[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

Frits Overmars a écrit:

Yes.

in our kart 125cc engines there was always sayd that a lower balncefactor gives more power in high-revving engines and higher balncefactor lets stard the engines with the power already in lower rpm. this is all nonsense?

thanks manuel

Yes Oui Ja Jawohl Sì Kyllä Taip Da Vαί Tak Sim Po Tau Ya Wi Iva Imo Ano Evet Igen Да Ndiyo Vâng יאָ! ใช่ 是 כֵּן! نعم हां ಹೌದು はい 예 होय ஆம்

Frits Overmars a écrit:

Yes.

thanks Frits

then I just have to find the right balance factor for the inclination of the cylinder that I balance the vibrations as best as possible.

thanks a lot.

Frits Overmars a écrit:

Jan Thiel a écrit:

22 years ago I had an interesting experience. Working on a certain engine we had crankshafts with 20 and 22mm crankpins.

That must have been the Rumi engine. But didn't we use a 24 mm crankpin then, Jan?

I did not want to mention the bastard's name Frits!
The most dishonest person I met in my life....

Yes, maybe is was 24mm.
There was insufficient material on the outside of the big-end hole in the crankshaft.
It seems that the crankshaft, when it was new, was stiffer than the crankshaft with the 20 mm crankpin.
After some running this stiffness 'went away' and the engine gave less power!
Studies at Aprilia later revealed that a crankshaft is only really stiff 1 time.
The first time it is put together, later it loses stiffness, and consequently power!

Merci Mr. Bruneau

English translation is:
In the picture presented by Francis: the first left crank with rods and two Yamaha cast segments for sealing, so dynamic labyrinth seal.
right before the latest version with rods fabrications made ​​by myself, is sealed by two thin steel rings and crank pin diameter 24 mm.
above (removed) the latest version with rods Honda (gp 3 cylinders) and ditto edited segment.

The first version of which the vertical cylinder in the other direction, exhaust back. Question for Fritz: we lose power in this case? the rear or transfer it is less filled because the crankshaft is not rotating in the direction of filling the transfer

Riley Will a écrit:

two Yamaha cast segments for sealing,

In French, a piston ring is a segment. I think JBB is saying he used Yamaha iron piston rings as the sealing element...

JB : j'ai bien compris, ce sont des segments de piston que tu as adapté ?

GrahamB a écrit:

Riley Will a écrit:

two Yamaha cast segments for sealing,

In French, a piston ring is a segment. I think JBB is saying he used Yamaha iron piston rings as the sealing element...

JB : j'ai bien compris, ce sont des segments de piston que tu as adapté ?

Pas exactement. Ce sont des lamelles Fey, des segments pour étanchéité par labyrinthe, pour l'industrie.

Jan Thiel a écrit:

Frits Overmars a écrit:

Jan Thiel a écrit:

22 years ago I had an interesting experience. Working on a certain engine we had crankshafts with 20 and 22mm crankpins.

That must have been the Rumi engine. But didn't we use a 24 mm crankpin then, Jan?

I did not want to mention the bastard's name Frits!
The most dishonest person I met in my life....

Yes, maybe is was 24mm.
There was insufficient material on the outside of the big-end hole in the crankshaft.
It seems that the crankshaft, when it was new, was stiffer than the crankshaft with the 20 mm crankpin.
After some running this stiffness 'went away' and the engine gave less power!
Studies at Aprilia later revealed that a crankshaft is only really stiff 1 time.
The first time it is put together, later it loses stiffness, and consequently power!

This topic intrigues me, I would like to know more about the fit tolerances. Possibly the yeid strength of the crank material is indirectly exceeded.
Example a Conrod bolt MUST only be tightened to its maximum permissible torque value and NO greater, while the bolt is able to cope with a greater tightening torque value in a staticly loaded application it can not survive in a dynamically loaded environment. The additional loads of the piston, pin, conrod, ring propelled about at TDC on a 4stroke engines exhaust stroke will try to pull the bolt apart, if it is tightened correctly it will survive as intended, if it is over tightened the additional loads will exceed the bolts ultimate tensile strength resulting in the bolts failure quit quickly.
2stroke guys tend to want a really tight fit for the crank pin, I'm sure if the fit is to tight the same Conrod bolts excessive material loading will result,
Jan & Frits what sorts of fit tolerances have you used on various engines such as the RSW, RSA, RUMI, ETC and what materials were used for crank wheels

Ah, OK merci... le "Yamaha" s'est déplacé entre les bielles et les segments chez Google...

