EC 300 Downsized to 250

[v-tec]

Hi all, 1st of all Happy new year.
Ok I as had some spare time this weekend I thought it was time to down size my mates 2011 CC 300 to a 250 ,
It had always been very vibey ,so bad that it made your feet tingle , and could also feel some up/down free play in the main bearing on the flywheel side,

He has a S3 head kit (3 inserts ) and a S3 piston,
It's all built back up, So we can Carrie out some measurement to sort out squish and compression ratio,

My 1st Gripe is that all 3 inserts appear to have the same head volume ,the only differences being the squish , What's that all about then,
This is where I'm at, at the moment just for a starting point,
.5 + .3 base gasket, this makes the piston 1.0 mm above the bottom of the exhaust port @ BDC, Will this make it flat on top end ? Should I add another .3

Carried out a CC check on the combustion chamber with the black insert, Squish is 1.35mm And it's 16 cc That's a UCCR of close to 16:1
These head inserts are a waste of money, They are nowhere near plug and play,
Carried out a compression check with a calibrated gauge and we have 225 PSI
Much to high.
So it looks like some head machine work is needed,Mybe something close to 20 or 21cc
May have well just machined up a standard 250 head,

How do my findings compare with anyone's

Also what sort of jet sizes. Needle type for the 250 set up. Temp 10-20 celceus
0-500ft above sea level
Thanks
V-tec

 

[Jakobi]

http://www.gasgasrider.org/forum/showthread.php?t=11970

Some light reading on the subject

"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" Post #8

 

[v-tec]

http://www.gasgasrider.org/forum/showthread.php?t=11970

Some light reading on the subject

"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" Post #8

Cheers jakobi, I will have a read,
We did the whole motor this weekend, it's late pm here in the Uk,
So just need to do some final important settings,
Hope it feels smoother, LOL

 

[Jakobi]

To summarise, I used the black insert with a single 0.5mm base gasket. That gave me a squish height of 1.25mm. Then machined the dome out to 21cc (from memory) for an UCCR 14:1

Noticed a significant decrease in vibes, however you still get them through the bars at the right rpm (buzzing down the road). Not so much through the entire chasis anymore.