TZR250 3MA
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Sometime ideas are coming when you browsing on E-bay.

Someone was selling a changed TZR cylinder, first thoughts where is it a changed SP cylinder but I was missing the O-ring cutout. It turns out to be, hand made exhaust sub ports.

And what I liked about them was the size "there huge" compared with a SP cylinder and they are also bigger than a 3MA cylinder, so it had my attention.

Contacted the seller and we had immediately a nice conversation,
he made more cylinders like this a true hobbyist with the know how to do it.
So Stephan thanks for the cylinder it is giving me a good starting point.

In rough lines the cylinder is ready, I only want to smooth things a little bid so it has my own thatch on it.
With a fresh one size up piston it should be good to go.

I'm very interested how this one is performing.

Look at those nice big sub ports

As I sad, it needs some small attention but the big lines are there

Today I finished the Special cylinder.

Made the exhaust ports equally to each other, and machined the pv to match the changed port height.

Had to machine the pv busch a tiny bid to make it all fit

Changed ypvs

Smoothed the exhaust shape

From top

From bottom

Made a port map to give a impression how it looks, clearly you see the sub ports are huge compare with even a SP cylinder.
This is a experimental setup, as I don't have experience with this kind off exhaust ports

Ports are now equally to a Y-2 Cylinder.
With exception off the C-port

New piston in freshly honed cylinder

Did the last measurements and changing to the cylinder, now it is all mounded together and ready to go.
Hope to test it soon

Looking trough the YPVS opening

Could test my new measuring devise to set piston in top position

After measurement, I needed to enlarge the squish band I tiny bid du to the bigger piston.
Head volume 12,5cc with a 0,7mm squish

The well know O-ring setup

Not really proud in this part, as I thought the larger piston could hit the YPVS I machined it a bid.
Turns out that it didn't needed it, its now a tiny bid off as you can see.

After testing the cylinder (ended with 27HP rear wheel) it looks like there is a bid more in it then right now.
We will lift the transfer timing to what is possible

Piston after +/-25 Dyno runs

Head after +/-25 dyno runs

Update: 24-02-18

Martin77 has lifted the transverse from a 40,3 to a 38,6mm it will be interesting to see what this brings

A nicely done job

Needed to smooth the top, as it was rough

With weatherproof sandpaper and a glass plate

It came out nice

Head needed the cleanup to

And came out nice to

I have tried to remove the strange curve in the transfer (purple arrow)
A lot off work I should get better tools for this


Indication direction for more power

My Dremel set is does not mean much but until now I have done all the work I planned
Someday I will infest in proper tuning material

I shortened the 90 degree tool so it fits the cylinder

As you can see not much room, but it works


Done both sides

Did not cut the cylinder legs, only rounded them is bid off

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