[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)

brokedown a écrit:: i think theres a couple different 64mm yamaha racing pistons. i have one with 15* dome angle. top edge of the wristpin to top edge of the piston is 38mm. wristpin diam is 16mm. top edge of the ring to top edge of piston is about 3.3mm. i dont have the rings but the top ring groove is about 1.25mm tall. bottom ring groove is about 1.5mm tall. groove depth is about 3.3mm. not sure if they have this piston in single ring version. also it has 2 square inlet windows.

Brokedown, hang on to those pistons of yours because I think you have got something unique there;
I haven't seen Yamaha racing two-stroke pistons with more than one ring since 1963.

Mestre,Could you not use the TZ piston with a 10mm cylinder base spacer?You may need longer cylinder studs,but they would be cheaper than custom pistons..Crankcase volume would increase also.[/quote]

Bonsoir de Normandie

It will be difficult , I have made a crankcase 4 mm higher than the genuine one for the conrods lenght and if I put 8 mm more it will be impossible to fit the engine in the frame !!!

Bonne soirée Jean-Paul

there is also a 64mm piston from ktm but i dont know anything about it [Vous devez être inscrit et connecté pour voir ce lien]

Bonsoir Brokedown

Yes this the one I use since 4 years with perfect results , but this is a flat one and I wish to try a domed piston .

A bientôt Jean-Paul

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

Frits or Jan, your opinions on this piston mod ?
I believe it to be an old attempt to change compression ratio's, stacking more or less plates ?

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

lol!

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

Mestre a écrit:: Bonsoir Brokedown

Yes this the one I use since 4 years with perfect results , but this is a flat one and I wish to try a domed piston .

A bientôt Jean-Paul

if you dont mind inlet windows you can try one of these yamaha versions. the dome angle is about 15*. vertex, prox, namura, wiseco, wossner, oem each make one.

JanBros a écrit:: Frits or Jan, your opinions on this piston mod ? I believe it to be an old attempt to change compression ratio's, stacking more or less plates ? [Vous devez être inscrit et connecté pour voir cette image]

Yes, this is an attempt to change the compression ratio, from zero to something above zero, because you can bet that there is an unintentional hole under that plate.

Tss Frits, the hole in there was for a better cooling in the kettle !!!

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

Frits Overmars a écrit:: Yes, this is an attempt to change the compression ratio, from zero to something above zero, because you can bet that there is an unintentional hole under that plate.

looking at all the carbon deposit on it, I believe it to be something more than above zero (but off course you are right about the hole). it must have run for quite some time like that .

Nombre de messages : 57 Localisation : DFW,Texas Date d'inscription : 15/11/2013

Wow.

Just when a guy thinks he's seen it all....

That has to be some of the finest N-gger-Riggin' ever !

And being from Texas, not to mention well-accustomed to all things Harley-Davidson, I have seen a bunch of Southern Engineerin' .

Or, thinking deeper into the past....

THIS might be what Roky Erickson, he a pioneer of 60's psychedelic music, had seen before he sang :

" Bedouins in tribes ascending from the egg into the flower ..."

Yep, the poetry of mechanical mayhem is unending & the road goes on forever.

Hi guys.

Here is some cross sections of a solex racing engine. My question is: would you modify the cylinder skirt to enhance the intake flow ?
Due to our rules (diameter 44 between cylinder base plate and crankcase), it is hard to lower the position of the reed valves so i have to keep it like that.
As Frits previously said, it takes five crankshaft revs for the intake flow to enter the cylinder. Considering that fact, should I worry about enhancing the flow in front of the skirt ?
[Vous devez être inscrit et connecté pour voir cette image]

Thanks

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

this is from today ! original ducts before i change them

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brokedown a écrit:: this is from today ! original ducts before i change them

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

Hi Brokedown,
Well it remains a lot to do, bad designed for me.
Try doing something like this.
[Vous devez être inscrit et connecté pour voir ce lien]
Good luck and good work.

