Author Topic: Triple 2 stroke SPE FS3  (Read 452 times)

Offline AlexS

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Triple 2 stroke SPE FS3
« on: May 10, 2022, 08:54:44 PM »
Hello and welcome.

Let's introduce you to the new triple two stroke engine.

I always dreamed about designing and building a two stroke engine using moped parts and homemade parts. Wouldn't start with the 4t V3 engine, because I could easier modified this engine for serious usage.

Being a Yamaha RD 250 owner, last year busy with tuning and modifying the bike (still needs some work :)). Lastly I have make a new set of expansion pipes that turned out well. That taste like more, in the form of, let's make a homemade two stroke engine!

As said, being a Yamaha guy. I was looking for moped parts of that brand. Beside outboard motors, there aren't Yamaha triples as far I know (air cooled).
I know that my dad had owned, before he had a RD motorcycle, a Yamaha FS1.
There are nowadays still aftermarket parts. Other option was RD/DT 50. But I saw that the cylinder sizes are quit larger than the FS1 ones (40mm each).

The FS1 produce stock horsepower of 4.8 hp at 9000 rpm. Multiply that with 3 that sounds sweet, same as the exhaust note it produce! Could power a air or water propeller?!

So the SPE (own named branch) FS3.

40 mm bore 39.7 mm stroke make it 150cc total.
Fitted with RD/DT50 16 mm Mikuni imitation carbs and reed valves. Using the FS1 carbs is not a great idea. The FS1 was build as rotary valve inlet or membrane. There for the carb is fitted axial to the crankcase and behind the crankcase cover. So there is no air hose connection for a air filter.

So the carbs and membranes need to fit on the crankcase rater than the barrels. And the cool fins of the barrels and heads are vertical. I decided to place the cylinders horizontally. Later as upgrade I could make a forced air cooling sheetmetal like a 2CV or using the air propeller and mike it a aircraft look-a-like engine. Other idea to make watercooled heads if I want to use the engine as powerplant for something in the water (!)

So far. Making a crankshaft out of multiple pieces. Would be challenging to make it straight and true. Then building a crankcase around it. As you see the crank would be quit large and heavy. Yes, she would be not light. I've been looking to make the crank cheeks thinner. But this resulted from a crankcase of 4 extra parts. The crankcase must follow the shape of the crankshaft with bearings and seals.
So the crankshaft is more the flywheel 1-one and the disc at the front would be more the trigger wheel to fit the 3 or 4 magnets for the ignition. So the trigger wheel / flywheel could be made of aluminium.

I have made a motion video of the engine.

Last pictures shows the materials and first parts of the crankshaft.
« Last Edit: May 10, 2022, 08:58:44 PM by AlexS »

Offline Admiral_dk

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Re: Triple 2 stroke SPE FS3
« Reply #1 on: May 10, 2022, 10:44:16 PM »
Fun and interesting project  :D   I'm old enough to remember the FS1 as part of my youth  ;D  :-X

I can see that you are not going after power .... or should I say - that if you where - look at something like my nephews Yamaha YZ85. Here the membrane housing is on level with the bottom end of the Transfer-Channels. This feeds ALL off them directly when the engine is "on the Pipe" + works well all the way from idle to max RPM.

I will certainly follow this project with interest  :cheers:   :popcorn:

Best wishes

Per

Offline AlexS

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Re: Triple 2 stroke SPE FS3
« Reply #2 on: May 11, 2022, 10:09:09 PM »
Great you are in Per!

I am to young, but I have seen one riding really fast by and was thinking, is that a moped!

Indeed I am not going tot make max power out of it. Otherwise would choice for water cooled modern cylinders. Just make a nice and fun to build engine!

I see what you try to say about the positions of the membranes :thinking: if membranes mounted on top of Carter and horizontal to cylinder Bottom end, it is difficult to get carter halfs fitting (bolt together) and mill a flat surface. I hope you understand what I try to say :)
« Last Edit: May 12, 2022, 02:29:09 PM by AlexS »

Offline Admiral_dk

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Re: Triple 2 stroke SPE FS3
« Reply #3 on: May 12, 2022, 11:36:36 AM »
I think I understand you and your reasons  :ThumbsUp:

We must not forget that Yamaha (and other makers) have huge R&D budgets, CAD/CAM etc. - all in all, completely out of our leguage + the engine I mentioned has to compete against other Manufators ....
It was just an eyeopener for me, when I had to change some of the parts in his gearbox - seeing how much the knowledge about how to make a fast Two-Stroke Engine with a broad Powerband is made now - compared to the Fizzer ....  ;)

Just wished that I had been smart enough to take pictures back then - so I could have shown.

Per

Offline AlexS

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Re: Triple 2 stroke SPE FS3
« Reply #4 on: May 12, 2022, 02:27:18 PM »
Agree! Even back in the '70 they had alot of knowledge about porting and tuning for example the transfer flow.

The new membranes of for example V-Force are common for two stroke motorcross engines. But it would be cool if some manufacturing choice for rotary inlet, maybe with modern servo technology it could also make it adjustable for different loads or rpm's.

Yes the modern two stroke motocross are very compact build! Years back I had a RM125 and was also amazed that the gearbox is so small, even with 6 speed and those peak loads when racing.

Offline Admiral_dk

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Re: Triple 2 stroke SPE FS3
« Reply #5 on: May 12, 2022, 04:45:00 PM »
Have a look at the Aprillia 125 & 250 RR models. They used a rotary inlet turned 90 degrees to the crank - just pulled by a very narrov toothed belt from the crank. On the 250 the disks overlap each other - so that could easily be upped to tre or more cylinders.

I actually meant how much they have learned about porting since 2000 - the Seventies is very old style in that sense. Superficially they look similar - but when you go into details they are very different ...!!!

Per

Offline Roger B

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Re: Triple 2 stroke SPE FS3
« Reply #6 on: May 12, 2022, 07:53:56 PM »
Looks to be a fun project, especially as you are intending to use the engine in a bike  :)  :)  :ThumbsUp:  :wine1:

I have very limited experience of two strokes however I will be following and learning  :thinking:
Best regards

Roger

Offline Lew Hartswick

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Re: Triple 2 stroke SPE FS3
« Reply #7 on: May 27, 2022, 10:29:20 PM »
Shades of my Berkley from the 60's :-)  That was neet little car. Till it got "squished" between a bridge side and a big old Mecury. :-(

   ...lew...