’Rolssi’ a 1936 vintage 4-stroke engine of Finnish origin.

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May I present you a 4-stroke model aero engine ’Rolssi’ a true Finnish classic originally designed back in 1936 at Vyborg Finland by Urho Purhonen and Aarne Heikkinen.

My friend and model engine builder colleague KalleR made the CAD model couple of years ago and built a fine example of this same design about a year ago. This is the second succesful replica of the original engine built. The build started in October and the first run of the engine was achieved first of February 2024.

Rolssi seems to be quite sound design given its age and is an easy starter and puts out over 0,2HP at around 6800rpms.

My example has ran now 8th times in total on a cdi ignition and future plans hold a proper vintage spark ignition with coil and points and also a vintage style period correct wooden propeller.

The performance with Master Airscrew 12x5 Scimitar propeller is 7000rpms (0.24bhp) and fuel consumption around 236ml/h!
 

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very nicely done, sounds good too. A good combination of casting and cutting from solid. The three gear setup is good as it avoids the need for helical gears that a lot of engines used which are hard to source or make .
 
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Nicely executed interesting design. Great result!
 
A nice model and interesting engine. Do you have plans and castings for sale? - Or can the crankcase, head, etc. be machined from solid? This design looks worthy of more than just your 2 models.
Congratulations!
K2
 
Crankcase is cut from solid in the video, only the head and conrod appear cast. Conrod would be fairly easy from solid but head would need a lot of fine handwork or the CNC if you wanted to fully replicate the fins etc
 


May I present you a 4-stroke model aero engine ’Rolssi’ a true Finnish classic originally designed back in 1936 at Vyborg Finland by Urho Purhonen and Aarne Heikkinen.

My friend and model engine builder colleague KalleR made the CAD model couple of years ago and built a fine example of this same design about a year ago. This is the second succesful replica of the original engine built. The build started in October and the first run of the engine was achieved first of February 2024.

Rolssi seems to be quite sound design given its age and is an easy starter and puts out over 0,2HP at around 6800rpms.

My example has ran now 8th times in total on a cdi ignition and future plans hold a proper vintage spark ignition with coil and points and also a vintage style period correct wooden propeller.

The performance with Master Airscrew 12x5 Scimitar propeller is 7000rpms (0.24bhp) and fuel consumption around 236ml/h!

That's got to be bigger than 6.28ccs?
 
What makes you think it is bigger Dick?

Another one not watching the video maybe?

Two times it can be seen that it is a nominal 20mm bore, stroke not given but would look to be about the same based on some other known sizes such as the tool bit shank so 20 x 20 just happens to be 6.28cc

Edit another one who can't see what the crankcase looks like. Pat's videos look to be the Monsun crankcase
 
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What makes you think it is bigger Dick?

Another one not watching the video maybe?

Two times it can be seen that it is a nominal 20mm bore, stroke not given but would look to be about the same based on some other known sizes such as the tool bit shank so 20 x 20 just happens to be 6.28cc

Edit another one who can't see what the crankcase looks like. Pat's videos look to be the Monsun crankcase
Oh my, you must be more careful what you say on line, someone (not me) might take offense. I quote you: "bigger Dick". Well I used to have one but in old age it shrunk. What a sad dissappointment.

Anyway, to answer your question, when a person is attracted to something, it SEEMS bigger than it really might be (for instgance "bigger ...."). So judging from the size of the person's thumb in the vid, It certainly ;looks larger than it apparently is. Also, I never saw explicitly the stroke (OMG, better be careful here, someone is SURE to take offense) nor the diameter of the cylinder.

As for my jokes, I hope you realize they are just in good fun. If not then we can start a war. LOL
 
Look at the DRO reading when the liner is being bored and also the calculations for the piston rings.

You only need the bore to work out the stroke if the capacity is given and 20mm looks to be about right based on other known sizes like the tool shank that I mentioned which is being used to support the crankshaft.
 
Thank you for the kind comments! Yes the bore is 20mm (19,96 to be exact) and the stroke is 20mm aswell. That I can’t easily measure more accurately. I know I drilled the offset turning jig right at 10,00mm mark to turn the crankshaft pin.

The case surely seems ’bigger’ as it has a lot of empty space inside! It is one of those features that I suppose I would do differently if re-designing this one (also the rockers being at 43 degree angle is a bit cumbersome) but as it is an as accurate replica as possible from the original engine that was designed in 1935-36 so we didn’t want to change those features. And as this was my first 4-stroke engine I have built, there was plenty enough to learn figuring out all these parts as is 😬

Regards
Olli
 

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Oh and yes the previously linked casting videos are of the Monsun build. That was my first time casting aluminium and I made those videos to hopefully help other newbies with casting. They are not that good in terms of technical quality but show the major parts of basic sand casting I hope.

On this one the head and the conrod was cast. I think the original used a machined head, atleast it was stated so in the only material Kalle had on hand to work with (an article from year 1972).
 

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