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I’m putting a Wiseco piston in my 91 KX 200. The Wiseco instructions are telling me if it has an exhaust bridge to make some marks below the bottom ring where that exhaust bridge is supposed to be. Mine does not have a bridge in the main exhaust port. Everything I’m seeing says it should have an exhaust bridge. Any thoughts?

I'm not entirely sure what you mean by making marks below the bottom ring. Do you mean drill holes for lubrication?
These bikes have 2 exhaust bridges, which are between the main exhaust outlet and where the subvalves are. The last Wiseco piston I got for my 92 200 already had 2 holes drilled for both of the bridges, likely because it'd be a pain in the butt to measure out where they need to go exactly because the bridges are offset unlike a lot of 2 stroke cylinders (at least 90's+ MX cylinders) where the exhaust bridge splits the main exhaust outlet straight down the middle, likely because there are no subvalves, unlike the KDX.
(Or I'm just slow and it would just pain for me to figure out where the holes go, but we all have our downfalls :) )

Does your piston already have 2 holes on each side of the arrow on the piston? Those holes should line up with the exhaust bridges in the cylinder. I'm sure you already know but that arrow points towards the exhaust side of the cylinder. Make sure it goes that way when you put it together, or bad things await.

Ok that makes sense. I was expecting a bridge dividing the center exhaust port. Yes my new Wiseco piston does have the lubrication holes. The instructions showed drawing a pencil line on each side of the bridge and then removing the piston and drilling holes in between the pencil lines below the bottom ring.
I should be good to go. Thank you for clarifying that for me.

Glad you got it figured out. Have fun riding!

I’ve got a set of power valves coming. There wasn’t much left of them. I found a page from the manual on the site that shows the timing of the gears but I’m not seeing where it talks about the one in the front of the head. Do you happen to know how that one should be timed?
Thx

I generally grab the manual from cyclepedia with the 1 year sub. Print the whole manual before your year is up. Well worth it. I don't remember off the top of my head how that timing goes. Last time I rebuilt my power valves was probably 5 years back or more.

Somehow I missed your reply, my apologies. When I timed my valves I was thrown off as well because it did not show the process for the center (main) valve. I eventually found this amazing post by keystone here on the forum that does a great job detailing the process of the install of the valves.

viewtopic.php?t=15320
Hope this helps!

WOW!! What an excellent tutorial still! Thanks SpruceItUp for the link!!!!