Wiseco piston install questions

[martinfan30]

I notice in the piston kit that the instructions say you need to drill holes for oiling. I also read on here that when you do the skirt chamfer to the new piston, that drilling holes is not necessary. Your thoughts?

Also, is piston pin retainer end gap location critical?

[KXcam22]

That is interresting.  I don't recall that on my wiseco and I did not drill any holes in it.  Where do the instructions say to drill holes. Generally its only done in a central exhaust port bridge which the K5 does NOT have. Let me know. Cam.

[martinfan30]

The instructions mention to do this if the cylinder has an exhaust bridge. Apparently, this cylinder does not?

What about the clip orientation?

[BDI]

Drilling the holes is typically done on non powervalve engines that have a single exhaust port with a single bridge in the middle, Like the cr500. The kx500 does not need this mod.

[cbxracer30]

I do this mod to K5 piston I install. I dry fit the piston on rod and slide the cylinder on , then mark the outer edges of the piston with a pencil , then pull it all back apart and just outside the pencil marks I drill 3 vertical holes about 1/4 inch down from bottom ring and about 1/4 inch apart . I use a 3/32 drill bit and chamfer the top edge with an 1/8 inch bit.this is the piston I just took out after 3 years of racing .

[BDI]

I have never had a problem with the kx500 exhaust port bridges getting hot, bulging out and damaging the piston. I would think that drilling holes in the skirt like that would hurt the bikes primary comp ratio and impact the engines efficiency. Maybe it's necessary on an engine with a cast iron sleeve. That would be one more reason not to sleeve a kx500.

[KXcam22]

I also never experienced any wear in those spots.  The bridge is actually quite thick in those spots.  I am helping a friend with a YZ125 (powervalve with a center bridge) and the stock piston comes drilled.  I have not seen the  wiseco replacement he got so I may have to drill holes in that one. Cam.

[muleman]

I was always told to put the retainer clip gap up or stright down. Not any other way.

[martinfan30]

I was always told to put the retainer clip gap up or stright down. Not any other way.

Is there a reason why?

[speedywent]

Piston goes up and down not sideways. Circlip is more difficult to collapse from G's and release.