Frits, thanks for your reply last weekend RE tz350 ex ports.
I would like some advice on where to locate the ignitech digital cdi box which has just been delivered. The loom is long enough to fit the cdi under the seat, this would keep the wiring up the front around the rev counter alot more neat and tidy. All modern road bikes two and foul stroke seem to do this.or, should it be mounted in the position of the original Hitachi box. This would shorten the length of all the loom, but have the traditional ' bids nest ' of wires under the rev counter.
Many thanks
Paul

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

Vortex a écrit:: Hi Brokedown,
Well it remains a lot to do, bad designed for me.

Good luck and good work.

yes they are a very bad design indeed. ill do the best i can but im afraid they cant be perfect. there simply isnt enough material to work with since its a twin cylinder cramped close together

how did yours release so well ? mine took some time to remove. maybe ill try some light oil on the duct walls next time

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

hi frits i have a question about a window divider. ive always thought a pointed leading edge was a bad idea but i wanted to see what you think about my idea. if the divider frontal edge is pointed then it seems like it would then become more of a air diverter. pushing the central portion of air towards the outside walls as it goes through the windows. in my mind that eqauls a less affective window because the air isnt simply flowing past the divider but its being diverted or pushed outwards. for that reason i was thinking the leading edge shape should be more round. do you agree with this ?

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

this is why i think a rounded shape would be better

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

Paul Gane a écrit:: I would like some advice on where to locate the ignitech digital cdi box which has just been delivered. The loom is long enough to fit the cdi under the seat, this would keep the wiring up the front around the rev counter alot more neat and tidy. Or should it be mounted in the position of the original Hitachi box. This would shorten the length of all the loom, but have the traditional ' bids nest ' of wires under the rev counter.

That 'bird's nest' might unintentionally function like a coil, which could cause strange interferences, so this may be a reason to put the electronics under the seat. But don't ever put anything behind the seat; each gram there will adversely influence the bike's handling.

brokedown a écrit:: hi frits i have a question about a window divider. ive always thought a pointed leading edge was a bad idea but i wanted to see what you think about my idea. if the divider frontal edge is pointed then it seems like it would then become more of a air diverter. pushing the central portion of air towards the outside walls as it goes through the windows. in my mind that eqauls a less affective window because the air isnt simply flowing past the divider but its being diverted or pushed outwards. for that reason i was thinking the leading edge shape should be more round. do you agree with this ?
[Vous devez être inscrit et connecté pour voir cette image]

I agree, Brokedown. But there is more to it than just the divider's round nose. Even more important is the fact that in your final picture the divider's flanks (the blue lines) are curved with a big radius and end up running parallel to each other.

Frits Overmars a écrit:: I agree, Brokedown. But there is more to it than just the divider's round nose. Even more important is the fact that in your final picture the divider's flanks (the blue lines) are curved with a big radius and end up running parallel to each other.

So my concern is close to this one. Considering my previous post, should I make some radiuses on my cylinder skirt edges ? Even reduce its height ?

patouille a écrit:: Considering my previous post, should I make some radiuses on my cylinder skirt edges ? Even reduce its height ?

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

Nombre de messages : 44 Localisation : Portugal Date d'inscription : 08/11/2011

I was going to ask about the double ramp with the dimple in the middle, but Mr. Frits replied first.

Nombre de messages : 56 Localisation : Austria Date d'inscription : 02/03/2014

After how many hours were pistons and rings usually replaced on the RSA/RSW engines?
Thanks for your time!

Don't bother on the divider on Banshee barrels , they are not restrictiv .....

Senne s a écrit:: After how many hours were pistons and rings usually replaced on the RSA/RSW engines?

Here you go Senne, like the title says: "All that you wanted to know on Aprilia RSA 125": [Vous devez être inscrit et connecté pour voir ce lien]

Nombre de messages : 56 Localisation : Austria Date d'inscription : 02/03/2014

Thanks a lot Frits! Really appreciate it!

Nombre de messages : 39 Localisation : Gironde Date d'inscription : 22/07/2014

Frits Overmars a écrit:

patouille a écrit:: Considering my previous post, should I make some radiuses on my cylinder skirt edges ? Even reduce its height ?

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

Hi Frits !

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

What goal to make these shapes ? Your opinion maters to me [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 22 809262

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 22 809262

(Sorry for my english) lol!

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