Barry,
Regardless of whether or not you are correct, those points actually
"make sense". It's certainly worth further investigation.
Joe Curry
Barry Schwartz wrote:
>
> Maybe a little additional information about the changes would help. In
> 1971 along with the body changes to the MK4 here in the states, the
> Block was changed to the big bearing 1296 motor, I assume to get ready
> for the 1500 increase. In 1972 the block was changed to the recessed
> head gasket variety. Then in 1974 the stroke was increased to provide
> the 1493 increase. There may have been a few late 71's with the
> recessed heads. The rods from 71-on are the same (and by the way are
> the same rods as used on the later GT6 and TR6), and the rods for the
> MK3 and earlier are the same (for the most part). The crankshaft is
> unique to the 71-72 model years(only to incorporate the bearing change,
> not the stroke change). This much I know, the rest is speculation. Now
> something has to be different from 71-72, and from 73 on, because you
> can't just put a 73 crank in using the same rods and pistons. It stands
> to reason that if you increase the stroke by changing the throw on the
> crank to a longer one, AND NOTHING ELSE, (which is what appears to have
> happened, same pistons, and rods) the pistons would hit the head,
> because they are going farther up and down. You also have to change the
> crank center to head deck height to accommodate the additional travel.
> The blocks from 71-72 are also unique to those models, and herein lies
> the catch. These blocks have a crank center to head deck surface for
> the 1296 engines, and the 1500 blocks have the additional increase from
> the crank centerline to head deck height for the stroke change. So it
> appears that one cannot simply use a crankshaft from a 1500 in a big
> bearing 1296 to get a stroke increase. I may be all wet here, because I
> haven’t actually measured these block’s and someone will correct me if
> I’m wrong I’m sure.-
>
> Barry Schwartz (San Diego) bschwart@pacbell.net
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