Going to have to replace head gasket

[dr qwerty]

Going to brake down the engine,

What is a good head gasket to go with links please for the 426ex also should i add the HD head studs, CRF cam chain from what year? Upgraded springs did you use? Larger valves which ones did you use? Maybe a Cam or just a rev box...?

[CJM]

Im very happy with cometic gaskets, my entire engine has them, cost 75 bucks for an entire engine kit and I bought the best one they had.

[brokenmike]

Go with the factory style MLS (multi layer steel) gasket. I have a 440 with a 11:1 piston and stock head studs and NEVER had a problem in 7 years!

[flyboy1294]

Originally posted by dr qwerty
Going to brake down the engine,

What is a good head gasket to go with links please for the 426ex also should i add the HD head studs, CRF cam chain from what year? Upgraded springs did you use? Larger valves which ones did you use? Maybe a Cam or just a rev box...?

As stated above, MLS is the only way to go. I have had great experience with Cometic.

Here is a link to where I get most my engine parts for the 400. eBay carries gaskets also.
http://www.ctracing.com/trx400ex1.htm

If you want an HD cam chain, go with the CRF450R 02-08 one. It's 112 links.

As for the HD studs, I don't 'think' its needed for your application unless you are running some pretty high compression, but I can tell you first hand, if you do go with them, they are solid.

Do you mean valve springs? Kibblewhite lightweight TI springs are the only way to go imo. Just be ready to upgrade to rockers and a hard-weld cam. (IE: If you get the springs, you'll need to HD rockers, TI valves, a Webcam, and probably a pretty good P&P to open things up. You're looking at dishing out some serious cash for this head, it might be unnecessary if you don't ride competitively)

As for valves, Kibblewhites are great, but if you're planning on building a head with an extremely high-lift cam, Terra valves are known to hold up a bit better. But be warned, if you decide to go with +1mm oversize valves, it will seriously change the powerband of your quad. When you go oversize, it makes the quad more torque-y at high RPM, so it will be more difficult to trail ride

Assuming you just ride recreationally, I would go with a CRF cam chain (just because your stock one was worn and HD is the same price as a replacement), a Stage 2 Hotcam (assuming you are running the stock one) and Cometic gaskets. Don't bother with the valves or anything, it's not really needed. You may want to replace your valve-seals though, just so it doesn't start smoking later on down the road.

And by the way, don't touch that rev box. Stock one works fine, aftermarket can potentially screw with your timing.

[dr qwerty]

Originally posted by flyboy1294
As stated above, MLS is the only way to go. I have had great experience with Cometic.

Here is a link to where I get most my engine parts for the 400. eBay carries gaskets also.
http://www.ctracing.com/trx400ex1.htm

If you want an HD cam chain, go with the CRF450R 02-08 one. It's 112 links.

As for the HD studs, I don't 'think' its needed for your application unless you are running some pretty high compression, but I can tell you first hand, if you do go with them, they are solid.

Do you mean valve springs? Kibblewhite lightweight TI springs are the only way to go imo. Just be ready to upgrade to rockers and a hard-weld cam. (IE: If you get the springs, you'll need to HD rockers, TI valves, a Webcam, and probably a pretty good P&P to open things up. You're looking at dishing out some serious cash for this head, it might be unnecessary if you don't ride competitively)

As for valves, Kibblewhites are great, but if you're planning on building a head with an extremely high-lift cam, Terra valves are known to hold up a bit better. But be warned, if you decide to go with +1mm oversize valves, it will seriously change the powerband of your quad. When you go oversize, it makes the quad more torque-y at high RPM, so it will be more difficult to trail ride

Assuming you just ride recreationally, I would go with a CRF cam chain (just because your stock one was worn and HD is the same price as a replacement), a Stage 2 Hotcam (assuming you are running the stock one) and Cometic gaskets. Don't bother with the valves or anything, it's not really needed. You may want to replace your valve-seals though, just so it doesn't start smoking later on down the road.

And by the way, don't touch that rev box. Stock one works fine, aftermarket can potentially screw with your timing.


Thanks man, will do....

Stupid noob question what size mm is my 426ex 89mm?

[flyboy1294]

Originally posted by dr qwerty
Thanks man, will do....

Stupid noob question what size mm is my 426ex 89mm?

Anytime,

and 426 is an 88mm.

[MisterGraphic]

Hey,
Thinking about rebuilding my motor instead of doing a swap... ($$)

Quick question about the 426 (88mm)
Which size cometic should be used ?

I see they have 86mm and 89mm ?

Thanks for the help!

[flyboy1294]

Originally posted by MisterGraphic
Hey,
Thinking about rebuilding my motor instead of doing a swap... ($$)

Quick question about the 426 (88mm)
Which size cometic should be used ?

I see they have 86mm and 89mm ?

Thanks for the help!

I 'think' that as long as it isn't stock bore, most people just use 89mm gaskets. I'm not 100% sure though, maybe someone else can chime in.

[F-16Guy]

Fix the studs, get a Cometic 87mm MLS top end gasket kit (available on their website for $36, stock #C7924), and get a HotCams Stage 2 cam.

There is some debate over the best/cheapest way to fix the stud problem. If you know a good local machinist, you can have them install threaded inserts to repair and strengthen the threads in the cylinder and just re-use the stock studs. You can also send your cylinder to GT Thunder and have them install their oversized stud kit. However you do it, your head gasket blew for a reason, and just installing a new gasket isn't going to fix the underlying problem. Like a lot of other people, I had the same problem. I replaced the head gasket only to have it blow again, and then I had GTT do the studs and it's been rock solid for years. Mods in my sig.

[flyboy1294]

Another thing I forgot to mention,

if you have a local machinist, have him mill around .001" off the head surface. These engines are air-cooled, so they see much more heat than a liquid cooled engine. Because of this, the head surface gets warped very slightly. This can cause a new gasket to not seal well, which can make it blow.

Just an idea, I had it done to mine to be safe. But if you blew a gasket before, it's added insurance.

[tri5ron]

all good solid info here.