head gasket

[DISHO1]

i am looking for a very thin head gasket for my 400ex. the xr400 has three layers and has anyone pulled the gasket apart to use just one of the layers for a head gasket?

Why do you need to have thinner than .025 on your head gasket?

[beyer05]

Mickey Dunlap said something about using the xr400 head gasket and silicone for base gasket to bring the deck heigth into the right position. Has anyone done this? Which year xr400 head gasket? Do you have to pull the layers apart? Also, if you do this, what will it bring the compression up to with a stock piston? An 11:1 piston?

Ok what your trying to do is solve a problem with the wiseco (some others too like my J&E/ IMS) big bore kit (440).

First check out a post (do a search) called have you decked the cylinder. This will answer most of your questions and some before you even think of them, yes its a great post.

If you do not have a big bore kit on your 400EX then a lot of the problems discussed in that thread may not apply. I do not think the piston height in the cyl is a problem with the stock set up. I would think that you could change over to the thinner gaskets and still get a boost in the compression no matter which set up you have.

All late model XR400 use the thin .025 head gasket or you can get one from cometic gaskets.

Just be carefull not to end up with too little piston to valve clearance as you may get the valves hitting the piston or have too high a compression and overstress the bottom end etc.

[beyer05]

"On most after-market pistons, the pin to deck height is the same as stock. You should have a minimum of .040 clearance between the piston and head with everything torqued down. Right now the piston is about .043 too low and you are not getting a true compression ratio as advertised by most piston companies. For instance, a 440 11:1 flat top piston advertised is really only about 9.75:1 if you measured the volume correctly. In order to get the deck heights better, I use Honda HT silicone seal on the cylinder base and an XR400 gasket if you are running an 80 over piston or smaller. This will get you close to what your deck height should be. Keeping the squish clearance down to .040 gives a better quench area around the outside of the piston keeping it cool and less chance for detonation. You will be able to run an 11:1 motor on pump gas in most cases and have a more efficient flame travel and quicker burn rate across the top of the piston."

This is what I got off of the ask Mickey Dunlap section. He says to do this with .080" over or less pistons. What I want to know is, if I do this with a 12:1 or so piston, what will my compression really be? Will it make it a 'true' 12:1? Or more?

[Scott]

The answer to your question is, it all depends on how you put it together. If you buy a 12:1 piston, make the appropriate changes so that the piston is at the correct location in relation to the top of the cylinder when you reach top-dead-center, then yes you will have a 12:1. If you buy a piston, slap the thing together, and end up with the piston low in the cylinder at top-dead-center, then no you won't have a 12:1 C.R.