ESE's works engine tuner

[husaberg]

Sorry if this was asked already... Jan and Frits, what was the reason the 250ccm 2 cylinder gp engine had 2 crankshafts? the engine would have been much more simple if it had only 1 crankshaft. but you knew that back then of course and decided to make it a 2 crank engine nevertheless. why?

Frits and Jan forgive me for speaking out of turn

The two single cranks can be contra rotating resulting in better balance without the need for a balance shaft.
Two single crankshafts are also likely easier to service as well as not having a large rocking couple a wide spaced single crankshaft would have.
They can also have a simpler ignition system as they both fire at the same time
Also with a single crankshaft engine both carbs can be on one side. This can make it easier for servicing and well as packaging a decent airbox
Additionally when the tandem Rotax was converted to a V formation the weight distribution improved as it could be mounted further forward with its rear facing front exhaust.
It could also use many already in use, Rotax parts. A big consideration for a small factory.


Also here are two further pics that might better illustrate Jans story.

[Frits Overmars]

Frits and Jan forgive me for speaking out of turn.

I didn't even know there were turns Husa. Besides, I welcome a bit of anarchy. And you're absolutely right on all accounts.
But allow me to stipulate one drawback of both the Rotax tandem-twin and the Aprilia V-twin: the vertically split crankcases make working on them a lot harder than horizontally-split cases would. Especially the first Rotax engines with their shrink-fit/press-fit crankshaft ball bearings were a pain.

[jamathi]

Jamathi:
In the picture where someone is holding a exhaust flange there is a pipe attached to the flange. Was this an attempt to cool that flange?
Also keep the thoughts and insights flowing. Great information.

No, that was the attachment for the exhaust temperature sensor.

[Niels Abildgaard]

Frits and Jan forgive me for speaking out of turn

The two single cranks can be contra rotating resulting in better balance without the need for a balance shaft.
Two single crankshafts are also likely easier to service as well as not having a large rocking couple a wide spaced single crankshaft would have.
They can also have a simpler ignition system as they both fire at the same time
Also with a single crankshaft engine both carbs can be on one side. This can make it easier for servicing and well as packaging a decent airbox
Additionally when the tandem Rotax was converted to a V formation the weight distribution improved as it could be mounted further forward with its rear facing front exhaust.
It could also use many already in use, Rotax parts. A big consideration for a small factory.


Also here are two further pics that might better illustrate Jans story.

The 258 drawing is only 23 kB and very difficult to read?

[husaberg]

The 258 drawing is only 23 kB and very difficult to read?

You may need new glasses its also in Austrian
It was all there was on the Net sorry.
http://www.artmotorsport.com.au/new/...nual%20Pt1.pdf
There are plenty of pics here of the crankcases
including a scaled down wood pattern someone made for 50cc cylinders.

https://www.kiwibiker.co.nz/forums/a...p?albumid=4839

https://www.kiwibiker.co.nz/forums/a...5&d=1413591174
https://www.kiwibiker.co.nz/forums/a...6&d=1413591175
https://www.kiwibiker.co.nz/forums/a...9&d=1413021975

[Niels Abildgaard]

I could have done even better with the original Hoeckle-drawing of that crankshaft but I lent it to a friend who is building a 50 cc V-twin.
Attachment 330075 Attachment 330076 Attachment 330077

Thank You for very clear pictures.
I wake up every morning hoping that somebody has seen the shining ligth and made a 50 ccm V2 with a one throw crank ,one carb and crankcase.
I will either have to make it myself or get very old.
Maybe making a 100ccm is easier.
Can one find reasonably powerfull(up to date) 50 ccm cylinders,pistons and exhausts without silly money and where?

[husaberg]

Can one find reasonably powerfull(up to date) 50 ccm cylinders,pistons and exhausts without silly money and where?

09 onwards KTM50

[jamathi]

[QUOTE=Martin1981;1131040981]Sorry if this was asked already... Jan and Frits, what was the reason the 250ccm 2 cylinder gp engine had 2 crankshafts? the engine would have been much more simple if it had only 1 crankshaft. but you knew that back then of course and decided to make it a 2 crank engine nevertheless. why?

I did not design this engine, nor did Frits.
It was Aprilia who wanted their 'own' engine.
The designs and the engines were made by ROTAX.
I still consider a V engine with a single crankshaft as the best solution!!

[jamathi]

[QUOTE=jamathi;1131041110][QUOTE=Martin1981;1131040981]Sorry if this was asked already... Jan and Frits, what was the reason the 250ccm 2 cylinder gp engine had 2 crankshafts? the engine would have been much more simple if it had only 1 crankshaft. but you knew that back then of course and decided to make it a 2 crank engine nevertheless. why?

I did not design this engine, nor did Frits, who never worked for Aprilia.
It was Aprilia who wanted their 'own' engine.
The designs and the engines were made by ROTAX.
I still consider a V engine with a single crankshaft as the best solution!!
Much more compact, less friction losses and vibration free!
And lighter....

[Niels Abildgaard]

09 onwards KTM50

Thank You and have found a dealer 150 km away.After easter.

[jamathi]

The original ROTAX tandem gave 62HP 'out of the box' in 1981.
So you can see a 31HP cylinder on the left, and a 53HP cylinder on the right.

[jamathi]

I discovered that making the underside of the transfer ports even with the piston in BDC
was very important: considerably more power, less detonation and far better piston cooling.
We started to have the exhaust ducts CNC machined in 1999 I think.
But first we had to overcome the new fuel regulations in 1998
102 octane had to be used instead of 130 octane.
We expected BIG problems.....
But within a couple of month's we had more power than before!
The compression ratio was lowered from 19,5:1 to 16:1
And the tailpipe restrictor was made 0,25mm bigger.
Then a very serious combustion chamber development was started.
The result was that parallel squish was the best, with a squish height of 0,75mm
Less squish height would give more torque but less revs.
At 0,45 the piston touched the head....
Then a head insert with a much wider squish band (50% of cylinder surface) was tried.
And that proved to be the final touch.
We now had more power than with the 130 octane fuels, and less problems.
The sharp edge between combustion chamber and squish band proved to be very important.
Even a small radius would give 0,5HP less..

[jamathi]

Transfer ducts.

Many transfer ducts with small differences were tried.
We found more power by enlarging the A-port in the direction of the exhaust.
Only the lower half, but it was important to give the A-duct an inclination away from the exhaust!
The ducts were very conical, the smallest point being the port.
In and outside walls of the ducts had a constant radius from top to bottom.
The flow remained attached to the inside radius and so cooled the piston and eliminated detonation.
Flow bench testing and the Jante type testing proved useless for power improvement.
Giving the rear side of the B-duct an inclination versus the middle of the cylinder gave a big improvemet

[jamathi]

Pistons:

We had cast and forged pistons.
Cast pistons gave slightly more HP, but sometimes cracked.
0,8mm piston rings gave more HP than 1mm rings.
As the auxiliaries and transfers overlapped each other a certain power los was caused by this.
So closing the pin hole in the piston was tried.
There were many solutions that were tested, but they all caused some trouble.
In the end the best, and most reliable, solution was welding then closed.
This was very well done by PANKL in Austria, and never caused any trouble!

[Peter1962]

Was that Garelli the one with the washer/shim labyrinth seal that you posted earlier?

I think you are referring to the JBB 250 cc.
http://www.50c.nl/Archief%20Ton%20Ko...JBB/index.html