Two-stroke performance tuning?

**SS90** · 17th June 2009, 09:41

Originally Posted by TZ350

Sorry if I am stealing someones thunder but:-

The counter weight portion of the crank may or may-not necessarily be dead opposite the bigend.

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That brings up a (slightly) different part of the subject.

There are a few engineers who chose the point where there balance the crank

i.e what position the crankpin is at (looking at it from the taper sider, what degree is it at.....12 oclock, one oclock, sometimes two oclock.

It depends on who you talk to. It seems common practice that MOST people balance it at the 12 oclock position, yet having ridden bikes with both approaches, I have never noticed a difference.

I suspect it is because a single cylinder vibrates so much anyway, that a slight change in either direction is unnoticed.

This one was checked in the 12 oclock position.

As a matter of interest with the subject of getting the correct factor on the crank I made (52%) I would have to add 35gm's to the counter weight (webs) or remove weight from the crank pin. (drilling the centre),

I suspect that would be courting disaster though.

Other than speedpro's jig set up, there is also dynamic balancing....... the advantage of dynamic balancing, is that, for example, on the "static" set up (per Speedpro's example) you can only add (or subtract) weight from the webs in an approximate fashion...... (you just have to do your best to add/remove it as evenly as possible from each side of the webs.

If you don't take/add the weight evenly from each side of the web, you get "twist" in the webs as they spin (because they in turn are out of balance with each other)

This is what is termed "rocking couple"

Having a dynamic balancer, enables you (via computer controlled measurements) to remove/add weight as is needed, evenly from the webs.

It doesn't make any difference to the overall balance factor, but if the webs are badly out of balance with each other, the result is "twisting" of the webs, and before too long, the webs simply "twist off"

I have seen this on a very high performance engine (with extremely light crank)

It is also a good idea to put your flywheel on when measuring your balance.... be it static or dynamic

If you take it to a machine shop now days, chances are they will have a dynamic balancer, static is quite labour intensive.

Kind of like a tyre balancing machine compared to an axle stand, the result is more or less the same, but the machine does it faster and more accurately, as well as the operator needs less training.

**SS90** · 17th June 2009, 09:45

Originally Posted by k14

No what everyone is doing is taking a "general commuter item" and trying to turn it into a 14000rpm honda or aprilia gp bike. So taking the tuning data from one of those and applying it to what we have is the already proven method. Of course there are compromises but those bikes are the benchmark and by copying as many aspects of them as possible everyone hopes to end up with a fast bike!!

That's pretty much as I see it as well.

Converting a road bike to a race bike does suggest there is a logical pattern to follow.

**Buckets4Me** · 17th June 2009, 10:35

Originally Posted by F5 Dave

I've just worked it out. SS90 = Winston Peters.

Well think about it; - can't answer a straight question in anything other than "I've already answered that question" or dodging around it with another supposition.

I mean it makes sense, he turned up at about the same time, cagey about his identity. . . Well?

I hope you've given that ministerial car back buddy!

is this another whine gate ?????

**Yow Ling** · 17th June 2009, 14:03

Originally Posted by TZ350

2009 KX250F
Engine Displacement: 249cc
Max Horsepower: 32.8 HP @ 12,200 rpm
Max Torque: 17.2 lb-ft @ 8400 rpm

Remember you heard it from TZ350 first.

.

Interesting figures there, Kawasaki should use vespa engines, cos they make 25 to 30ps from 140cc, maybe they havnt got the whole swirl pattern thing yet.

**Buckets4Me** · 17th June 2009, 20:42

Originally Posted by Yow Ling

Interesting figures there, Kawasaki should use vespa engines, cos they make 25 to 30ps from 140cc, maybe they havnt got the whole swirl pattern thing yet.

it's 125 cc you nob havent you been reading what SS90 posts

it's not a 182 big bore kit on the vespa and it's still got a 24mm carb

**SS90** · 22nd June 2009, 10:25

Originally Posted by Buckets4Me

it's 125 cc you nob

Welcome to the "Real World"

It is certainly not a Vespa, but it is made in Europe, and I did spend the last 2 days in the factory.

Lich ich mein arsh.

**SS90** · 22nd June 2009, 10:47

Oh, and by the way, one is for the road, and one is for the street........one is "Membrane Induction" and one is "Dreh Schiebe"

One is for the road (prototype) and one is for 125 GP....

**SS90** · 22nd June 2009, 10:53

Havn't seen this in Vietnam?

YOU?

**F5 Dave** · 22nd June 2009, 11:01

No doubt they were asking for your advice & you were telling them how they were doing it all wrong.

Why are you posting with Germany quotes when you know most people can't read it? Does it make you feel superior? I'm sure Thomas could post in Vietnamese & few here would be able to translate it. Well, not without Babelfish.

**SS90** · 22nd June 2009, 11:05

Originally Posted by F5 Dave

No doubt they were asking for your advice & you were telling them how they were doing it all wrong.

Why are you posting with Germany quotes when you know most people can't read it? Does it make you feel superior? I'm sure Thomas could post in Vietnamese & few here would be able to translate it. Well, not without Babelfish.

That's the funny thing, where is Thomas?....one monment he is all things amazing, then he is only the guy who makes jigs for balancing....

Am I the only Kiwi in the world who thinks that "Thomas" is just a name for something that Teezee found on google last night?

**k14** · 22nd June 2009, 11:13

Originally Posted by SS90

Welcome to the "Real World"

It is certainly not a Vespa, but it is made in Europe, and I did spend the last 2 days in the factory.

Lich ich mein arsh.

The first pic is a RSW aprillia (was the works bike but they changed in 07 I think) the second is an RSA. Could be smiths, simons, or someones from last year. They changed the configuration of the engine quite majorly. The RSA has the carb in the "normal" place for a reed valve inducted engine (ala Honda RS125, Yamaha TZ125) but it is still rotary valve induction. There is a bevel gear that runs it apparently. That engine (I'm told, info on this stuff is very hard to find!) is designed and built by derbi for aprillia. So sort of makes a mockery of having a "derbi" and "aprillia" team fighting for the manufacturers championship in 125GP. They are both owned by the same company.

Below is talmacsi's bike from Philip Island in 07. Its the "old" RSW that he won the world championship on. Notice the airbox comes in the side to the traditionally mounted carb position for a rotary valve 2 stroke. I was told the reason they changed the engine layout was to get a better flow through the airbox? I doubt that was the only reason but it certainly makes the whole bike more symmetrical.

**SS90** · 22nd June 2009, 11:17

Originally Posted by k14

The first pic is a RSW aprillia (was the works bike but they changed in 07 I think) the second is an RSA. Could be smiths, simons, or someones from last year. They changed the configuration of the engine quite majorly. The RSA has the carb in the "normal" place for a reed valve inducted engine (ala Honda RS125, Yamaha TZ125) but it is still rotary valve induction. There is a bevel gear that runs it apparently. That engine (I'm told, info on this stuff is very hard to find!) is designed and built by derbi for aprillia. So sort of makes a mockery of having a "derbi" and "aprillia" team fighting for the manufacturers championship in 125GP. They are both owned by the same company.

Below is talmacsi's bike from Philip Island in 07. Its the "old" RSW that he won the world championship on. Notice the airbox comes in the side to the traditionally mounted carb position for a rotary valve 2 stroke. I was told the reason they changed the engine layout was to get a better flow through the airbox? I doubt that was the only reason but it certainly makes the whole bike more symmetrical.

From

Well done man!

Hope yourinjury is coming on well.....

How about these?