[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

Thank you for your reply Frits and happy late Christmas for everyone!

Soo that wasnt a too bright idea

Btw I am riding a 1975 50cc Jawa scooter, Its a pretty old construction (air cooled cylinder with cast iron sleeve and the trnsfers are lacking an inner radius)  I try to tune and optimalise it for road use only no competition. In Czech republic theres an offroad and GP championship tho, A frend of mine who is a silent follower of this thread managed to get 17000 rpm of it, no dyno test so the HP is a mistery.

The reason why I am interested in YEIS is because I would like to try it on my am6 reed valve cylinder that I am building with my friends help, 38mm bore 44mm stroke  (just like a simson engine) 122* transfer and 171* exhaust. Exhaust port width 0,7xbore.  Originally it has only 2 transfer ports I added +1 12mm wide port to it,
But I may have messed it up already with my funky intake port,

Originally I planned to make one rectangular intake port and two cylindrical sub ports leaning towards the end of the cylinder, but then I decided to maximalise the intake port area so I made those sub ports rectangular shape and I ended up with a T in the middle of my intake port......
Do you think it would break?  its 3x4mm  with radiuses,

Should I leave it like it is or should I take it off?   The reason I didnt take it off is that I couldnt make a nice radius to the end of the port (I ran out of material )  Or could it help to grinnd it back a little bit like they use to do with the exhaust port divider?

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If I would do it over I would make a longer rectangular intake port with a nice radius on the bottom side.

thanks for any advice and thanks for the MS-paint tip

I can't say if your 'T' will break, Eugen. I think it will be safest to leave it as it is now.
But I wonder about your gearbox. 171° exhaust timing is really not enough if you want to make any power. So unless you have a single-speed transmission, you might try 186° timing, maybe more.

The original gearbox is 3 speed, i upgraded it to a 5 speed so I could go big now :) Ill try 186* Thank you very much for your advice!

Hey! I would like to have another question .
I was wondering what is the best way to mount the crankshaft into the engine?

Some people use a tight press fit like fit between the crank and the inner bearing race,

some people grind the sahft ends 0,005mm undersize so the crank can slide into a classic ball bearings inner race so it can have a 0,4mm or so side-to-side float,

and some people use roller bearings which too allows for the crank to float side-to-side but I am not sure if the inner race is fitted with a tight fit(?)

thanks

Jenco a écrit:

I was wondering what is the best way to mount the crankshaft into the engine? Some people use a tight press fit like fit between the crank  and the inner bearing race, some people grind the sahft ends 0,005mm undersize so the crank can slide into a classic ball bearings inner race so it can have a 0,4mm or so side-to-side float, and some people use roller bearings which too allows for the crank to float side-to-side but I am not sure if the inner race is fitted with a tight fit(?)

Roller bearings with a tight fit for both the inner and the outer rings; 0,4 mm lateral float for a 125 cc engine.

The ONLY good way for crank bearings is applying NEEDLE bearings. You pay with a little more friction but the crank will behave much stiffer and squish control is an awful lot better. Why is evereybody still dreaming?

Hello Jan and Frits
Several engine manufactures told me the crankcases mold (like on Aprilia RSW) are better for the warmth dispertion. It is correct? If yes why the crankcases are billet on the Aprilia rsa?
Thanks in advance for your answer
KR.

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A non bead blasted crankcase that has not been painted black is not smart at all. Look at the Mohrenkopf of BMW in the 50's. Do know the history of your trade, dear fiddler boys. The same applies to cylinder heads and cylinders, whether aircooled or watercooled. My mate Jan Thiel got EVERY engine he worked on once
cooled from the building water system he worked in and he never saw better torque figures. Another smart way of cooling for short duration events is building a box around cylinder and crankcase and filled with dry ice. With development you need to think out of the box, most people cant and dont.
Enough food for thoughts today.. Get awake for good sake.

marlow a écrit:

His prices are ridiculous when you compare with $15 dentist kits

Do not look at the price, look at the quality. It will be a tool you will be proud of and will NOT let you down time and time again. Do NOT encourage the Chinese by purchasing their rubbish. Too much is bought 'on price' only and always regret it afterwards. All my apprentices have learn't not to hand me a Chinese spanner for they will never see it again, they are basically just land fill. Save up and buy quality tools, look after them!

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Hey Frits,

Roller bearings with a tight fit for both the inner and the outer rings; 0,4 mm lateral float for a 125 cc engine. a écrit:

Can you please explan me the advantages of it over using ball bearings?,
and what lateral float would be recommended for a 50cc and what does that depend on?

Thank you

I thought I would make my first post - thanks Jan, Frits and all for the contribution to these threads, they make interesting reading!

I am an undergraduate engineering student - in preparation for my thesis I am dissecting a particular twostroke engine to gather all internal an external geometric data.

The model below is an irregular stl mesh, though soon it will be converted into a standard feature based model.

See the below picture, can anyone guess the engine?  


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Honda EXP-2

dutch a écrit:

Honda EXP-2

I wish I had acess to Honda's exp-2 engine!

You're close though, it is actually the production 250cc engine (CRM250 AR)

A couple more pictures of the STL's

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and a picture of a cross-section slice :)

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After the EXP-2 Honda make the crm for the Brazilian market ( fuel Ethanol )

dutch a écrit:

After the EXP-2    Honda make the crm for the Brazilian market ( fuel Ethanol )

Brazil??

I thought the CRM250 was a Japanese market bike?

Sugarcane-based ethanol very big in Brazil

Cylinder Scan;

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Cross section view of ports;

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Nice job . It will give people a bit more insight in cylinder construction.

I wish I had a 3D printer for a lost wax casting...

Bentou,
1. All you need is a 3D printer.  Cheap these days.
2. Some wax filament:
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3. The software (eg Solidworks, Catia for you to show nationalism) etc and/or a solid model of the target design
4. The equipment and skill to produce the investment mould and then do the casting, yours or another

Let us know tomorrow how you went.  

bentou a écrit:

I wish I had a 3D printer for a lost wax casting...

May I suggest SLM (Selective Laser Melting)? Then you will have the cylinder directly in metal, no casting required any more
(minor problem: you will need a watercooled credit card).

In the UK is a SLM specialist company that offered me to do a cylinder for less that 1500 pounds sterling, about 2 years ago. I reckon this is interesting for serious people.

Jan Thiel just told me that he is considering selling a helmet that was given to him by Valentino Rossi in 1997,
the year that Rossi became a world champion for the first time. The helmet is signed by Rossi.