ESE's works engine tuner

[SS90]

Pic-1 the cast reinforcing web that gets cut away to unmask the transfer on my engine.

Pic-2 the Wiesco piston does not have this web and may be a better bet.

Pic-3 a Honda RS125 piston.

Pic-4 Kawasaki cast piston and Wiesco forged piston.

Pic-5 Kawasaki piston with cutouts like SS90 has been discribing.

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I believe that if you where to cut away too much of the piston you use, you would be "dating disaster", bit I think you mentioned when you took too much away previously you had cracking problems? This I would believe!

The wiesco piston looks more heavily engineered (which is why I suspect it has no webbing), and as such it's safe to assume you can remove more material than the other pistons, as the skirt thickness is much more substantial.

An advantage of the Wiesco piston (in my opinion) is because of the thick skirt walls, you are more likely to be able to have a closer to semetrical shape in the cutaway.

The RS125 Piston (although you cant use it) would be the best one. It has a nice big cutaway, and the webbing runs all around it radius.... nice and strong!

The Kawasaki piston also would be wort a second look.... I wonder if that piston has webbing running all through it's cutaway radius?

I don't know, (I suspect that it does though)

But, yea, the Wiesco looks quite "rugged" and could easily stand some removal of material!

[SS90]

SS90 I am also unsure what you mean by a "boost port".

Yea, sorry, it's easy to get confused when you use different terminology! Sorry!

Like Yowling suggested, when I refer to a "transfer boost port", I do mean the Eric Boysen designed reed petal controlled system, it's just that it has been out of copyright for so long now, that it is more often reffered to a "transfer boost", or I have recently heard it reffered to an "auxillery transfer port"

But, of course, there are other types boost ports, depending on what type of intake system you have (piston window induction, or crankcase induction etc) and I use this term (in the context of your engine) in reference to any extra port, or series of (controlled by the piston normally) that aid in scavenging of the crankcase at BDC.

[SS90]

no such luck I think Boysen ports use Boysen Reeds which seems to be 2 sets of reeds arranged in a vee .
And you need a bigger port to accomidate them.
2 strokes are not all the same as you have rotary disk engines that uses a hole in one of the crankcase webs instead of reeds and the air-fuel mixture is inducted into the crancase to the tranfer slots and a cut out in the side of the piston uncover hole thru to the cylinder.

there are heaps of links in this thread that explain the different workings of the different 2 strokes k

Yea, your right Crasin, I guess your comment about Apples and Pears is quite correct.

Teezee's engine is "Disc Valve", and as such, "boysen ports" (or transfer boosts, as I called them) are not relevent!

To compare the boost port systems of a piston window induction (like the ones I posted) to Teezee's Cylinder is indeed "Apples to Pears"

I included them because I wanted to demonstrate how previously manufacturers, if they used this "Boysen port", they did not have the need to worry so much about crankcase scavenging, as they compensated for this by simply "putting more fuel into the transfers"

And, as such the piston cutaways are quite alot smaller than they should really be, particularly in an engine like Teezee's GP125, where crankcase scavenging has become more important (due to some limitations of the design, etc)

In the picture I posted, I had tried to use both "styles" of tuning..... Like Trinity do with there RZ350 variant cylinders (although they use ports cut above the piston gudgeon pin, (like the Royal Enfield racers from the 30's, or Malossi tuning), and I simply cut away as much of the piston cutaway as I can, without weakening the piston too much!

[TZ350]

SS90 thanks for the explination.

[SS90]

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GP125 crank with the inlet side champhered and the bigend pin hole bored out from 19mm to 22mm. This was done when I thought that I needed a better rod to withstand the extra reves. As things have worked out the standard rods/bigends have worked well in the other team ESE bikes. The plan is to stuff the ballance holes with devcon F putty.

Pic 1 and Pic 2, modified GP125 crank.

Pic 3 GP125 rod/bigend and on the right hand side RD350 rod/bigend.

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OK, great! That's awesome!

There is quite alot you can do with this crank, but first you need to do some "donkey work" I am afraid!

