ESE's works engine tuner

[SS90]

From:- http://www.kartsport.org.nz/technica...e_seizures.htm

Four corner seizure: Both sides of the piston will show heavy scoring and seizure marks on each side of the wrist pin hole. The pattern of these four seizure points often appears to be a perfect square, hence the slang term "four corner". The scoring takes place in this pattern because those areas of the piston casting are the thickest. When the piston is seriously overheated, the thick areas will expand and distort the most.


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And this is why pistons have "cam grind"..... "Modern" pistons (like the one Teezee uses) have a high silicone content (I think 8% from memory (as well as Nickel), and as such suffer much less from 4 point seizure problems than older pistons.

[SS90]

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From:- http://www.smellofdeath.com/lloydy/p...diag_guide.htm

Loydys Lambrettas Two Stroke Piston Diagnosis

PERFECT BROWN CROWN
The crown of this piston shows an ideal carbon pattern. The transfer ports of this two-stroke engine are flowing equally and the color of the carbon pattern is chocolate brown. That indicates that this engine's carb is jetted correctly.



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Hahah, while I have to agree that the shape ("pattern") is quite good, I am unsure if the colour of the crown is "chocolate brown"....looks more like black (too rich) too me!.....

[SS90]

Didn't TZ have that problem at Taupo?

Interesting that 4 point seizure, and explination is from a Scooter shop too.

"The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range."



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Yes, not quite right there Chambers. As skunk pointed out, this article points out as to what happens.... (the piston expands too much) not as to what causes it.

The following paragraph starts........

"The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range."

This refers to the problem of a seizure mark on the piston opposite the exhaust bridge. (not 4 point seizure) In a water cooled bike, if you see this it is normally termed "cold seizure", and a result of not warming the engine up to Normal operating temp before thrashing it. But is also offers other reasons for the same problem. (wrong jetting, or too hot spark plug)

The last two reasons cause increased overall cylinder temperature, and as such increase the temperature of the exhaust port,(and exhaust port area of the piston crown) which is already a hot area (because of it's large port time area) due to the fact that with a bridge, you can safely exceed the 70% rule,as the bridge stops the ring protruding into the exhaust port at high R.P.M, a draw back of large exhaust port time areas is extreme localised heat around the piston crown on the exhaust side.

On a bridged exhaust, it the engine suffers heat related piston damage, it is normally on the exhaust side of the crown.

On a non bridged cylinder, heat related piston damaged normally shows it'self as a "holed" piston..... As because the exhaust port is much narrower (70% of the bore area or less) and simply not as hot as the wider bridged version. And as such, the centre of the piston seems to be the hottest point on these engines.

Personally, I have seen all these 3 things cause the same fault (in air cooled and water cooled engines)

Basically, the bridge is subject to great heat, and expands faster than the rest of the cylinder.

One way of combating this is to drill 2 small holes in the piston in line with the bridge, allowing a small amount of oil and fuel to lubricate the bridge.

Works quite well actually.

I recently saw a company in england who are trialling a new (well, not really new idea, but an application of the exhaust bridge hole concept) idea to combat the problem of 4 point seizure on their Lambretta Nicasil tuning cylinder.

Using the same concept, they have drilled 4 holes in the piston in line with the studs, again, the idea is, like the exhaust bridge, fuel an oil mixture cools those areas.

While I like the concept, even the guy who is testing it is not overly optimistic on it's success..... I am waiting to hear back from them after they have tested it.

Another note on the wasted stud.

When was the last time you saw a high performance water cooled 2 stroke cylinder with through studs?

Granted, having a cylinder that is retained to the cases via base plate allows for more room for exhaust size, (no studs in the way) (among other things), another advantage is that the cylinder is not "clamped" down, it is free too expand "vertically" as much as it wants, unhindered by stud expansion (or rather "lack of" stud expansion)....... Don't forget, the masters of air cooled performance (VW/Porsche) reduced the thickness of their studs as the engines where developed for more power.... I assure you the reason was not cost cutting!

I even know of some one who adapted a base plate system to his cylinder (at great expense) to solve this very problem... worked perfectly.......

[TZ350]

Another note on the wasted stud.

