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Drilling two holes in the piston for the exhaust ports? WHY?

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Hi, everyone. I just wanted to ask those more knowledgable than me about this. I have an 06 YZ 125 and at rebuild time plan to use a Wiseco Pro Lite rebuild kit. My motor has been worked by PR2 Racing and it does have a bridge seperating the exhaust port into two ports. I saw in another thread someone suggest drilling two holes in the exhaust side of the piston (one for each side of the exhaust port). Is this really necessary? Why would you do this? Thanks for the knowledge!

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You drill the holes right over the bridge. The idea is to let some mix through to help cool the bridge. Doing so made a decent sized difference in the piston life on the Honda's I worked with. It takes very little effort to do so. The piston is super easy to drill. I would add them if you have the bridged exhaust port.

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The '05 YZ125 OEM pistons come with the holes, so Yamaha must think they're of some value. Have you removed your stock one to see if it has the holes?

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No, I havent removed it yet. Would you drill it then smooth out or chamfer the hole a little to be sure there is no burr on it?

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I did smooth them over, but it may be no big deal either way. I used one of the "high speed" polishers found in a dentist office. Actually, I did it in a dentist office. Even the drilling. Its a fun place to make awful noises. Especially when my buddy, the dentist, is working on a human just out of sight.

I will sometimes act like I am talkign to a person. Say somethign like, "This wont hurt a bit", then turn the Makita on.

The reason Wiseco does nto drill them in the first place is the bridge location varies a bit from cylinder to cylinder.

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thats weird, when i bought a pro lite kit for my 98 yz125, the piston came with holes already pre drilled.

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All should be drilled as it can only help things. I dont believe many oem's do thsi , but it cannot hurt anything.

Wiseco would drill the honda holes...well, that is if Honda could properly place the exhaust bridge. Its never in the same place.

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