[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

Jan, When you modified the B port duct with epoxy to direct the flow more centrally (before you modified your casting moulds), did the epoxy stay put during a race situation or did you just test the epoxy on the dyno? I want to try this modification but I am afraid the epoxy will detach and cause grief. Was there a certain type of epoxy that worked best? I have used Devcon aluminum putty and liquid aluminum with limited success. I have also tried JB weld. It seems all eventually work loose despite my best etching and roughening of the aluminum.. Welding in the port would be next to impossible.

Nombre de messages : 28 Localisation : Slovenia Date d'inscription : 19/03/2012

Howard, if I may add my experience with epoxies;
I also found that the usual aluminium-filled epoxies stick relatively poorly to the surfaces.
One very important thing about epoxies is post-curing. Room temperature cured epoxy softens at relatively low temperatures (glass transition temperature; Tg, around 40-60°C, depending on type). So they require post curing, that means keeping the epoxy heated at higher temperatures for a certain time. Keeping the epoxy at 100°C for about 3-5 hours will rise substantialy the Tg.
The best working epoxy for me is Loctite 9492. I even repaired the exhaust duct (I cut a hole into the water jacket). With filling the transfers I had no problems at all trough the whole race season.

Regards.

Howard Gifford a écrit:: Jan, When you modified the B port duct with epoxy to direct the flow more centrally (before you modified your casting moulds), did the epoxy stay put during a race situation or did you just test the epoxy on the dyno? I want to try this modification but I am afraid the epoxy will detach and cause grief. Was there a certain type of epoxy that worked best? I have used Devcon aluminum putty and liquid aluminum with limited success. I have also tried JB weld. It seems all eventually work loose despite my best etching and roughening of the aluminum.. Welding in the port would be next to impossible.

At Aprilia we had a very good epoxy, called 'stucco verde' in Italian.
Never worked loose and even withstood replating!
Sorry I do not know were it was made!

XpTpSMTT a écrit:: yes,I have found the importance of ring gap the hard (and expensive)way!
But still 0,3mm seems large
(???),does it have to do with the breaking in of the new piston and cylinder
or lack of?How was it done(braking in)
What should the correct gap be then for 67mm bore?steel rings.

Thank you for the advance curve,it says 100% throtlle
Was it corrected from the TPS reading or other factors?

(edit:eg for smooth acceleration inside corners)

Braking in was done on the dyno, 3 minutes full throttle at 10000 rpm. followed by 30 seconds at 12000

Less than 0,3 mm gap would break the ring.

There were different ignition settings for part throttle.
I think more advance was used.
There was no way of avoiding part-throttle detonation through the ignition setting.
As it was 'auto-ignition'

Jan Thiel a écrit:: [There was no way of avoiding part-throttle detonation through the ignition setting.
As it was 'auto-ignition'

Hi Jan

I have never thought of it like that before. I had always assumed detonation (either part or full-throttle) was initiated by the sudden rise in pressure once the sparkplug had fired and ignition commenced and that retarding the ignition would tend to reduce that detonation.

Of course I have always noted that changes in piston (flat or dome), transfer port design, squish band design and clearance, compression and fuel quality also have major effects on onset of detonation.

This way of thinking might explain some problems I had been puzzling over.

Many thanks for provoking my thoughts . . . . again!!

Best Regards

Ian

"At Aprilia we had a very good epoxy, called 'stucco verde' in Italian.
Never worked loose and even withstood replating!
Sorry I do not know were it was made!"

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I tried to search this resin too but the problem is that in Italian "Stucco verde" just mean "green resin" so the search is quite difficult!! 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 809262

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 809262

I can't find the green stuff but the Titanium putty from Devcon works perfect too .....
Wink

ridley a écrit:: "At Aprilia we had a very good epoxy, called 'stucco verde' in Italian.
Never worked loose and even withstood replating!
Sorry I do not know were it was made!"

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Yes, that's it!

Ian Harrison a écrit:

Jan Thiel a écrit:: [There was no way of avoiding part-throttle detonation through the ignition setting.
As it was 'auto-ignition'

Hi Jan

I have never thought of it like that before. I had always assumed detonation (either part or full-throttle) was initiated by the sudden rise in pressure once the sparkplug had fired and ignition commenced and that retarding the ignition would tend to reduce that detonation.

Of course I have always noted that changes in piston (flat or dome), transfer port design, squish band design and clearance, compression and fuel quality also have major effects on onset of detonation.

This way of thinking might explain some problems I had been puzzling over.

Many thanks for provoking my thoughts . . . . again!!

Best Regards

Ian

Thank's for your nice reaction Ian!
It gives me some relieve on a difficult day.
Sometimes I think all I did during my life was totally useless!

Jan, your work is totally not useless!! Unfortunately some persons wanted to kill 2 strokes since few years but all the works you have done is very important and interesting for people who really know and love 2 strokes like many persons who comme on this forum and thread from all the world every day.

I wonder like many others here that the 2 stroke will return at the highest level of competition and your work will be very usefull for this.

Many thanks to you and Frits for your knowledge exchange!!

