Author Topic: Restoring a Gannet 4-stroke petrol engine  (Read 393 times)

Offline Zephyrin

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Restoring a Gannet 4-stroke petrol engine
« on: July 13, 2021, 06:52:58 PM »

Hi,

Recently I had the opportunity to overhaul a Gannet gasoline engine for a fellow at my club…Yes the Gannet, a large 15 cm3 4-stroke model engine, water cooled for model boat, from 1960, a famous vintage engine if not an antique one.

The contact breaker and its cam were totally out of use, and the old magneto looked in poor condition; so the owner wished an electronic ignition, for ease of start and faithfulness, to use it again in a model boat in the years to come...
I kept the magneto for further inspection, hoping to test it on one of my engine someday…

The rear crankcase cover with the bearing for the magneto was replaced by a plain cover and a new bearing for the camshaft was made, with a simple ring with a magnet on the camshaft and an adjustable support for the Hall sensor in front of the rotating magnet for adjusting the timing of the ignition. 

Combustion chamber and gas ports, heavily coated with burnt oil, were de-carbonized, and the valves and valve seats lapped. The piston rings were polished with an India stone as I suspected that the very sharp cut on the rings was the cause of the scratches visible in the cylinder liner, as the rings are really stiff.
The compression is tremendous, hand start will be difficult I fear !

The engine was then installed on a wooden test bench, with a tank for the cooling water, and then driven with a belt and the hand drill, a powerful but horribly noisy system.
A simple stream of butane in the intake lets hear the first explosions once the ignition was properly set, very encouraging for the next step : running on plain gasoline !
The carburettor -of very simple design- is put in place, with a fuel tank.

From the first turns, it appears that a "positive” water cooling with a flow of coldwater in required,  a simple convection is very insufficient; the engine becomes shortly extremely hot, therefore I add a small water pump for the continuation of the tests, not to risk a seizure!

A muffler also is mandatory as the noise is on the high range !

The carburettor was also isolated from the very hot cylinder head with a thick gasket. The engine responds immediately to the throttle, up to 8000 rpm, very sensitive, the idling near 2300 rpm is very rich, (hence the carbonized exhaust ways) being easily flooded too, I would recommend a more efficient carburettor for long and pleasant runs when installed in a RC runabout or other speedboat.

the tests:
and other pictures of the repair
https://photos.app.goo.gl/M8sPA3qbg6rz43bG6

Cheers


Offline Roger B

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #1 on: July 13, 2021, 07:04:19 PM »
Excellent  :ThumbsUp:  :ThumbsUp:  :wine1: Quite a beast  8)
Best regards

Roger

Offline Jasonb

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #2 on: July 13, 2021, 07:27:54 PM »
That's running well again. I've always liked the look of these engines in the Miniature Engineering Museum's albums.

Do the two cams sit either side of a central skew gear and if so are the cams and gear all cut from the solid or are they separate parts fitted to a shaft?

Offline michaelr

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #3 on: July 13, 2021, 07:58:58 PM »
Now that brings back memories of my model boating days way back, I had a 15cc Magneto Ignition Gannet a fine engine in it's day it was very reliable always a good starter.
A couple of pictures of my boat.


Offline Zephyrin

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #4 on: July 14, 2021, 08:54:12 AM »
Hi;
RogerB : yes, impressive, a great change from my diminutive engines…

Michaelr : wow, great pictures, this is exactly the project of the owner of this engine, in a large Chris-Craft look alike model, with a nice bow wave.
A difficult point will be to find a pond where combustion engines are allowed...
JasonB :
the two cams are separate parts in very tough steel pined to the shaft on both side of the bronze helical gear.


Offline Jasonb

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #5 on: July 14, 2021, 12:30:22 PM »
Thanks for the extra detail, I missed your link to the rest of the photos until just now.

Big question is did you measure it up while apart so you could make a replica :LittleDevil:

Offline ShopShoe

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #6 on: July 14, 2021, 12:58:36 PM »
Zephyrin,

Thank You for sharing your work on this engine. I agree that it would be at home in another boat.

It certainly has that "marine" sound as it runs.

michaelr,

Thank You for the pictures. The Chris Craft look is distinctive.

ShopShoe

Offline Zephyrin

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #7 on: July 14, 2021, 03:00:04 PM »
   I would have preferred to restore the engine with the magneto, in its original configuration, but it is not my engine, and the owner, a buddy from the live steam club, does not want to hear about an ignition other than electronic, Hence the RCEXL module !

  The positive point is that I kept the magneto; the coil (Wipac so551) is still available if it has to be changed.
 
  No I didn’t do all measurements, just a few, I measured 28mm for the bore instead of 1” as noted in the documentation.

  If I had to make I replica certainly I would amend a few points, such as adding a cooling water pathway through the cylinder head, or larger threading and metric screws, each of these bloody screws here has its own particular standard, BSF, BSEF, BA, UNF (?)...
The aluminium castings does not come from the best foundry!
The design is very classical, quite in the style of ETW, very close to the KIWI, but simplified.

Offline michaelr

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #8 on: July 14, 2021, 03:36:31 PM »
Thanks for the comments on my Gannet powered boat, when I bought this engine I also bought the optional extra which was a Amal float chamber this allowed the fuel to stay at a constant level which I think helped with the easy starting and reliable running, I had some pictures of the engine installed in the boat but I can't find them.

Mike.

Offline Jasonb

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Re: Restoring a Gannet 4-stroke petrol engine
« Reply #9 on: July 14, 2021, 03:38:30 PM »
I think Westbury's Apex Minor is very close to this layout.