ESE's works engine tuner

[Grumph]

I guess if it was relevant no bike would come with less then a 20 sproket from factory but lets see what can be said here about it.

Apples vs oranges. A gear with less than 20 teeth is weak as the gear cuts go too deep into the core material. They're stress raisers.
A sprocket can go down to around 12 teeth without losing strength as the bottom of the teeth are of appreciable radius thus much kinder to the
material used.


There are a lot of reasons for choosing a size for a final drive sprocket. You seldom see a big bike now with less than 18 teeth on the front sprocket - usually more.
Less angularity usually means longer chain life.

[ken seeber]

In Awestralia, the Yamaha KT100S engine was the mainstay of karting. Because they revved to around 15k rpm, they typically, in sprint/bitumen, used a 10T sprocket on the crank, driving an 85T or so axle sprocket, using a 219 chain.

However, these engines are very common in the increasingly popular dirt track karting scene. These tracks are usually shorter than bitumen tracks with lots of tight corners. Because of this, most use a 9T engine sprocket.

Not that I’m close to this. But I do know chain life is shorter, because of the dirt, the extra tension (11%) in the chain and the greater change of angle of each link over the sprocket (40deg vs 36deg).

[RomeuPT]

In Awestralia, the Yamaha KT100S engine was the mainstay of karting. Because they revved to around 15k rpm, they typically, in sprint/bitumen, used a 10T sprocket on the crank, driving an 85T or so axle sprocket, using a 219 chain.

However, these engines are very common in the increasingly popular dirt track karting scene. These tracks are usually shorter than bitumen tracks with lots of tight corners. Because of this, most use a 9T engine sprocket.

Not that I’m close to this. But I do know chain life is shorter, because of the dirt, the extra tension (11%) in the chain and the greater change of angle of each link over the sprocket (40deg vs 36deg).

I would say that if the chain is being eroded faster by too small sproket then a bit of the engine power is being consumed there instead of being spent on the road/dirt.

Most dirt bikes use 12/13/14 sprokets. Only for Aprilia or Honda RS its like 16 to 20....

This is probably known and tested...

[Peljhan]

Small sprockets also induce polygon effect. Smaller the sprocket, greater speed fluctuations in chain speed. One would think that this also put stress on chain and reduce it's life span.

[speedpro]

Out of interest, my 250 single road racer that is geared for 110 mph has a 17 front sprocket and a 38 rear 2,2:1. My TZ350 had 14 front and 34 rear 2,4:1. The TZ reeved harder and went faster. I will have to check the primary and top gear ratios to make any sense of it.

Pukekohe gearing on my McIntosh was 15:27. I have a 16T I bought in the USA but haven't used it. The bike would pull it no problem, apart from me chickening out.

[TZ350]

More from 2Stroke Stuffing's shed.

[husaberg]

[diesel pig]

Watching that Pro-Am race one part of me was like those crazy young lunatic's with no fear and another part of me was I wish I was young again.

[Peljhan]

I am bulding low power Puch E50 engine with 70cc kit. Will make about 5-7hp. Exhaust will be very long and I am wondering what kind of effect would have a reverse cone modification, if I would cut it in half in the middle and turned last part around so the spike would protrude towards mid section. Stinger pipe would again revese towards outside and this reverse cone would make nice place for silencer packing.
Does this modification shortens returning pulse and makes it of higher amplitude?
Should I than make the reverse cone with more shallow angle?

I believe Frits or Vannik would have some idea about theroretical effect of this modification.

Made quick sketch in paint. (blue color is silencer packing).


P.S. Frits, what program are you using for sketches, they come out quite nice?

Edit: spelling

[Frits Overmars]

Cutting the reverse cone in half and turning the last part around as in your above drawing would be like making a reverse cone with half the length and twice the steepness of the original reverse cone. It would be the oppositie of what you need for your low power Puch.
I know length can be a problem. Maybe you can make a curled header, like in the prictures below.
Thank you for your comment about my sketches. Some of those are generated by the software I wrote, some are made with Autocad, and some are produced with Microsoft Paint, so nothing fancy.

[wobbly]

The backwards cone idea doesnt work , been there done that 30 years ago . Easy solution is to go with the simple direct drive kart pipe with the rear cone full of small holes and enclosed within the tube body.
Neels has even got this modelled already - works really well for low power over a wide range.
I used this on a 2 cylinder fan cooled micro aircraft engine years ago , the pilot loved it - got up on the prop way faster and had a ton more overev power that gave alot more flight speed.

[Peljhan]

Thanks.

The problem is Frits, I dont know where to curve it anymore. I tried aiming it towards floor but forks are in the way. I try to keep it tidy.

A bit of insight. Our general medical insurance does not provide electric attachment (like Batec) to young paraplegics, their agument is funding and that we have healthy hands. I live in 500m deep walley full of mountain roads.
And this attachemnt cost about 6-8000eur It is also underpowered with just 1200W electric engine.

So I decided to do it my way. Found a Puch E50 in the attic and after weeks of abusing Solidworks (or Solidworks abusing me) and some reverse engineering from my friends Batec, I came up with that.
It is also a nice tribute to two strokes and laugh against electrification.

Wobbly, do i need to make enclosure for perforated rear cone like straight pipe with cap, or full cone few cm behind perforated cone?
Frits, I am using paint for simple sketches but it's not good for more precise or detailed sketches.

[Frits Overmars]

The problem is Frits, I dont know where to curve it anymore. I tried aiming it towards floor but forks are in the way. I try to keep it tidy.

I'm sure you've put more thought into it than I have, so maybe I'm missing something, but I do see potential in the header. A big part of it appears to be straight in your drawings. For the engine power you are aiming for, that header does not necessarily have to be conical; it may also consist of parallel piping. And 90°-elbows are available for many diameters, for example from companies that build four-stroke exhaust systems. You can build a knot using such elbows, so to speak, without much welding being required.

One more note, the power train on your Flying Puchman looks rather similar to another front-wheel drive two-stroke I've dabbled in: the Solex.
I have noticed that for light operation and sufficient feedback you have to keep the polar inertia around the steering axis as low as possible.
So build the engine as close to the steering head as you can.

[Grumph]

For looped headers, donuts are a good starting place. Available from 4T exhaust bend suppliers in a range of OD's and sometimes radii.
Cut and twist.

[Peljhan]

I build many complete pipes with hydroforming. But I just finished excel driven sheet for Solidworks and decided to make it that way. It will be faster as cnc laser company is close and I weld it up in a day or two and I never tried hydroforming on stainless. Additionally I have to send it to laser cut anyway as my forks and frame is welded up from sheet metal.

Local company that builds 4t pipes is Akrapovič
But they got only large diameters available, like 40mm+
Stainles steel stores have mostly 1,5mm wall thickness and nothing on stock.

I attach pipe dimensions. For now header is 0,7/1,4°. Cone angles are half angles as I am used to that. And rear cone is one piece.
Made to run 167°-170° of exhaust timing and around 6700rpm peak power. 128° transfer timing. Will se how that will fit as I never made so low rpm tuned engine. And rpm needs to be low as it will be used onl up to 30km/h. I have better ways to die.
Cylinder is dmp70, 4 transfers with rear side 2 booster transfers.



Would put it into EngMod but I want to drive around over the summer, so no time for that for now.

Polar inertia = moment of inertia around steering axis?
I made forks as you can se in a way that axle is a bit more forward and steering axis is quite inclined, so it tends to keep the direction of riding = harder to steer. But because mass is high I believed it will easen on turning the steering bar. We will see