Lubricating hole in Jackpiner piston?

[pentonpal]

I am in the process of having a sleeve installed in my 72 Jackpiner cylinder and will soon be fitting a new standard bore piston.  My Penton instuction manual details a section on drilling a lubricating hole in the piston.

I must admit that I am not too keen on drilling holes in a brand new piston unless absolutely necessary.  What do those in the know think - lubricating hole or no lubricating hole?

[john durrill]

pentonpal,
You need the hole or holes. I do 2 and some piston kits show 2 with the instructions.
The holes cool and lube the exhaust port bridge. Because of the bridges size and location it " grows " with the engine running. Expands out and closes up the clearance between piston and cylinder at that point. That usually leads to a seizure on the exhaust side of the piston and damaged rings.
  Assemble the piston  and cylinder on the engine. You can use a magic marker ( paint the piston exhaust side before assemblies ) and a scribe to mark the placement and width of your bridge on the piston. Pull the top end off. Then in a padded vise ( protect the piston from dings and  not enough force to distort the piston in the vise ) drill the hole or holes as shown centered between the two marks you scribed ( center of the bridge , this is very important ) so the crankcase mixture can not go out the exhaust port and hot exhaust gases can not find there way into the crankcase.
 If you do not have the right size bit you can get # drill bits from most hardware stores that will be with in 2 or 3 thousands and work fine.
Did this help any?
John D.

[pentonpal]

John,

Yes, very informative.  I appreciate the help and will be off to the hardware for some bits.

Scott

[Mike OReilly]

Also, the size isn't critical. I don't have all of the specs. in front of me so I won't talk specifics.

But, a few years ago I was scrambling around getting ready to go to Unadilla and I wasted a lot of time running around trying to find the exactly correct drill bit size - which in fact wasn't easily available at the local hardware store. (I found one at a machine shop courtesy of a friend). I later learned that the smallest commonly available size at a hardware store would have worked just fine. (What's the smallest common size at a hardware store, 1/64?? whatever it is, it will work)

The moral of the story is that yes, the hole (or holes) are important, and that if in doubt, go larger rather than smaller. Then sand it lightly to chamfer the hole and remove any burrs.

Mike

[Lew Mayer]

The sheet supplied with pistons now says drill 2 holes (.060-.090") in the center of your two scribe lines, approx 0.300" below the bottom ring, and .375" (3/8") apart then remove all burrs from the holes. I chamfer the holes with a larger size bit. Years ago, they only called for one hole but I guess there must have been a need to add the second hole.
If you have a fax machine, I could fax you these instructions.
Hope this helps.

Lew Mayer

[sixdazed]

On the later bikes we just relieve the exhaust bridge a couple thou. with a file after boring-would this apply to Jackpiner as well?
                                                   Ric

ric emmal

[G Ellis]

Ric this will work. Also if you cut back a 45 degree angle on the rings, the width of the bridge this works great. I do it on all of my 175, This is an old parts tip that is still good today. If you are using L ring type piston Elko, mal. Later Gary

[pentonpal]

Well, much to consider.  Thanks to all who have offered up advice.  I appreciate all of the input.

Scott

[john durrill]

Scott,
 It might be wise to get the tec sheet from Lew and follow the directions it gives.
 Its not something that should be omitted. The bevel on the rings should be in the shop manual

 and the holes in the tec sheet Lew has. We fixed more than one that customers put together and didn't do the mods on. The rings can catch and its almost sure the bridge will cause you a problem unless the bike is ridden very easy all the time.
 Hope this thread was some help. [B)]
John D.