I am sure you are aware why the cutouts are there in the crankweb..... are you able to take a picture of the position of these cutouts (with the crank in one case half, with the piston on the rod, at BDC)

see then what masking you have in regards to the crank web/piston cutout area......

Then, you need to fill your balancing holes as you suggested, and, with out further mods, accurately measure your primary compression..... when you know that, I can show you some methods of improving this area.... (It's all work that can be done at home, but requires removal of material from your webs, and as such will lower the primary compression.... and I like to see no less than 1.48:1

[Skunk]

I am sure you are aware why the cutouts are there in the crankweb...

I'm not. Can you explain please?

[SS90]

Pic-1 The cylinder in the case and the liner cutout does not match the transferport exactly.

Pic-2 Shows the size of the transferport window with the piston at BDC.

Pic-3 Shows the size of the transferport window with the long rod and 13mm cylinder packer, the window is much larger and the transfer divider looks like it could be brought down to here.

In pic-3 you can see how much of the pistion needs to be cut away to completly unmask the transfer window. There are limitations of course like leaving enough piston skirt to cover the exhaust port at TDC.

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Yea, it really is quite bad........ by the amount of material you need to remove (not all of course), I am starting to think that the Kawasaki piston is a better option.... how much so you feel you can remove from the Wiseco piston?

I personally run into such problems when I "stroke" an engine, (be it one of mine, or another manufacturer (Poloini, Malossi, Falc, Quatrinni, whatever) and the only pistons I use in these situations have large webbing that allow alot of material to be removed!

Either that, or the manufacturer (particularly Falc allow for this in their pistons, and use a piston that is of high quality, and thick enough in the skirt wall section to not need webbing... I suspect much like the Wiesco one you showed!)

[TZ350]

I am sure you are aware why the cutouts are there in the crankweb..... are you able to take a picture of the position of these cutouts (with the crank in one case half, with the piston on the rod, at BDC)

I have allways thought the cutouts unmask the bigend thereby facillitating its lubrication. The cutouts would be at BDC when the piston is at BDC. Is there another purpose for these cutouts?

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[SS90]

I'm not. Can you explain please?

Ok, well, it may be best to explain it like this.

The air and fuel, after it has entered the crankcase (via the timed disc), is pushed up to the cylinder via the transfer ports...... the fuel and air, goes between the crankwebs (not around the outside........) the cutaways are designed to improve this!

It primarily increases lubrication to the bearings......but you can use the same concept to improve transfer operation!

By that I mean, cutouts added to the inner edge of the webs when the piston is at BDC

[SS90]

I have allways thought the cutouts unmask the bigend thereby facillitating its lubrication. The cutouts would be at BDC when the piston is at BDC. Is there another purpose for these cutouts?

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Yes, you are quite right, but, also using the same concept, with new cut outs in the web (when the piston is at BDC new cutouts that align with the cutouts in the piston ), particularly when you have masking problems (such as you do) this can really help (with out having to take so much off the piston)...It is a technique that is quite often used when you "stroke" a cylinder, not so much as a result of the longer stroke of the crank, but because doing so requires the spacing up of the cylinder (like you have done, but for different reasons ), and as you see, the piston now masks the transfer area, and you are unable to use the extra crankcase volume effectively!

It's not 100% effective, but every little bit helps (and it requires only a small amount of time)

[F5 Dave]

I don't think that the MB is crankcase induction either, The reeds go into the back of the barrel, I was under the impression a case inducted motor was when the reeds feed straight in the back of the crankcase, leaving the opportunity to play with quite significant boost port sizes and more space for transfers.

Sorry to take this off topic, what head volume do you think would be optimum for the H100 dave? I was going to set it up at about 14:1 as the gear box works well, so a narrow power band isn't a problem.

Nobody so far has referred to what fuel they are running when talking compression ratios. Type of power & pipe, particularly baffle are important, as is general head design. The H was pretty touchy on ignition timing as the baffle was real steep angle, I suspect your RS pipe will not be anywhere as bad. I'll look up my old notes & PM you. 14:1 in that 100cc engine on 98 should be fine. I was running Av, although that brings up throttle response issues in some engines, never seemed to be a problem.