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 1993206895

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 1993206895

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 199739

Nombre de messages : 55 Localisation : Germany Date d'inscription : 20/02/2012

How many of the people who read this thread do write in it? I guess they are less than 1%... What I want so say with it: A MASS of people is reading all your information quietly and gets very happy about that. And what is more useful than making people happy? 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 771973

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 771973

julien #41 a écrit:: I wonder like many others here that the 2 stroke will return at the highest level of competition and your work will be very usefull for this.

Even if they don't come back, the work and its story is beautiful. If we wait long enough, everything becomes outdated, but the things that come later could not have come without the earlier work. 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 241515

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 241515

(that would be three cheers)

Daniel A. a écrit:: How many of the people who read this thread do write in it? I guess they are less than 1%... What I want so say with it: A MASS of people is reading all your information quietly and gets very happy about that. And what is more useful than making people happy?

NOTHING in the world!

Thank you.

In our type of racing two strokes are alive and well. The manufacturers are pressured to get emissions down and BRP (Rotax) has succeeded in using direct injection in a snowmobile giving it superb fuel efficiency, light weight, and reliable whilst reducing the emissions below a foul stroke and exceeding any foul stroke power output.
The racing end of our sport still use full race prepped two strokes with carburetors. The information I have learned on here is so valuable you wont believe it and I am so appreciative.
I just hope my competition has not found this forum. 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 116295

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 116295

Never useless Jan to share freely passion knowledge and experience and yes reading this topic make me so happy you learn me a lot and also how much i screwedup massively in many time even if the engine i work on was for MX
So definitly 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 241515

Dernière édition par Marc le Mer 3 Oct 2012 - 20:37, édité 1 fois

Are you kiding, Jan?
Do you realy think that your work is useless, even today?

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1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 1993206895

Nombre de messages : 37 Localisation : Hellas Date d'inscription : 08/02/2012

Jan Thiel a écrit:: .........
Sometimes I think all I did during my life was totally useless!....

Generaly speaking,if what you did in your life was totaly useless then many(but MANY) ,including me,must go throw ourselfs off a cliff.... lol!

The point is,did you enjoy the ride?

"stucco verde"the most popular search on the internet the last couple of days!!

Sujet: Useless - never Jeu 4 Oct 2012 - 2:15

Hi Jan,
The hardest critic in a man’s life is himself - but he is an unfair judge as he sees only a one sided view of his life and that from his own basis and unfulfilled dreams.

The best judge of a man’s life is what he leaves after he is gone; his legacy to the world – is it a better place because of him and has he improved his fellow man’s enjoyment of life?
From my point of view, I am better for having met you on this forum and reading about your knowledge of two strokes has improved my enjoyment of this life.

Thanks to you and Frits for generously sharing your knowledge with all of us. 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 241515

Best regards
Allan.

Sujet: conrod Ven 5 Oct 2012 - 16:17

I have a question:

witch longer the conrod to do in the RSA engine?

Bruno

Nombre de messages : 62 Localisation : Denmark Date d'inscription : 12/02/2012

MINGRET01 a écrit:: I have a question:

witch longer the conrod to do in the RSA engine?

Bruno

Have you tried the search funtion?

This has already been covered. It's 120 mm.

Nombre de messages : 1 Localisation : Germany Date d'inscription : 08/12/2011

Daniel A. a écrit:: How many of the people who read this thread do write in it? I guess they are less than 1%... What I want so say with it: A MASS of people is reading all your information quietly and gets very happy about that. And what is more useful than making people happy?

I agree.
Many thanks to you and Frits.

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 241515

Mic a écrit:

MINGRET01 a écrit:: I have a question:

witch longer the conrod to do in the RSA engine?

Bruno

Have you tried the search funtion?

This has already been covered. It's 120 mm.

Originally it was 115.
Due to insufficient flow between crankshaft and cylinder it was lengthened to 120.

Frits I have a question regarding inlet diameter versus carb diameter. My new rotary design used a large disc with big ports centered on the con rod The carbs are restricted to 34 mm. My thought was a big port where the disc is located would flow more air but the airflow (and power) actually went down. I suspect the big port slowed down the velocity and increased the case volume too much. I am ready to cut new ports in version 2 and I want to have your opinion. My thought is to give the port a slight taper starting at 34mm at the carb tapering out to 36mm at the plate and ending at 38mm where it enters the case. My plan is to leave as much material as possiblre in the case and just radius the end where it enters the case. Your thoughts would be appreciated.
1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 55116

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 13 55116

Don't worry about inlet velocity slowing down, Howard. It's not velocity you want, it's mass transport. If you enlarge the duct cross area by 10% and you lose 9% flow velocity, you are gaining. However, if there are sudden cross area changes in any duct, flow resistance will increase due to turbulence. In a static flow situation a duct widening at 8° would be optimal, but there is no such thing as a static situation in a combustion engine.
In your case, with the small carbs you are obliged to use, making the complete inlet tract as short as possible is paramount. And once the flow has passed the inlet disc, offer it some room to pass around the con rod. Don't worry about a large crankcase volume. As long as that volume is concentrated in one easily-accessed area (above the crankshaft and in the transfer ducts) and not scattered in nooks and crannies (cavities between crankshaft bearings and oil seals are a frequent spoilsport), the larger the better.

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