On Jul 28, 11:05 pm, Anthony W wrote:

After Bob Hoover's recommendation of the double eagle, I fond myself at
the DE website and thinking I've found my first (maybe only) plane.

I already have a stock 1600cc bug engine to use that is ready to put
together other than a few bits but I'd like to try Bob's suggestions and
go with the 78mm crank. Anybody have a good recommendation on a 78mm crank?

All the AFFORDABLE forged cranks come from China these days, and
seemingly from the same supplier. I got my 82mm crank from California
Imports. I also like Aircooled.net for parts. I can't recall if my
engine builder magnafluxed it; I know he balanced it (as an assembly,
with the rods, the prop hub and extension, and the dynamo hub at the
fan end) and he said it took a bit of grinding to get it to come into
balance. All the journals miked out OK.

DeMello will be taking a German forged crank as a core, and welding
and grinding on it to make what you need. His prices are pretty
reasonable, IMHO, but it will be more than a forged ChinCom crank.

You'll have a choice of journal sizes either way. Chevy journals lock
you into new rods (also ChinCom, at pretty attractive prices these
days). But they will mean less clearancing. The smaller journals
also mean a weaker, less stiff crank. A bad thing in a high RPM
engine, where the inertial forces of the rods and pistons try and yank
the pistons out through the top of the heads. A weak crank will, at
high RPM, let the pistons hit the heads...but at our low RPMs, a case
can be made that Chevy Journals are OK. But then we put prop loads on
that crank...you make your choices.

"Clearanced" VW Journal rods are just run through a grinder so they
don't hang up as much. If you're really on the cheap, you can do that
yourself, just make sure you keep them reasonably balanced, both the
whole rod, and the "big end" and "Little end", see later issues of the
Idiot Book, the HiPo pages in the back, for that. Clearancing the
rods in this way weakens them. You may not need to do this for a 78mm
crank, or you may decide to clearance the case a little more, and
leave the rods alone. IF you are clearancing the case yourself,
you'll need a die grinder.

Steve Bennet's book is a really good reference for building any
stroker engine, and I highly recommend it.

Reusing your existing pistons with the longer stroke crank will pop
the pistons right out the top of the jugs at TDC (negative Deck
Clearance), thus the need for the spacers Veeduber alluded to. Or
new pistons; the "B" style for stroker cranks, with the rod pin moved
down. (Although there is not much call for "B" 85.5mm
pistons.....they may be hard to source). My understanding is that
using the "B" pistons, and a 78mm Chevy Journal crank makes a very
nice stroker engine, with little if any clearancing needed, and few if
any spacers, while still keeping the compression low. I've never
built such an engine, and it would require new pistons and cylinders,
a new crank, and new rods. Starting to get Not So Cheap. Maybe better
you should just slap the Flywheel end hub and extension on your 1600
and have done with it...your call.

I will be turning the engine around and mounting the prop on the big
bearing end of the engine but I'm not sure how I'm going to do that
right now. The Great Planes rear drive looks overly complicated but the
only other system I've seen was on a German website a couple years ago
on a type 4.

Use the new-ish Great Plains "Flywheel Drive" bits. Heavily
influenced by Veeduber.