Xr 426

I just finished my top-end rebuild on my 01 XR 400. I bought it earlier this year. It started & ran very well, but it did seem to use more oil than Id cared for. Aprox 1 quart every 1000 miles.

I decided to go with an Polydyn coated Wiesco 426 kit. 11:1 compression. I also replaced all valves with new Kibblewhites. The valve guides mic'd out like new so I replaced the valve seals only.

PB080494.jpg

I've been breaking the bike in for the last few days. The increase in power is very noticeable. Very big increase in torque right off the bottom. Wheelies were amazingly easy in any of the first 3 gears.

Top end there was really not much difference. Im sure a cam would open up the powerband well, but Im pretty happy with just the piston thus far.

The bike starts just as, if not easier than before. I am running it on premium 93 octane fuel & haven't noticed any problems with detonation.

Its definitely well worth the money for anyone looking for a relatively inexpensive mod to do. Especially if you are due for a top end.:excuseme:

Thats good to hear. I have been thinking about a 426 kit for awile. Where did you buy your kit? And how did you go about getting the the cylinder bored out? Can you just take it to a normal engine machine shop?

I bought a Wiesco piston kit, which included a Wiesco top end gasket kit, from Ebay. $155.00

I took my cylinder & head to a local machinist who does machine work for a Moto Dealership I used to work for some years ago. Any machine ship that bores cylinders should be able to easily do the job.

$60 to rebuild the head, & $60 to bore the cylinder, although he said he cut me a deal on the boring.

Definitely a great bang for the buck mod, especially if you do the wrenching yourself. :excuseme:

Its worth doing if your rebuilding anyway, good usable torque gain while only sacrificing a little bit of rpm. The money saved by boring rather than resleaving will almost pay for a cam if you want to liven up the powerband a bit more. No heat or reliability issues that I've found so far with the thinner liner.

I decided to go with an Polydyn coated Wiesco 426 kit. 11:1 compression.

I'm not familiar with that coating, what does it do for the piston?

BTW, thanks for the report! :excuseme:

Coatings reduce friction and keep detonation at bay.

I'm not familiar with that coating, what does it do for the piston?

BTW, thanks for the report! :excuseme:

ZO6PSI is correct. The coating is mainly to reduce detonation & prolong the life of the piston.

Here is a link to the coating.

http://www.polydyn.com/coated_pistons.htm

The are used a lot in the forced induction world in high performance cars. I have a set of Diamond coated pistons in my supercharged Corvette.

Thanks!

How many miles on break in so far? I noticed on my 280 it took awhile before the power was completely there.

I have a few general big bore questions.

416, 426 you bore the stock liner? And 440 you fit new liner?

Do all 440 kits just increase bore or are there some that increase stroke?

How easy is it to get replacement head gaskets (and base gaskets for bigger liner)?

Sorry to hijack thread, that is a nice looking piston.

I have a few general big bore questions.

416, 426 you bore the stock liner? And 440 you fit new liner?

Do all 440 kits just increase bore or are there some that increase stroke?

How easy is it to get replacement head gaskets (and base gaskets for bigger liner)?

Sorry to hijack thread, that is a nice looking piston.

Hi Garth,

Yes, all use the stock sleeve/liner except for the 440

All 440 big-bore kits only increase bore. They probably sell 440 stroker kits, but they would cost much more to install than a piston/sleeve kit.

Replacement gasket kits are readily available. The kit I bought included a top-end gasket kit that matched the new bore size.

RedRider3141, I have less than 20 miles on it as of right now. Hopefully she will free up a few more ponies after it is properly broken in.:excuseme:

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