4 cylinder/4 stroke mystery engine

[rapmoz]

Santa has been generous this year and I just receive his gift : this 1M25 Chris Craft is superb and the home made engine inside is very interesting and well made with a high craftmanship.

It features a water pump for cooling, a gear box (forward/neutral/reverse) and an interesting hand start lever (white knob).
Check also the great ignition system, exactly as on the real thing...

I think the cruiser could be dated from the 60's, the RX, TX and radio gear seem home made too.

Unfortunately, the carburetor is missing. Any suggestion where to find a new one?

Also, I wonder about the origin of this engine (probably around 20CC or 1.2CI), have you already seen such a design or do you think is it entirely scratch made including plans ?
Every info or suggestion will be welcome !

Thanks, Chris.

 

[Longboy]

A Chris Craft Corvette from the 50's. If you have no history on the model, rummage around on the model watercraft forums. Seems like that engine and transmission might be a commercial product. But if no script or numbers on the block, a great engineer put his love into this marine project!
You can adapt to the manifold a .15 size carb for a 20CC engine.

 

[Tim Wescott]

.15 is 2.5cc -- that's an order of magnitude smaller than 20cc.

If it were pure suction feed, you could use a carburetor off of a 20cc glow engine (there were a few that big). But looking at that fuel pump, I'm thinking you may just need a carb with a float, and that's a different story.

I think just to get it running I might try a carb off of a 20cc glow engine -- or even a .46, because I have a couple of those!

 

[Longboy]

.15 is 2.5cc -- that's an order of magnitude smaller than 20cc.

If it were pure suction feed, you could use a carburetor off of a 20cc glow engine (there were a few that big). But looking at that fuel pump, I'm thinking you may just need a carb with a float, and that's a different story.

I think just to get it running I might try a carb off of a 20cc glow engine -- or even a .46, because I have a couple of those!

I was thinking direct draw off the fuel tank. A .15 carb is plenty for a small 20cc gas engine. The .46 carbs might work but really large for that capacity of a low RPM engine. How did you determine its displacement? If it has a fuel pump, most likely a larger engine. Maybe something out of a lawnmower shop the right source for a new carb. Just can't get a sense of the dimensions without a 6 inch rule for reference in your photos.

 

[rapmoz]

Tim and Longboy, many thanks for your helpful suggestions !

May be I'm wrong but in my mind, a carb that has to feed a 4 cylinder engine 20CC should have basically the same size as a carb intended for a 5cc single cylinder engine : the four 5CC cylinders of a 20 CC engine need to be fed one after the others.
Also, the good size of the future carb is given by the internal diameter of the existing intake pipe.
I have selected some carbs from my spare box and of course, the one who seems to be the more adapted has no needle valve!

 

[rapmoz]

Longboy,
Sorry, no inch rule here but I estimated the displacement with the total length of the jacket (130 MM or around 5 inch) including a water cooling chamber all around this jacket and the stroke of 22.5 MM or .86 inch but don't know if it's right ...

 

[RobStrunz]

I’m wondering if that engine is one designed by ET Westbury. Perhaps a Westbury Seal. If so it’s 15 cc and the designs for it are readily available.

https://www.stationroadsteam.com/westbury-seal-4-cylinder-engine-stock-code-5091/

There was also the Seal Major and the Sealion. Castings and drawings are available from Hemingway Kits.

 

[Noitoen]

For 20cc 4 cylinder a small 5 cc engine carburetor should be enough. You only draw 1 cylinder at a time

 

[Longboy]

Thanks rapmoz. Got an idea of scale now with you ruler. 20cc seems reasonable. Your instinct on the intake manifold is right. If that is the manifold gasket in the photos of the carbs, that's a good guide to the throat size of the carb originally on there. You can fill a cylinder with a lite oil through the spark plug hole, syphon out and cc the results for a rainy day experiment determining displacement.

