ESE's works engine tuner

[Frits Overmars]

I was fiddling around with port arrangements and came to think about the inner radius of the ports... Has anyone done any tests on the subject? I have felt that cylinders have gone against a bigger bulge over the last 10 years without having put any major thought on it

Looking at your picture on the previous page I get the impression that the relation between the outer bulge and the inner radii of the ducts is way off, Muhr.
Someone has done some tests on the subject, a feller named Jan Thiel.
Below is the Aprilia RSA A-duct geometry, showing the inner and outer radii dimensions and the whereabouts of their centers.

The Yamaha paper... studied port arrangement extensively and their conclusion was that for a 125 an inner radius of 15mm and an outer of 55 gave the best transfer ratio.

The 32,44 mm outer radius of the Aprilia is noticeably smaller than the 55 mm Yamaha radius, confirming Swepatricks remark:

My experience with porting both twostroke and foulstrokes is that one should beware of too tapered design in runners.

The main difference between Aprilia and Yamaha (and Honda for that matter) is in the inner radius: the 22,6 mm RSA-radius is 50% bigger, which makes a huge difference in flow attachment, flow coefficient and flow direction stability.
There was some difference in horsepower as well...

[Muhr]

Looking at your picture on the previous page I get the impression that the relation between the outer bulge and the inner radii of the ducts is way off, Muhr.
Someone has done some tests on the subject, a feller named Jan Thiel.
Below is the Aprilia RSA A-duct geometry, showing the inner and outer radii dimensions and the whereabouts of their centers.


The 32,44 mm outer radius of the Aprilia is noticeably smaller than the 55 mm Yamaha radius, confirming Swepatricks remark:

The main difference between Aprilia and Yamaha (and Honda for that matter) is in the inner radius: the 22,6 mm RSA-radius is 50% bigger, which makes a huge difference in flow attachment, flow coefficient and flow direction stability.
There was some difference in horsepower as well...

Thank you for all the answers

Yes, Frits is true, I have stretched the outer radius to be able to drive an other cylinder in the same crankcase for comparison. but that's obviously something I can give up.
I have also had to shorten them 4mm because of shorter conrod, piston height and probably crankcase deck height (in comparison).
To the left is so close to an RSA I can come.

[Jannem]

Thank you for all the answers

Yes, Frits is true, I have stretched the outer radius to be able to drive an other cylinder in the same crankcase for comparison. but that's obviously something I can give up.
I have also had to shorten them 4mm because of shorter conrod, piston height and probably crankcase deck height (in comparison).
To the left is so close to an RSA I can come.

Did you keep the inner radius the same?

[Muhr]

Did you keep the inner radius the same?

It's changed! The bulge is 0.7mm less so it's hard to see

[Brett S]

New piston wiseco

"the piston to self-adjust to the cylinder. The Racer Elite 2-Stroke Series pistons have enough clearance for the smallest cylinder, adequate clearance for the largest cylinder, and everything in between."

http://blog.wiseco.com/one-size-fits...stroke-pistons

I see their anti rotation pin for the piston ring has grooved the bottom of the ring land.

[SwePatrick]

Look inside the hole for the wristpin.
I wouldn´t be happy with that machining, rough cut has left almost none material left to set tolerance in with hone.

[Muhr]

Thank you for all the answers

Yes, Frits is true, I have stretched the outer radius to be able to drive an other cylinder in the same crankcase for comparison. but that's obviously something I can give up.
I have also had to shorten them 4mm because of shorter conrod, piston height and probably crankcase deck height (in comparison).
To the left is so close to an RSA I can come.

If anyone thinks it's interesting

[Jannem]

It's changed! The bulge is 0.7mm less so it's hard to see

Wonder if logarithmic inner radius would work? (closer the exit, bigger the radius)
Flow usually wants to separate from the short turn after the apex.

[SwePatrick]

When designing transfers and crankhouse.
Shouldn´t one calculate with that Aprilia is a 'closed' volume and reedengines are 'open'?

If pipe is overscavenging a reedengine, the reed´s can open at a point were a rotatingdiscsystyem is closed.
Thereby flow after 'puncturing' crankhouse when transfers is opening are different between the two?

