ESE's works engine tuner

[Frits Overmars]

sae 2004-01-3561

Thank you, I'd like to think i had my own data soon but it would be good to read what I might find beforehand.

I tried to download that paper for you Neil, but somehow it refused to go past the introduction page. Maybe you'll have more success.
Attachment 332890

[Lef16]

what size of piston do you have ? I have a few old spares of various sizes that might be what you can use to drill a hole. you can have it free if its the right size

Thank you pee,but it isn't necessary,I just had this question in general,so when I want to measure an engines crankcase cr I wont have to destroy a piston.
Now,for the past few days I'm messing around with crankshaft balancing.I cant really get what excactly does a-say-80%balance factor instead of 50% and what balance factor is good for my engine.
Cheers

[wobbly]

General rule for a 2T race engine with a near vertical cylinder is 58% is the best compromise.
As you tip the cylinder forward the factor reduces to when its horizontal,35% is the go.
Al the changing factor does is move the peak shaking force from a horizontal bias at 58% to the vertical plane as the % is reduced.
Vertical shake is perceived as much more annoying to the riders hands/feet/crotch,than a horizontal shake.

[Tim Ey]

General rule for a 2T race engine with a near vertical cylinder is 58% is the best compromise.
As you tip the cylinder forward the factor reduces to when its horizontal,35% is the go.
Al the changing factor does is move the peak shaking force from a horizontal bias at 58% to the vertical plane as the % is reduced.
Vertical shake is perceived as much more annoying to the riders hands/feet/crotch,than a horizontal shake.

Hi Wob and everyone.
Is there some math in the background? Or it this sheer experience?
Hence I have seen a few motocross engines with 70-80%, I changed my latest crank to be in that ballpark.

Talking balancing factors: To which percentages would you change a 90° Twin (Aprilia RS 250)?
I have asked this question some time ago and I think Frits answered, that it should have the same percentage as a single cylinder with a balancing shaft.
In theory this means both cranks want to have 100% to eliminate the first order frequency.
But as I have just witnessed an engine with balancing shaft and ~50% running smooth as a electro motor, I doubt the 100%.
Would be happy to hear your opinion on that

Thanks!
Tim

[Frits Overmars]

sae 2004-01-3561

Here is the complete paper, thanks to Vannik.SAE 2004-01-3561.zip

[Frits Overmars]

To which percentages would you change a 90° Twin (Aprilia RS 250)? I have asked this question some time ago and I think Frits answered, that it should have the same percentage as a single cylinder with a balancing shaft.
In theory this means both cranks want to have 100% to eliminate the first order frequency. But as I have just witnessed an engine with balancing shaft and ~50% running smooth as a electro motor, I doubt the 100%.

There may be more than one misunderstanding here, Tim. First of all: an Aprilia RS 250 can be either a street bike with a 90° Suzuki V-twin engine, which for balancing purposes should be regarded as two single cylinder engines, or it can be an Aprilia racing engine with two contra-rotating crankshafts.

A single cylinder engine with a balance shaft should theoretically have a 50% balance factor in the crankshaft (in practice it's usually a bit more in order to compensate for the effects of the finite con rod length). The other 50% is then provided by the balance shaft.

The Aprilia racing engine is quite a different animal. Usually it's called a V-twin, but I'd rather call it a W-twin because of its two separate, contra-rotating crankshafts, one above the other.
In a contra-rotating tandem twin such as the Rotax 256, with parallel cylinders, one behind the other, each crankshaft doubles as a balance shaft for the other crankshaft. So each crankshaft has a 50% balance factor to compensate the reciprocating mass of its own piston + con rod, and it has a 50% balance factor in order to fulfil its function as a balance shaft. In sum, each crankshaft of a contra-rotating tandem twin has a 100% balance factor.

The Aprilia racing engine is a twin and it's contra-rotating, but it's not a tandem. Its cylinders encase a 90° angle, and that has an effect on the angular location of the balance masses, as shown in the picture below left. Below right you can see the angular offset in practice, in the crank webs of an Aprilia RSW 250.
I'll leave it to you to work out the balance factor of this strange beast. A bit of intellectual exercise won't hurt .

[Tim Ey]

First of all: an Aprilia RS 250 can be either a street bike with a 90° Suzuki V-twin engine, which for balancing purposes should be regarded as two single cylinder engines, or it can be an Aprilia racing engine with two contra-rotating crankshafts.

Oh, i wish to own a "real" Aprilia RS250 - Standing in my shed are actually the suzuki leftovers with aprilias balsamic dressing...
Therefore I politely decline your suggested interlectual excercise about the "real" thing.

