3ma restore third time lucky

[Need4speed]

as the rattling sound belongs to a racer

WAS THAT neccessary 

[jodydid]

What is the advantage of the sp crank? Is it just strength? Or is it lighter

[Louis]

WAS THAT neccessary 

Sorry

Still working on my dry clutch project using stock parts
Will update my site with pictures to give a better idea about that

[Louis]

What is the advantage of the sp crank? Is it just strength? Or is it lighter

Haven't weight a SP crank. But they seems to be not lighter then a stock one.
But they are definitively build stronger. (Its designed to bent/stretch less)

[Need4speed]

But they are definitively build stronger

and they are bigger in volumen - meaning the free volume in the crankcase will be less - and with less space -
the speed of air/gasoline mix will increase -  i think ...

[maccas]

The downside is there aren't many about so if one of the webs has corrosion damage you migjt aswell throw the crank in the bin as the chances of finding a replacement web are slim. I'mkiccking myself for not buying that one that was on ebay :-(

Dan

[Louis]

and they are bigger in volumen - meaning the free volume in the crankcase will be less - and with less space -
the speed of air/gasoline mix will increase -  i think ...

This is discussed on other forums a lot.
From what I have been reading, making the crank case less is worse

It was used on older tuning theory, by thinking the piston is pushing the gases trough the ports.

Now later tuning theory proves that a bigger crank case volume is better.
It is already hard to explain in Dutch, but I'll try it.
In big lines (from what I have been reading) When the exhaust ar coming in there powerband they start to suck the mixture trough the ports, a larger crank case volume is working like a buffer So the Gas stream is more dense.

Some copy off other forums

The idea is that a large expansion ratio takes away exhaust gas energy that could otherwise be more useful supercharging the cylinder, so the next bang will be bigger, and the bang after that bigger still, and... you'll get the picture.
A low secondary compression/expansion ratio provides for more exhaust gas energy; it also provides for a larger cylinder volume above the exhaust port so the exhaust pipe has an easier time shoving washed-through fresh charge back into the cylinder because the resulting cylinder pressure rise will be smaller.

A indication off crank case volume from a competitive engine;

The Aprilia RSA125 has a TDC crankcase volume of 675 cc. That gives a primary compression ratio of 675 / (675 - 125) = 1,23

From memory Lozza and Dan are active on there to.
Perhaps they can explain better.

[maccas]

That first quote is talking about the compression ratio louis not the crankcase compression ratio unfortunately.

From what i have read it seems that a bigger crankcase volume is preferable so there is more mixture available for the exhaust pipe to suck on. Has anyone else read the same thing?

Jody,

Sorry for the thread hijack!

Dan

[Louis]

Yes You are right Dan, Sorry it was late when I tried to find some texts about it

It is discussed on ''Pit lane'' and ''deraceheldenvanwelheer''
I know that you and lozza where reading/active there.

Well you confirmed that you have read it , lager crank case volume is preferable

The rsa have a big volume.
I wanted to measure the 3MA to, have already made a piston with a hole in it
But haven't fount the time to do it jet

[41juergen]

Hey Loius,
what Dan has written is also my understanding (still trying to read also the 800 pages on the KIWI forum...  ) from what Frits has written in the pitlane-biz. I measured the volume on my RZ ending with a 480cc CCV and already increased to 510ccm (very less compared to the RSA  ) , but testing is still pending.

Juergen

[Louis]

Hello Juergen,

what Dan has written is also my understanding

Yes, that is what I have understand from it to.

When the exhaust ar coming in there powerband they start to suck the mixture trough the ports, a larger crank case volume is working like a buffer So the Gas stream is more dense.

Have a somewhat same explanation.

It was also something with buffer and pulses, also there was a different between disk inlet of reed inlet
Making the volume extremely big wasn't good either, its bound at rules

Going from 480cc to 510cc did you measure a big difference?

[jodydid]

What part of the carb do you measure to find out its size I measured where it pushes into the carb rubbers is this right??? Or do you measure where the atomiser/emulsion tube comes out

I'm seem to be on a roll might recheck the scabby carbs down the shed you never know 

[Louis]

What part of the carb do you measure to find out its size I measured where it pushes into the carb rubbers is this righ

Yes, you measure the inside diameter on the location where you pushes the carb in the rubbers (back end off the carb)

3MA1= 32mm
3MA3/5= 30mm
3Ma4=34mm

I'm seem to be on a roll might recheck the scabby carbs down the shed you never know

Yes, you definitively need to measure them up , you already have a half SP

[jodydid]

There 32mm at reed rubber side and 34mm at the carb slide and also the atomiser has had the holes soldered up and sanded flat they are rusty on all the fittings but I'm going to rebuild these with all the good non rusty bits from my other set

[jodydid]

Just emailed gecko motorcycles he has a set for sale his are 32mm inside and 40 outside like mine what bit is 34 I'm confused