[Muhr]

Wonder if logarithmic inner radius would work? (closer the exit, bigger the radius)
Flow usually wants to separate from the short turn after the apex.

With my amateur knowledge of CFD (next to none), it feels like there may be something in what your saying.

[1948rod]

Best of luck to ken Seeber on Monday for your plumbing operation. Be well buddy.

[Twopints]

Husaberg

"also tha 120mm c-c rod is very long for a piston port yam compared to others in the range
maybe its from the Longer stroke TR2 series or from an outboard do you have the numbers on the corned"

the rod i have is attached to a crank i bought on eBay as NOS for a YA6 , it has a large chamfer on one wheel for a Disk valve

the rod has yamaha on one side and the letter "C" and i think what is a japanese character that looks like a reversed F in a circle ,no numbers

Grumph

Kevin bought 4 sets of parts and i believe every thing was new, a mate of mine started his apprenticeship in 1967 he said that he was getting $16 a week so a crank half would have been 2 weeks wages for him

TZ 350

when you change rod length do you use a different piston ? or do you space the barrel up or down ? what piston do you use ?

I am keeping my eye out for YDS2 crank to measure up and a YL2 disk valve to measure up

any one recognise the Carb in this photo ?
http://collingrovehillclimb.com.au/s...alve%20jpg.jpg
mikuni 24mm ?

Thanks every one that has replied with advice

[husaberg]

Husaberg

"also tha 120mm c-c rod is very long for a piston port yam compared to others in the range
maybe its from the Longer stroke TR2 series or from an outboard do you have the numbers on the corned"

the rod i have is attached to a crank i bought on eBay as NOS for a YA6 , it has a large chamfer on one wheel for a Disk valve

the rod has yamaha on one side and the letter "C" and i think what is a japanese character that looks like a reversed F in a circle ,no numbers

Grumph

Kevin bought 4 sets of parts and i believe every thing was new, a mate of mine started his apprenticeship in 1967 he said that he was getting $16 a week so a crank half would have been 2 weeks wages for him

TZ 350

when you change rod length do you use a different piston ? or do you space the barrel up or down ? what piston do you use ?

I am keeping my eye out for YDS2 crank to measure up and a YL2 disk valve to measure up

any one recognise the Carb in this photo ?
http://collingrovehillclimb.com.au/s...alve%20jpg.jpg
mikuni 24mm ?

Thanks every one that has replied with advice

carb is a Mikuni VM
Look for kawasaki ke125/ks125 carbs on ebay.
actually is that a clip on version? so maybe early 90cc suzuki ie rv90 or a100 would be the easiest cheaply obtainable option
if you were attempting to build a repo unit or restore an old engine mock up the measurements of the origional and work from there.
If you give the the measurements of what you want i can sift through a few sites i know to give you some modern options.
The conrod is likely to be arround 100mm as it was the style of the time to run stroke times 2 for rod length.

[TZ350]

TZ 350 when you change rod length do you use a different piston ? or do you space the barrel up or down ? what piston do you use ?

I use single ring motor cross pistons with a crown height similar to the original GP piston and the cylinder is spaced up. For me the longer rod is about increasing the crankcase volume.



For even more crankcase volume the cases were spaced apart by 12mm and the insides of the crank webs were faced off until they were completely flat, without any shrouding of the big end at all.

I worked on the assumption that more volume was better and even more volume would be better still. I have no idea of how much crankcase volume there is now, it must be more than most. I will have to measure it next time the motor is out of the bike.

My motors breathing development is becoming very dependent on the suction action of the pipe.

[Frits Overmars]

Wonder if logarithmic inner radius would work? (closer the exit, bigger the radius). Flow usually wants to separate from the short turn after the apex.

In principle it would work, Jannem. You'll notice that in the transfer picture I posted the other day, the centers of the inner and outer transfer radii do not coincide.
This gives a gradually reducing cross section area, building up pressure at the outer wall, which helps to prevent flow separation from the inner wall.
The advantage of this approach is that we can use constant-magnitude radii, which used to be of practical value to model makers.
Nowadays with CNC we could also use logarithmically variing radii but their effect over the restricted length of a transfer duct would be limited.