Base Gasket

[gtsnowcrack]

Has anyone played with the number/thickness of the base gaskets on their bikes? I'm doing a top end to investigate the powervalve issue and because my bike needs a top end .

I know that you can change the base gaskets to affect the timing and compression and was thinking of going to .5 from stock of .65.

'04 EC 200

[Gonzo]

After having read several manuals and seeing that the compression is effectively lowered in the higher revs, I imagine a thicker base gasket would [in theory] help the motor spin up a bit quicker and possibly give you a bit more power.

Don't quote me on that, though.

[iancp5]

I used the minimum base gasket at the last top end strip. It had the standard 2 on there and I swapped to the thinnest single. It is a lot harder to kick over but that may have been because I replaced the piston and rings at the same time. Can't say I noticed any difference riding but there was 2 weeks between rides.

[jeffd]

Ron Black @ RB-Designs suggests using one .5 mm gasket for greater reliability - this is discussed in his technical article on measuring squish. Bottom line - going with a .5mm is a good idea; It is my understanding that the thinnest gasket is to be used only in conjuction with another gasket (either the .3 or .5mm gasket) to set deck height for the cylinder.

Reducing the number of gaskets has the following effects...

1. Changes port timing - increasing bottom end slightly (at the cost of top).
2. Increases compression slightly - again, increasing bottom end at the cost of top.
3. Tightens up the squish band clearance slightly - but not enough to get it close to an optimal figure. Net effect, the bike will run slightly more efficiently - but not as efficient as if you have the head mod performed by RB-Designs.

If it were me, I would measure the squish while you have it apart (and do it with a .50 mm base gasket) - even if you don't decide to have the squish dial'ed in now - you will know where you are at. And you will have an idea of what might be had if you decide to have this done. (e.g. better fuel mileage and cleaner running).

jeff

[GMP]

I think what Ron means is that ONE gasket is to used for greater reliability instead of two. Either the .5mm or the .3mm would be fine. The .15 is used for fine adjustment (at the factory). I've went with a single .3mm on two different 250s and its not much of a difference. Its just a very small change that when combined with other small mods adds up to a significant change.

[jeffd]

I stand corrected. Yes, a single gasket of sufficient thickness to do the job - either .3 or .5; I am helping a friend do this soon and we are going to go to a single .5mm gasket - it stuck in my brain - sorry...

jeff

[Hawkeye]

On my '02 300XC, I'm running a .3mm gasket AND I milled .025" off the cylinder bottom. I have not have the squish changed. Better low and no loss of top, but I do run a 50/50 mix of 112 octane race gas with premium pump.

The squish gap went from over .080" down to .052" with these mods. GG sets these engines up with a lot of clearance, but mine runs better with it tightened up to more "normal" specs. I suspect from reading everyone's posts that there might be more bottom available in having the head done, if it was a 250 I would have done this already. 50 hours on the motor since the last rebuild and still running strong. This winter it is scheduled for a teardown and I might give RB a call.

Decking the cylinder only cost me $25.