ESE's works engine tuner

[TZ350]

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A jpg file of a degree wheel that you can download and print out.

http://www.eurospares.com/graphics/degreew.jpg


And also from Euro Spares a "Bibliography of Technical Books."

http://www.eurospares.com/techbook.htm

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[Chambers]

TZ I finaly got the gist of the SAE paper on crankcase volumes you refered me too.

Last paragraph page 175: The drop in delivery ratio caused by increasing the crankcase volume can be fairly well compensated for by tuning the inlet and exhaust system.

http://www.edj.net/2stroke/jennings/...ase_volume.pdf

Second paragraph of the discusion section page 188: Small crankcase volume is best for high speed and large volume for low speed. Explanation: with small volume and low speed the crankcase discharges to fast into the cylinder and for the rest of the transfer-port-open period there is reverse flow.

Forth paragraph of the discusion section page 188: If the engine speed is selected to best suit the crankcase clearance volume the clearance volume does not effect the delivery ratio. Tuning either the inlet or exhaust pipe or both increases the delivery ratio.

So from reading the SAE paper, you have to have the right crank case volume for the intended engine rev's and it needs to be a smaller clearance volume ie., a higher primary compression ratio thats closer to 1.5:1 the higher the rev's.

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[F5 Dave]

The Two-Stroke Shop
Stephen Rothwell and Wayne Wright (Wobbly)

www.twostrokeshop.com
Email: info@twostrokeshop.com


THE most advanced high-performance two-stroke motorcycle engine on the market today.

http://www.twostrokeshop.com/two_str...op_engines.htm

Toroidal head and flat top piston.

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Well that's stretching it to claim it is the most advanced 2 stroke on the market & bear in mind I own one (ok without the toroidal head). But the cylinders while light-years better than the original are compromised crankcases not being full crankcase reed induction & not having the room between the bores for sweeping transfer paths (despite going to a monoblock).

Seems to me the Toroidal head suits larger bores by positioning the plug closer to the action. The smaller the cylinder the less use it is likely to be, it is possible to get too close, I have seen good evidence of this. Obviously there is applications to fuel matching as Kirk points out.

[bucketracer]

Well that's stretching it to claim it is the most advanced 2 stroke on the market.

I guess even " www.twostrokeshop.com " can't resist a bit of "Sales Speek".

[F5 Dave]

I've spoken to Steve & he's a passionate guy, even before he started TSS. Nice guy & seems on the level.

[TZ350]

With 7 of 8 rounds done I am 6th in A grade. There are many better riders but my result is the fruits of consistency, having started/finished every race so far.

http://www.amcc.co.nz/results_bucket/0809ABUC.html

Last Sunday (round 7) was forecast to rain, although it remained fine for the races. I was still struggling to shake of the flu. I was feeling to ill to try competing but with a fast start and finishing the race. I figured I will pick up useful points.

So the plan became, use practice to experiment with the suspension, the pre-lim races to practice fast starts against the others as the starts are everything at Mt Wellington and for the points races to just relax back, take my time and experiment with powering on earlier in the corners.

Poor Chambers was not ready for the flag drop in the first points race and he made a flustered start, then he missed a gear into the first corner and this completely threw him and he pulled off in disgust.

So no points for him and enough points for me that its unlikely he will be able to better me on the point’s table this year.

I had been listening to Warrick and a couple of the other riders talking before practice and the conversation was about how the difference between a good days racing and a bad day was where they were at in their heads. Its certinly true for me.

The ESE bikes are consistently good, but little things can really throw you and it’s often just the morale of the rider that makes the difference on the day.

Nicholas and Daniel Lancaster on their CB125’s were really flying, as were Tim and Rick, they were having a very good day. Steve on his new 2-stroke was going well and looking smooth untill a gremlin got into the motor.

At the end of racing I was pleased to get off home as I was away to Dunedin Monday morning and the forcast was for hail storms and snow, just great, as I was going to be working outside on the coast for the next few days.

