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]

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.

 

[Jakobi]

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...

I'm pretty sure I spoke with Dave re your top end He felt that setting your ports flush left a bit of a flat spot right before the power valve opened which is why he opted to set it up that way. He has also graphed in the past showing that .6/.7mm above the ports gives a good boost without too much sacrifice to top end and if opening the exhaust port a bit you will retain the top as per stock. Going to 1mm however cuts top end big time. I'm uncertain at this point where I will time my ports. I will probably aim for flush, but it will all depend on how this S3 cylinder matches up once on the cases. My 300 took a gasket stack of 1.3mm to time them flush.

To be honest, the interchangable inserts are a bit of a joke. They all measure the same volume and are just set at varying heights. For example the low compression insert results in a large squish height. The high one a tigher. I would have rather had them with different chamber volumes so you can set the squish around 1.2/1.3mm and then actually select for compression. I have a feeling that I will be modifying the high high black insert and lapping a bit off the head, which will mean the remaining 2 inserts won't fit unless also being turned down some. If anyones interested in buying an insert I promise I won't charge the $90 that S3 does. I'll also probably have silver and red, both for sale, in 250 or 300 sizes.

 

[(F5)]

1.2mm or 1.3mm is still heaps. I'm going to pull my 300 down to 1mm. These things don't rev high. My 200 on the dyno was all over at 9300 & over rev barely touched 10, normally you wouldn't pull that high. The bigger bikes probably don't go past high 8s, maybe 9.

I'll then pull out some metal from the chamber to reduce the compression back down to it's std 12.5:1 which is easy enough to kickstart & suit our 95 gas. My 200 I had raised to 13:5:1 (at squish 1.1 but that was where it ended up).

 

[Jakobi]

1.2mm or 1.3mm is still heaps. I'm going to pull my 300 down to 1mm. These things don't rev high. My 200 on the dyno was all over at 9300 & over rev barely touched 10, normally you wouldn't pull that high. The bigger bikes probably don't go past high 8s, maybe 9.

I'll then pull out some metal from the chamber to reduce the compression back down to it's std 12.5:1 which is easy enough to kickstart & suit our 95 gas. My 200 I had raised to 13:5:1 (at squish 1.1 but that was where it ended up).

Everything I've read about yz250's suggests that the ideal squish height is between 1.14 mm to 1.27 mm. I'd imagine it would be close to the same for an EC250. What dangers or problems could you see arising from going tighter? and when is tight too tight? I'll be having the head work performed elsewhere so will be liaising with them. I feel that 1.2mm and 12.5CR would be a nice safe option. I sometimes find myself in remote areas where crap fuel is present, even if its only 1/2 a tank. I don't want to sacrifice any reliability in the name of power either.

I've also got the tacho hooked up on my 300 and while I think it would be fair to say the power would be signing off by 9000rpm it will stretch its legs to 9800rpm when asked to.

 

[(F5)]

Well I run my race 50 at 0.5mm & at 14000 it almost grazes the head. If I reuse the double base gaskets too many time it just makes a noise.

But clearly the stroke is much larger on the 300. The other consideration is the MSV, which can be alleviated by taking some squish area out, but it isn't that big so I don't think its a problem & revs low so another lack of concern.

The closer you can run the head & piston the better (obviously without bumping the two together). Any mixture trapped there is lost to the cause, & the further away the less the piston gets the cooling effect of the head.

But lets not get too worried about it. The 300 has stacks of power, just closing the gap up should aid better combustion & thus fuel economy.

 

[stainlesscycle]

To be honest, the interchangable inserts are a bit of a joke. They all measure the same volume and are just set at varying heights. For example the low compression insert results in a large squish height. The high one a tigher. I would have rather had them with different chamber volumes so you can set the squish around 1.2/1.3mm and then actually select for compression.

that sucks, i was under the impression the volume changed on them. would have been the main reason i was thinking about getting a set...

 

[Jakobi]

Thanks for the info F5. Good stuff indeed. I'll discuss it with a few others but I'd say I'll probably aim around 1.2 to keep some clearance and stay on the safe side of things. It seems to be whats accepted around the place from those in the know. It sure sounds like you have some experience yourself in building race bikes! You blokes on the other side of the lake are well smart!

Stainless, the volumes on the S3 actually measure the same as the stock head (or at least it did on the 300 that I cc'd).

 

[Jakobi]

Rings and Piston

Crunching some numbers now to determine correct ring end gap. Mostly for reference for myself. Working off the 66.4mm bore and using wiseco's calc bore x .004" top, and x .005" bottom.

Top ring: 0.27mm
Bottom: 0.33mm

As delivered the stock S3 rings measured in with gaps as follows (measured about an inch in the cylinder top, pushed down with the piston)
0.25mm and 0.28mm

The S3 piston is stamped A 66.33 S3 Vertex. Piston to bore clearance will not be measured as I don't have the tools to do so accurately, however dropping the piston into the cylinder it will slide in easily under its own weight. There is no notable play side to side.

Reminder to self, rings are installed with the marked side facing up.

I'll wait for a few opinions before making any adjustments. At this point planning on keeping the 0.28mm ring as the top, and opening the other to 0.33m for the bottom. Does anyone feel these are too tight and should be opened up a bit more?

Piston

Clearance

 

[Jakobi]

Bump for those with engine building experience. How's the ring gaps I've specified sound? Looking for some feedback. Thanks

 

[Fred1956]

I'm not a rocket scientist but your math is correct and I've never had an issue using the Wiseco specs. Unless you're going to be pushing the maximum on your RPM all the time then I go with those #s. I have (in the pits between motos) installed a new piston & rings and just eyeballed the end gap to be sure there was some with no problems. While the numbers are there for a reason, I've discovered through the years (55 of them) that they are very forgiving in most cases.

 

[Jakobi]

Thanks Fred Was pretty sure they were ok. One of those measure twice, cut once things. I don't have the experience to fall back on. This last year has been a steep learning curve, so I feel its better to ask and be sure!

I wish I could ride this thing at max RPM more often!

 

[(F5)]

. . .
Reminder to self, rings are installed with the marked side facing up.
. .

Yeah & the piston goes the other way up as well, but hey, that's only a suggestion

 

[Jakobi]

GOLD!

..too lazy to flip the jug for the pic and nothing to hold onto the otherway! Hah!

Ordered myself a C-Clipper today! I feel somewhat sad that the challenge of installing the clips will be no more, yet a little relieved that the stresses of worrying about a clip flying across the room, or worse into the crank cases, has been minimised.

 

[(F5)]

Or poking it into your finger! Do you really not want that experience?