Jerry E. Howell Model Project Plans & Kits
Outpost Enterprises, LTD - 695 Godfrey Road - Hollansburg - Ohio 45332 - USA
(World Wide Supplier of Quality Model Project
Plans & Kits Since 1992)
Why Won't My Stirling Engine Run?
If your new stirling engine refuses to run, here are some
things to check:
Power Cylinder - The cylinder must be true
and straight, no taper, bell mouth or barrel shapes allowed! If
it was accurately machined with a nice surface finish then all
that is needed is a nice polish. The closer to a mirror finish
the better.
Power Piston - The piston must also be
true with no taper, etc. as the cylinder above. The graphite piston
must be within .0005" of the cylinder diameter. Pistons over
.750" can be a little smaller than that and pistons smaller
than .600" should be a little larger than that. The correct
fit is when the piston will fall through the cylinder of it's
own weight, but when the piston is pushed into the cylinder with
the bottom closed it feels like there is a spring under it. Both
cylinder and piston must be clean, dry and absolutely oil free.
Mechanical Tightness or Binding - Model
stirling engines produce little power. Because of that if they
are to run properly, or at all, the mechanical aspects must not
rob power. If there is any tightness or binding it must be tracked
down and corrected. Even a small amount of tightness or binding
will rob much more power than you would expect. Better a little
loose that too tight.
Displacer Timing - For all practical purposes,
the displacer movement should be 1/4 crankshaft revolution (90
degrees) ahead of the power piston - ie crank pin to crank pin.
This is not critical and can vary a few degrees one way or the
other. Not all engines will be at optimum performance at 90 degrees
but it is the best test setting for a new engine.
Engine Balance - If the engine is a "Miser"
or other low temperature difference engine, balance is important.
With compression relieved by loosening or removing the bottom
plate, adjust the balance disk so that the engine will stop at
random places when given a spin. If the engine can't be balanced,
gradually enlarge or plug the balance disk holes as needed. If
the engine is unbalanced, it will require more heat and operate
at a higher RPM than it would if balanced.
Air Leakage - Other than minute leakage
around the piston and displacer rod bushing, there should not
be any other air leaks. When given a spin, the engine should exibit
some compression by coming to a stop at about the 3:00 o'clock
or 9:00 o'clock power piston crankpin positions (vertical engine
example). If it exhibits no compression and all else above is
well, there is an air leak somewhere that must be found and corrected.
Don't overlook the displacer itself. It must be a sealed air tight
can. If you put it in the freezer and get it very cold and then
submerge it into near boiling hot water it should not show any
bubbles coming from it. Low temperature "Miser" type
engines should have non pourus foam displacers and are exempt
from this test.
If your engine is of sound basic design and it passes all the
above tests it will be nearly impossible for it NOT to run! One
last caveat - be careful not to use too large a flame to operate
your engine as small models can easily be damaged by overheating.
An alcohol or propane flame of 1/4" diameter and around 1/2"
high (or less) will easily operate any of my engine designs. Miser
should NEVER be operated over any flame.
If you are building to one of Jerry's plans and need more help,
feel free to e-mail us at allen@outpostenterprises.com.
However, Dad was the expert and I won't be able to answer very many
technical questions. I highly recommend that you signup for
our user forum
and post your questions there. Others builders who have built
these projects are much more likely to have an answer. Good luck!
© Copyright 1999 - 2007 Jerry
E. Howell - All rights reserved