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

RAW a écrit:: Your assuming that those holes spinning about would have something going in & out of them the same as the cylinder does ( empty. Fill, empty ) I'm sure you can regard this Volume as non existent from a crankcase volume perspective, the centrifugal forces wouldn't allow entry. The disturbance about these holes may actually assist in the lubrication of the big end, but if substituting for a heavier rod then these may be of some use if filled to achieve a more conducive balance factor

Compensating for a heavier rod would necessitate bigger, not smaller or filled holes.
But your main point seems to be the centrifugal forces preventing mixture flow into the holes. Then what about oil flow into the big end?
You can calculate the centrifugal pressure and it is not nearly enough to prevent flow into and out of these holes.
But empty volumes at awkward places in the crankcase act as pneumatic dampers on the case resonance. Sharp-edged holes spinning around certainly qualify, so it's a good thing to close them.

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

Sorry Frits i was thinking bigger holes pluged but did convey this correctly, as to the oiling of the big end I assumed this wasn't a problem given it would be smashing into a mixture of elements before it as opposed to within a circular disc as per the shielded holes of the crank,
NOW the bit I was hoping you would clarify, the holes operating as a dampener, how much of a effect can this have ? If we had say 4 holes of 16mm diameter & 14mm wide or any size you wish to use for ease of reference Vs the same amount of volume increase at the case / barrel joint be it by a spacer plate and or gaskets.
I'm intrigued in the resonance side. Of this

RAW a écrit:: the holes operating as a dampener, how much of a effect can this have ? If we had say 4 holes of 16mm diameter & 14mm wide or any size you wish to use for ease of reference Vs the same amount of volume increase at the case / barrel joint be it by a spacer plate and or gaskets.

Impossible to say. It depends on the holes' shape (diameter, depth), their edges (sharp or rounded, and if so, with what radius), the clearance between the crank webs, the clearance between the webs and the case walls, the presence of other cavities (for example between bearings and sealings), the crankcase compression ratio, and so on.

Frits Overmars a écrit:: The column of mixture would be less tortuous and shorter, so the available pressure difference between cylinder and crankcase could accelerate it to a higher flow velocity and 'pull the mixture apart' less; its density would remain higher, so you would get more mass into the cylinder.

Is my memory correct, that shorter ducts get the flow started earlier? With the mixture at a higher density and more mass should have the effect of running richer?

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

hi frits what do you think the best way i can plug them large holes ? i heard of people using cork and some type of resin. for example if the hole is 20mm wide they would insert a round piece of cork 10mm wide and center it then use 5mm resin on each side. does this sound ok or is there something better ? maybe green stucco putty ?

brokedown a écrit:: hi frits what do you think the best way i can plug them large holes ? i heard of people using cork and some type of resin. for example if the hole is 20mm wide they would insert a round piece of cork 10mm wide and center it then use 5mm resin on each side. does this sound ok or is there something better ? maybe green stucco putty ?

I would not use regular resin there; it may not be up to the local temperature. I'd rather glue in a couple of light-alloy caps with maybe 0,5 mm wall thickness.

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

hi frits i took apart this engine to change the ports alittle and wanted to ask you about the piston which has only a couple hrs run time on it. does the black underside suggest the crown is getting too hot and if so would the over sqaure dimensions have anything to do with it or is the black ok ? i thought i recall jan saying the over sqaure engine can really heat up the piston crown. carb seemed tuned pretty good and i was using 6% castor, ign timing was in original location. thnx for any assistance. and yes i know over sqaure is a bad idea, you and jan said it 1000 times but i like these 500cc singles aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 809262

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 809262

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brokedown a écrit:: ... wanted to ask you about the piston which has only a couple hrs run time on it. does the black underside suggest the crown is getting too hot?

Yes, the crown is getting too hot for the oil you use; the oil carbonizes and forms a heat-insulating layer which means that the piston will heat up more and more.

Citation :: i know over sqaure is a bad idea, you and jan said it 1000 times but i like these 500cc singles

Who-ever said a 500 cc single has to be oversquare?

Hi Frits I am building a single cylinder engine for snowmobile racing in the single cylinder builders class.
Unfortunately the rule is for air cooled only. I will be using some e bay parts
I am using a rotax twin cylinder800 cc for the crankshaft and crankcase cut and rewelded as a single
The crank outer ends have real heavy double bearings so it lends itself well as a single
It has a stroke of 75.7mm. The ignition is programmable
The cylinder I chose is a 1978 YZ400 cylinder reed. It had a stroke of 70 mm so I will need to do some port mods to accommodate the longer stroke.
My question to you is what would you expect (HP) from an engine like this. My target rpm is around 7500.
We race in very cold air so cooling shouldn't be a problem.
I will be using good race fuel VP C12

My dear Howard, you have given me two dimensions: the original stroke and the one you will be using.
Now if you gave me another 100 or so dimensions, maybe I could make an educated guess.....

I have never even seen the inside of a 1978 YZ400 cylinder. And even if I had, I wouldn't know what 'some port mods' would implicate. And my crystal ball is still out for servicing Wink

.

Ok Frits the bore will be 85 mm stroke 75.7 mm for a displacement of 426cc
The compression ratio will be 12-1. The exhaust width will be 78% of the bore width
I plan to open the exhaust at 79 deg atdc
Open the c port at 112 and the A and B ports at 114
The exhaust port is approx 44mm at the flange
It is a single port with no variable valve
The carburetor is a 44 round slide feeding through a VForce 2 cage
The head will have .050 squish with 50% squish area
The head has dual plugs but I plan to only use a single plug
The ignition is programmable but I don't plan to have more than about 12 or 13 degrees as my finish timing at 7500 rpm and above. I am hoping for around 75-80 hp with a good pipe.
My crystal ball repair shop does good work btw. Send me your ball and I will give it a good overhaul.

