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

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

Op ebay USA zetten en de hoofdprijs vangen. Reserve op 5000 dollar.

hi...I have one small question about side rotary valve sealing... It is necessary for good sealing both oil seals as in the picture, or it suffices only oil seal 1 (in the picture)...in kreidler drawings looks that is only one oilseal... thanks
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# 1 is enough.

thanks

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

Just use INA needle bearing seals. Small, low friction and not expensive.

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

INA Dichtringe Baureihe G Buna S Gummi

Nombre de messages : 19 Localisation : UK Date d'inscription : 12/05/2013

Bob van der Zijden a écrit:: INA Dichtringe Baureihe G Buna S Gummi

Bob, I think you meant Buna N (NBR). It is oil and heat resistant, and good for oilseals.

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

You're right tjbw, I was wrong. Buna N is the correct quality.

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

hello

i remember that Jan said: in a cooling system it is best to have
a big radiator with a small amount of water and a pump that has a high l/h rate. and that is better to have the circuit under a good presure of ca. 1,8 bar.
(i hope i remember correct)

Is it possible to use this type of cooling system anywhere? (E.g. In a racing car 4 strocker)

thanks manuel

Manuel Rainer a écrit:: hello i remember that Jan said: in a cooling system it is best to have a big radiator with a small amount of water and a pump that has a high l/h rate and that is better to have the circuit under a good presure of ca. 1,8 bar (i hope i remember correct). Is it possible to use this type of cooling system anywhere? (E.g. In a racing car 4 strocker). thanks manuel

Yes Manuel.

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Frits Overmars a écrit:

Manuel Rainer a écrit:: hello i remember that Jan said: in a cooling system it is best to have a big radiator with a small amount of water and a pump that has a high l/h rate and that is better to have the circuit under a good presure of ca. 1,8 bar (i hope i remember correct). Is it possible to use this type of cooling system anywhere? (E.g. In a racing car 4 strocker). thanks manuel

Yes Manuel.

if i don't have a very high water flow, is it better to have more water capacity in the circuit or can we always say: better to have 3 (Big radiator, small Water volume and pressure) of the 4 (high water flow) then only 2.

thanks Manuel

Manuel Rainer a écrit:: hello i remember that Jan said: in a cooling system it is best to have a big radiator with a small amount of water and a pump that has a high l/h rate and that is better to have the circuit under a good presure of ca. 1,8 bar....

if i don't have a very high water flow, is it better to have more water capacity in the circuit or can we always say: better to have 3 (Big radiator, small Water volume and pressure) of the 4 (high water flow) then only 2.

The way you formulated that question gave me a headache Manuel.
More water capacity only means that it will take longer before a stable water temperature is reached. But how high this final temperature will be, depends on radiator capacity and flow velocity.
The function of pressure in the cooling system is to counteract local boiling and so avoid hot spots in the cylinder.

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

Frits Overmars a écrit:: The way you formulated that question gave me a headache Manuel.
More water capacity only means that it will take longer before a stable water temperature is reached. But how high this final temperature will be, depends on radiator capacity and flow velocity.
The function of pressure in the cooling system is to counteract local boiling and so avoid hot spots in the cylinder.

hello

excuse me firts. and thanks

now it's clear.
can we say it is not possible to have not enough water. if the cooling circuit is made efficient and it is full of water, it is enough. all extra volume addeth means that it will take longer before a stable water temperature is reached.

thanks manuel

Hi Jan and Frits. Some time back in this thread you mentioned that you had a static dyno for measuring engine power while changing timing etc but found that it didn't work.

I have a inertia dyno and am adding 100hp of brakes to it. I was going to be doing just what you trialed. My thoughts were that inertia dyno just doesn't get air cooled engines up to a stable temp, hence adding the load would improve things. I was going to monitor EGT and CHT while playing with timing and mixture. I may not get the best power out the motor on the dyno but if I can at least get a feeling for CHTs and EGTs with regard to timing and mixture, it will be a plus.

