125-200cc CR125 Piston oil holes for exhaust bridge

I'm doing a top end on a 2008 CR125 and ordered a piston from vertex. The Vertex piston does not have oil holes for the exhaust bridge like the original oe piston. Do these need to be drilled or is it ok using the piston as is?



Also do all of the years get both the o-ring and the washer on the pipe at the cylinder. According to the 2008 parts catalog the 08 gets the metal washer(part3) and no o-ring (part2). Interestingly when I pulled the pipe it had the o-ring but there was no washer. Looks like most of the other years show both in the parts list.

I would drill the holes only because I know of a bike that nipped up after fitting one that was not drilled very shortly after being replaced.
Another piston was fitted with the holes drilled and all was fine.
As for the washer I have never seen a 125 of any year that has not been fitted with one, Cant see that it would be harmful not to run one as most makes of bikes dont bother fitting one.

I think the washer is there to prevent the spring tension from causing the pipe to wear into the aluminum. Mine was in the bore the pipe fits into all gummed up wth oil and carbon. It must be an optical illusion from the angle but the piston appear to be slightly different in height?

Do yourself a favor and drill these holes- i knew from beeing a YZ125 rider these holes will keep your engine last- if they are not there the exhaust bridge tend to crack due to extreme heat or it will expand to much and cause a seizure...

Unless the exhaust bridge was relieved for heat expansion ,drill the holes. Most companies that re plate cylinders put a relief in bridge...OEM has as well, but the confidence of not second guessing and drilling the holes is your best bet. Wiseco made that mistake many years ago by not pre-drilling holes and allowing unexperienced owner repaired not to "follow the enclosed directions" that were most likely thrown away instead of read.
Still trying to figure how your Vertex piston is not pre-drilled...I have a new one in front of me #22600C and it is drilled. I even checked 2 prior piston changes ,that I never throw away for some reason, and are drilled ???? Take your new piston, without rings, install it on rod with pin and wrist pin bearing(won't need to put clips on at this point ) slide the cylinder on, down to cases ,move the piston so the ring groove is barely showing at top, thru exhaust port hole, and use a nice sharp "pencil" and scribe lines on piston, on both sides of bridge, from top to bottom . carefully remove cylinder and piston and check your lines. My 2 piston holes are 1/16" ...the first hole measured from TOP of piston down is at .453'' (29/64") and the second hole down from top of piston is at .906" (29/32"). Take your time ,measure ,check your measure and drill in the MIDDLE of the 2 lines you marked with pencil. I would buy a new split point drill bit if possible...helps for drilling into curved surfaces.

drill it per directions. new oring and flat washer on the pipe.it will serve you well. that old piston was spanked

Started on a YZ125, too. Was lucky to find a good machinist who showed me how to drill the holes and relieve the bridge, back when I didn't know $#!+. Got great life out of the motor where others were having reliability issues. Drill with a sharp bit as to minimize stress risers around the holes, and ride it like...

My 125 had no washer. I never knew it should till now. I installed the WB pipe by reusing mymold.o.ring and no washer. Guess thats 2 more things i need to fix

Sorry for reviving this old thread, well some movement to the forum can not hurt neither

I always read that you should only drill forged pistons, never cast ones, as they could later crack .... Now I see that you drilled a cast Vertex and I'm confused ...
I have a Honda CR250 cylinder with a exhaust bridge and I am not sure if I can/should drill the cast Vertex piston I have already bought or just install it as it.

I searched the web and got across this site from a cylinder repair shop from NZ: http://nzcylinders.com/Exhaust bridges.html

Cheers !