Calling all Gilbert Thunderhead people.

[Robert McHam]

I have recently brought into my home a new(to me) engine. It is one of thr Gilbert Thunderhead .074 engines.

I have heard from many venues that they were not great performers and I just want to state I didn't buy it for performance. I bought it mostly because I never had one and also because (with the exhaust headers) it just rocks in retro "cool power"!!!

However there was something I never noticed in all the picures I have seen of the .11 and .074 Thunderheads. The "headers" (Gilbert called them silencers and also " muffler assemblies") are not matched! For some reading this, there is no surprise. for others you may be.

I began a search for all the pictures of Gilbert engines I could find and most indeed are mismatched. Here is a picture from virginiahobbysports who still sells the Gilbert .11. As can be plainly be seen the headers are quite different.

Why is this? There must have been some reason for this!

I have also found a few which are matched but I think this was done on purpose by finding another matching header.

Robert   

[George]

A third type "muffler":

George

[Robert McHam]

Yes George, and even those look as though they may be two different sizes athough in this picture it may only be the perspective angle making the closer one to appear as though it meeds a longer screw.
I have other pictures of the "pipe" type as shown in my first post but because of ther perspective angle the size difference is not so obvious.

Thanks, Robert

[George]

All of mine were the same size, except the .11 at the top which had no muffler or thrust washer (yard sale). BTW, the thrust washer from a Fox slant plug .15 fits the Gilbert .11.

George

[Robert McHam]

Just as I thought. The perspective.

George, What I have is the .074. Have you any suggestions on how to remove the head without the special wrench? I bet there isin't... Not without damaging the head with ugly marks.

Robert

[George]

George, What I have is the .074. Have you any suggestions on how to remove the head without the special wrench? I bet there isin't... Not without damaging the head with ugly marks. Robert

I bought my Gilbert .07's through a close-out from Polks many years ago. Some came unassembled in plastic bags. The two with flywheels came ripped out of plastic models (props and mounting screws with plastic still on them), also in plastic bags. I believe this was shortly after AC Gilbert went out of business.
Somewhere along the way, one had a wrench included. I don't remember buying it separately.

There is a hobby shop (Virginia Hobbies?) that still sells them. Perhaps they have spare parts and wrenches.

George

[LARRY RICE]

I believe that A. C. Gilbert made 4 different model airplanes using these engines. The engines were offset to the outside to maintain line tension and the mufflers were unequal to hide that fact. One muffler had an insert to muffle the noise from that port the other was empty to prevent back pressure from slowing the engine. All of the inserts seem to have disappeared when A. C. died and engines made after his death do not have the inserts. The latest engines need a lot of break in but will run well after that. These were never considered to be performance engines. The .074 is like a very heavy .049 and the .11 like a .09. The Wing Thing would have equal mufflers as it was free flight.
Larry

[Robert McHam]

Thanks Larry, that would make sense. It just seems so darned odd to look at! I knew there must be some reason.

What I do know for sure is that it makes for lots of "cool factor  " for these engines.In fact that is what led me to want one. Sure is heavy though... over three and three quarters of an ounce for the whole assembly which includes the spring starter, factory prop, factory propnut (much longer than standard nuts) and factory spinner. Because it has a spinner I believe it once started life as one of the plastic model engines. I will have to say that the factory prop by itself could lose a lot of weight around its oversized hub! of course it was designed to blend the spinner and spring starter together. It does this really well.
 My headers both have a conical aluminum insert in the ends. The cone shape is inside and only evident when looking into the insert. Neither seal the opening completely. I wish I had a camera that would do macro but sadly do not.

May be I will find another set of these headers and then be able to use them in symetrical pairs. To me it would look better.

Robert 

[LARRY RICE]

Do not use the prop... that nylon is over 50 years old and it will shatter and can be dangerous. I have some glow plugs and other parts like new crank cases. Did you want the wrench? All of the Gilbert engines were ment to go into plastic planes. Fox will not admit it but it is believed that Fox made the engines but that is a long story. Several parts are the same as a .09 engine that Fox made at the same time.
Larry

[Robert McHam]

Larry, yes I would like a wrench and no I was not planning on running the OEM prop It looks great for display purposes but even if it were safe to run I would ditch it in a heartbeat for something lighter for flying!

The OEM prop and spinner looks sweet indeed but for something this small would not afford much gain in the streamlining department unless I were going for all out performance with a racer of some sort. And as we all know this is not a race worthy engine unless there were to be a "Gilbert class" racing event! Heh! I guess it could happen as most anything is possible but I won't hold my breath waiting for it to happen!

I looked a little closer and the head has some pretty bad damage to one of the slots and a chunk of the head is missing. I have yet to see if it works but I am betting the head is bad from the teeth marks around the head. I think someone took a flathead screwdriver and a hammer to the head trying to break it free... Hence the missing chunk.

Robert

[Bill Mohrbacher]

Bob Pelfry did a lot of research and gave a very nice presentation on the history of these engines at our Model Engine Collectors Assn (MECA) meeting maybe 3 years ago.  The common belief was that these were made by Fox since they resembled the older Fox Rocket .09.  In fact they were designed by Bob Holland (Wasp, Hornet) and made by Dynamic Models (formerly Johnson).  There was an .07 and an .11.  In later years, Gilbert made them themselves.  Jim Ivey, Combat and Stunt champion and former employee of Hi Johnson, said that Fox did make the steel screw machine parts of the engines, but no castings or assembly.

When installed in CL RTFs, the engines had a TON of offset.  The angle on the mufflers matched this offset, so when installed, the mufflers were parallel to the CL of the airplane.

When Gilbert went out of business, Polks bought their stock and in 1975 sold the engines under their name.

Bob may have parts available, including mufflers:  bobco60@wirefire.com

[Russell Shaffer]

Try a homemade wrench:

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Just grind a notch in a piece of flat steel.  It works fine on Cox heads, so I don't see a problem with a Gilbert. 

[LARRY RICE]

Robert, E-mail me an ADDRESS!!!!!!!
Larry

[Robert McHam]

Russell You are right, If I didn't live in an apartment, had a grinder, a workbench tro mount it on and a basement or garage to keep the workbench in! Maybe one day I will be able to move up a bit. Till then...

Larry, Email sent.

Bill, great info and pics too! Thanks!

Robert

[LARRY RICE]

Anyone wanting new .074 glow heads I have them for $5.00 each
Larry

[Bill Mohrbacher]

Bob,

An article by Bob Pelfry with history and pictures of the Thunderheads was published in Volume #5, Issue #173, September 2005 Engine Collectors' Journal.  You can get a copy for $3 from:

Tim Dannels
28795 CR331
Buena Vista, CO  81211

Tim's Email:

ecj@chaffee.net