Double Eagle + orphaned engine = a winner?

wrote:
In so far as I know, clearancing and other 'hand-work' is not
considered 'machining' in that it is a 'go/no-go' sort of thing. You
simply remove metal until you have adequate clearance.

As a point of interest, the last air-cooled engines made by Volkswagen
were apparently designed to accept a 74mm crankshaft, which will drop
into a 1600 crankcase without any clearancing at all. With 85.5mm jugs
this gives a displacement of 1699cc and appears to reflect
Volkswagen's assumption that the USA would not adopt the stringent
California air-pollution laws.

The normal method of increasing the VW's displacement is to replace
the stock 85.5mm cylinders with those having a larger diameter. This
requires boring a hole, centered on the existing hole in the
crankcase, and a matching hole in the heads Most don't realize it but
the accuracy of these eight is of critical importance to the
durability of the engine. This is a task best done on a milling
machine. Unfortunately, most VW conversions are done with portable
tooling and the accuracy is all over the map.

By increasing the STROKE rather than the bore you not only eliminate
the need to machine the eight holes, you have eliminated a chronic
source of compression leaks that arise from inaccurate spigot bores.

-R.S.Hoover

I was assuming that this was hand work but I wasn't sure. Thanx for
cleaning it up. In the mean time I will be looking for a good deal on a
78mm crank.

Tony

On Jul 29, 3:33 pm, Anthony W wrote:

I was assuming that this was hand work but I wasn't sure. Thanx for
cleaning it up. In the mean time I will be looking for a good deal on a
78mm crank.
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Dear Tony,

A 78mm stroke under a stock jug will give you a displacement of
1791cc.
76mm x 85.5 = 1745
74mm x 85.5 = 1699

You may wish to consider ANY crank having a throw greater than 69 but
less than 82. But your primary qualification is the QUALITY of the
crank. Unless the thing is offered at a give-away price (meaning you
can always pass it along to the dune-buggy crowd) full blue-printing
and NDT must be a condition of sale. (This is why it makes good sense
to have someone like Tony make the crank to your specs.)

For ANY increase in stroke you will see an increase in displacement
AND an iincrease in torque. But what makes this configuration of
value in FLYING VW conversions is that the altered ratio of bore-to-
stroke causes the torque to peak BELOW the rpm. This phenomenon may
be enhanced by careful selection of the cam. In fact, even the stock
cam can provide a significant improvement by simply retarding its
timing by a few degrees. This allows you to use a longer propeller
with a more aggresive pitch, resulting in greater efficiency.

If that sounds too good to be true, it is :-) The greater efficiency
is the product of tailoring your valve-train geometry to take full
advantage of the engine's configuration. This is an alien world to
the typical dune-buggy guru for whom success is defined as maximum
horsepower at high rpm. What you will end up with is an engine that
produces high torque at a relatively LOW rpm, making it the perfect
choice for slinging a prop. You won't find a lot of information on
engines of this configuration... unless you study aircraft engines.
Or industrial engines.

Keep in mind that the changes are relative to the change in
displacement and the ratio of bore to stroke. You will see anything
very dramatic but you will see your usable power coming in at a lower
rpm. That lower rpm will lend itself to the engine's durability. It
may not be much but over the life of the engine, it is signifcant;
more than enough to justify the configuration even if the output is
the SAME as before.

-R.S.Hoover