MECOA's Model Engine Forum & Swap Shop

[tarbee]

Hello All,

I am going to be building from scratch a wooden model fishing boat 1/7th scale - 20 inches across by 66 inches in length. I would really like an engine with a nice realistic sound and not a buzzing sound of a regular 2 stroke/ high rpm engine.

Could anyone recommend a nice realistic sounding marine engine to me that I could use - I am open to all suggestions!!

Many thanks in anticipation!

Paul

[chiefss]

Years ago, OS made a 40 size four cycle marine engine. I don't think anyone makes them anymore. You might check Ebay but I don't think you're going to find one.

Electric is your best bet.

[SteveM]

Another option to a glow motor is electric as they can provide much more realistic scale speeds. You can also buy electronic diesel sound devices that connect through the speed control and increase and decrease with the throtle. Robbe and Graupner make some of the nicest units but there may be others.

[tarbee]

Hi


Many thanks for the advice. I really don't want to use a motor and really want an engine-brum-brum!!

If anyone else has any ideas it would be very much appreciated?

[propwobble]

Have you thought about using and fan and duct on an air cooled 4 cycle? It seems to have worked in a lot of automobiles. There are thermometers that you could use to help design and experiment. It is also not impossible to make a water jacket to fit just about any engine but I'd think it would be really difficult to deal with the complicated shapes on a four stroke even for a good sheet metal guy. I'd try the duct and fan.

[chiefss]

Your options were pretty much stated. Try and find an old OS40 four cycle marine or use an electric motor. The only other relatively common marine four cycle was the OS60 and they are very hard to find and expensive. It would make a boat your size into hydrplane.

You don't like whiney two cycles so those are pretty much your options.

[tarbee]

The duct and fan idea sounds great. Is there anywhere I can have a peek at a picture of a setup perhaps? This seems so far the best route for me to go.

Many thanks!!!

[propwobble]

It is something that has been done but is not common and I cannot point you to a specific design. It is an alternative to the option of finding a water cooled four stroke or going electric. The idea is to simply provide a fan (not propeller) on the the drive shaft of the motor that will move sufficient air across the cooling fin surfaces of the engine. If you really feel up to making this, you should probably be up to researching it.

[tarbee]

Thats great! Many thanks for all your assistance with my query. I shall now go away and do some research...

Cheers!

[propwobble]

I know I have seen a fan cooling system in one of the old model mags at some point but I can't recall where as it was years ago. I am not a boat guy by nature but the concept of a buried engine intrigued me and caused me to build a radiator for a water cooled two stroke. I wish I could remember the article,sorry. I used a thermometer, which I got from tower hobbies with a remote sensor to measure head temp . They no longer have it but I know there are others out there. A model engine tachometer will be helpful in your process as well.


Your application will be similar in some ways but not truly like a ducted fan jet airplane model where the fan provides thrust, with yours, the fan needs to consume much less power to just push air. For ease of finding an appropriate fan, one of the type for a ducted fan aircraft engine with a few ( perhaps half or more depending on if it pushes enough air) blades removed might do the trick. The less air pushed= more power to the drive shaft. For any fan system, the pitch, diameter and number of blades plus the size of the duct and the number of bends you have to put in i twill determine the power consumption and the air flow. The fewer bends the better. Of course the goal is to put enough air over the cooling fins of the engine, especially the head and definitely in the area of the exhaust valve. Heat increases with engine speed but so does shaft speed/fan speed half good, half not so good. You might even be able to use a fan from a computer fan if you can figure out how to attach it to you drive shaft; I think I'd prefer one from the model ducted fan industry. If you go another way, it would be wise to try to use a fan that is designed to run at speeds more than what you will run but still be efficient. Fans can come apart if run over-speed. Four strokes vibrate too, so a nylon type fan with a good sized hub might be best. Vibration is an enemy and causes metal fatigue, avoid a metal fan.

Clearly you get the idea and if you are willing to experiment, you will likely succeed. Be careful, use a protective shield some sort (clear plexiglas or better yet: lexan)_ when you are exposed to the running system until you confirm it is safe.


The boat you are building sounds like an ambitious project that will take some time to construct. The fact that you are thinking in terms of satisfying a specific desire and seem determined to create a realistic model indicates you have the tenacity to figure it out.


If you could find a water cooled four stroke you would save yourself a lot of time. In addition to the OS there is one from the UK called Gannet that occasionally turn up as well. They are out of production and spendy. They are spark ignition 15cc. There also is British Magnum out of production, not the Asian Magnum, made a glow marine four stroke of 15cc.

You might want to look at Ebay #150396257487

best of luck

[tarbee]

Thanks Propwobble thats some great info you have given me there. I will certainly look into the ducted fan side of things and contenders for my 4 stroke engine. I definitely want to do this so I am willing to put-in the time/research and get what I need.

I just have this image of a lovely engine in my boat chugging away with plenty of smoke and a nice sound as well!!