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anorak:Carryfast:
The question was DAF shareholding ■■ in Leyland before the ‘merger’ .Also the government calling a takeover a merger including the issue of the 60% controlling interest.Yep normal design criterea for a forced induction truck engine is all about mitigating compressive loads.Not inertial tensile loads at 2,000 rpm or less.
Are you seriously suggesting that big end bearing cap fastenings are the same tensile spec as mains and head bolts.
■■■■■■■ ISX for example same grade for both head and main caps.Nothing about big ends.
Tightening of 300 lbft + 90 degrees head and 110 lbft + 180 degrees main caps and 50 lbft + 60 degrees big end caps is also a clue.Tensile loads aren’t an issue and if even they were a larger piston at higher engine speed isn’t going to help in that regard.
No I’m not saying that I’m better than AEC’s designers 50 years ago.I’m saying that RR’s and Volvo’s and ■■■■■■■■ and Mack’s and even to an extent Gardner’s were.I also don’t believe that most of AEC’s designs were dictated by what the designers ideally wanted but meeting location ideals and cash restraints.No one jumps from the bore stroke ratios of the 173 and 590 to the TL12 to meet any bs ‘tensile’ loading concerns.
Designers consider all loads and stresses in all areas. They do not launch alehouse bragging campaigns about one bolt versus another. In the 1970s, engines of a range of bore/stroke ratios were competitive. As usual, you are trying to judge engineering from years ago, against the specifications of modern engines, ISX for example. That does not qualify you to judge the designers of AEC, Gardner or ■■■■■■■■
Torque wrench settings do not tell us much about the loads on the joints. Why don’t you calculate the in-service tensile stress of the three bolts? That is, after all, what the engineer specifying the bolts would have at the front of his mind. You could then calculate the shear stress in the threads, then specify a suitable grade of cast iron for the cylinder block, and forging steel for the rods.
That in a nutshell is a great summary. In one of Bob Fryars’ papers on the design of the AEC 470 engine he goes to great lengths to explain how the correct “strength” of big end fixings was calculated. It was far too technical for my limited engineering knowledge to grasp, but it did illustrate the detail into which engine designers went, and probably explains why straight configuration AEC engines of all types and sizes never gave any bottom end problems. When building an engine it wasn’t a case of going to the parts store and getting a handful of any nuts and bolts.
If you look at three engines in the 12 /12.5 litre category, namely TL12, RR Eagle, and Gardner 6LXDT, all were designed to produce 270 bhp, at various times in their production lives, although the Gardner came into being 10 years after the other two. The three designs had different bore and stroke dimensions, the Gardner with the longest stroke of the three. But the three designs produced the power they were designed for. So how can anyone say which was the right design and which was a wrong design? As for long term development, in the early 1970s who could forecast what the power requirements would be in the 1990s. As it happens I have been looking at the typical fleet engine power rating in the mid-1990s. It was 320 - 360 bhp for 38 tonnes gvw. A very modest increase from the 270 bhp of 20 years before. There were, of course, more powerful engines available, but the bread and butter fleet market, was and still is, where manufacturers make their profits. That is where the volume sales are. Scania will make more profit margin on a 720 bhp V8 engine than it will on a 450 bhp unit, but it wouldn’t survive as a volume manufacturer if that was the only engine option it offered. The mass market for that power at that price simply isn’t there. Today the fleet engine is typically 450 bhp, so in almost 50 years since the TL12 can it be honestly said that there has been a massive increase in power outputs? It has been steady, not spectacular, development.