So, human version:
The earlier crank on the left had two Yamaha rods and cast-iron sealing rings to create a dynamic labyrinth seal.A second version used rods welded up by JBB. The final version used rods from the Honda RS500 triple, with thin steel shim labyrinth seals, made by Fey for industrial use.

Probably still approximate because a tablet is suboptimal for multi-page browsing... so my apologies for mangling JB's explanation.

hi frits and jan. thanks for sharing your knowledge. i learn more in 1 month here than 5 years at other sites  . i was thinking to weld my exh duct at the end so theres a step where it meets the flange (old ktm engine). do you think this would be worth the effort ? hoping you can give me advice before i try it

Hi there, Brokedown, welcome here.
How old is this old KTM of yours? Are you talking about a road racer or a dirt bike? Is the cylinder capacity 50, 65, 85, 125, 150, 250 or 300 cc? See my problem?
Anyway, neither Jan nor I have data about these bikes, so it is impossible for us to give you a decent advice; sorry.

well thnx for the responce frits. its actually ktm dirtbike 500cc. mostly in the previous question i was just wondering if a step transition to the exh manifold would work eqaully good for all high performance 2t engines. yamaha and honda has used it on some dirtbike engines but other manufacturers havent, so im suspicious if it can work well on every engine. i hope im not mistaken but i thought the rsa125 has this step transition. but i see on your FOS cylinder it doesnt appear to be the same. unless your cylinder will also have a step transition with a slightly larger pipe diameter where it mates to the end of the exh duct ??

i guess the best thing for me is to try it and see. if it losses power i can just grind out the weld back to original shape

brokedown a écrit:

well thnx for the responce frits. its actually ktm dirtbike 500cc.  mostly in the previous question i was just wondering if a step transition to the exh manifold would work eqaully good for all high performance 2t engines. yamaha and honda has used it on some dirtbike engines but other manufacturers havent, so im suspicious if it can work well on every engine. i hope im not mistaken but i thought the rsa125 has this step transition. but i see on your FOS cylinder it doesnt appear to be the same. unless your cylinder will also have a step transition with a slightly larger pipe diameter where it mates to the end of the exh duct ??  

i guess the best thing for me is to try it and see. if it losses power i can just grind out the weld back to original shape

The step transition is not so important.
What is important is reducing the exhaust duct volume.
Best done at the underside.
Will give an improvement on most 2stroke engines.
Better than welding is making an insert and fix this somehow.

Jan Thiel a écrit:

The step transition is not so important.
What is important is reducing the exhaust duct volume.

Hello Jan,

And is it possible, that the step transition could take away power in some cases?

For example: I have a 100cm³ engine without auxiliary exhaust ports (and thus relative low blowdown) and an exhaust duct diameter of 25mm. This area is already bigger than the blowdown area, so of course I don't want to make it bigger to keep the duct volume low.

The FOS exhaust concept suggests an exhaust begin diameter of 31mm. Should I use these 31mm for the exhaust resulting in a step transition from 25 to 31mm or should I use 25mm for the exhaust, too?

In my opinion 25mm exhaust begin diameter should work better than 31mm, because of the better flow. But I'm not really sure.

Regards,
Daniel

Jan Thiel a écrit:

Mic a écrit:

Jan Thiel a écrit:

For the RSA125 a 22mm crankpin was chosen by the technical director, against my will!
He also decided on the very troublesome 8 mm disk drive shaft!
Now he is expected to resolve all Ducati's problems!
Of course I wish him good luck!

Crazy of Gigi Dall'Igna not to listen to the guys with the knowledge

The reason was that he did not want 3 main bearings, like the RSW had.
All I can say about that is that we tried the RSW without  the 3rd bearing a couple of times.
In this condition it always gave less power!
Because the 3rd bearing made the crankshaft flex less!
The most logical thing to do, I thought, was to fit 4 main bearings.

22 years ago I had an interesting experience.
Working on a certain engine we had crankshafts with 20 and 22mm crankpins.
With a 22mm crankpin there was a LOT more power.
After some track time I repeated the same test again.
The power difference had disappeared completely!

Was crank flex, why you did the crank trigger on the crank wheel of the Derbi and RSW?
or was it just for packaging reasons?
[Vous devez être inscrit et connecté pour voir cette image][img(50%px,50%px)][Vous devez être inscrit et connecté pour voir ce lien]
I recall the works BSA triple ran a quill drive to calm down the erratic timing with the whip of the crankshafts.

