Graham Stretch wrote:
There are two sizes of crank shaft for the 2 litre engine, the change came
about at around the same time as the 2500 engine was developed so that both
engines were more common. the 2500 even uses the same con rods with less
height from the gudgeon (wrist?) pin to the piston crown. So only the crank
and pistons determine the capacity!
I'll drink to that. For those who are interested, below are two paragraphs
from a very long article currently being chopped up into manageable sections
for The Vintage Triumph on the history and evolution of the SC (small car)
engine. It may explain a why and wherefore or two?
Jonmac
Quote "It all came about through Standard-Triumph engineers realising that
if the diameter and width of the main and big end bearings were increased to
the same dimensions as those on the sister 1998cc and 2498cc engines,
production line machining could be standardised. Better still, conrods and
bearings on the sixes could also be used. As a resullt, a new crankshaft and
cylinder block for the 1300 engine came into existence and the marketing
people were quick to capitalise on this change. The claim that increased
bearing size would extend engine life wasn't exactly what it appeared to be
because there had been little, if any evidence, that bearing life on the
older engine was suspect or finite.
But there were other constraints in taking the engine to its limits. Few are
aware that Triumph had fitted a 1500cc engine to a development car as early
as 1966 - nearly a year before the Mk 3 Spitfire went into production but as
the smaller engined car was selling so well, no-one was in a hurry to
upgrade the unit. However, the time had arrived to increase engine size for
one major market - and the cost hawks were still circling! From the outset,
it was clear this had to be achieved with minimum additional tooling costs
and the increase in stroke also had to be achieved without increasing block
height. It also went without saying that as many current components as
possible in the current parts bin should be used. In the case of the six
cylinder engine being taken to 2498cc, the crankshaft throw had been
extended by 9.5mm and a similar increase on the Spitfire crankshaft would
have resulted in a cubic capacity of 1621cc!!!!!!!!!!! Ideal though this may
have appeared in having a 1600cc engine rather than a 1500cc unit, the
revised crank throw was pegged at 5.75mm. The resulting 11.5mm stroke
increase came from shorter pistons on existing con-rods and also overcame
the requirement for not increasing block height. There was a nominal change
to the block but only a slight 'barrelling'at the base for the extra
crankshaft throw. The cylinder head remained unchanged, though the
combustion chambers were deepened." unquote
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