The good part was, Eileen was with me and we got to stay at a wonderful B&B that did evening meals. It was run by a chef and his wife, the house was built in 1865, http://www.lisburnhouse.co.nz/ it had a big log fire and the food was just out of this world.

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[TZ350]

Tomas gets back to working on porting the GP125 cylinder.

Pic-1 He bends a wire template to the curve of the transfer port.

Pic-2 Tomas and Alexi heat and bend some rifler files to the shape they want.

Pic-3 Using the wire template to judge the amount of bend needed.

Pic-4 Re-Hardening the file by dunking it in an oil bath.

There is special oil for this but just about any oil will do. If you use water the file will be to hard and brittle.

Pic-5 Some of the modified files.

Pic-6 Tomas finds his new files work well.

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[TZ350]

Tomas explained to me, how the surface finish of the ports should be. This is what I remember of what he told me.

Pic-1 Tomas said that if fine file marks are made across the direction of air flow then small air vortices develop and these act like ball bearings and the air mass slides easily over them.

Pic-2 He says its easy to get a polishing mop and go mad mirror polishing the port, curve (1) but you often wind up with a ripply surface and this is bad.

He says it's much better to have a smooth contour, curve (2) even if that means a rougher surface finish like you get with a fine file.

It used to be all the rage to polish the ports but with a mirror polish in the port, the air boundry layer that clings to the port wall is quite thick and moves like treacle.

But a surface finish that promotes micro vortices that act like small ball bearings reduces the boundry layer too next to nothing and the air mass's resistance to flowing along the port is greatly reduced.

Tomas says a smooth polished surface that has been sand blasted is best and a fine file or sandpaper finish that cuts across the air flow is also very good but file or sand paper marks that go in the direction of air flow don't help much.

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[F5 Dave]

While we're on it (not easy for transfers mind); Small rotary carbide bits seem to work ok but are very good at leaving ripples, large flame type ones are much better but need a grunty Bosh(sp) or air powered with decent compressor to drive. Decent Stone bits take out irregularities leaving a flat surface with a honed appearance, mighty fine.

[Fooman]

It used to be all the rage to polish the ports but with a mirror polish in the port, the air boundry layer that clings to the port wall is quite thick and moves like treacle.

But a surface finish that promotes micro vortices that act like small ball bearings reduces the boundry layer too next to nothing and the air mass's resistance to flowing along the port is greatly reduced.

As a point of information, this is why golf balls are dimpled, rather than smooth - less drag, so they go further.

A quick check of my old fluids text (Massey, Mechanics of Fluids 6th Ed.) says the (thin) turbulent boundary layer promoted by the rough surface delays separation of the flow, reducing the drag caused by the gross separation (turbulence) of the flow across the surface.

I feel old. That textbook is 20 years old now...

Cheers,
FM

[Skunk]

That textbook is 20 years old now...

And people STILL insist on have polished ports and stuff...

[bucketracer]

Decent Stone bits take out irregularities leaving a flat surface with a honed appearance, mighty fine.

The good thing about stone and resin bits is that they can be re-shaped by running them up in a hand drill and working them against the side of a spining stone wheel in a bench grinder.

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[F5 Dave]

Good tip I haven’t tried that, usually most of the stones I run on the smaller Dremel or the air grinder are flame shaped which seems most useful.

CRC will help keep carbide tips from clogging, but a wire brush every so often is par for the course to keep cutting clean & smooth. Good sealing Eye protection is so important.

[TZ350]

It might be Karts, but there is a bit of interesting reading here.

www.kartweb.com/TechArt/2Stroke/chapter1.doc

www.kartweb.com/TechArt/2Stroke/chapter2.doc

www.kartweb.com/TechArt/2Stroke/chapter3.doc

chapter 3 is on chambers.

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[TZ350]

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Someone else's efforts at porting:- http://www.teamsmoke.com/photo4.html

Lots of pictures, I particularly like the tool he made for measuring the transfer port opening height's.

He also made a real trick tool for holding the tip of a round file at just the right angle for the transfer port roofs.

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