Measured Squish @ 1.83mm!

[GG27]

I just measured my cylinder head squish band and it is 1.83mm with a .5mm base gasket! Stock it had both .5mm + .3mm gaskets so the stock squish must have been over 2mm!. No wonder I couldn't get my jetting right. It got better when I removed the .3mm base gasket but still no where near what this engine can produce.

Since I have opened up the engine for a piston change and I know the ideal squish is between 1.4 and 1.5mm should I mill .1mm from the head and use the .3mm gasket or shouldI use the .15mm gasket? My mechanic thinks that I will blow the engine if I go down to a 1.4 squish by too much compression.

Also how can I measure the Combustion chamber volume to the ideal 21.5cc?

Can I just blank of the spark plug hole and fill the cylinder head with a syringe till the water reaches the circumference of the head? If I get hold of a pressure tester what is the ideal compression in psi, 185?

 

[GMP]

There is a lot more to it than that. The squish band clearance is not even across its width relative to the piston dome. You have to take a big cut to bring the worst (inside edge) in and then recut the outside for consistancy as well as cut the dome for proper compression. On a 250 200 PSI is at the limit for US pump premium fuel.

 

[widebear]

Your squish is not the culprit in your jetting problems. Ive perfectly jetted stock ec's with 2 mm squish.For real world conditions I personally would not exceed 155 psi cranking compression at sea level unless your base elevation is above 1200 metres. If you go to the homepage you can read Ron Blacks exellent and generous article on squish band measurment and correction.

 

[GG27]

I know that the squish band has to be reshaped with a closer angle to the piston dome. There is no reputable machine shop in Athens that can guarantee this mod, so I'll drop the cylinder with the .3 or .15mm base gasket. I also measured the standard head volume and it is 19.5cc!! which is way of the ideal 21.5cc. I'm going to measure the MC head tomorrow and if it has a larger volume with a tighter squish I'll put that one on and maybe try to correct the stock EC head to RB's specs.

 

[nick790]

I was hping to do this mod here in the U.K. as the shipping makes it to expencive to get RB to do the work. Where can I get some more info on the mod?

 

[iancp5]

I was hping to do this mod here in the U.K. as the shipping makes it to expencive to get RB to do the work. Where can I get some more info on the mod?

This is standard 2 stroke work. Just pick a reputable 2 stroke tuner and they will be very familiar with the mod.

 

[GG27]

I measured the CC volume and it is a bit less than the EC head (19.2 cc compared to 19.5cc) The squish thickness is still at 1.8mm. The squish band width is less at 8mm compared to 1.2 of the EC head. If I put the MC head will I lose on the bottom but gain on mid and over rev? Any opinions?

 

[ECRider]

I just measured my cylinder head squish band and it is 1.83mm with a .5mm base gasket! Stock it had both .5mm + .3mm gaskets so the stock squish must have been over 2mm!. No wonder I couldn't get my jetting right. It got better when I removed the .3mm base gasket but still no where near what this engine can produce.

Since I have opened up the engine for a piston change and I know the ideal squish is between 1.4 and 1.5mm should I mill .1mm from the head and use the .3mm gasket or shouldI use the .15mm gasket? My mechanic thinks that I will blow the engine if I go down to a 1.4 squish by too much compression.

Also how can I measure the Combustion chamber volume to the ideal 21.5cc?

Can I just blank of the spark plug hole and fill the cylinder head with a syringe till the water reaches the circumference of the head? If I get hold of a pressure tester what is the ideal compression in psi, 185?

I have just gone through this same excercise with my 08 EC250, having measured a similar original squish clearance to you. Original head vol was 22.2 cc & compression was 170 psi.
After reading other posts on base gasket thickness by Socialscott, I checked the transfer (side) ports @ BDC & found that the piston did not fully open these ports & boost port (intake side). I decided to raise the deck level 1.2mm over the original 0.5 + 0.3mm gaskets by making a 1mm aluminium spacer plate & adding 0.5mm gasket each side. The head was then machined by a 2 stroke tuner to 1.22mm squish at outside of piston & the volume slightly decreased to 20.5cc for a compression ratio of 13:1.
Compression is now 180psi. The bike had to be rejetted leaner & the end result was cleaner jetting, a similar bottom end, but noticeably more mid to top-end power at a recent enduro.
The tuner I went to said he goes down to 0.8mmm squish for 14:1 compression, however I was reluctant to go this far having read other posts. We are using 98 RON fuel here in Australia so that may influence how far you close the squish & jack-up the compression.

 

[GG27]

I finally got the engine together and still have not run her in but here is what I did:
I kept the same EC head, put in the 0.3mm base gasket, giving me a squish of around 1.6mm and head volume of 19.3 cc. What my mechanic did is matching and polish all the transfers and the PV flap.
Since I was looking for more bottom end and a smoother low to mid transition he tuned it this way. From the short ride I had on it it feels much more responsive with no hesitation. I've kept the LTR needle #3 with 42 and 180 jets with stock slide. I also use 98 ron super unleaded @ 2% full synthetic.
BTW cylinder had absolutely no wear while piston was at the limit!
I'll give my rider impression after the week end when I can open her up.

 

[noobi]

im about to do the squish measuring business. i emailed RB designs, he said the stock squish is 0.035" = 0.889mm ? he suggested it would benefit from being lowered to 0.030" = 0.0762mm ?
this thread seems to suggest that over +1.0mm of squish is enough?

thanks for the info though Ron