The pic of the Piston ring crank seal on the JBB gave me a giggle as i had posted something elsewhere with the DKW350 triple,
[Vous devez être inscrit et connecté pour voir ce lien]
That had similar seals,   It was meant to be worth 2hp compared to the std seals on a 250 Greeves back in the day, Herman Meier also used them on the works Arrow at the TT, Teflon i guess would be just as efficient these days.http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=288171&d=1380762814

Daniel A. a écrit:

Jan Thiel a écrit:

The step transition is not so important.
What is important is reducing the exhaust duct volume.

Hello Jan,

And is it possible, that the step transition could take away power in some cases?

For example: I have a 100cm³ engine without auxiliary exhaust ports (and thus relative low blowdown) and an exhaust duct diameter of 25mm. This area is already bigger than the blowdown area, so of course I don't want to make it bigger to keep the duct volume low.

The FOS exhaust concept suggests an exhaust begin diameter of 31mm. Should I use these 31mm for the exhaust resulting in a step transition from 25 to 31mm or should I use 25mm for the exhaust, too?

In my opinion 25mm exhaust begin diameter should work better than 31mm, because of the better flow. But I'm not really sure.

Regards,
Daniel

25mm is very small for a 100cc
It would even be too small for a 50cc!
For a 125 40mm was used.
So use at least 31.
An idea could be to make your exhaust duct exit 25X31 oval.

hi jan. maybe you can make a book then we dont have no more questions everyday. what do you say ?      what i meen if you make a book we dont bother you everyday with more questions  

Jan Thiel a écrit:

The step transition is not so important.
What is important is reducing the exhaust duct volume.
Best done at the underside.
Will give an improvement on most 2stroke engines.
Better than welding is making an insert and fix this somehow.

Jan Thiel a écrit:

25mm is very small for a 100cc
It would even be too small for a 50cc!
For a 125 40mm was used.
So use at least 31.
An idea could be to make your exhaust duct exit 25X31 oval.

Hi Masters  

I'm following very attentively this thread since its beginning, and i would like to thank everyone here.

There, you told us that reducing duct volume is important but we need also a certain width, isn't it ?

I thought that the thiner is the duct, the more rpm it gives.
Is there some compromise between width and length ?
I imagined that the length was first influenced by undulatory or acoustic phenomena.

Besides if you advise a reduction at the underside I understand why the oval shape is the most appropriate (following the example of the mk pro race)
But why a reduction on this side ?

 

hi

Jan or Frits which measure has the perforated plate from the silencer in the RSA? (hole size and hole spacing). were there tested different dimensions or make this no difference?

thanks Manuel

jamathi a écrit:

An idea could be to make your exhaust duct exit 25X31 oval.

now that is a nice info! what would you recommend for 50 jan or frits?

koenich a écrit:

jamathi a écrit:

An idea could be to make your exhaust duct exit 25X31 oval.

now that is a nice info! what would you recommend for 50 jan or frits?

I made this comparaison for 50cc

[Vous devez être inscrit et connecté pour voir cette image]

In the back row of the class, from left to right :
Airsal 72cc Derbi int 24 ext 34
Top perf 86 cc int 30 ext 32
Top perf "pink" 77cc int 25 ext 28

In the front   
AM6 113 50 cc int 22 ext 25
Airsal sport tuned 50 cc, int oval 24x28 ext 28, is that the kind of idea that you suggest Jan ?
Derbi euro 3 int 25 ext 35

For this last one look how deep are the aux. exhaust's duct.
[Vous devez être inscrit et connecté pour voir cette image]


They are much more than a Pro race 50 cc oval 22x26 mm
[Vous devez être inscrit et connecté pour voir cette image]


What do you think about it ? It's remerber me the ktm sx 65 !
[Vous devez être inscrit et connecté pour voir cette image]

Whereas on the 50 cc CRX there is no step at all ! d 28 mm
[Vous devez être inscrit et connecté pour voir cette image]

Thanks for all the pics! The KTM one is a SX50, I have several of the Euro2 Conti's and yeah their outlet duct is big somehow...

Hello!

wow, this thread is incredible, it will take ages but I will read all 3 parts of it!! Reading here and there I've seen the technical content is really exceptional!!

On a side note, quite OT, could I ask You experts to take a look at my post here?
[Vous devez être inscrit et connecté pour voir ce lien]

Cheers,
Tony

Maverock a écrit:

...could I ask You experts to take a look at my post here?
[Vous devez être inscrit et connecté pour voir ce lien]

Been there, done that  .

Thank You! :)