Looking at an old between the wars publication I noted a reference to the Mk II having "improved cast iron track rollers". I've not seen any other reference to this and its not the sort of thing you can tell from looking at a photo. I've often wondered if the Mk Is were particularly prone to mechanical failure and this contributed to their rapid disapearance before Arras. The fact that camo'd Mk I sponsons were available for fitting to Mk IIs suggests that some Mk Is at least 'died' away from the battlefield. Perhaps the Mk II and IIIs and IVs whilst not having any major design changes to the mechanics had some alterations to improve reliability? Possibly just better materials, tighter tolerances etc. Does anyone have any info on the "improved cast iron track rollers" and were there any other such changes?
I have no information on the specific change mentioned, but I do have evidence of changes in Mark IVs. According to my information very early Metropolitan built Mark IVs had drive sprockets cut from boiler plate! Obviously this didn't last long and they were soon replaced, but it was always intended as a stop-gap. This arose because there was a delay in Metropolitan receiving cast iron sprockets. Later still the cast iron sprockets were replaced in production by manganese steel ones.
David Fletcher in the recent Osprey on the Mark IV draws attention to the change in design of radiator, as well as the introduction of the 125hp Daimler engine.
There were also changes in production methods that would have improved reliability. A more rigorous test was introduced for "differential locking shafts" (can someone tell me what they were please?) in the Mark IV. This caused a memo to be issued that certain tanks already supplied to the Army had potentially faulty shafts, though I have no idea if anything was done about it. One of the affected tanks was 2732, well photographed after being destroyed by German artillery.
Differential locking shafts would be a means to lock the drive shafts to increase traction in difficult terrain/conditions. Although this would make steering more difficult.
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The rollers on the MkI were hollow, and I believe were fabricated from steel. They tended to collapse in situations where much of the tanks weight was balanced on a few track plates. As an expedient, the hollow rollers were filled, but on the MkII they were replaced by a more satisfactory solid cast iron unit. Due to the delay in production of spare parts for the tanks, it is quite likely that a lack of rollers may have sidelined many of the MkI's.
The rollers on the MkI were hollow, and I believe were fabricated from steel. They tended to collapse in situations where much of the tanks weight was balanced on a few track plates. As an expedient, the hollow rollers were filled, but on the MkII they were replaced by a more satisfactory solid cast iron unit. Due to the delay in production of spare parts for the tanks, it is quite likely that a lack of rollers may have sidelined many of the MkI's.
Thanks - it would explain a lot - for example the large numbers of tanks not even making it to the jumping off point at Flers - C.
