Barney

Steve, If you look carefully at an enlargement of this photo you can see that the front cross member is curved downwards and where the starting handle passes through the member you can see two bolts/nuts to the right hand side the shaft, presumably there are two others on the side that is hidden by the shaft. It looks very much like this lorry has a similar starting handle arrangement to the resiliant mounting unit you have; the shaft and bolt/nut orientation look to be the same. Best regards. John

Re; Starting Handle Shaft. It looks to me as though the shaft turns inside the eccentric component and as there also appears to be a greaser to lubricate the shaft my thoughts are that the eccentric is an outrigger bearing for the longer shaft and the rubber gives a resilient mounting into a circular bracket that bolts onto the front chassis cross member. Best regards. John Edit; The mounting bracket suggested is more likely to have been a pot shape rather than just a circle, the studs coming through rubber grommets in the front of the pot and nutted up to hold it all in place. If the engine is not resilient mounted then perhaps, as Tim says, the unit is from a later lorry or another application, a resilient mounted generator perhaps.

Yes Barry your last thought is exactly right; the acceleration rate is faster which makes the hammer blow stronger. Best regards. John

Firstly, congratulations are in order for the families fabulous engineering skills in remaking the governor mechanism. Secondly, with regard to the valve timing issue. I have an old book that gives the valve timing data of a number of petrol engines. In the larger engine sizes there are a fair range of values depending on the individual engine; unfortunately no Thornycroft engines are listed. Looking down the list of engines I find that the valve timings fall within the following ranges ---- Inlet valves open at between 5 and 10 degs Before Top Dead Centre and close at between 40 and 50 degs After Bottom Dead Centre. Exhaust valves open at between 40 and 50 degs Before Bottom Dead Centre and close at between 10 and 15 degs After Top Dead Centre. If the timing on your engine falls somewhere within the above ranges I don’t think that it will make very much difference to its performance even if the timing is not exactly as recommended by Thornycroft. I once owned an Austin Healy Sprite where the camshaft was out by one tooth of the camshaft chain sprocket and once corrected I can’t say that I noticed any difference to the cars performance during normal urban driving. It would, I think, have been noticeable on a race track but then I only brought the Sprite to impress the girl friend. I might add that the ignition timing was correct even though the valve timing was wrong. Tappet clearances; I think 12 thou hot should be OK for your engine. Most older engines are set within the range of 10 to 15 thou. If you increase the clearance beyond 15 thou. you will get a lot of clatter and rapid wear of the tappet/valve faces will occur. Best wishes. John

The video link above is from AET Systems Ltd in Daventry, Northamptonshire so perhaps it might be worth while taking the ‘onion’ to them to see if they are prepared to carry out the repairs. A satisfactory repair would be useful to you and a good recommendation for them if you were to promote them on the HMVF site (might even get the job done for free) so a win, win situation for both of you. Best regards. John

After receiving some feedback I feel I should clarify my post (No 579) on the knocking noises caused by worn crankshaft thrust washers. I believe this scenario to be very rare and I only encountered two engines that exhibited this problem. Both were four cylinder engines built in the 1930/40’s with chain driven camshafts; both were well worn but were running quite nicely without too much other noise. Unlike the rhythmic vertical forces exerted on the crankshaft during the firing stroke there are no similar forces applied to the crankshaft in the horizontal plane. Any horizontal movement of the crankshaft is totally random*, other than when the clutch is depressed, so the knocking noises, in the two engines I encountered, were also random in that a few knocks were heard then silence, then a few more knocks and silence again, etc, etc. The number and intensity of knocks and the time length between them was totally random and there was no pattern that could be discerned. The easy way to check for this problem is to depress the clutch slightly but not so far as to reduce the engine speed. This will force the crankshaft fully forward (or backwards in modern engines) and stop any horizontal oscillation whereupon any knocking from this source should cease. Please accept my apologies if I have misled anybody. * This may not be true in engines like the Thornycroft where helical cut timing gears are fitted. Best regards. John

Just to give a possible reason for the markings on the gears I give an instruction for replacing timing gears on the Morris VS15M engine that was fitted to Morris Oxford cars in the series MO, II, III and V and other derivatives. The VS15M engine is gear-driven. These gears are paired and if replaced the new gear must bear the same markings as the original. The gears are marked with the letter “T” and in addition are marked with a minus figure from 1 to 6. The sum of the markings on both gears must equal minus 6, e.g. a crankshaft gear marked -2 must be mated with a camshaft gear marked -4. Either gear can be renewed individually provided that these tolerances are observed. Presumably this arrangement is to give some tolerance during manufacture as was done with piston and bore markings. Is it not possible to clean up one set of original gears and shafts then using a motorcycle crankshaft protractor and dial gauge check the point at which the inlet and exhaust valves lift on the best part of the gear and cams. Then swap the gears/shafts around to what you require and recheck. Make sure that the tappet clearances (say 10 thou) are readjusted to the same reading if you change camshafts. If only I lived closer, Tony??? Best regards. John

Steve says; The float appears to be about 0.030" which feels OK but I don't know how much it should be. How much would you expect? Normally crankshaft end float is 2 to 3 thou., although I have an old book that shows a couple of 1930’s engines had as much as 6 thou. clearance. Sorry I can’t offer any scenario for 30 thou clearance, although I have seen, in engines where the thrust washers were badly worn, the crankshaft moving back and forth and creating a knocking noise. Also on engines where oil flingers and helical cut groves were used on the crankshaft, in place of oil seals or felts, the movement of the crank would sometimes cause an oil leak due to damage caused to the flinger when came into contact with its mating surface. The biggest load taken by the crankshaft thrust washers are from depressing the clutch. Unfair wear and tear is caused by ‘riding the clutch’ whilst driving or holding the clutch out for long periods whilst the vehicle is in gear and stationary; having to double declutch on vehicles with crash gearboxes doesn’t help either. On this engine a small amount of wear is also caused by the tooth angle of the helical cut timing gears trying to slide themselves out of mesh when under load. Best regards. John

Hi Steve, Another option would be to mount the grindstone, with bushes if necessary, on the end of a long rod that is the same diameter as the valve stem. True the stone in the lathe as you suggest and then slide the rod through the valve guide and tighten the end of the rod into the chuck of an electric drill. Switch on and gently, so as not to bend the rod, pull the stone onto the seat. Good luck. John ps. Please accept my apologies if you have already thought of this.

