2 Stroke - drilling holes in cast piston

SimonGreen
Just starting the top end rebuild on a CR125 and I have a Prox cast piston.

Is it recommended to drill the exhaust bridge lube holes on a cast piston? No instructions with the piston to do this but if it's not going to cause any issues I'd rather be safe than sorry!

Si
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Paw Paw 271
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Paw Paw 271 7/1/2019 9:15am
7/1/2019 9:15am
If your engine has an exhaust bridge, then yes it should be drilled for safety. Cast pistons don't expand as much as a forged piston, but it can still expand enough to cause issues and thus should be drilled.

Paw Paw
3
SimonGreen 7/1/2019 9:23am
7/1/2019 9:23am
Paw Paw 271 wrote:
If your engine has an exhaust bridge, then yes it should be drilled for safety. Cast pistons don't expand as much as a forged piston, but...
If your engine has an exhaust bridge, then yes it should be drilled for safety. Cast pistons don't expand as much as a forged piston, but it can still expand enough to cause issues and thus should be drilled.

Paw Paw
Thanks Paw Paw. Will proceed as planned!

Si
lumpy790
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lumpy790 7/1/2019 11:56am
7/1/2019 11:56am
Put the piston on the rod and slide the cylinder on. Using a magic marker up through exhaust port trace so you see where the bridge is on the piston and drill a couple very small holes in between. Also chamfer the holes slightly by hand turning a larger bit to clean and spread the cooling out a little more
2
SimonGreen 7/1/2019 2:19pm
7/1/2019 2:19pm
lumpy790 wrote:
Put the piston on the rod and slide the cylinder on. Using a magic marker up through exhaust port trace so you see where the bridge...
Put the piston on the rod and slide the cylinder on. Using a magic marker up through exhaust port trace so you see where the bridge is on the piston and drill a couple very small holes in between. Also chamfer the holes slightly by hand turning a larger bit to clean and spread the cooling out a little more
Thanks Lumpy!

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