When was the last time you saw a high performance water cooled 2 stroke cylinder with through studs?

Good point that. Becouse the cylinder studs on a GP125 protrude above the barrel they make it hard to get the head of.

I am planning on fitting shorter studs and using the long aluminium head bolt/nuts from the early TZ's.

The benifits are:- the ends of the studs would not get in the way and the aluminium TZ bolt/nuts would act as locating dowels between the head and barrel and possibly their heat expansion will reduce the crush effect that SS90 talks about.

The good thing about using "o" rings as head gaskets is that you dont have to tighten the head nuts up much as you don't need a lot of clamping force to retain the head gasket, as the "o" ring is retained by its grove. You only need enough clamping force to stop the head rattling around and lifting of the barrel on the power stroke.

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[SS90]

G
The benifits are:- the ends of the studs would not get in the way and the aluminium TZ bolt/nuts would act as locating dowels between the head and barrel and possibly their heat expansion will reduce the crush effect that SS90 talks about.

The good thing about using "o" rings as head gaskets is that you dont have to tighten the head nuts up much as you don't need a lot of clamping force to retain the head gasket, as the "o" ring is retained by its grove. You only need enough clamping force to stop the head rattling around and lifting of the barrel on the power stroke.

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That's a really good idea..... I hadn't thought of that! Do you think that Yamaha had that system for expansion, or for ease of access..... Maybe both?

[TZ350]

That's a really good idea..... I hadn't thought of that! Do you think that Yamaha had that system for expansion, or for ease of access..... Maybe both?

Hard to say, the TZ is based on the RD road bike. The road bike cylinder head bolt/nuts were made of steel and clamped a copper head gasket and it is pretty easy to get the RD head out without studs sticking up like they do on the GP.

I guess whoever at Yamaha designed the race bits used "o" ring head gaskets and just copied the head bolt/nuts in aluminum.

Which could have been lucky.

When you think about it. The early air cooled Suzuki RM125's were base mount with no through studs and so are the TF100/125's that were/are popular bucket engines.

Picture of a aluminum TZ head bolt/nut.
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[TZ350]

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The Relationship Between Port Shape and Engine Performance for Two-Stroke Engines

Document Number: 1999-01-3333
Date Published: September 1999
Author(s):

Hisatoshi Kinoshita - Yamaha Motor Co., Ltd.
Yuh Motoyama - Yamaha Motor Co., Ltd.

Abstract: Measurement using a three-dimensional anemometric tester was made for the gas flow inside the cylinder of a two-stroke engine while the shape of the transfer port was modified. The relationship between port shape and engine performance was investigated for various factors that characterize the flow in cylinder. In this paper, we focused mainly on two engine running conditions: the maximum output at 11,750 rpm and the output at 10,000 rpm. As a result, we found that the maximum output is most related to the tangential inclination angles of the main transfer port and the inner vent radius of the main transfer duct.

This paper can be read/printed here:- http://www.2stroke-tuning.nl/media/pdfjes/porting.pdf

In case you missed it earlier. Here is a little bit of a gold mine:- http://www.2stroke-tuning.nl/media/

Port maps etc, some of its in German.


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I am not sure that this is everything SS90 has been talking about but it is good information.

I had to draw pictures and high light stuff to get my head around this.

Pic 1. As more power is developed, a hole/dip (Point B) appears in the the power curve just before max output (Point A).

The drivability of the bike is affected by this dip just before max power.

There is a trade off between power and drivability. (as we all know)

The main things that make more power, are, and in order of priority (1) the primary transfer tangental angle, (2) the inner transfer port radius, (3) the main transfer port axial inclination, (4) and main transfer port open size and shape. All high lighted in pic 2.

Pic 3 data from tests that show the trade off between power and drivability for the different variables.

Pic 4 configuration of the better test cylinders.

Get a copy of the paper from here:- http://www.2stroke-tuning.nl/media/pdfjes/porting.pdf

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[TZ350]

I will measure the port layout on my GP and a RM to see how they compair.

As SS90 says, now's the time to get a Dyno curve of my existing setup and then I can start development.

There is gold to be had in the transfer port shape and flow patterns. Not that I didn't already know that, just didnt know how to go about it and wisely left it alone but now I can see some direction to work towards.

