426 ex head gasket leak

[opcon]

I'm very happy with my 426ex. It has performed well, has lots of power and torque, has been clocked at 72 mph on sand, and has been pretty reliable. It's way torqueier than my new stock YFZ 450. But last year I blew a head gasket riding in warm conditions over a week of hard riding at St. Anthony sand dunes, and this week I blew another head gasket riding fairly hard after a few days in the desert.

I always let the air cooled engine take a break after 20 to 30 minutes of hard riding. But I want to avoid another head gasket repair. Recommended Honda head bolt torque specs are always used.

Do you have any ideas to help prevent another head gasket blowout? Using gasket sealer on top or below the gasket? Using aftermarket hi-tensile strength head bolts. Or re-torqueing the head bolts after a hard week of riding?

I want to avoid installing a new larger oil cooler if I have to and I'm not sure that will cure the problem.:chinese:

[400exrider707]

What gaskets are you using?

[underpowered]

i would recommend installing HD head studs, and using Cometic Flexsteel gaskets. i have both and have not blown a head gasket since i have started using them.

[opcon]

The gasket that blew out last year was a Wiseco.

The gasket that blew recently was a Cometic, and have had pretty good results with Cometic on other bikes.

Where can I get HD head bolts?

[XXXRACER165]

I've had this happen to my 440EX before. I put two Helicoils (one on top of the other) on all 4 studs to prevent pulling the threads out of the soft aluminum cyl, and torque them to factory specs. That cured my problem. I also went through 3 head gaskets.

[opcon]

Thanks for the info.

I have also put one Heli-coil set in this bike. But I should probably bite the bullet and do it to all. It appears that the exhaust side of the head stretches more than the intake, and that's where the leak occurs.

I'm still interested in locating HD head studs.

[400exrider707]

Heli-coils have been proven to not last either. The heavy duty studs is the only way to go. I am fond of the GT Thunder ones. I would have my head sent right to laz and have him do it all, because it is quite involved. It needs to be done with a roll-form tap, which will leave the threads a lot stronger than a regular cutting style tap.

The exhaust side does it easier because it is hotter, and breaks down the aluminum easier.

[opcon]

Thanks. I found GT Thunder and their head bolt page and will most likely purchase a set and get the machining done on a vertical mill at a machine shop.

I don't want to go through this again.

Did you put an aftermarket or larger oil cooler on also?

[400exrider707]

Originally posted by opcon
Thanks. I found GT Thunder and their head bolt page and will most likely purchase a set and get the machining done on a vertical mill at a machine shop.

I don't want to go through this again.

Did you put an aftermarket or larger oil cooler on also?

I had bought the studs a 12.5:1 440 kit and a larger oil tank, but never got to install any of it, I sold it first. Running 11:1 compression you will probably be ok with just running a good quality synthetic oil (wet clutch safe) but more cooling never hurt.

[opcon]

full synthetic or semi-synthetic? And what is a good synthetic? I have never run synthetic before. Seems like there's literally dozens of clutch-safe brands out there.

[mikey726]

What you need is to add a couple foot- pounds of torque to your head nuts. I'm not 100% sure if that alone will fix the problem because I had HD studs put in after my 2nd gasket, but it makes sense- more compression needs more torque on the head. Anyway, C&D told me to add 4- 5 lbs, but I went with 7 to 40 ft-lbs on both the cylinder and head, and no more blown gaskets.

[opcon]

I will try more torque. I think the cross section area of the HD studs may be slightly greater than stock and a few more ft-lbs make sense.

Thanks for the advice, I really appreciate any experience out there.