>
>As you should know, I am a fiddler and fixer, not a "scratch builder". My
>mechanical experience lies with air tools and compressors.
>
> Altho' I mentioned that testing a chassis on air is not the same as steam
>(different qualities as you both mentioned) I must admit that of the 9 or
>10 Asters and O.S engines I have assembled, the air test has proved very
>satisfactory for the final steam test. I use a lot of "bubbles" in
>searching for leaks and won't complete the loco assembly until the engine
>runs on about 5psi or less. With these small engines, I believe that if a
>lot of "running in" is required something is wrong- expect excessive wear
>somewhere that may come back to haunt you. Most importantly it must be
>discovered where the binding is, hopefully never in the cylinders--and a
>crosshead bind can cock the pistons with resultant scoring of cyl and
>piston. Oh, by the way, forget testing the Merlins on air, the teflon (or
>whatever) pistons need heat to expand and seal against the cylinder walls.
>Sorry for the hot air!!
>
100% agreement Geoff. Well stated. The hydraulic effects of water vs. the
compressibility of air is really the difference I was alluding to. These
can both be used to advantage in designing and tuning. A chassis that isn't
smooth under zero compressive load will never run well under load.
And to add an anecdote that will make it impossible for me to ever sell my
GWR Pannier... I bought a RTR Pannier from my good friend Suzuki-san in
Yokohama. He had built the unit himself and is a master in our hobby.
This Pannier was very stiff though. Really stiff. Too stiff. Annoyingly
stiff.
I couldn't get it to behave at all and finally undertook this with
Suzuki-san. He was apologetic that he hadn't run the engine in for me and
we headed back to a shop area to run it in. He attached an air hose to a
vacant safety valve bushing, cranked the limiter up to 60 psi and then
opened the loco regulator up full bore. The poor little loco looked and
sounded like it was about to fly apart. He ran it in each direction, on
completely dry air, for 30 minutes or more. When he was done the
locomotive was totally smooth, ran great... and runs great to this day! To
Geoff's note I think this technique will somehow catch up to this little
loco and me someday... but who am I to question Suzuki-san? (I don't think
I'll be applying this technique in the future however!)
Regards!
-Richard
==================================================
Richard Finlayson
Check out: http://www.steamup.com/legend "Legend Steam Locomotives"
Check out: http://www.steamup.com/trailcreek "Trail Creek Models"
Check out: http://www.steamup.com "Steam In The Garden Online"
