David Herbert

One could certainly make the core for this in one piece but you would need quite a bit of draw to get the centre divideing part of the core box out cleanly. Normally this core box (or mould) would be in two pieces so that all the functional surfaces of the core were exactly defined. The core sand (probably bound with a CO2 setting resin) would be put in and rammed up via the outside faces of a couple of the core prints, and fairly substantial bits of wire / steel rod would be used to reinforce the weak bit in the middle. I would devide the core box on the same line as the main pattern as it makes it easier to make the draw of the core prints fit their registers in the main mould. The core prints that form the holes at the top of your drawing could be joined up outside the casting which would greatly strengthen the core. As you say, if you cast with the large solid face at the bottom, the core is then best supported as it tries to float. Also any dross (muck) in the molten metal will be easier to void from the much smaller area of the big face with two big holes in it. However I don't see that it would be significantly easier to not extend the core prints of the big front RH face (top when casting) and it will involve more work to remove the flash from the holes. Also it will reduce the support and location of the core which is important as untill the metal is poured in there is nothing supporting the corner of the core that is at the bottom / back of your drawing. It may be necessary for the moulder to use a small prop to keep everything in place untill pouring. This would be incorperated into the casting and would not show after machining. David

Now that is a very good idea ! David

Which is 10 thou. I would have thought that was as tight as one would want to be. I would be happy with anything up to 25 thou on a modern engine. WW1 engines run slower and at much lower pressures and will never do the mileages that we expect of a modern vehicle so I would have thought that if everything else was ok, ring gaps up to about 40 thou would be fine. I certainly wouldn't worry about 22 thou. But that's just my opinion ! David

It's also Rick's next project ! David

I prefer the RH one ! David

A Chieftain has a centrifugal clutch and a seperate gearbox that uses epicyclic gear trains and hydraulicly operated clutches / brake bands to engage each gear. The centrifugal clutch allows you to start off and then gearchanges are done entirely by manual command, immediately and under full power. If you try to move off against an impossible load, you melt the centrifugal clutch or spin the tracks. As you can imagine, clutches do not last for ever under normal use but actually work remarkably well and very smoothly. David

The side plates are held on by lots of 5/8" BSF bolts. All are countersunk into the plates but some are flush and have an Allen type hexagonal socket in them but most have a shallow male hexagon head that looks like a half depth standard bolt head. They usually unscrew reasonably easily IF you can get a grip on them. A good quality hexagonal socket (not 12 point) with the first 5mm ground off to remove the bevel at the beginning of the flats that engage the bolt will get a suprising number of the hexagon bolts, particularly if you clean the paint and muck away from around the head - every half mm of engagement helps! Similarly the right size allen key or hex bit will get the fully countersunk ones if they are not too rusted. If this fails then welding nuts onto the head gives you something to grip plus puts quite a lot of heat into the head. It also has the advantage that the bolt is generally fairly easy to repair and can be re used, reducing the number of new ones that you have to find. It is quite unusual for the threads to be propperly rusted up as these bolts should be well greased when they are fitted and that was usually done as it was the same guys that would have to remove them to change a spring or damper. They also don't need to be done up mega tight as there are so many of them and the plates are virtually sewn on. For those that have not seen the working parts of cruiser tank suspension, the big cylinder with the BC number stenciled onto it contains the suspension spring only. The smaller cylinder (not used on no.3 wheel station) is a hydraulic damper. All the structure including the inner skin is just mild steel, and not very thick. Only the bolt on armour plates are armour. It was only on Comets and late Cromwells that they welded the armour directly into the hull structure but still retained the removeable side plates for access to the suspension. David

Sorry to reawaken the brass plate etching subject but I understand that it is good to apply the black or whatever paint that fills in the etched surface before removing the resist film. that way you haven't got to clean it off the un-etched surface. I don't think that there is any reasion that the brass can't be polished before etching as long as it is very clean and certainly has no protective film of wax or anything else from the polish. David

Oh that is very nice indeed. It's a good thing I havn't got any money or I could get very excited about that truck. Funny thing is that the shed looks relatively new but the truck looks like it has been in the same spot for a long time. Is it in the UK ? David

What a great truck. The sprocket is not for roller chain but for the cast link chain that was popular for agricultural machinery (different shape teeth). That would agree with the idea that it is for some sort of machinery like a spreader that needs to be driven as the truck moves forward. I assume there is only the one on the RH side and not the LH side? I wonder how many gateposts and other things the milometer has collected over the years. It must produce a fairly violent effect on the steering wheel if you catch something with it. I like the repair to the right front tyre which has been tied onto the wheel with wire to stop it falling off. Would that be an MOT fail I wonder . David

Does it still have its engine and transmission ? Is it for sale ? Where is it ? David

Sorry to continue this diversion but if you search "photo etching brass" on YouTube you get some quite usefull tutorials on how to do it. The problem in the UK seems to be finding a supply of the photo resist film. Ebay can only offer it from China or Germany. The chemicals seem much easier. I have fancied having a go at this for years and you may well have given me the push I needed. David

