S3 Race 250 Port Matched Cylinder and Head

[Jakobi]

Hi Everyone,

As I've been saying in a few different threads on here I have decided to change my 2010 EC300R to a 250 to see which I prefer.

I ordered the parts through Mark at GoFasters who provided great customer support. He answered all my questions and had everything in the mail and headed towards Australia in no time. All up it was great value with the Cylinder, Piston, Rings and clips coming in at $625usd, and the S3 head with 3 inserts being another $210usd. Quite cheap for what you get.

The workman ship on the parts is stellar and levels above the stock cylinder. I will post pictures of my 300 jug when it comes off to show a comparison regarding the casting of the stock cylinder and the hand port matched work of the S3.

I am interested to see how the base gasket stack will go to get the port timing correct, where the squish band ends up after this, and what the trapped volume and compression ratio are using the black insert (high high comp). With my 300 and its S3 I found the CR came up higher than I would like, while still having the squish band bigger than ideal by around 0.5mm. If this is the case I will ship the 250 head off with the 300 and have them both machined to correct the squish and CR. The plan will be to machine the insert to required specs and then lap the base of the head to match the inserts new reduced height.

I'll also be cleaning up the ports on the 300 while its off the bike which may get a thread of its own.

See pics below.

[Jakobi]

Ports nice and clean

[Jakobi]

And some more on the head

[nambo-trev]

cant wait for the updates jakobi this is going to be a cool modification!

[(F5)]

That's quite odd, my 07 I was quite happy with the finish of the ports etc. I wonder if its a later model cost cutting thing?

[lonetree]

That set up looks really nice. I really like the idea of the interchangeable inserts, although i have just got my standard head back from TSP (dmcca).
out of curiosity, are you going to setup the base gasket with exhaust port level with piston (BDC)? Are the ports on the s3 different to standard?
-just to let ya know, my 250R, the piston is 0.6mm above the port, set from factory (not that it means much) but this thing will lug and rev to the moon...
i will be watching this thread with interest...

[Jakobi]

Originally Posted by (F5)

That's quite odd, my 07 I was quite happy with the finish of the ports etc. I wonder if its a later model cost cutting thing?

Doubt its a financial thing. Just the nature of casting I think. You get some good ones, and some not so good, depending on the particular cast and how long its been used for etc. The ports on my 300 were quite clean towards the nicasil side but where the meet the cases were quite sloppy. It won't take too much work to clean them up.

It will probably be another month at least before the 300 top end comes off. I still have a few more hours to put on it before its due to be changed.

When its time it will be like bike Christmas as I'll be doing the annual greasing of the bearings, exchanging the sachs internals for Ohlins TTX on the forks. Re springing front and back, and fitting a Motosportz damper, as well as the conversion to a 250cc (removing the reed spacer and jetting to suit).

If anyone has anything in particular they want me to check out or photograph while doing this just yell out and I'll do my best to remember. Usually once the tools are in hand the camera gets left on the bench so it won't be a step by step how to or anything. Just some progress pics and things of interest.

[nambo-trev]

You know Glenn I've had a lot of seat time on the 2 strokes over the last 3 years and what initially brought me over was riding my buddy's 250. Last year I had to ride a buddies new 250 up a few hills for him and was like "wow" this is so easy to climb with even with my 300. I also find as I've become a Better rider and am riding with expert and pro level riders I'm understanding that its not all about power. The 250s I've rode lug just fine and climb great but the BIG difference to me is the fitness part. These guys ride on a totally different level and a 4-5 hour ride chasing them I need to keep as much of my energy as I can I feel like the 250 helps me with that. The 300 gets very exhausting on big hills and tight single track from all that power pulling on me. I tried to fight it thinking the 300 was the weapon of choice but for me in order to reach that next level I feel a different weapon is required. I guess time will tell and hey if it doesn't work out the way I wanted someone here will get a great deal on a s3 cylinder kit!

[GMP]

Now you get the point of less is more, welcome to the club.

[Jakobi]

I don't think you'll be disappointed Trev. The only time I ever miss the 300s grunt is when I'm being lazy and running too many gears high into a hill and then get out of shape. Nothing that changing back down to the right gear can't fix.

With the 250 engine, and TTX suspension I honestly can't see things getting any better than this.

Glenn, I'm almost certain some of the newer bikes are using the same S3 cylinders. Next time I have mine off I'll check if its also stamped on the underside. The finish on the ports between the S3 and my stock cylinder were worlds apart.

I think I'll be having a go at doing my first bottom end some time this year so no doubt will just continue to add to this thread.