When I get the motor apart I will look at unmasking the transfer ports in the way F5 suggests.

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[SS90]

I will measure the port layout on my GP and a RM to see how they compair.

As SS90 says, now's the time to get a Dyno curve of my existing setup and then I can start development.

There is gold to be had in the transfer port shape and flow patterns. Not that I didn't already know that, just didnt know how to go about it and wisely left it alone but now I can see some direction to work towards.

When I get the motor apart I will look at unmasking the transfer ports in the way F5 suggests.

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Yea, I am really keen too see what your power and torque curves look like.... I would expect that it would not look too dissimilar to the 1st graph you posted above...by that I mean, quite a "peaky curve". This is O.K, and if I am right, it will be a result the scavenge pattern, exhaust design and masked transfers.

If this is the case, and Teezee changes these points (O.K, granted, a new chamber might not be happening soon, but I believe that will be the nest thing.

If the transfers are masked, and the scavenge pattern is given the "new gereration" treatment.... even with the "old school chamber", I would expect not so much a massive peak horsepower gain, but I certainly would expect to see more torque (across the whole range), and a MUCH flatter, longer, power curve. My experience tells me that the latter is a result of unmasked transfers.

A good method is to put the piston in the cylinder, with the piston at what is effectively B.D.C...... so the transfers are completely uncovered (open), then, look at the "cutaway" in the skirt of the piston, in relation to the "cutaway" in the cylinder liner. As you have used a different piston, there is a good chance that the piston "cutaway" is higher than the liner. Just matching the piston to the liner "cutaway" would yield substantial gains in the characteristics of the power delivery.

I have seen 10% gains in horsepower AND Torque in more than one engine.

But yes, one step at a time, first a "benchmark" to base results on!

[TZ350]

If the transfers are masked, and the scavenge pattern is given the "new gereration" treatment.... even with the "old school chamber", I would expect not so much a massive peak horsepower gain, but I certainly would expect to see more torque (across the whole range), and a MUCH flatter, longer, power curve. My experience tells me that the latter is a result of unmasked transfers.

But yes, one step at a time, first a "benchmark" to base results on!

I can allready see a big difference between the GP's main transfer port axial (upwards) angle of 10 degrees and the new generation angles of 23-29 degrees. Speedpro recently made a new chamber and cylinder with the more upswept main transfers and he reports that it works well for him, flater longer and powerfull.

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[Chambers]

Check this baby out. The sales blurb says 100cc 30Hp 18,000rpm.

Whatever but you can bet its a hot little number and more than 20hp. 200Hp/Litre.

Look at that finning and how short the exhaust tract is.

Isn’t TZ banging on about shortening his GP's exhaust tract to reduce heat uptake into the cooling system and how it's important to have the roots of the fins as close to the combustion chamber as possible.

Might be onto something there.

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[SS90]

I can allready see a big difference between the GP's main transfer port axial (upwards) angle of 10 degrees and the new generation angles of 23-29 degrees. Speedpro recently made a new chamber and cylinder with the more upswept main transfers and he reports that it works well for him, flater longer and powerfull.

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Yes, I have to agree, those angles are pretty much where you would need to end up. A few years ago, while I was aware of concept, I didn't fully appreciate the gains that you would make with such slight changes.

One thing that you cylinder doesn't have, is "dividers" running up the centre of the transfer ports..... This (the divider) also forms part of the scavenge pattern system on more modern cylinders.

However, if you can somehow "rerofit" some sort of divider (even if it is only at the bridge of the transfers into the port, there will be gains there as well.

This enables a "curtain" effect from one stream to the other.

I am unsure if "Devcon" would be suitable for the environment, and obviously removing the liner, and either welding a divider into the aluminium skin, or welding a divider to the liner, then pressing it back in would be better.

However, as it is a "cast in" liner, that's not an option.

But I feel that some "thinking outside the box" would really help here!

[SS90]

Check this baby out. The sales blurb says 100cc 30Hp 18,000rpm.

Whatever but you can bet its a hot little number and more than 20hp. 200Hp/Litre.

Look at that finning and how short the exhaust tract is.