 

[Tim Wescott]

I was totally not thinking of either the fact that a one-lung 2-stroke is going to have a very intermittent velocity (not to mention reverse flow in some circumstances), or that your engine is probably slower than a screaming modern Schnuerle ported production 2-stroke.

Carry on, you appear to be doing better than I would have! I like your rule of thumb to match the carb bore with the intake manifold bore.

 

[johnlaudano]

What a great boat and a great engine. Both inspire me to build more of each.
I’m intrigued with the clutch and gearbox. I realize this interest should be discussed in another separate post but if anyone has drawings or plans of a clutch and gearbox that would work in a model boat I’d be interested in corresponding.
If this boat and engine become for sale I’m interested in talking.
John

 

[Charles Lamont]

It is a lovely piece of kit but it isn't a Westbury design.

 

[RobStrunz]

It is a lovely piece of kit but it isn't a Westbury design.

 

[RobStrunz]

Are you sure it isn’t a modified seal?

 

[Charles Lamont]

Are you sure it isn’t a modified seal?

Yes.

 

[Mechanicboy]

As I can see it has has been fitted with a carburettor with a float chamber since a petrol pump is fitted to the engine block. Is it possible to get a drawing of the carburetor with a float chamber adapted for the model engine?

 

[holmes_ca]

I'm pretty sure the Seal is a side valve, and the Sealion is an overhead cam, I am building the Sealion it's about 90% complete,

Edmund...........Alberta

 

[rapmoz]

Happy new year to all and thanks for your suggestions and advices.

I don't think the engine is a Westbury design either, a very particular point is the arrangement of the plugs :
In most engines they are in the open. Here, you have to remove the cylinder head cover to unscrew them and in addition, the contact system between these plugs and their ignition wires could be a possible source of problem (?).

I also wonder about this head cover : it is superbly made (like the engine!) and it seems to me that it requires stamping and tools which are not within the reach of an amateur mechanic, however, I have been interested in model engines for a long time and this is the first time that I saw an engine with such an architecture.
All that I know is this engine was built in France by a Monsieur M... in the 60s and has been sold to me by his grandson, unfortunately, I have no plans or further informations ...

 

[Steamchick]

Hi Rapmoz... the ignition contact arrangement isn't too much concern, for the following reason. The voltage is very much higher than needed to jump the gap, if any exists between the contacts. If the engine is 7 : 1 compression, with a 0.015in gap of the spark plug, and the gap between the contact and the end of the spark plug, is 0.003in... then only about 3% of the spark energy will be lost getting the volts onto the plug. The spark generator should be able to make a voltage 2 to 2 1/2 times that needed to jump the gap at the spark plug. So it should be fine. Car distributors had moving gaps that had 0.01 in of air for the spark to cross to get the volts up to the spark plug.
So don't worry, until it doesn't run!
K2

 

[Steamchick]

On carbs.. my motorcycle experience suggests that 2-stroke carbs are about twice the cross-sectional area (choke, or venturi area), as the induction timing is much shorter than on a 4-stroke engine. I.E. on a 4-stroke, induction occurs over a whole stroke. On a 2-stroke, the porting means induction to the crankcase is limited to about 1/2 the stroke, the other half is a pumping of crankcase gases into the combustion chamber.
Therefore to get the air-fuel charge for a whole cylinder's worth of gas, when the gas passing through the carb is limited by "sonic" limits (laws of physics) then you need twice the area of venturi for the shorter induction time.
The may help you with you comparison of engines' sizes and chokes.
My V50 Guzzi uses a 26mm or 28mm diameter choke for a 250cc cylinder.
If you have 5cc displacement cylinders, the physics comparison suggests you need a 7 or 8 mm diameter choke of carburettor...? How does that compare to your estimates? A smaller carb will work - say 6mm choke - but restrict the full power of the engine. A carb that is "too big" can work but difficult to start and run a low throttle settings.
Hope that helps?
K2