I could see them all along. Maybe photos travel slower than text and need to stay the night somewhere on the way. I think that I would be tempted to build up the brake levers with some weld as one in particular seems to have gone a bit beyond having aquired extra character over the years. I am amazed that they were brazed onto the cross tube, and that it is a tube rather than solid. David

No it is repairable. You find another one that has had its rear end run over and weld them together. Simples ! David

Actually all the castings are different. look at the water manifold on top of the engine and the shape of the webs on the crankcase for example. Were these engines made under license by other makers to boost capacity ? David

I don't think that he intended to brake to the left but the small roller skate under the right track would have had less grip on the road than the rubber pads on the left track, hence the turn left. she must have pulled out with the tank just feet away and going at a good speed for the tank to have taken so long to stop. I think she was VERY lucky to survive that error of judgement. As Andy says above, people can pull out (or step out) on any of us, in any vehicle, but if we are driving a CVRT or FV432 there will be much more damage to the car and vast amounts of interest from the police and press. I have driven large tracked military vehicles on the public road and have come to think that it is simply too risky as the cars seem to turn into rabbits when they see you coming. David

Is it possible that the larger diameter round part that can be seen in the view looking down the cylinder bore, is actualy a roller that should be free to rotate on the small diameter of the retaining screw. It would still be an odd way to make it but there would be no other reasion to reduce the diameter of the retaining pin if the bigger diameter were part of it. The space that the bigger diameter part is in could have been cast into the cylinder as, if it is a roller, it would be located by the pin, not by the cavity. I suspect that the smaller diameter pin is supported either side of the cavity in close fitting holes and just won't come out of the one on the thread side of the cavity. These were a very common cylinder so it shouldn't be too hard to find a drawing, or parts if you need them. I have never taken one appart so would be interested in the final explanation. David

Very professional Steve ! I like the drilled holes to give the rake. I have made special cutters for doing one off jobs out of mild steel, turned and filed / angle ground to shape and then heavily case harden the business end in Kasenite. Then wire brush all over and clean up the cutting edge with an oil stone. I don't bother tempering them as they won't shatter because of the soft core and I usually am only doing one or two holes anyway so can be gentle with them. As you say it is actualy an advantage if the cutting edges are not regularly spaced as long as they are all at exactly the same height so creating them by eye is fine. David

I think that was a really good idea to post that list, particularly with what you needed them for. definately a public service ! :bow: David

I understand that you want a more accurate measurement than this but the drawing shows the top of the chassis exactly level with the top of the wheels. A 7.50 x 20 tire is 35" diameter which is 889mm. It will be interesting to see what the true figure is..... David

I'm fighting a rear guard action against people refering to my FV434 as a tank. I think that we have to accept that language moves on and that in the minds of the public, any tracked armoured vehicle is a tank in the same way that a steam locomotive is a train (which also gets me going). David

In these gearboxes selecting neutral SHOULD prevent any of the bands being tensioned when you release the gear change pedal. Therefor pressing the gear change pedal all the way is exactly the same as engaging neutral but harder on your left leg. There will always be some drag between the brake bands and the drums, if only from the oil that gets between them, which is why it is virtually impossible to select forward or reverse from F / R box neutral with the engine running. However with the vehicle stationary and foot on gear change pedal it should go from F to R or R to F quite smoothly IF you do it quickly. Too slow and the gearbox internals have time to start to spin and you will never get it into gear. Engine speed should not make much difference but obviously the slower the better. If things are not as I describe I would look for a band not fully relaxing when in neutral. Possibly a broken spring in that band's mechanism or the lining damaged and wedging between drum and band. All this assumes that you have the correct oil. Good luck, David

It also has, like Rick's, the later slightly wider track that was an upgrade on Cromwells at the end of the war, quite often with a higher ratio final drive (to reduce top speed) and better suspension with a slightly higher ride height. These mods were not done on Centaurs as far as I can tell. David

Mark, surely "hold the gun at the firing position" in A above means 'in battery', ie. not partly recoiled due to its own weight making it slide back if it was elevated. What elevation it is at is an entirely seperate subject and as you have said you should be either running around with the gun locked in its crutch or with the stabliser on. Even if it were perfecty balanced, as the vehicle moves it pitches slightly in all directions and to force the gun to do the same by locking it to the turret would put a huge strain on the lock, so it was easier to use the stabliser to keep it pointing in one direction regardless of vehicle movement. Without the stabaliser on it WILL bounce around uncontrolably. Think of how much easier it is to carry a long heavy object (6m of steel pipe for example) by holding it in the middle and not trying to tip it forward and back with every step you take. But if you don't guide it and you arn't holding it dead in the middle it will not stay horizontal by itself. David

Is it for connecting the free end of the winch cable (or a pulley block) when winching with a 2 or 3 to one pull ? That way the force goes into the spade without going via the hull so less strain on the hinges and less tendency to lift the front of the vehicle. David