Isn’t TZ banging on about shortening his GP's exhaust tract to reduce heat uptake into the cooling system and how it's important to have the roots of the fins as close to the combustion chamber as possible.

Might be onto something there.

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Here we touch on an interesting part of two stroke development!

To me, while I am unsure of the Manufacturer, it looks like a "fixed gear" Kart sport engine.

There are some anomolies with "fixed gear" Kart engines, and sadly, not all the tuning techniques that Kart sport use, are applicable to "geared" two stroke engines.

However, one comparison is "scooterMatic" (Twist and go).

As we are all aware, with an air cooled engine, you can't really SAFELY go lower that 1mm "squish", before you have problems with the piston touching the head.

However, because "fixed gear" Kart sport engines, and "scootermatics" do not have the demands placed on the power train that a geared engine does.

By that, I mean Kart sport engines and scootermatics are subject to "maximum R.P.M through most all of their operation.....where as a geared engine, the R.P.M goes from maximum, and then, when you change gear, it drops, say 4000 R.P.M, then when the gear is engaged, it goes back up again to maximum......there is alot of mechanical stress on the power train.

Like Teezee pointed out, there is up to .5mm stretch in the rod (he refers to "dynamic compression ratios"

On Kart sport and scootermatic engines, there is less mechanical stress on these parts (rod etc), therefore less stretch, and as such, the clearance is LESS variable.

As such, you can run "squish clearances" MUCH MUCH tighter than a Geared engine (0.5mm for example)

This, as we all know gives us the potential for more power.

While it is feasable to believe 100cc two stroke 30 P.S (I would like too see a curve or 2), if you attempted to put that power plant through a conventional gearbox, (also, let's not forget the amount of power that a gearbox "consumes"...... 30 Horsepower through no gearbox, but with a gearbox, I would say approx. 27 Horsepower would be realsistic) I surmise you would have a 25 gear close ratio "yo-yo"
Or, a scootermatic "constantly variable transmission"

As your "power band" on this engine would be the width of a mouses pubic hair!

The radial head is, in my opinion the best solution to displacing some heat, and it has been mentioned before (with reference to the last of the air cooled motocross bikes)

I think when Teezee talks of exhaust length, he refers to the distance from the cylinder liner, to the beginning of the the header, rather than having a header like the one in the picture........ Great for R.P.M, and stuff all else!

Becasuse, again, you CANNOT simply copy a Kart sport or scootermatic design concept (exhaust, scavenge pattern,compression,cylinder head design, EVEN PRIMARY COMPRESSION.... on Kart sport fixed gear engines, this is often higher than 1.5:1, as the engine is only operated at top R.P.M, and runs much higher compressions, so the "pumping losses" are reduced.)

The requirements of an engine (operating speeds,purpose, AND available gear ratios) are a big limiting factor in your set up (and therefore maximum power achieved)

That is why so many scootermatic (and Kart sport) tuners are able to get such high power results.

A point of interest, while the Kart sport and scootermatic boys get more power for the same engine capacity as motorcycle tuners (by default quite often), they always have very low torque results.... due to the fact that they run such big port time areas... the biggest "Thief" of torque (particularly in the lower R.P.M)

In my opinion, Kart sport and scootermatic tuners (not all, but most) base their concepts on "There is no substitute for R.P.M", and while this is clearly true, you can only get maximum benifit with this concept alone if you are not hindered by your available gear ratios, and carb size.... (like a 5 speed GP125 engine, with a 24mm carb!)

[F5 Dave]

Here you go TZ I was at the TeManawa show & came across this fine eastern block blaster with an oversized head & thought of you (aww) sadly my camera had got knocked onto a weird setting so excuse quality of pic.

While we are at it (bit of a sidetrack interlude) at it there was this piece of rolling history in somewhat of a sad state of repair but would still be pretty competitive today in 50 class & is current NZ 50cc record land speed holder (complete with bucket of parts, oh hilarious). . . .+ some other knock up, a replica of course, but 'the' replica.

[speedpro]

I am unsure if "Devcon" would be suitable for the environment,

Devcon seems to be made for this sort of effort. It does only last for about 1 dyno run in the exhaust port though. Been there etc etc . . . .