50mm taiwan bore info

Madman · Post by **Madman** » Wed May 16, 2012 11:07 pm

Red Eft Performance wrote:
evilone wrote:
bakaracer wrote:yeah thats a bit tight. you want more like .20mm or.23mm range.
I've been second guessing myself all day at work....bakaracer, why does it need to be .20mm - .23mm range?
That would be .008" to .009" when typically they are around .002" to .004"
That would mean madmans piston to cylinder wall clearance would be a little under .006" which is actually a little on the big side. Is it a Ruima thing or what?
First off Evilone how are you getting your measurement? Are you measuring the same way madman is in the pic above?
You guys should be measuring at the bottom of the piston 90 degrees out from the piston pin on the skirt. That is typically the largest point on the piston. Its very hard to get a accurate measurement with a feeler gauge. Really not the best way to do this.

Baka would know better than I what the best clearances would be for these bores.

So with that said if you are measuring with a feeler gauge you have to take your measurement and Divide it by 2. cause you are pushing one side of the piston against the cylinder wall and you are actually measuring the gap of both sides. So if you take Bakas suggestion of .008" your clearance is actually .004"

I will admit .004" seems a bit big for a 50mm bore. But maybe thats what needed do to the low quality of these bores. Again Baka has alot of experience with this stuff.

Thanks I followed your advice and re measured, I only have a feeler gauge So I used that, the measurement was almost nothing used the second smallest gauge. 0.04mm was a little
Tight but 0.06 was super tight!!

Madman · Post by **Madman** » Thu May 17, 2012 12:14 am

Ok so for comparison I measured my old standard bore with 16000km on it. And a new 74.9cc kit from kn kikaku and discovered a few things ok first the standard bore.

0.06mm

But the real surprise was the ring gap!! Add these together and you get it!

Ok the kn bore:
It is the same 0.04 as the Chinese Taiwan bore,(funny that it's also from Taiwan)

And at the top: 0.2mm a .5mm larger than the other Taiwanese bore!

But here is where stuff gets
interesting!
Lots of crudd in those ports but they are chamfered.

Now what is this port it is not on either the standard or 50mm bore?

And take a look at the kn piston! It's shorter and totally different in shape!

So that is what I have discovered so far.

bakaracer · Post by **bakaracer** » Thu May 17, 2012 1:19 am

the quality of that new bore you have looks pretty good port wise. the height difference could be because the other bore has a higher deck to base length than the new bore you have. so a taller piston is needed. you can measure the 2 and see if there is a difference.

bakaracer · Post by **bakaracer** » Thu May 17, 2012 1:22 am

evilone wrote:
bakaracer wrote:yeah thats a bit tight. you want more like .20mm or.23mm range.
I've been second guessing myself all day at work....bakaracer, why does it need to be .20mm - .23mm range?
That would be .008" to .009" when typically they are around .002" to .004"
That would mean madmans piston to cylinder wall clearance would be a little under .006" which is actually a little on the big side. Is it a Ruima thing or what?

that .20 is for the top since mad posted a top measurement.

Madman · Post by **Madman** » Thu May 17, 2012 2:09 am

bakaracer wrote:
evilone wrote:
bakaracer wrote:yeah thats a bit tight. you want more like .20mm or.23mm range.
I've been second guessing myself all day at work....bakaracer, why does it need to be .20mm - .23mm range?
That would be .008" to .009" when typically they are around .002" to .004"
That would mean madmans piston to cylinder wall clearance would be a little under .006" which is actually a little on the big side. Is it a Ruima thing or what?
that .20 is for the top since mad posted a top measurement.

That's what I figured too!

bakaracer · Post by **bakaracer** » Thu May 17, 2012 3:28 am

When you used the .04 gauge,did the piston slide easy? On the piston bottom all the way around bevel the edges. Also on the bottom you have the side cutouts, round the corners.

