ESE's works engine tuner

[marsheng]

Probably wrong forum but the right readers. I have a chap bring down a truck from Tauranga to ChCh in 2 weeks time. Looking for bikes to fill it. Cheers Wallace 03 3237449

[jonny quest]

The late ignition timing results in hotter exhaust gasses and pipe temp, which fake out the pipe to acting shorter. This is what helps over rev

Oops read a question way to fast. And tried to delete this response.

[marsheng]

Not less than 1 mm all around, taking axial movement of the crank into account as well.

I have checked my crank case /crank clearance and in total it is only 1.5 mm, which means 0.75 each side. If I need to make this 1 mm, I will have to reduce the bigend pin by 0.5 mm. Obviously, I'll have to trim the crank webs to still give the 0.5 mm clearance on the big end/conrod. Is this recommended ?

Cheers Wallace

[Frits Overmars]

I seem to remember you saying, Frits, that the Ryger had changed your opinion of what was possible in time/areas.... But of course, here you qualify the statement by prefacing it with "a conventional two-stroke". Leaves a lot of questions about just what the Ryger would be described as...

I would certainly not describe it as a conventional two-stroke, Grumph. No surprise there, I presume.

Has anyone an idea why less advance below the pipe makes more power

I think we all know that at 2/3 of maximum torque rpm there is a torque dip because the return pulse from the pipe messes things up in the cylinder.
But still further down below in the rpm band, this exhaust pulse travels twice through the pipe before exhaust closure and then it can do some good again.
In this rpm area power can be gained by changing the advance from 30° or thereabouts to something less, so the pipe is fed with exhaust gas containing more energy.

I have checked my crank case /crank clearance and in total it is only 1.5 mm, which means 0.75 each side. If I need to make this 1 mm, I will have to reduce the bigend pin by 0.5 mm. Obviously, I'll have to trim the crank webs to still give the 0.5 mm clearance on the big end/conrod. Is this recommended ?

I'd rather leave the crank alone and look at the cases.

[marsheng]

I'd rather leave the crank alone and look at the cases.

Thanks for info Fritz. The casing has inserts to match the 250 cranks as the casing is the same for the 440. It is a possibility to re-machine the inserts but they are already quite thin. The next is to machine the cases but I'm hesitant to do that.

Maico has a reputation for tight bigend fits so I think I will be ok.

I have done the one side with the magneto. I'll ponder the drive side, however I still have to remove 1.5 mm for the larger crank. Another 0.5 I don't think is that much more.

[marsheng]

I forgot to mention that the crank is locked in position on the drive side so it cannot move. The other side is a roller bearing.

[Frits Overmars]

The casing has inserts to match the 250 cranks as the casing is the same for the 440. It is a possibility to re-machine the inserts but they are already quite thin.

Throw the inserts out.
Once upon a time, way back in the previous century, Rotax made a kart engine, the Rotax 124, by fitting a 125 cc-crank into 250cc-cases. No inserts.
The radial clearance was about 5 mm. It became a world-beater.

[Lef16]

Hey Frits,
I didn't understand something.
Wich crank case/crank clearence are you refering to?
I made 2 (awful ) drawings.My problem is that in the 1st one the clearence on my engine is 0.3mm on one side and 0.4mm on the other one.
Is it too small?I think it is,possible a kaboom


Cheers

[husaberg]

Hey Frits,
I didn't understand something.
Wich crank case/crank clearence are you refering to?
I made 2 (awful ) drawings.My problem is that in the 1st one the clearence on my engine is 0.3mm on one side and 0.4mm on the other one.
Is it too small?I think it is,possible a kaboom


Cheers

Both in my best Dutch accent. 1mm minimum. ie all surfaces.
Scold yourself in an accent of your choosing regarding the drawings.
Id start with Spanish. kawpowl...........

For further giggles the answer plus some more is back here.
http://www.kiwibiker.co.nz/forums/sh...post1130895842

Good point, Dave; in fact several good points.
Most of the volume is concentrated in the transfer ducts. Then there is the volume inside the piston of course, and the 1 mm shear-avoiding clearance at all surfaces of the crank.But that is not nearly enough volume. If you take another look at the Aprilia crank below left, you will notice that the space between the crank webs is the same as the space needed for the big end bearing. In other words: the crank webs have flat insides, good for another 60 cc or so, if I remember correctly.
Additional benefits: the con rod has an easier time pushing the mixture aside as it moves between the webs, and the big end bearing gets a lot more cooling and lubrication because it is not shrouded in any way.
Because there are no overhung bobweights, the crank webs are stuffed with tungsten to get the balance factor right.
In the RSA125, the con rod was lengthened from the RSW's 115 mm to 120 mm to create even more crankcase volume.

The paddling is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture.
Smooth, full-circle crank webs have the advantage that there is little mixture hiding in nooks and crannies. An example of it's importance: in a certain engine there were 20 mm spaces between the crankshaft bearings and the seals. these ill-accessible volumes acted as pneumatic dampers on the crankcase pressure fluctuation. Filling those volumes with plastic bushes gave a measurable improvement.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

[Frits Overmars]

Thanks Husa.

[seattle smitty]

(Quoting Husa quoting Frits):

" . . . The padding is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture."


But . . . "Crankshafts should be small and smooth."

Frits, understood that the inside surface of the crank throws should preferably be flat or nearly so. But where someone is machining the balance pad off of a production crankshaft (as marsheng looks set to do with his Maico in the photo), would there be any advantage in leaving a couple of millimeters-worth of that pad sticking up, and then mill some grooves or other intentional surface roughness there to accomplish the first purpose of churning up the fuel/air mixture?? Could this be a good compromise between big-end lubrication, fairly low crevice volume, and mixture homogenization?

[Frits Overmars]

(Quoting Husa quoting Frits): " . . . The padding is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture."

I wrote paddling, not padding; there's a difference.
You would have to try your suggestion to see if it works out positive or negative.

[marsheng]

Throw the inserts out.
Once upon a time, way back in the previous century, Rotax made a kart engine, the Rotax 124, by fitting a 125 cc-crank into 250cc-cases. No inserts.
The radial clearance was about 5 mm. It became a world-beater.

Damn Fritz !! Why didn't I think of that. The net result is I will remove the insert next to the drive side and that will probably make enough space for me to not machine that web at all. I'll make sure that the conrod is still in the middle of the bore.

[marsheng]

It is going to increase the crankcase volume quite a bit !




I know this may improve top end but I'm more after bottom to middle. What are the opinions? If it doesn't need it why did Maico install them ?


Thanks everyone for the input.



Cheers Wallace

[wobbly]

Wallace you are making too many assumptions ( errors waiting to be revealed ) when saying the Ignitech rpm sensing is affected by in cycle
speed variation.
This is not the case - the ECU measures the time taken between the voltage pulses from the trigger, with an algorithm that averages the previous
3 cycles and this predicts the current acceleration rate, that then calculates the rpm for the cycle about to be given a spark.
This is the trickery that allows the system to fire a spark before or after the static set base timing.
Thus its the time taken per complete rev that is used in the calculation, instantaneous radial velocity is irrelevant.