorded wall thickness in the 9's and 10's (mm) with a one off low of 7.8 this is well good enough to fit a standard liner and the pistons will be turned down to suit as was originally intended. This is wonderful news and I was surprised to hear the good thickness readings, which must be down to reduced corrosion on the water side. The only downer is the radiused corners on the piston tops, but that's not going to stop it running and everything else will be as standard. One question, will I need new rings or just re gap the old ones ? The difference in bores will be 20 thou. smaller.

All pistons are marked 30.C on the tops. This should mean +30 thou. Size C, which was the only oversize piston available post war. In fact the pistons measure just under +20 thou. and have been turned down to match worn bores, with their top corners rounded off to avoid the step , ( just visible in the previous pics.) This apparently was common practice in the day. During the war no oversize pistons were supplied and the Army ended up casting their own at Base Workshops to prolong the life of engines. Info; "Auriga" Book of the Thornycroft p.87-89 The plan is therefore to attempt to fit liners to standard size A and turn down the pistons to match. This all depends on the remaining wall thickness, which is due to be measured with an ultrasonic gismo by an ex Williams racing engineer on Friday. Exciting stuff this isn't it ?

More Meat. Went for a piston tugging session at Stan's workshop. The omens were good as No 4 came out by hand after I found the piston was turning in the bore. The others were not so keen so Stan created an impromptu jacking device which was simple, but effective. This comprised a piece of good solid plate bolted through the con rod big end holes and then jacked up with a pair of home made turn buckles underneath. Two large nuts were tacked below the plate to prevent any 'walking'. Each piston in turn was jacked and blocked and gave little resistance once the initial reluctance was overcome. The pistons once cleaned, were in good order with free rings. Bores are good until you get above the pistons, where there is some pitting unfortunately. Further investigation continues.

Ah, not a problem. The originals were painted service green along with the rest of the engine. Once I have checked for porosity I will etch prime and paint accordingly.

That of course, is the million dollar question. However, the stuff has cured to a rock like consistency and a good rub down with 80 grit produced fairly minimal result. I am quietly confident, but will test with deisel before use.