XR400 head gasket and eliminating base gasket

[Metzroth]

Ok, I saw this in the tech articles where Mickey Dunlap answered some questions.
Yes, you could put an XR400 head gasket and eliminate the base gasket to get higher compression with your stock piston

How can you completely get rid of the base gasket without reprocussions? I don't understand it, im not doubting that hes right, would just like to know b4 i attempt it :P

[CRE Performance]

If im not mistaken, the base is machined good enough to seal pretty accurately. It has no compression on it like the upper gasket, it simply seals oil with no pressure other than what crankcase pressure it has (relatively none) so a good RTV (glue) is enough to seal it.

[Metzroth]

so this will make a dif with compression right? What kind of glue?

[CRE Performance]

Originally posted by Metzroth
so this will make a dif with compression right? What kind of glue?

Yes, a light coating of glue will be thinner than a base gasket in terms lowering the jug and making the piston closer to the top for a better quench. The glue is sold by the honda dealers, I cant remember the exact name of it.

[Metzroth]

alright then ill talk to a dealer and see what they reccomend for glue. there isnt going to be a chance of valves hitting the piston with the lower height of the head is there? Well right now they are tapping slightly but I plan on adjusting them soon.

[toby400ex]

Your dealer will more than likely tell u not to do this at all. Just get some yamabond, or basically any kind of gasket maker. I used high temp spray paint.

[Metzroth]

I guess ill just use yamabond. This is the good stuff right?

[kickin440]

Its called honda bond at a honda dealer and yamabond at yamaha or go to your local auto parts store and ask for threebond its all the same stuff.:)

[440ex2001]

get some hondabond and run a thin layer around the base. I have been running this for about 3 months with no probs or leaks. My compression went up at least a 1/2 a point cause i have to run 115/93 mix now. I was at 11.2:1 anyone know how much it goes up?

[Metzroth]

Could u feel any difference when riding because of this over the gasket?

[BLEEDRED]

Just to give you an idea of your compression you can go to www.rosspistons.com and click on the compression ratio calculator. On a stock 400EX use these numbers, all numbers are approx, but close:

Bore: 3.346
Stroke: 2.756
Head Volume: 37.2
Gasket Thickness: .035" (head gasket)
Deck Height: .035"
Dome Vol./Valve Pkt.: -1

Now make your adjustments by changing the deck height to reflect removing the base gasket...the stock piston sits about .035" in the hole at true TDC, this is your deck height. The stock base gasket is .020". If you remove the base gasket you can get the deck height down to about .017" (allow about .002" for the hondabond). Use the calc. and see how removing the base gasket will change your compression. Also see what will happen as you change the head gasket thickness.

Remeber to be careful when changing these clearences. It's get super technical when you start talking squish, but it is important to keep everything in mind. You might want to do some more reading. Here are a couple of more things to help...

The Squish Band or "Quench" is defined as that area between
the flat of the piston and the flat of the cylinder head at
top dead center (TDC). On the compression stroke, as the
piston approaches TDC, the compressed mixture of fuel and air
is "squished" to the remaining space of the combustion
chamber where the spark plug and valves reside.
The "squeezing" of the mixture creates turbulence and is
expected to promote a better and more complete combustion.

Deck Height: The distance between the flat "quench" surface
of the piston and the top of the bare cylinder (no head
gasket). Typically an engine is set to zero deck height with
the head gasket (compressed value) defining the "squish band"
value. If the value is negative this indicates the
piston's "quench" surface extends above the top of the bare
cylinder.

[wilkin250r]

Originally posted by Metzroth
alright then ill talk to a dealer and see what they reccomend for glue. there isnt going to be a chance of valves hitting the piston with the lower height of the head is there? Well right now they are tapping slightly but I plan on adjusting them soon.

How do you know your valves are tapping the piston? Did you physically take apart your motor and see the marks on your piston?

It is REALLY unlikely that your valves are hitting your piston.

[BLEEDRED]

It is REALLY unlikely that your valves are hitting your piston.

Agree!!!

