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

Nombre de messages : 8 Localisation : Germany Date d'inscription : 19/08/2013

Hi everyone,

is this pocket instead of a straight line a DEA thing or was it part of the later RSA main exhaust?
Has anyone of you done some dyno testing on this?

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The experts will shortly tell you that it makes more power. It sure looks wrong to me, backwards, in fact. It looks like a place that exhaust gases coming around the abrupt edge of the port can go into a turbulent tumble in that pocket. But what do I know, LOL.

I think you are right smitty, but probably it is mechanically stronger!

Nombre de messages : 47 Localisation : SW Pa USA Date d'inscription : 01/06/2012

In 1999 Yamaha put out a paper testing different shapes of ports and in this paper they stated that widening the exhaust port this way gave a slight increase in both power and torque by helping reduce the flow coefficient.

jfn2 a écrit:: In 1999 Yamaha put out a paper testing different shapes of ports and in this paper they stated that widening the exhaust port this way gave a slight increase in both power and torque by helping reduce the flow coefficient.

Hi
Very interesting.
Do someone have thos papers per hasard?
Thx

Nombre de messages : 47 Localisation : SW Pa USA Date d'inscription : 01/06/2012

The paper # is SAE 1999-01-3333

jfn2 a écrit:: The paper # is SAE 1999-01-3333

You can buy it here: [Vous devez être inscrit et connecté pour voir ce lien]

Or get it free here: [Vous devez être inscrit et connecté pour voir ce lien]

Best Regards

Ian Very Happy

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

JanBros a écrit:: a general question to anybody who has some experience on the subject :
tuning a KR1S almost always ends with some day cylinders cracking arround the base where they are bolted on the crankcase.
they always crack first at the back, so people reinfocre the back like this :

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but then they possibly crack at the front :

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and at the front there is no space to weld something on.

I don't want to do any welding as it's expensive (entire cylindre will distored, needs to be trued and newly nicasiled. I want another solution that I can use cylinders as they are, so I came up with something like this :

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original conrods are 106mm, change them for 115mm rods from RD400, have a 9mm spacer under the cylinders, make brackets that bolt on top of the head with the cylinder head bolts and like that bolt them onto the spacer.

will a 9mm aluminium spacer be strong enough ?

I have recently seen cylinders that have cracked / broken the mounting lugs off. Every cylinder that has been spot faced so the nut will sit square / flat seems not to have an issue. Every cylinder with the nut against a as cast face has broken quite quickly

Nombre de messages : 351 Localisation : Belgique Date d'inscription : 05/12/2011

RAW a écrit:: I have recently seen cylinders that have cracked / broken the mounting lugs off. Every cylinder that has been spot faced so the nut will sit square / flat seems not to have an issue. Every cylinder with the nut against a as cast face has broken quite quickly

are you talking about KR1 cylinders or in general ?
no one with a stock KR engine has this problem, everyone going to 70BHP or more sooner or later faces this problem.

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

Well, I really should not comment, but nobody here is shy, sooooo........

Like we used to say in the early days when * many * things failed due to weakness / junky Coke can material........

Jap Crap !

Nombre de messages : 86 Localisation : Australia Date d'inscription : 05/05/2012

JanBros a écrit:

RAW a écrit:: I have recently seen cylinders that have cracked / broken the mounting lugs off. Every cylinder that has been spot faced so the nut will sit square / flat seems not to have an issue. Every cylinder with the nut against a as cast face has broken quite quickly

are you talking about KR1 cylinders or in general ?
no one with a stock KR engine has this problem, everyone going to 70BHP or more sooner or later faces this problem.

Cylinders in general with rough cast surfaces usually out of square

RAW a écrit:

JanBros a écrit:

RAW a écrit:: I have recently seen cylinders that have cracked / broken the mounting lugs off. Every cylinder that has been spot faced so the nut will sit square / flat seems not to have an issue. Every cylinder with the nut against a as cast face has broken quite quickly

are you talking about KR1 cylinders or in general ?
no one with a stock KR engine has this problem, everyone going to 70BHP or more sooner or later faces this problem.

Cylinders in general with rough cast surfaces usually out of square

We have the same problem with some CR250 02 mainly cylinders due to some releif pockets in the base of the cylinder
I have welded round the lug and filled the pocket with weld without issue of distorting cylinder bore but the gasket face must be remachined. Your cylinders have very tight radius in the corners which is a bad point and the lug is very short also not good.
Unfortunately the manufacturer had not design for the power to be increased which will allways give rise to extra stress. The cylinders that the nut sits on a cast area that is not flat will be causing a stress raiser as full contact
is not occuring. The Girddle as it has been called in the USA design you show has been used with good effect on the Rotax 257 engine as this also has a poorly designed cylinder.

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

you might try some low temp rod. i used it on mine. not because the cylinder was prone to cracking but so i could add additional ports and enlarge the ports that it currently has but in your situation it might work well for strengthening the stud pockets and i wouldnt think it would distort the cylinder. then again the girdle idea aint bad either and you wouldnt have to apply any heat to the cylinder

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

Age Old Truisms :

A new racing machine will soon become a liabilty.

A used racing machine is a liability.

Horsepower costs money.

Using horsepower is expensive.

Maintaining horsepower requires additional funding and greater expenses are to be expected.

RAW's idea that any bolt-hole should be spot-faced (and maybe then put light chamfers on the sharp edges of the holes) sounds right, but also maybe look at the thickness of the gasket. Way back in the earliest years of kart racing in the USA, Power Products engines were fast but tended to break flanges until they stopped the rocking of their cylinders by going to thinner cylinder base gaskets. Cut shimstock as needed to retain port timing. My own favorite gasket material for a cylinder base usually is the paper in airline schedules, with a light coat of copper gasket spray.

I think, and have always thought, that fitting a cylinder to the crankcase at the underside
is wrong.
No combustion forces should act on the cylinder!
Please take a look at the MBA solution.
That is the ideal way.
Except that the bolts should be at the outside wall.
Like the 80cc Zundapp engine made by Herbert Rittberger.
Someone surely will have a photo....

I think, and have always thought, that fitting a cylinder to the crankcase at the underside
is wrong.
No combustion forces should act on the cylinder!
Please take a look at the MBA solution.
That is the ideal way.
Except that the bolts should be at the outside wall.
Like the 80cc Zundapp engine made by Herbert Rittberger.
Someone surely will have a photo....

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

Like dis ?

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I thought he meant having the cylinder block and half of the case as a single piece down to where the case splits over the centerline of the crankshaft (Konig 4-cylinders were like this) . . . .

seattle smitty a écrit:: I thought he meant having the cylinder block and half of the case as a single piece down to where the case splits over the centerline of the crankshaft (Konig 4-cylinders were like this) . . . .

Jan certainly did not mean a cylinder block and a crankcase upper half as a single piece.
That would be much too cumbersome when working on the cylinder.

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

Yes Sir, unitized would be a bear.

Unless Dremel can build me a better mouse trap, I'd have to send that port job to brokedown.

God guiding the handles, one good candle and a Dremel an' a chisel has always worked for me, but a man must know his limitations.

Hey, the pros DO still use a Dremel, right ?

No, that would be completely crazy!

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system? I have heard rumors such engines have been made before however they were probably made before my time. If anyone can provide a specific example or recall how well they worked I would be very interested in learning more.

I'm pondering a big bore two-stroke design and don't think I can get enough intake area into the crankcase itself.

Oh, duh, I see now that he must have just meant get rid of flange bolts. (sigh!)

» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)