OS 46FX-H too much compression !

[Olivier PASQUIER]

Hello,

I have a curious issue with one of my OS46 FX-H (the ring one). After
about 150 flights (home made fuel 18% Micromotul oil and 5% nitro), its
compression has increased to a point I cannot anymore start it with my
electric starter (it broke several time the bearings of my starter and
it was not due to fuel lock). It sounds incredible but it has now more
compression than that of my OS61 SX-H WC. But when I can manage to start
it, it runs really fine with a lot of power and stable rpm all over the
range of pitch.
Obviously, I opened it and it is clean inside, I did not notice anything
wrong.
What should I try to reduce this compression and by the way, what could
have generated this problem ? Could it come from a increased proof of
the ring ?
Thanks for any help.
Olivier

[Robert Mulligan]

"Olivier PASQUIER" <opfd@free.fr> wrote in message
news:3EE3783F.A6DFC997@free.fr...
> Hello,
>
> I have a curious issue with one of my OS46 FX-H (the ring one). After
> about 150 flights (home made fuel 18% Micromotul oil and 5% nitro), its
> compression has increased to a point I cannot anymore start it with my
> electric starter (it broke several time the bearings of my starter and
> it was not due to fuel lock). It sounds incredible but it has now more
> compression than that of my OS61 SX-H WC. But when I can manage to start
> it, it runs really fine with a lot of power and stable rpm all over the
> range of pitch.
> Obviously, I opened it and it is clean inside, I did not notice anything
> wrong.
> What should I try to reduce this compression and by the way, what could
> have generated this problem ? Could it come from a increased proof of
> the ring ?
> Thanks for any help.
> Olivier
>
You can do one of two things. You can add a head shim and reduce compression
that way, or you can leave it alone and loosen the glow plug when starting
and allow some of the preassure to escape that way.. (remember to tighten
the plug again before you take off...) eventually normal wear will lessen
the pressure and you won't have to do it again until you rebuild.

I suggest the head shim, you can always remove it when the engine wears in
and add it again later after a rebuild.

[Joe landy]

Hi.
I had a Rossi 60 engine do exactly the same thing. It was second hand, so
didn't know what fuel had been through it, but the problem was serious
quantities of carbon in the cylinder bore.
Damaged my hexagon starter shaft, and never did get it to turn over. Did the
following to cure it:
Removed head, backplate and piston, rubbed with very fine emery (P1200), and
away it went. You need to be careful not to damage the chromed lining
though. Even on your ringed engine. Only rub carbon away, as soon as you see
silver, move onto the next it.
Sometimes cellulose thinners will remove excess carbon, but it usually
requires mechanical removal!
Good luck.
Joe landy.
Weather crap, but will start flying again soon. Only had a few days out this
year so far.
Bye.


"Olivier PASQUIER" <opfd@free.fr> wrote in message
news:3EE3783F.A6DFC997@free.fr...
> Hello,
>
> I have a curious issue with one of my OS46 FX-H (the ring one). After
> about 150 flights (home made fuel 18% Micromotul oil and 5% nitro), its
> compression has increased to a point I cannot anymore start it with my
> electric starter (it broke several time the bearings of my starter and
> it was not due to fuel lock). It sounds incredible but it has now more
> compression than that of my OS61 SX-H WC. But when I can manage to start
> it, it runs really fine with a lot of power and stable rpm all over the
> range of pitch.
> Obviously, I opened it and it is clean inside, I did not notice anything
> wrong.
> What should I try to reduce this compression and by the way, what could
> have generated this problem ? Could it come from a increased proof of
> the ring ?
> Thanks for any help.
> Olivier
>