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

howard im interested in how your project turns out. photos would be cool if you have the chance. mostly i would like to know how well them port timings do. last cylinder i tried 200/130. next one im gonna go alittle more conservative i think, atleast ill start alittle more conservative and who knows where ill end up. aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 771973

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 771973

Nombre de messages : 41 Localisation : Italia Date d'inscription : 20/11/2012

Hello, how could I do replicate the "bump" into the lower wall of exhaust duct, Aprilia style?
Epoxy resin will bear the temperature?

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

the ends of the seal on the outside of a head, does it need to be glued together, or are the squizing forces enough to push the ends against each other ?

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Je ne comprend pas ta question. aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 55116

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 5 55116

On pourrait croire que tu as "fabriqué" le joint torique à partir de tore au mètre ?

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

fpayart a écrit:: Je ne comprend pas ta question.
On pourrait croire que tu as "fabriqué" le joint torique à partir de tore au mètre ?

oui, c'est juste.

quand j'avais transormer une culasse originals pour utiliser des domes, j'avais "coller" ( ? glued i english) le join aux "astuces" (? the ends) et ça à bien marcher, mais je me demande si c'est nécessaire : est-ce que la pression sur le joint est assez pour "l'étancheité" (? the sealing))

I handed you the stick using French but I think it would have been better to use Flemish, so I continue in English.
It is better to use a closed O-ring rather than a meter/torus, which is difficult to ensure tightness.

Nombre de messages : 8 Localisation : UK Date d'inscription : 23/01/2013

Hi guys,

I posted many many pages back regarding my yamaha tzr250 3xv SP v-twin model that I am developing. It is still ongoing.

I have a question about the match between the carb rubber and the carburettor bore. The standard parts have a large mis-match as shown here:

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Now looking at the rubber, this mismatch is deliberate. The bore in the carb rubber is larger than the carb bore and offset from the centre. Does this have some form of benefit? Bear in mind in standard trim the bike is a road bike.

Would it be sensible to build up the carb rubber with some form of fuel resistant potting compound in order to make it flush with the carb bore all the way around?

Any thoughts, experience and advice welcome :-)

Thanks for your time everyone.

Dan

maccas a écrit:: Now looking at the rubber, this mismatch is deliberate. The bore in the carb rubber is larger than the carb bore and offset from the centre. Does this have some form of benefit?...Would it be sensible to build up the carb rubber with some form of fuel resistant potting compound in order to make it flush with the carb bore all the way around?

It certainly looks deliberate, Dan, assuming that the rubbers and carbs belong together. You could smoothen the gap but the outcome could be adverse as well as positive, so I would not bother.
What you have now, is an anti-reverse ridge that hinders backflow, which is not a bad thing to have.

Nombre de messages : 8 Localisation : UK Date d'inscription : 23/01/2013

Hi Frits,

Thank you very much for your response. I will leave it alone for now then :-). At some point i will try and make a removable insert and dyno test with and without the step.

Best regards,

Dan

Nombre de messages : 5 Localisation : Auckland Date d'inscription : 08/05/2013

maccas a écrit:: Hi guys,

I posted many many pages back regarding my yamaha tzr250 3xv SP v-twin model that I am developing. It is still ongoing.

I have a question about the match between the carb rubber and the carburettor bore. The standard parts have a large mis-match as shown here:

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

Now looking at the rubber, this mismatch is deliberate. The bore in the carb rubber is larger than the carb bore and offset from the centre. Does this have some form of benefit? Bear in mind in standard trim the bike is a road bike.

Would it be sensible to build up the carb rubber with some form of fuel resistant potting compound in order to make it flush with the carb bore all the way around?

Any thoughts, experience and advice welcome :-)

Thanks for your time everyone.

Dan

It's looks to me that the step is designed to promote flow into the boost bottle set up on the top of the manifold.

maccas a écrit:: Hi guys,

I posted many many pages back regarding my yamaha tzr250 3xv SP v-twin model that I am developing. It is still ongoing.

I have a question about the match between the carb rubber and the carburettor bore. The standard parts have a large mis-match as shown here:

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

Now looking at the rubber, this mismatch is deliberate. The bore in the carb rubber is larger than the carb bore and offset from the centre. Does this have some form of benefit? Bear in mind in standard trim the bike is a road bike.

Would it be sensible to build up the carb rubber with some form of fuel resistant potting compound in order to make it flush with the carb bore all the way around?

Any thoughts, experience and advice welcome :-)

Thanks for your time everyone.

Dan

The step down is not such an issue as a step up. Would be just as easy to make that fit perfect so it's been made like that for a reason RGV is the same

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

Where the aprilia exhaustport bridges relieved?
Is it a necessity with auxiliary exhaust port bridges?
This is what I mean:
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Jan and Frits,
have you ever tried a piston that has a radiused edge rather than the reasonably sharp edge usually used? There might be some benefit in breathing of partially closed ports. Additionally it might help create more cooling of the piston crown above the ring lands. Of course the rings might have to be lowered somewhat depending on the radius.

Senne s a écrit:: Where the aprilia exhaustport bridges relieved?
Is it a necessity with auxiliary exhaust port bridges?
This is what I mean:
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Relieving was tried.
But it proved to be unnesessary.

» [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 1) (Locked)
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