A single cylinder engine with a balance shaft should theoretically have a 50% balance factor in the crankshaft (in practice it's usually a bit more in order to compensate for the effects of the finite con rod length). The other 50% is then provided by the balance shaft.

Does this mean the procentual factor of an engine with balancing shaft is not depending on whether the engine is horizontal or vertical?
Or asking about my japanese italian twin - would it need to be 50% left / 50% right or 58% left / 58 % right (the right cylinder is facing down. Does it make him equal to a cylinder that got the same angle upwards? Adegnes, what is your experience with the Billet IAME Engine?)

Thanks!
Tim

[SwePatrick]

General rule for a 2T race engine with a near vertical cylinder is 58% is the best compromise.

I need to make it crystal clear for myself

58% with or without balanceshaft with 'vertical' cylinder?

Rgds

[Frits Overmars]

Does this mean the procentual factor of an engine with balancing shaft is not depending on whether the engine is horizontal or vertical?

That's right. A balance shaft neutralizes all primary unbalance forces, so it won't really matter anymore if the cylinder is horizontal, vertical or somewhere in-between.

asking about my japanese italian twin - would it need to be 50% left / 50% right or 58% left / 58 % right (the right cylinder is facing down. Does it make him equal to a cylinder that got the same angle upwards?

If your Suzaprilia has a balance shaft: see above. If it hasn't: see Wobbly's post.
One more detail: if you engine does not have a balance shaft, the balance masses in the crank webs will not only partly balance the reciprocating masses; they will also set up a rocking couple.
Therefore it could pay to concentrate the balance masses on the inner crank webs, so they are closer together and will cause a smaller rocking couple.

[Lbracing]

Hello everyone ,

My name is Luc from LBracing , I have read the whole thread twice over the last two years and I must say the amount of information is mindblowing . I would also like to thank EVERYONE who contributed to making this happen .

We are based in Canada and build chaisaw engines for speed cutting ranging from 50cc to 140cc and have been for close to ten years now . We manufacture our own pistons , heads , cylinders and carburetors all from billet .

The only limitations are :
cc class
Production based ( mostly look like a production chainsaw except from the pipe )

Wich means we can run any fuel ( usually methanol with 20 up to 30% nitro ) .

We always run the stock ignition coil ( sem AM50 , AM33 (flat line ignition)) but I have been looking to upgrade to something more powerful and reliable . I have been looking at universal PVL and selettra ignitions but I am totally lost as I don't know anything about them . Maybe some of you guys can help me ? ( wobbly , kart ignition ? )

Here are factors to consider :
-Acceleration speed is important for categories where we must start the chainsaw from the ground and then do the usual 3 cuts .
-Low and mid power is unimportant , only peak power is .
-Peak power is ranging from 14000 to 16000 depending on the engine size .
-Ignition must have a low rpm cut in point ( 500 rpm )
-We run R7376 plug in all our engines .
-Compression ratio is usually around 19:1 .
-It usually takes under 3 second to complete the cutting so heating the engine is very unlikely to happen .
-Ignition advance is currently 25-27* .

Thank you for your time !

[jonny quest]

That's a lot of compression for the fuel you're running

[SwePatrick]

Maybe very little or no squishband?
thereby the high compression and high ignitionvalues?

[Lbracing]

Our engines are VERY oversquare ( 1.4 ratio ) by stroking and making the piston smaller I get them under the 1.15 .

Being oversquare from what I have found makes the engine less prone to detonation , that combined to VERY short run time (2-3 second ) and the low temperature our engines operate at is what allows us to run such high level of nitro , comp and ignition .

Squish band usually ends up around 55% of bore . Heads are toroidal with flat top pistons . When my post count goes up I will gladly share some pic

[wobbly]

Hey a new Luc on here - welcome.
The PVL ignition is " better " than the equivalent Selettra, I have done direct back to back dyno tests.
I have posted on here before about the PVL setup, but the basics are as follows.
The stator coil winding spec does two things.
The higher the number of wire " turns " sets the amount the ignition will retard, they are usually set up so that the timing lines align at 10,000 rpm.
The kart ignition has the least number of turns ( measures 50 ohms ) and delivers most high rpm " power " to the plug, but less voltage at low rpm, and has no retard.
I would suggest a stator with around 2000 turns, these are around 200 ohms ,do have some retard and give more voltage at the plug when starting.
The 5000 wind coils ( the maximum ) were designed for Banshee quads, that hardly have any rpm at kickover, but they suffer from high speed misfire if used with high com
or lots of power.

[Lef16]

I need to make it crystal clear for myself

58% with or without balanceshaft with 'vertical' cylinder?

Rgds

+1 here,
also,I think YZ 125 & 250 are running without a balance shaft,am I right?
Does anyone know balance factor's used there?
Cheers