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Discussion Starter · #1 ·
I tried to do a search but couldnt find the exact information I was looking for. So we all know the xr400 head gasket works on the 400ex and is slightly thinner. Does the base gasket also fit on the 400ex? Also, when i search for the xr400 gasket on cometics website, it shows as having the same thickness (0.027") as their 400ex head gasket. What is the stock thickness of a 400ex head gasket? And stock thickness of a xr400 headgasket?

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The xr400 base gasket is the same. Cometic topend gasket kits say 400ex/xr400 on the back of them so they are identical thickness through cometic for sure. As far as stock thickness i dont know. One thing you will want to do if you go with cometic which i really suggest. The stock base gasket is a fiber gasket. Cometic is metal. So where the case halves come togeather you will want to put some hondabond or it will start leaking. The fiber gasket seals it but the metal dosnt have the squish that the fiber gasket has. I just had to pull mine apart this winter for this exact reason. And believe me it sucks pulling apart a perfect running motor to fix such a small oil seep. I did my kibblewhite +1 valves and springs to make it worth while. Welcome to the forums!
 

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Discussion Starter · #3 ·
The xr400 base gasket is the same. Cometic topend gasket kits say 400ex/xr400 on the back of them so they are identical thickness through cometic for sure. As far as stock thickness i dont know. One thing you will want to do if you go with cometic which i really suggest. The stock base gasket is a fiber gasket. Cometic is metal. So where the case halves come togeather you will want to put some hondabond or it will start leaking. The fiber gasket seals it but the metal dosnt have the squish that the fiber gasket has. I just had to pull mine apart this winter for this exact reason. And believe me it sucks pulling apart a perfect running motor to fix such a small oil seep. I did my kibblewhite +1 valves and springs to make it worth while. Welcome to the forums!
Thanks for the info! That hondabond is a good idea. Mine was leaking there after I rebuilt it and used cometic gaskets. Now I know why haha. Ill probably just go with the cometic again but I read about guys gaining a little power from the higher compression with the thinner gasket. 10 hours after rebuild the head gasket blew so its time for heavy duty head studs hah

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You can have the head decked or jug decked also to gain the same bump in compression. But it isnt going to make a noticable difference. It will also put your timing slightly off. But thats splitting hairs so its honestly not worth the headache IMO. What mods do you have done already? If you only made it 10 hours on a headgasket i would have to guess 440?
 

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Discussion Starter · #5 ·
Not a 440 actually. Only a 406. But with an 11:1 wiseco, full exhaust and cam. Im not sure why it blew so quick but i just sent it out for heavy duty studs

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Send it to snure interlocking? Ru still on a stock clutch? If so you could gain cheap power there. The stock clutch is junk and will slip when you start making any real power. As far as why the head gasket blew. Did you use a torque wrench? Did you re-torque after heat cycling? And did you make sure your head isnt warped? I always have my machine guy run a file across the surface to be sure its perfectly flat. If it isnt you will blow headgaskets quick. Gt thunder studs can take so much more ft. Lbs. Of torque it will pretty much unwarp the head even if it is alittle warped.
 

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Discussion Starter · #7 ·
Yep sent it out to snure and yes still stock clutch. I used a torque wrench but didnt re-torque after heat cycle as I didn't know i was supposed to.

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Its a good idea. I have found every 400ex i have built that 2 out of the 4 head nuts turn about half a turn or so after heat cycling.

And good jeff snure is a good guy! Does really clean quality work. His machine shop is 45 minutes from me so i drove there to have mine done. But i have built 416s for 3 of my buddies amd we sent theres to him and always get quality work back.
 

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Discussion Starter · #9 ·
Ill make sure to do it this time lol.

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Do that and crisscross torque in 3 steps. I usually go 20, 30, and 45 with the hd studs. And then leave it sit for about 15 minutes and go back and click all of them one more time. They will move alittle bit more there. Then i heat cycle pull the valve cover and re-torque. Then your ready to rip.
 
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