Carryfast:
Tomdhu:
I think we could all continue deliberating about bore and stroke dimensions and ratios until the Atki with the 6LW comes into the yard. But it is pure speculation unless we have access to more comprehensive information relative to the cylinder blocks, cylinder heads, crankcases and cranks.Critically we need dimensions such as:-
- Bore spacing and distance from front to rear of the cylinder block.
- Distance from C/L crank to top of cylinder block,
- Clearance available in crank case to take a bigger swing,
- Distance from top of cylinder block down to bottom of bore (bore depth)
No.1 in my view is the most crucial as it affects:-
a) Bore and liner stability,
b) Coolant flow and oil circulation capacity through to the cylinder heads
c) Strength potential for anchoring the cylinder head studs.Please step forward anyone who has access to either an o.680 or AV760 cylinder block.
All the above information would be most useful however the real “gold dust “ would be input from the actual engine designers who were involved but, as all this was 50+ years ago, then this becomes increasingly unlikely.
Which leaves the question was there actually anything really preventing the ability of the 760’s/TL12’s designers from calling for any changes required in the architecture of the engine to meet the required aims of at least matching the 6 inch stroke of the Eagle and 14 litre ■■■■■■■ in the upgrade of the 690 ?..
CF,
As to what prevented the engineers calling for changes, I would submit my views as follows:-
Having developed the AV760 from the AV691 in 1964, the AEC engineers probably held the view that this engine had reached the limit of its potential i.e. the physical dimensions of the block were inadequate to provide greater output without compromising the reliability/durability of the engine.
Bear in mind also that around 1961/2, AEC had embarked on their V8 design project. Consequently, these same engineers weren’t going to flog an old horse (the AV691) whilst they were nourishing their own new “clean sheet” V8 project. It was Bob Fryars’ baby and only he and his team, are the ones to elucidate meaningfully on this.
Don’t forget, a similar dilemma was encountered by BMC with their old 6 cylinder engine from the 1950’s. To get more power, BMC engineers decided to take the easiest course and increase the bore size to 100mm. They released the product on the market and it was an unmitigated disaster. There were many problems, not the least of which was instability of the bores together with the blocks warping. Add in cooling issues and in-production problems and it was a major calamity resulting in huge warranty claims and loss of market share.
Sometime after the merger with BMC in 1968, Leyland engineers studied the problem and eventually came up with a strategy. The main element of the strategy was to reduce the bore to 98mm and increase the stroke. They kept the swept volume at 5.7 litres. This restored structural integrity. The production issues were addressed also. In 1972 the revised design appeared and it was a success. That was a total of 10 years after the original problem emerged!
It proves conclusively that engines are very complex assemblies involving materials, tolerances, mechanical issues, thermo dynamics, thermal stress, coolant circulation, lubrication etc etc. Getting it right takes the right brains plus lots of money and time. Without researching further at this stage, I am sure many other engine manufacturers have over-stretched some of their best designs.
Whilst assessing an engine purely from a design perspective, we must always acknowledge that a business has to be run at a profit and directors make decisions primarily based on that. Directors continually have to consider a multitude of competing requests for expenditure. Do they approve investment in a new transfer CNC line for cylinder head manufacture, or development of a new 10 speed synchro splitter gearbox or a new induction furnace in the foundry etc etc? It is certainly not a simple question of do we increase the stroke or do we do another particular thing or not based on engineering logic.
Nobody prevented the engineers from calling for changes. It is up to them to create a business case for requesting investment funds – fully costed and fully justified with complete conviction on their part ie heads on the block commitment. Did they do that? Or did they keep their heads down and let things develop? The engineering director was on the board. It was up to him to make the case to his fellow directors. Did he do that?
Let’s assume he did then, never forget, directors perform a continual juggling act of priorities - whilst using finite resources be they financial, human or otherwise. The directors, as a board, decide.
where are the engines for the current DAFs made,?
