Dear Piper_Chuck & Bill Robison:

The PIPE here once more...and I'm about to get one of the Austrian made VT-21's myself within a month or two!

I've got the RCM 1980s era book on four stroke engines, and Clarence Lee did a review on the VT-21 for the magazine, which also showed up in the book I've got.

What JWN reported with the VT-21's idle he had observed is something Clarence mentioned in his article, too...

"The only blemish on the whole engine performance was the idle. I could not get the engine to idle reliably below 3500, with 4000 being a safer figure."

He did try using a homebrew fuel mix using ONLY 10% Klotz oil, 10% nitromethane, 2% propylene oxide igniter and 78% methanol, and got the idle down to "only 3500 rpm"...so perhaps a "high idle" MIGHT be expected. The idle DID stay lit as low as 2700 rpm with glow power connected with that fuel mix...so, perhaps a LIGHTWEIGHT glow plug power system might be advisable? Perhaps, if Clarence could have heard the advice that Ed Cregger was telling us about the need for a silicone sealant around the carb's entry into the cylinder head...most likely the brick-red-colored "copper-bearing" high temperature type, that I've seen in auto parts shops...maybe any possible air leaks (a BANE of four stroke engines!) cold have been avoided, and the VT-21 Clarence was testing might have idled a bit slower...!

The VT-21 didn't SEEM very "picky" about just what glow plug was used with it, in Clarence's review...K&B, Fox, Fireball (Swanson Associates), and the old GloBee plugs were tried and all were found to work...and from what Ed Cregger was saying, Clarence was TRULY "tempting fate" in trying an OS Type F four stroke plug in the VT-21 (which he DID do successfully)...I'm hoping that Clarence had a STACK of glow plug washers (in addition to the 1.6mm-or-1/16th inch thick "special spacer" that HP has provided for this engine) keeping the "hose-nose" business end of the Type F plug AWAY from the rotary valve's outer surface! I'd stick to trying short reach Fox 1.2 volt and Fireball units first (unless K & B plugs are still available) when I try firing up the slightly used VT-21 I'll be getting...later this autumn...either with the special HP washer, OR two or three stacked "regular" glow plug washers!

Clarence's article also mentioned the "proper plumbing" relating to the apparent need for a fuel line between the muffler pressure fitting and the similar fitting on the cylinder head on the VT-21...and then the crankcase vent under the engine's nose section was hooked up to the FUEL TANK??? Clarence just hooked up the muffler pressure fitting up to the tank, and advised periodic oiling (with Marvel air-tool oil, I suppose?) of the gears driving the rotary valve in place of the curious factory advice on those unusually connected fuel lines. Clarence stated that he was worried about possible metal powder (from engine break-in, etc.) getting back into the engine through the fuel tank with the factory hookup in that article.

Just wondering, Ed, DID your idle get better (hopefully with a lower minimum RPM) with silicone sealant around the carb's entry into the cylinder head?

The Balsa USA Swizzle Stick 30 plans I got last spring from another RCU member will be the recipient of the VT-21 I'll be getting soon...it was said by the seller of those plans that the VT-21 should be a "perfect" engine for it.

It will be interesting to see HOW the VT-21 does on my engine test stand...Clarence's prop RPM top end tests went like this...all with OLDER style round-tipped Top Flite props...with Cool Power 10% nitro fuel (not stated if it was 2 or 4 stroke fuel)...

7 x 6: 14700 rpm
8 x 6: 12700 rpm
9 x 5: 10800 rpm
9 x 6: 10200 rpm
10 x 6: 8200 rpm
11 x 6: 6500 rpm
...and even a 12 x 6: 5600 rpm...!

Now a "Swizzler" is a slow flying bird (basically a crutch with a box stuck atop it for a radio enclosure and wing mount, the engine stuck on the "top" and a tail stuck on the "bottom" ), so I'd most likely be using a 9x6 or 10x4 prop on the VT-21 for the Swiz-30.

I've heard one of the VT-21's run before, many years ago...and it IS a VERY QUIET four stroker...at idle it's "almost inaudible", even only a few feet away from the engine...so THAT should make it a very desirable engine to power an "early flying" aircraft, that could be possiblly flown at 7:30 AM...when my club's ( http://www.wingbusters.org/ ) field opens for "fueled flying" needs, I suppose that I COULD take it up even a little earlier, and fake people out into thinking the Swiz-30 MIGHT be an electric...the VT-21 COULD be that quiet of an engine!

I'll use all this advice in setting up my VT-21 on the test stand that I've got in this thread...as well as what Clarence had to say himself (EXCEPT his perilous attempt in trying an OS Type F plug in it!)...can't wait to pick up the engine later this autumn!

Yours Sincerely,

The PIPE!