Limbach VW engine quirc

Hi all!
It's been a while since I visited this group, I've been busy putting a
Scotish Aviation Bulldog on civilian register with a group of people
at the Swedish Air Force Museum. But now a friend of mine visited a
cousin in the US and whent on an airboat ride in the Everglades and
that hooked him so he has decided on building an airboat for himself.
Got the plans and everything and was looking for a suitable engine. I
happend to know a guy who swapped his VW for a Rotax in his Jodel D18,
so I called him to hear where his engine went but it was sold. The
flying club however had no less than two Limbachs lying around, one
aledgedly working that came out of a motor glider (also converted to
Rotax) and the other one with a crooked cranc shaft after a prop
strike. He got both at a bargain, but now we are puzzled because none
of the engines can be turned. Tops are off as well as magnetos and
fuel pump, but something clanks after approx. 340 degress of rotation.
Turning it forward it stops some way past TDC for the front cylinders
and turning it backwards is stops immediatley after TDC of the rear
cylinders, so it is not the pistons getting caught. If it was
something with the valve lifters I would have assumed that it would
get caught at close to 720 degrees, not close to 360 degrees, since
the cam shaft rotates at half the cranc shaft speed.

Most likley we are missing something obvious, so please feel free to
have a laugh at our ignorance, if only you can point out what we are
not thinking about!

Thanks!
/Lars

P.S. Remove the obvious from the email address if you want to mail me
directly. D.S.