Madman · Post by **Madman** » Thu May 17, 2012 5:20 am

bakaracer wrote:When you used the .04 gauge,did the piston slide easy? On the piston bottom all the way around bevel the edges. Also on the bottom you have the side cutouts, round the corners.

The piston with the 0.04 did slide a little! And I will be beveling thanks for the Heads up!

bakaracer · Post by **bakaracer** » Thu May 17, 2012 5:40 am

Madman wrote:
bakaracer wrote:When you used the .04 gauge,did the piston slide easy? On the piston bottom all the way around bevel the edges. Also on the bottom you have the side cutouts, round the corners.

The piston with the 0.04 did slide a little! And I will be beveling thanks for the Heads up!

how tight was the one you seized measured in the same area?

Madman · Post by **Madman** » Thu May 17, 2012 6:27 am

bakaracer wrote:
Madman wrote:
bakaracer wrote:When you used the .04 gauge,did the piston slide easy? On the piston bottom all the way around bevel the edges. Also on the bottom you have the side cutouts, round the corners.

The piston with the 0.04 did slide a little! And I will be beveling thanks for the Heads up!
how tight was the one you seized measured in the same area?

The one I seized was about the same on the skirt of the piston for tightness with 0.04 but the crown of the piston was noticeably tighter at 0.15 clearance compared to 0.2 clearance on the new set!

I have also ordered another 50mm kit
from Taida in Taiwan including two pistons, as I plan to hone my original 50mm kit and run it with the new piston taking care of clearances and pressure testing the case. I just like the idea of having the 50 mm kit.

So the 48mm 75cc kit is a spare the new 50mm kit is a spare and I hope to use it on a future build. This has kinda been good as I'm learning a lot through this process and am acquiring new tools which I can use in the future!

That's the plan!

Madman · Post by **Madman** » Thu May 17, 2012 11:52 pm

Ok made some port maps for the Taiwanese 50mm bore just for fun!
This is just for fun and maybe later I'll
Try to arrange more aggressive porting, but gotta get one of these suckers running first!

bakaracer · Post by **bakaracer** » Fri May 18, 2012 12:36 am

did you measure the cylinder height of the 2 bores you have? from the deck to base length. those numbers you posted are really low for a stock stroke. with 44.1 or 44.4 stroke the numbers look better duration wise. for stock stroke those numbers should be more like ex. 23, intake 33 , boost 34

Madman · Post by **Madman** » Fri May 18, 2012 1:03 am

bakaracer wrote:did you measure the cylinder height of the 2 bores you have? from the deck to base length. those numbers you posted are really low for a stock stroke. with 44.1 or 44.4 stroke the numbers look better duration wise. for stock stroke those numbers should be more like ex. 23, intake 33 , boost 34

Thanks Baka I'm running a stock stroke on this setup. I have not yet compared the deck height of my two bores. Will post more as this thread is becoming a good source of information on Taiwanese bore kits!

Madman · Post by **Madman** » Fri May 18, 2012 5:13 am

I think you are correct with the height from the top of the bore!! The other one I have is a lot closer to the top! Also I must add I missed two of the intake ports in my map so I will update that tonight! Also with the bore from kn kikaku for comparison!

Madman · Post by **Madman** » Fri May 18, 2012 5:55 am

Ok here is the kn kikaku 75cc kit!

Madman · Post by **Madman** » Fri May 18, 2012 8:21 am

bakaracer wrote:did you measure the cylinder height of the 2 bores you have? from the deck to base length. those numbers you posted are really low for a stock stroke. with 44.1 or 44.4 stroke the numbers look better duration wise. for stock stroke those numbers should be more like ex. 23, intake 33 , boost 34

man check that out! On the KN bore (which admitatly cost me 3 times of the other) you were right on the money for the port timings! you are like master yoda of the twostroke scooter, I really gotta take my hat off to you man you sure know what you are talking about! Thanks for your help thusfar I really appreciate it!

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