No cylinder base gasket?

[SaboTron]

I am putting my 440ex engine back together and read that you can make a small increase in compression by not using the cylinder base gasket (use silicone) and for the head gasket using only the middle gasket of the Cometic metal gasket.

Has anyone had any problems doing this? Can you notice any gains?

Thanks

[enduro400rider]

its been done, the compression will increase but not much, i talked to guys at Hetricks Racing about doing that back when i had my 440, they said its not a good idea and that you should run a gasket.

[F-16Guy]

The purpose of the gasket thing is not really for the compression increase. What it's really intended to achieve is a higher deck height, which is how far down the piston sits in the cylinder at Top Dead Center. By altering/removing gaskets, you are lowering the cylinder slightly (effectively raising the piston) to reduce the gap between the edge of the piston and the cylinder head at TDC. That area is known as the "squish band". The correct squish band will force the fuel/air charge toward the center of the combustion chamber and make the burn more efficient, transferring more energy to the piston and helping the engine run cooler. I think a lot of engine builders have realized that the deck height on the 400ex is too low, but the correct way to change the deck height is to have the cylinder decked, not to mess with the gaskets. The gasket thing could work fairly well except for one thing: The oil passage for the valvetrain goes from the oil filter housing, through the right side case, and up through the side of the cylinder. The passage goes right through where the cylinder and case meet, and uses the base gasket to seal it up. Gasket maker will seal well, but when you torque the cylinder down, it's possible for it to squeeze into the passage and block it. You wouldn't know what happened until it was too late.

[SaboTron]

Thanks for the great information and details. I am going to use the base gasket and full Cometic.

[250X_project]

Yeah its deff. not worth it. I tried it on my 250 and anded up frying it up, cam and brand new Wiseco piston...needless to say it didn't run any better or cooler - acually hotter...:ermm:

[Quad Dude]

i have run my ex this way ever since i got it with no problems at all i even when ahead and took a part the head gasket and only put the two thin ones in seems to work for my i dont know if it did any thing but it runs fine.

[cals400ex]

i have done it on 6 different 400ex's. i am not saying everyone has to do it. we used hondabond as the sealant. we applied it very very thing (so not as much excess would get all over the place). we never had a problem but i could see where a problem might exist. would i do it again? yep, probably.