[TZ350]

Nobody so far has referred to what fuel they are running when talking compression ratios. Type of power & pipe, particularly baffle are important, as is general head design. The H was pretty touchy on ignition timing as the baffle was real steep angle, I suspect your RS pipe will not be anywhere as bad. I'll look up my old notes & PM you. 14:1 in that 100cc engine on 98 should be fine. I was running Av, although that brings up throttle response issues in some engines, never seemed to be a problem.

Running 91, we are currently running Av gas but when we have worked through our current issue (crankcase scavinging) we are planing on using one bike to explore the possibilites of using 91. As we have the idea that a lower octane fuel is faster burning. Allowing us to retard the ignition and get less negative work on the piston BTDC. I remember you hinting at this before. Do you have any pointers to set us off in the right direction or are we staring down yet another blind alley.

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[k14]

Running 91, we are currently running Av gas but when we have worked through our current issue (crankcase scavinging) we are planing on using one bike to explore the possibilites of using 91. As we have the idea that a lower octane fuel is faster burning. Allowing us to retard the ignition and get less negative work on the piston BTDC. I remember you hinting at this before. Do you have any pointers to set us off in the right direction or are we staring down yet another blind alley.

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Stick with avgas. All the GP bikes love it, it makes the parts last longer and it very good at avoiding detonation. If you are helbent on using unleaded then I think the only option would be 98. This is just from experience from running my RS125.

[F5 Dave]

Um fuel is a difficult one, the best stuff I’ve used is the leaded super from the early 90s. I’ve read many articles, mainly MX based as to why Av Gas is a crap fuel in a high performance high revving 2 stroke.

From this point you will get as many opinions as if you were stupid enough to ask what the best oil to run is.[arrrgh]
[edit] (not aimed at Kirk above, I was mid type when he posted)

Of course you can’t just buy VP or whatever at the local shop as cheap as Americans or Europeans can. Specifically illegal for buckets anyway.


Best option is to trial & see what work in your application. Our 3 (4?) options are of course 91, 95/98 & Av

In my dirtbikes I run ½ av & ½ 91. The theory being that 91 has the least aromatics (which are also bad for throttle response) & mixing it with a reasonable dose of leaded fuel should bring the octane up to about 98 (it’s not just a averaging of the ratings) & hopefully cocktail the closest approximation to what we used to get. The preceding is just conjecture, with no real testing except that they run real nice & are consistent with jetting & give good response & power using reasonably high compression ratios which suits enduro & trials bikes.

Straight 91 you may run into detonation issues pretty quickly. Lead is a great octane booster (& the only one legal in F4/F5 before the backyard chemists start up). You don’t need much Av to do quite a bit.

The class rules (& plain expense) means we have to make the best with some pretty average options. Trial what works best with your combustion solution.

[edit] high octane does not = highest calorific value, think about this.

[k14]

Um fuel is a difficult one, the best stuff I’ve used is the leaded super from the early 90s. I’ve read many articles, mainly MX based as to why Av Gas is a crap fuel in a high performance high revving 2 stroke.

From this point you will get as many opinions as if you were stupid enough to ask what the best oil to run is.[arrrgh]
[edit] (not aimed at Kirk above, I was mid type when he posted)

Yeah I have thought about going to unleaded (elf) and/or some high octane leaded (vp etc) but no one else in NZ does so why should I. The biggest incentive to keep using leaded for me is the lubrication help it has on service life. Apparently you can get around double piston and crank life using it (and with a piston costing nearly as much as a crank at $400 it adds up quickly). However I have modified the ignition timing, head volume etc to sufficiently account for the different characteristics of the fuel as the standard cdi is setup for unleaded. If it ain't broke, don't fix it I say.

As I said though, all my experience is from 125GP bikes and you are dealing with a completly different kettle of fish. Sorry for the slight hijack.