1992 XT400 oversize pistons

[TuckerBag]

I am about to do a rebore, piston, and rings on my '92 jap import XT400 "Artesia".

I would like to bore it out to about 425-ish cc just to squeeze that little bit more power out of it without having to change cams or valves etc.

It has an 87mm bore and 67.2mm stroke.
89mm bore = 418.1cc
90mm bore = 427.5cc

The XT600 (not 400) piston is approx 97mm bore I believe. I think this is too big.

Does anybody have any idea if a suitable piston exists?
I am open to any words of wisdom on what I am attempting to do here.

I have read some posts by a KB member "Motu" who did something not quite similar to what I am trying to do.

And yes,... I do realise that I should just burn this bike and get something decent,.. but,... well..., I am going to persist for now.

Cheers.

[Motu]

Apart from Yamaha,I don't know where you would get another piston.Yamaha don't like to waste product - and I bet there is another piston from another bike in the range that would slot right in.Look for a Yamaha of the same era with a 89 or 90mm piston....I reckon it might be close.

I had mine as a 395cc,495cc,595cc and finally 621cc.Looking back,I enjoyed the bike far better as a 400.Sure,the big 621 solved the passing and holding it's own on a hill or head wind,and it sure had some stomp coming out of corners...but the larger capacity brought it's own problems.

I much prefer to push a lower powered bike to the limits of it's performance,and a larger capacity brings it's own baggage to the show.On gravel I just WOT the 400 through the gears,then down into the turns,maybe a slight set up slide into the corner...I could keep my corner speed high,and slam it WOT very early and flick through the gears coming out....it was very stable doing this,and I could just concentrate on corner speed.The larger capacities brought the troubles of engine braking - loss of rear wheel control,and front wheel weighting.Carrying that too far into the corner,and then coping with too much wheelspin on the exits.Lots of fun,and lots of work,but I much prefer giving a bike all I have to give,and not have the bike giving me any problems.

Lessons learned with the XT have allowed me to choose the ''small'' R65 for my current gravel road bike - less reciprocating mass and free revving engine gives me a bike I can ride harder with less bike produced problems.

[TuckerBag]

Thanks for that Motu.
I really can relate to what you say. I find that the less powerful 400 gives a more relaxed and controlled feel to the riding. And it is always fun wringing the neck out of a bike trying to keep up with other more poweful machines.
Considering that I have a 96KTM360SX and 92CR250R for when I really want to cut loose on a trail, I will probably be reasonably happy to keep the XT400 as a somewhat more sedate and reliable adventure putt putt.