WISECO VS OEM Pistons

[wfopete]

I'm getting ready to install a Wiseco piston and ring set in my 74 Jackpiner.  In comparison to the OEM piston the Wiseco, is of course, a forged unit but is also a touch heavier with thicker and wider skirts. The Wiseco also lacks the drilled holes on the exhaust port side.  Do I need those lube holes drilled in the Wiseco to prevent scuffing/seizures?

Do these differences add up to a better (more reliable/better performance) motor or will the motor/rider never know the differance?


Pete Petrick
175 Jackpiner
Slow but Good

[454MRW]

All of the Wiseco pistons I have used in Penton/KTM engines have included instructions on drilling the hole(s) on the exhaust side to lubricate/cool the exhaust port bridge. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S
1975 Can Am 175 TNT & 77 250 Black Widow
1979 Husqvarna OR250 & OR390
1976-78 RM & 77-79 PE Suzuki's
1974 CR250M 07 CR125R

[chicagojerry]

even the nos hipoint replacement pistons were made by wiseco. they work just fine but i would prefer to have mahle but good luck finding those.  i always drill the lube holes.  chi jer

[Kip Kern]

Pete

2 Holes drilled on exhaust side of piston.  .060 diameter each, the first .300  below bottom piston ring groove then the second .375 below the first hole drilled.  Make sure to mark the exhaust bridge on the piston properly to correctly center the holes under the bridge before drilling.  This info should be in your Piner manual.  Dont forget to clean the piston after drilling.

[wfopete]

Thanks guys, looks like a good excuse to buy a drill press!

Pete Petrick
175 Jackpiner
Slow but Good

[SouthRider]

Even the OEM Mahle pistons did not come with the holes pre-drilled.

This was something that the dealer or owner had to do and was always a part of any KTM engine top end rebuild.

We always installed the piston without rings or circlips and slipped the cylinder on in order to scribe the exhaust port with the correct rotation.

These pistons used to last significantly longer than say an equivalent size Husky with a large open exhaust port that had no bridge. That little bit of pre-mix coming through the hole keeps the bridge from getting red hot from the exhaust gasses, and the inclusion of the bridge keeps the rings from hanging in the port and helps to keep the skirt from rattling around.

A great setup, but it requires a little extra work. I used to lightly center punch the hole location and then drill them holding the piston in my lap using a small right angle drill. A shop rag around the piston and careful insertion in a vice will work too. Take special care when drilling as those little bitty bits break easily.

The OEM pistons used to come with the correct drill bit taped to the piston......

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"We the willing, led by the unknowing, are doing the impossible, for the ungrateful. We have done so much, for so long, with so little, that we are now qualified to do almost anything, with nothing."

1972 Penton Berkshire 100
1983 Husqvarna 250 XC
2011 Jayco 31.5 RLDS
2009 Chevy 2500 HD Duramax

[G Ellis]

Pete on all of the 175 motors I have rebuild, I file the edges back on both rings. This would be just enough and the width of the bridge area. Top and bottom of each ring. This is how you will get longer life from the rings on a 175. Hope this helps, if you have any questions give me a call 217 260 0237 later Gary