Piston drilling cr500

So I've been hearing about piston drilling, what is it? How is it done? Does it have to be done? Thanks

It is drilling holes in the piston skirt, to help oil the exhaust bridge, that some 2 strokes have.  My rule is, if there is a bridge, I drill the piston.  Regardless if is cast or forged.  

Edited by Kirkes

Ok so mine wasn't drilled and it has the bridge in it, should I put it back in the shop strip down and drill it? Or leave it as it is now its done over 200ks on this piston, also when drilling, any techniques to the holes and there placement

If it were my bike I would at least take the pipe off and have a look at the exhaust side of the piston. As owners we care more about our bikes then the paid local mechanic does. That is why it is important "we" learn how to work on them. It is time you learn how to work on your bikes and stop paying someone else to do so. It is common knowledge that the Cr500 bridge HAS to be relieved to it so it does not swell into the piston.

Keep asking question we will help ya.

the info for drilling the holes, size, and placement was in the box with the piston. Just from memory, they are two holes, about .050" big, one above the other, placed inline, centered on the bridge. I just don't remember how far down the holes need to be placed.

Edited by Kirkes

I do all my own work on my bike, I just use my mechanic for advise, parts and to have the barrel re bored etc, I've always worked on my own engines, nothing beats being in the shed with a beer in one hand and a spanner in the other

what piston do you have in it?




Pro x piston I think, have to look at the box

I wouldn't even put a ProX in my 500. Too many failures on 500's here in Sweden with cracked inlet skirts on them. I drill two 2mm holes in mine as Wiseco recommends, and i degree the holes afterwards. I also relieve my bridge 1/10 mm at least.


Edited by Johnnymannen

isn't drilling the piston mainly required for the Wiseco\forged pistons?

I personally run Vertex pistons in my CR500, don't remember if these came pre-drilled or not, but if they don't, I've never drilled them.

vertex (atleast for the 250) comes pre-drilled.


i wouldnt worry about it to much with a cast, but. the next time you re-build i wouldnt forget to drill the holes. it does help.

Is it worth while stripping it back down to do the bridge gap now I've already been riding for a while?

Just use castor oil mixed at a high ratio like 32:1 and keep your jetting towards the rich side and the exhaust bridge will never be a problem.


castor oil won't burn off the bridge like synthetic and has incredibly high film strength. castor is also an extreme pressure lubricant that isn't easily pressed out from between 2 metal surfaces. you have no power valve in a 500, so castor will not be a problem for you.

and you libe in a place were the temp doesnt dip below 10*C..another pluse for the castor oil.


also, i have never had castor gum up my PV's.


is it worth stripping it...that depends on how much longer you are going to run the piston really...

bridge should be relieved. hard to say if youll have a problem or not. roll of the dice. cast pistons  are famous for crackin on the intake side so keep a eye on it

I don't think honda would ship something out that would give people that kind of problem. i'm sure the bridge is relieved during the manufacturing process.


why would they ship something with an exhaust bridge that is going to expand into the piston. yes, it's the hottest part of the cylinder, so change your oil type to castor and forget about it. why do you think i'm running 16:1 ? because i like to piss up money on 2-stroke oil ? I mix @ 16:1 for several very obvious reasons and to avoid future problems.



the exhaust bridge on my 06" cr250 is the last thing on my mind when i go out riding. i've all but forgot there is a miniscule chance there could be a problem in that area.


i'm sure my exhaust bridge is able to keep it's cool with all the cooling oil contantly being sprayed on it. I know for a fact all the castor isn't burning up during combustion, yet i don't have excessive spooge either.

Edited by Atieri

As stated above the hole are used in forged pistons for cooling and lubrication and the exaust bridge must be relieved or removed over all it adds 10 minutes of work . Here imy piston after I got it back from porting I have well over 100 hours of abuse still going strong .I pull the reed cage every month to check for cracks in the skirt that will happen before you lose compression. Oh and I will only run chevron 2cycle oil



That drilling seems excessive.  Is it necessary on a CR5?

I think it is excessive but I asked the guy doing the porting to get me everything he could on pump gas.it seems to be holding up just as well as stock with huge gains from off idle to top.

I dont know about a 500 but for my 03 cr250 wiseco gives instructions on where to drill, but wossner dis not so I called them to ask if yhe wossner needed drilled and they told me not to drill the piston and that I didnt need to drill there piston so I will see how it holds up the quality looks great though so im sure it will be fine.

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