Any comments?

marsheng a écrit:: Hi Jan and Frits. Some time back in this thread you mentioned that you had a static dyno for measuring engine power while changing timing etc but found that it didn't work.

I have a inertia dyno and am adding 100hp of brakes to it. I was going to be doing just what you trialed. My thoughts were that inertia dyno just doesn't get air cooled engines up to a stable temp, hence adding the load would improve things. I was going to monitor EGT and CHT while playing with timing and mixture. I may not get the best power out the motor on the dyno but if I can at least get a feeling for CHTs and EGTs with regard to timing and mixture, it will be a plus.
Any comments?

Good thinking Marsheng. But much will depend on the capacity of your cooling.
Imitating the air velocity of a speeding bike will require a huge blower.

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

In order to get a good air supply apart from using a large blower the air from the blower can be made laminair and the engine tunneld. Not expensive but some more work Creating a laminair air flow can be achieved by making a plywood honeycomb structure.

Hi Jan and Bob

I accept that it may be difficult to match track conditions but my thoughts were,

Set the motor to bottom of the start of the power range,
Start with a low ignition advance, say 14 deg
Set a load and get the bike stabled.
Watch EGT and CHT and increase the advance.
I think at some point, the CHT will start to run away.
Note how many degrees you moved from stable to runaway.
Increase RPM by 1000 and repeat.
Start the whole process again with a different jet.

At the track, if I see the CHT rising, I now have an idea on how much to move the ignition or mixture.

Just typing this out is long, so it's going to be even longer in the dyno shed. !!!

Cheers Wallace.

marsheng a écrit:: ... it may be difficult to match track conditions... Set a load and get the bike stabled. Watch EGT...

Setting a load and getting the bike stabled is the complete opposite of matching track conditions, and will cause huge differences in the Exhaust Gas Temperature (better not assume that everybody is familiar with english technical abbreviations on this french-speaking forum, Wallace).

The problem I have is that I played with 2 strokes 45 years ago when I knew nothing. Now i have done a lot of reading and limited experimental time with my Macio 250 over the past 3 years.

I'm trying to learn a bit quicker than waiting for race days every 6 weeks or so and I would like to work on other 2 strokes so I'm hoping that the braked dyno is going to help me learn much more about cause and effect.

See here 1/2 way down the first page. My reasoning.

Dyno

Post number #8

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Apio Verde to you.

Hi Jan and Frits. I am building a rotary valve motor using as much of the RSA technology as I can. It is a twin cylinder Rotax 460 cc inline twin using a common rotary valve disc to control both intakes. I plan to run VM44 carburetors. Other engines I have seen have the port necked down to 42 mm. Is there justification to neck it down or do you believe that the inlet should be at least as large diameter as the carbs?

Howard Gifford a écrit:: Hi Jan and Frits. I am building a rotary valve motor using as much of the RSA technology as I can. It is a twin cylinder Rotax 460 cc inline twin using a common rotary valve disc to control both intakes. I plan to run VM44 carburetors. Other engines I have seen have the port necked down to 42 mm. Is there justification to neck it down or do you believe that the inlet should be at least as large diameter as the carbs?

I can see no reason to reduce the inlet diameter downstream of the carb, Howard, unless it's some rulebook requirement. In fact it helps if the inlet duct downstream of the disc offers a sudden cross flow area increase, by way of a step, opening at the trailing side. This step will act as an anti-reverse treshold when the disc is almost closing and the flow may try to reverse from the crankcase to the outside world.
By the way, the RSA used 42 or 43 mm carbs, on a 125 cc cylinder. This means that your 460 cc twin could do with a couple of 50 mm carbs....

Thanks Frits that's exactly what I thought. When designing the motor' is a square motor (bore vs stroke) the ideal or do you think slightly over square (longer stroke than bore) is better? The rules limit us to 460 cc and we can choose any bore / stroke combination as long as we don't exceed 460 cc. BTW what 50 mm carb would you recommend? Maybe a pair of Lectrons?

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