ESE's works engine tuner

[bucketracer]

Those transfer dividers could do with some sharpening though, not sure you could shave with them just yet.

I was taking the piss ....

Sharpen the transfer septums and I will personally bend you over and do horrid things with your arse.

I had a dig around in the shed to check, and found the transfer dividers on a TF/TS are sharp standard.

[Yow Ling]

The planets came into alignment with my engine this week, things started moving.
My piston arrived from Strike in Perth, its a KT100J 50.220 that leaves me heaps of oversizes before I hit the limit at 51.25mm. Also in the mail were an Ignitech ignition and V Force 3 reeds from Wobbly in Tauranga.

Now that I finally had a piston I was able to bore the cylinder, the instructions say to allow 0.08mm, talk about pressure, I thought I would take a few light cuts untill I figured out if my toolsetting was on the money. Seemed to go OK. Piston 50.22mm bore 50.25 leaves me 0.05 left to hone.

Had to go round to diesel pigs to borrow a MB100 small end bearing so I could have a trial fit. Looks pretty good, piston has 8mm interference with the head, ha squish is just for sissys.

Earlier in the week I did a bit on the engine mounts, still have a few mm to go here and there but heading in the right direction.

Heres a few pics of the progress

[Yow Ling]

Couple of engine mount pics

[F5 Dave]

WTF?! what is with that piston? Is that what a J piston looks like? It's um, unusual to say the least. lot of mixture stored under that crown. Am I missing something? Doesn't look anything like an S piston.

[Yow Ling]

WTF?! what is with that piston? Is that what a J piston looks like? It's um, unusual to say the least. lot of mixture stored under that crown. Am I missing something? Doesn't look anything like an S piston.

The big difference is the J piston is legal in this engine a S isnt

[wobbly]

I have looked into the "overangled" issue that creates a problem when using the electronic powerjet carbs.
Its worth plenty of horsepower to keep the intake dead straight, and I am building a KTM250 for a open class kart at present.
I have bored the 38 to 40.5 and mounted it on a straight rubber manifold.
This sits the carb too steep, in that the siphon hole for the powerjet circuit in the side of the bowl is only just "underwater" when sitting static.
Get some serious G forces working and this will be sucking air.
It looks easy enough to Araldite a small external tube running forward to the front of the bowl that has plenty of fuel height above it at all times.
Or maybe drill a hole thru at an angle forwards, and press a small brass tube into this to collect fuel from the front side of the bowl.
I will pic this when I have done it.

[speedpro]

I was looking at this exact thing today with the 36mm Keihin

[richban]

I thought I would post these here just coz the people that visit this thread are mostly old school, bucket racers.

The first Bucket. It also had a full faring that never really got mounted. Not sure what happened to it. And also the 50 I used to ride to school. Check the pipe on it. I am quite sure it never did anything but make a big noise. Did anyone ever race down in Tauranga? Good old Bay Park. We used to lift the bikes over the fence and rip around for ages.

[marsheng]

Am I now taking to the Dark side ???

Ok As with 4 strokes, you scale up the details from small engines to larger ones and there is some cutting back on cam timing and compression ratios as you get bigger.

On 2 strokes, will the ports basically follow the same scaling but maybe not quite as radical due to the max RPM is being lowered.

Assuming that we are working with track bikes, are the angles of the ports into the combustion chamber for A B and C ports (or Main Aux and boost port depending on your naming) roughly the same, the height from the top of the cylinder being the main variable to change. (Ie Timing)

Can I take it that the lower part of the transfer ports all come in at the same angle as the piston crown, either flat or 8-12 degrees and the tops of the ports are angled at 12 for A 25 for B and 55 for C as a rough start.

My assumption is that a 50 mm bore and a 75 will scavenge the same. Possibly a 50 bore and x 50 stroke may scavenge differently to a 50 x 75.

Cheers Wallace

[wobbly]

Plenty of unfounded assumptions in there mate.
Big 4 strokes can use more radical cams as the cubes overcomes the lumpyness.
Scaling ports in a 2T is a complete waste of time, the STA numbers are different for every bore/stroke ratio, rpm and swept volume.
In general you want to keep as close to square as you can, as this maximizes the angle area available, and maximizes the safe rpm for the swept volume.
ie a 74 bore on a 58 stroke for 250cc will never make as much power as a 68 square 250 as the angle area of the ports is reduced way more than the short strokes ability to rev ( piston weight notwithstanding) and make power.
The roof angles for A,B,C were reversed years ago from your convention ie 25,8 ,55 , and the floor angles depend upon the inner turn radius size.
Scavenging patterns will be similar for similar bore/stroke ratios ie a 50 square, will be similar to a 75 square, IF the STA numbers are equalized for the max rpm achievable.
ie reving a 50 stroke 100 to only 12500 is nothing like reving a 125 Gp engine to 14500.
Bottom line is that to maximize power, the transfers will need to occupy ALL of the wall area not taken by the Exhaust, and once this is achieved then blowdown STA will ultimately set the power achievable.

[ac3_snow]

The big difference is the J piston is legal in this engine a S isnt

Care to elaborate re J and S pistons? How did you get on with the power valves and the sleeve, I assume you would have had to move the valves to meet the 'new' cylinder (sleeve) wall?

WTF?! what is with that piston? Is that what a J piston looks like? It's um, unusual to say the least. lot of mixture stored under that crown. Am I missing something? Doesn't look anything like an S piston.

Are you just referring to the amount of space between the piston crown and ring?

[Yow Ling]

Care to elaborate re J and S pistons? How did you get on with the power valves and the sleeve, I assume you would have had to move the valves to meet the 'new' cylinder (sleeve) wall?

KT100J pistons are for a junior class, they are 50 to 51mm bore, KT100S are around 52-53mm which would exceed the 104cc limit for my engines stroke

The PV question, to be honest I dont really know, I have read the gap to the piston face isnt critical, time will tell

[marsheng]

[/QUOTE]Scavenging patterns will be similar for similar bore/stroke ratios ie a 50 square, will be similar to a 75 square, IF the STA numbers are equalized for the max rpm achievable.
[/QUOTE]

Thanks for the info. My Bore and stroke is 67 and 70. It was originally an off road bike motor. My measurements are Exhaust 88, Boost 124, and Aux & Main 122 from TDC. The ports narrow quite a bit entering the cylinder. so I will try and enlarge them.

AG Bells book says that for 8500 RPM the transfer ports should be open for approx 126 deg. At 124 from TDC only gives a duration of 112 degs. Is this worth raising for a track bike ?

For the exhaust - he recommends 186 - I have 184 so that seems ok.

It is a Maico reed valve motor.

[marsheng]

floor angles depend upon the inner turn radius siz

I thought the floor angles were there to keep a stream of fuel/air over the piston to keep it cool.

Cheers

[kel]

AG Bells book says that for 8500 RPM the transfer ports should be open for approx 126 deg. At 124 from TDC only gives a duration of 112 degs. Is this worth raising for a track bike ?
For the exhaust - he recommends 186 - I have 184 so that seems ok.
It is a Maico reed valve motor.

Careful as you go. Read as much as you can, dont just go on Bells work from the 80's as its well outdated (yet still relevant in some respects). Try Blairs book for good design over view (theres a link in this thread somewhere, will find and send to you), Jennings for time area analysis, port map analyser software, etc, etc. Its very easy to start cutting the ports only to find out it wasnt the best move. 2 strokes are quarrelsome beasts, not an easy mistress like a four stroke.