Wiseco piston set

[James England]

Does anyone have any views, opinions or experience of the Wiseco piston kit? From what I've seen, it comes in a variety of oversizes, with pistons, rings, gidgeon pins, circlips etc.. also a head gasket. The pistons are forged apparently.... what's that actually mean and how does it compare to the OEM pistons?

Presumably a rebore of the cylinders is needed but does anything need to be done to the cylinder head?

If anyone has any experience of these, or views, I'd be very interested

http://cgi.ebay.com/ebaymotors/YAMAH...Q5fAccessories

[crazy steve]

Well, different people will have different motivations for getting one of these kits...

If you have a motor that the cylinders/pistons are worn beyond spec where just a re-ring is no longer a good idea, then these kits are a very viable choice for a rebuild given the cost/difficulty in finding factory replacement oversizes. But by the time you add in the other costs (boring, gasket set, etc), most owners just get another bike or motor.

Another reason would be for a power increase; increasing the displacement to either 1179 or 1196cc (depending on the kit) will give you a bit more power, but it's rather expensive horsepower. Figure somewhere in the neighborhood of $70-80 per one horsepower increase. Speed costs money, how fast do you want to go...

As far as the forged pistons, I don't know what the XS has stock, but most OEM pistons are cast. Forged is stronger, but expands more when heated so they require 'looser' cold clearances compared to cast. They can sometimes be quite a bit noisier than stock pistons until they warm up.

As far as the head, you shouldn't have to do anything. Any overbore will increase the compression ratio, so some power is to be had there. I believe the Wiseco kits use flat-top pistons (to keep the compression ratio from getting too high), so that can change combustion chamber dynamics slightly.

[DiverRay]

TC has had an 1176 kit in his bike for years now. He does not put the miles on it some of us do, but it's been running fine for him. The big valve engines, '80 and newer, do not get the same compression bump the early engine does because of head/piston design differences.
As Steve said, if you want to keep the "stock" engine, or just want more HP, it's a good way to go. IF you do, make sure that when the shop does the bore, they keep the slight chamfer(sp?) at the bottom of the barrels. If they don't put that back in, you will EASILY break rings trying to put the engine together.