The Home-made Home-builders Engine

On May 31, 12:35*am, Veeduber wrote:
On May 30, 9:21*am, bildan wrote:

To build this engine would require making a case, crank and rods with
the planetary in a nose case with thrust bearings. *(Of course a lot
of other fiddly bits would need to be made as well.) *However, the
heads, cylinders and pistons are the hard part and they are available
cheap.

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I disagree with regard to the heads and cylinders. *But you are
correct when it comes to the gear reduction unit.

As several others have pointed out, publicly and in private messages,
there has been significant advances in metallurgy since the Pobjoy
first ran in 1926.

The Pobjoy had its share of problems, from its inception until its
production was finally dropped in 1946. *But those problems would
probably not apply if the engine were produced today. *For example,
the use of a planetary gear reduction system would eliminate the wear
problems encountered with the original herringbone gear, while a
modern, fully sealed valve train would improve the engine's mean time
before failure.

As for the question of using existing cylinders and heads, an aircraft
engine uses a different design philosophy than is used when producing
any other type of engine, although a stationary industrial engine
comes very close.

Ideally, the heads should follow standard aircraft engine practice in
the use of forgings rather than castings, although if the engine were
kitted, even partially so -- perhaps a pre-assembled lower end plus a
kit of parts for the cylinders and heads -- *the price may be low
enough to satisfy the home-builder's budget limitations. *For example,
if the heads were already machined, it does not take a great deal of
skill to swage the valve seats into place nor to stone them.
Volkswagen parts could be used for almost the entire valve train.

As a point of interest, while the basic idea is to produce an engine
sufficiently low in cost as to fulfill the needs of home-builders
around the world, should we be able to tap into a manufacturer at this
level, it is most likely they might be convinced to use their
facilities to produce *the Fat-fin head needed to make the Volkswagen
engine more suitable than the existing engines by producing heads
having an honest sixty-five horsepower's-worth of fin area. *Indeed,
this could be a method of subsidizing the cost of a 'replica' radial
-- OR OTHER ENGINE -- *in that home-builders in those parts of the
world where Volkswagen components are still in good supply would
probably buy enough Fat-fin heads that their sale would provide the
start-up funds needed to get a more appropriate engine into
production.

Toward this end, while I mentioned the Pobjoy because of its excellent
ratio of power-to-weight, I also mentioned that an in-line engine such
as the de Havilland would be the least expensive.

This is another case where modern-day metallurgy may prove beneficial,
in that Lost Foam Casting might be used to produce the head and lower
end, using aftermarket air-cooled cylinders. *The key to success in
this case would be the existence of a suitable crankshaft. *That is,
one in which the throws are spaced sufficiently far apart to allow the
use of finned barrels.

-R.S.Hoover

With respect, motorcycle heads are CNC machined from high strength
forged alloy billet. To my knowledge, no such head has ever failed
even under severe racing conditions.

The only 'top end' failures I'm aware of resulted from revving way
over red line RPM which caused valve failure. I know of a few which
suffered bent rods when the owner tried to start a hydraulically
locked engine after fuel had drained into a cylinder.

I would SWAG that top end motorcycle heads and cylinder blocks are
over designed for aircraft use by around 5X. The motorcycle news
group I belongs to recently asked if anyone had EVER overhauled their
engine due to simple wear. No one reported they had even though some
reported over 300,000 miles on their bikes. One reported tearing down
a high-mileage engine after the bike was wrecked just to find out what
the tolerances were - and to possibly re-use the parts. He reported
no measurable wear.

These are enormously strong engines and I think homebuilders should
take a serious look at them.