Aren't we talking a stock set up here? I'm pretty sure that as long as you have .035" of quench your valves won't hit your piston...the stock set up has .070". The only way I would worry is if you got below .040" with your gasket adjustments and your riding style put you up against the rev limiter all the time.

[UglyMotha™]

he never said they were hitting the piston he just said they were tapping and i believe he's refering to the rockers arms since he said he was goin to adjust them :o




uhh yes i'm running no base gasket and only one layer of the three layer head gasket permabond goes on the base high temp spray paint goes on the head gasket, with this mod i've only put 2 valves thru the top of the piston

will you notice an increase in power with this just alone........ NOPE don't expect a seat of the pants increase, does it help.......... YUP every little bit helps it all adds up

i've ran it all year without any problems "no valve damage" it was a joke, how long will it last......... who knows i rebuild my engine every year, i do know it lasted a year

[Rico]

LMFAO

You guys izzz Krazy.

I run all the gaskets that Honda recommends. Yeah I might not gain that extra 10th of a horse power but that's just me.

When I called GT Thunder and asked Laz about not running a base gasket and only 2 of the head gaskets he said, run all gaskets and don't cut the 3 layer head gasket down to 1 or 2. So thats what I did. I ran my last rebuild for 3 years with all gaskets installed so I'll go with what's recommended. Nothing against those that want every little bit HP you can get, I just think differently and I guess I"m just skeeert to not put it back together the way it was built...:eek2:

[BLEEDRED]

Maybe I am missing something, I don't get it. But when using the compression ratio calculator that I talked about on www.rosspistons.com, this is what I come up with for my 440...

Had I went to final set up using the .010" Cometic base gasket and the .027" Cometic head gasket I would have had 10.3:1 CR and that was with a Wiseco 11:1 piston (watch those advertised CR's). I went with no base and that bumped me up to 10.55:1. Now had I gone with only one layer of head gasket it would have put me at 11.19:1.

Moral of the story: Messing with deck height and gasket thickness can make a huge difference.

[Metzroth]

Ok so how should i do this? Buy the cometic head gasket kit and some threebond at the auto parts store. Take off the head and the mid section remove the base gasket and replace with a thin layer of threebond. Then I use one of the three layers of the cometic gasket kit and that will put me at a higher compression?

(I'm buying an HMF Full so I am not going to do this until I can afford a 11:1 piston and a new cam)

[cals400ex]

i run a thin cosmetic head gasket with no base gasket. i bought the hondabond from my dealer. just use a very thin amount of hondabond. also, make sure none gets near the oil passages in the engine. it wouldn't take much to plug it up. clean all metal surfaces really well with a razer and acetone before installing everything.

[UglyMotha™]

Originally posted by Metzroth
Ok so how should i do this? Buy the cometic head gasket kit and some threebond at the auto parts store. Take off the head and the mid section remove the base gasket and replace with a thin layer of threebond. Then I use one of the three layers of the cometic gasket kit and that will put me at a higher compression?

(I'm buying an HMF Full so I am not going to do this until I can afford a 11:1 piston and a new cam)




you forgot to list new rings and a hone job since you pulled the jug off

[BLEEDRED]

And IMO all new fastners to make a good reliable build...

[Kansas T]

Thanks BLEEDRED for posting numbers and the calculator link. That makes it much easier to figure.

The other question we need to ask is what will that do for cam timing if I installed a thinner head gasket and remove the base gasket? It looks like the cam would be about .026" closer to the crank. How many degrees will this advance or retard the cam?

[wilkin250r]

I will certainly change your cam timing, and I believe it retards it, but I could be wrong on that.

The actual amount of change isn't very significant. The total degrees of change would be equal to moving the outer edge of the cam sprocket 0.026 inch. Less than 1 degree.

[BLEEDRED]

Thanks BLEEDRED for posting numbers and the calculator link. That makes it much easier to figure.

No problem. Let us know how it turns out.

[400exdad]

You should be able to put in different thicknesses of base and head gaskets to calculate your new compression. I didn't want any leaks with my motor, as I don't really like to do maintenance like that. I ordered a .012 thick base gasket for mine from Cometic.