Who has had a 440 big bore kit in a 400EX for a long time? Just wondering about reliability.
What kind of cams are being used?

 

i have had a 440 kit since april. In may I broke a timing chain. Everyone I spoke to said they had never heard of it. About &250.00 later i was riding again. In may, memorial day weekend, it blew up again. This time an exhaust valve broke. Web cam said the rocker arm failed. The only thing I probably didn't do when the engine was built was have the rocker arms hardened. So, $2,000 more dollars later (in addition to the $3,000 original dollars) I am riding again. For your answer to reliability, hopefully someone will have better luck.

 

Only had mine done since April, man it hauls and haven't had any problems yet. Powroll did my work for me, worst part was waiting to get it back as they were backed up at the time. I ride it hard and like alot of us I take good care of my quad, like I said no problems yet and worth EVERY penny.

 

We have a high performance shop and were told by Wiseco that after installing the 440 kit, if you should ever require any oversizing due to a scored cylinder, you'll have to resleave the cylinder again since over sizing for repairs isn't possible. We were told that the 426 kit is your best bet.

 

I have had my 440 kit since June of 99 and have raced two cross country events this year. The only problem I have ever had was a blown head gasket, which was my own fault. I chose a White Brothers all around cam instead of a race cam to ensure reliability.

 

If you bore to 88mm which is 426cc you're in the same boat....

So it depends on how much money you want to spend on the first go around, since when worn out or damaged, you'll be sleeving either way you go.