440 big bore

[265 sleeper]

Can you run a 440 on stock head cam valves etc . With a 12:1 piston. It's blowing head gaskets could all that be a problem.

[Stickman400]

Should be able to. You should deff. put GT Thunder HD studs in it though. Also should make sure the jetting is spot on and possibly think about adding a larger aftermarket oil tank and/or a SPAL fan just for insurance.

[265 sleeper]

Also the head and cylinder was decked

[Stickman400]

It should still work.

[CJM]

You raised the compression even more by decking the head and cylinder.

You need to run minimum 100 octane, have heavy duty head studs and make sure your jetting is right.

[265 sleeper]

Yes I'm aware of all that I've built a few 400 but never a 440 and don't know much about all there counter parts on what works and what don't . I mainly deal with 2 strokes or cars.

[265 sleeper]

Jetting will cause blown head gaskets ? Lean or rich

[chronicsmoke]

Pretty common if you have the stock studs, they can't handle the extra ponies you're pumping out.. GT Thunder has what you need. :macho

[CJM]

Originally posted by 265 sleeper
Jetting will cause blown head gaskets ? Lean or rich

Too lean, you cook the topend.

2 things:

-Main jet should be approx 180+
-You need the GT Thunder HD head studs.

Should fix your issues. Id also make sure you use cometic brand MLS gaskets as well-they are the best.

[jman7290]

Also get the GT Thunder HD head gasket to go along with the head studs. That solved my issue with the blown head gaskets.

[265 sleeper]

I wasn't asking jetting question I was asking which one is going to cause my head gasket to leak. I build 2 strokes jet ski banshee and 250r. And I never heard a head gasket leaking because of jetting.

[CJM]

On an aircooled engine like the 400ex has (based off the XR400), if you dont jet it right the machine doesnt have enough fuel. The fuel cools it a bit even tho its aircooled.

Dont jet it right, topend heats up, the head studs by the exhaust tend to pull out and blammo there goes the HG.

Make sense?

[265 sleeper]

I can see that . Never had that happen on my h1 500 but ill take yall word for it. Thanks for all the input

[CJM]

Very common problem on these quads when you generate too much heat.