Hi Steve, Both garages where I worked had a Black and Decker Vibro-Centric valve seat grinding set. An expensive tool normally only found in garages or engine rebuild workshops. It comprised of an electric drill with a ball hex drive which fitted into an arbour onto which could be screwed an angled grindstone. A shaft was then fitted into the guide and the arbour complete with stone would be mounted on this shaft and then be driven around by the drill. The set included an assortment of different sized/angled stones and an assortment of shafts that fitted the different sized valve guides. The set also came with a stone dresser and extension/flexible ball hex drives. There is a video on youtube. Link here Also if your quick there is one on ebay with lots of photos; I tried to download the photos but once enlarged they aren’t very clear. Link here http://www.ebay.co.uk/itm/Black-and-Decker-Vibro-Centric-Valve-Seat-Grinder-Set-/170911991703?pt=Motors_Automotive_Tools&hash=item27cb260797 Best regards. John

When fitting new valve guides to a cylinder head it is common practice to regrind the valve seats. I was always surprised as to how far out of line the old seat was in relation to the new guide and assumed this was caused by the rockers pushing the valve to one side. Although a side valve engine tappet has a direct upward push on the valve stem I still found that sometimes the seats would be out of line. I always preferred to regrind the valves and seats even if new guides were not necessary as it was far easier and less arm aching to give the seats a quick rub-in with fine paste rather than bashing away for ages with course and then fine pastes. One point about regrinding seats is to make sure that they do not end up too wide as this causes burning of the seat. Wide seats would be reduced by topping off with a low angle stone to leave a seat about 1/8” wide. Really bad seats would require the head to be machined and an insert fitted. Normally cast iron heads were the worst effected by excessive burning or wear; alloy heads, which had inserts from new, were not usually a problem although occasionally an insert would work loose. Keep up the good work. John

According to the Hampshire County Council web page Hantsweb http://www3.hants.gov.uk/thornycroft/lorries/basingstoke-factory.htm Thornycroft brought in castings and forgings from outside suppliers although they did machine them at the Basingstoke factory. With most companies engaged on war work the demand for military equipment far outstripped the companies normal peace time production so probably during WW1 Thornycroft were being supplied by more than one foundry. Some form of identification would be required to trace the supplier so that any issues with unsatisfactory castings could be addressed before the next batch was supplied. Sorry I can’t help with who FN might have been. John

By far the safest solution would be to reline all four bores. You may even be able to pick up four suitable pistons and bore the liners to suit these. As there are no balance weights on the crankshaft it would not matter whether the pistons were alloy or cast. The only critical measurements are the distance from the gudgeon pin centre to the piston crown and the position of the scraper ring at bottom dead centre. A commercial engine overhaul specialist should have a list of piston size data that may help you. John

Steve, Many years ago I worked on a couple of Coventry Climax 4 cylinder engines. The engines were around 1200cc and they had aluminium blocks and dry liners. The liners were a hand push fit in the aluminium bores and were retained at the top by a flange which was trapped between the block and the cylinder head and gasket, in a similar way to that which you are proposing. No other retaining method was used so I presume that the expansion of the liner was sufficient to hold it firm and enable the heat to transfer into the block. John

Steve, I post the following in the hope that it may be useful to you in your choice of a liner retention method; if you already have this or updated info please accept my apologies. If my memory serves me correctly the mean burn temperature of fuel in an IC engine cylinder is around 700 degsC. Due to the constant exhausting of the hot gasses, the induction of the cold fuel mixture and the heat dissipated through the cylinder block into the coolant the cylinder wall surface temperature is held fairly constant at around 350 degsC. I surmise that a thin wall liner would be at this temperature throughout most of its thickness and probably for around half its length. I don’t remember there being any different figures for petrol or diesel engines so presume the above figures relate to both engines. However, today’s unleaded petrol is certainly more volatile than the old pool petrol that was available probably 60 or 70 years ago when these readings were taken so the figures may be slightly altered now. Also, if you speak to the Loctite people it may be worth asking if the Loctite layer, being basically a plastic compound, will impede the heat transfer between the liner and the block. John

Many thanks for your kind words Tony. I would be very wary of fitting a stepped liner which is a loose fit above the step or a Loctited liner to these Thornycroft pots; Loctite requires a working clearance of about 2 thou. Normally on engines where a separate (bolt down) cylinder head is used both wet and loose dry liners are fitted so that the tops of the liners protrude above the block face; around 3 to 5 thou in the case of loose dry liners. The head gasket then covers the top edge of the liner so protecting it from the heat of combustion. When fitted in a pot the top of the liner is not protected and any gap, however small, between liner and block will lead to localised burning of the liner's top edge. John

To ovoid damage to thin liners we used to, in my motor engineering days, use a liner with an undersize bore; press it in as normal and then bore to the finished size, this then removed any chance of the liner splitting whilst it was being pressed in. Some liners were pegged and you could do this by using a tight fitting (oversize thread) screwed peg or pegs through the side of the cylinder and through the liner, low down in the area where there is no water jacket. This should, of course, be done before boring the liner to size. John