Ok ...

Here we go again .
I dismantled my ST G21/.35 engine today and found that is hasn't got circlips retaining the wrist pin .
The pin is hollow and the hole in the piston looks as it has been bushed around the wrist pin (like a sleeve) .
I tried cleaning , to loosen up the parts in an U/S cleaner , to no avail ...
The crankcase has the rear screw for removal of wrist pin , so I'm thinking "no circlips" ?
The con rod won't slide on the wrist pin , so I can' get the con rod off of the crank pin .
Any ideas ?

Thanks

As usual, Randy is right.  Use heat and penetrating oil liberally, it may take 5 or more heating and oiling cycles.  You should have a steel tube wrist pin with aluminum or brass end pads pressed in at each end, to prevent scuffing the cylinder wall.  Remove the sleeve by putting a matchstick or so in the exhaust port, using the piston to push the sleeve up and out.  Take your time, and use lots of heat and oil.  To pull the wrist pin from the piston, you'll have to run a sheet metal screw inside the wrist pin to get the threads to engage on the inside of the wrist pin or end pad.  Lots of heat and small vise grips on the screw, and a firm, smooth pull.  If you have luck, the whole pin and the end pads will come out.  If not, you'll pull just the rear end pad, leaving the wrist pin and forward end pad in place.  Select a longer sheet metal screw, grind the tip so it has no excess length beyond that necessary to engage the forward end pad, heat and pull again.  If it has really serious varnish, it may take a session or two in the anti freeze tank.  Use lots of heat and penetrating oil.  Try this at least 5-6 times before rolling out the heavy artillery...
      IF it won't move any other way, put the piston at BDC, and mount the engine in your drill press nose down.  Pick a drill bit with .030 or so  clearance from the wrist pin hole in the back of the case.  Hold the piston at BDC, out of the way, and carefully drill a hole through the hole in the back of the case, across/above the piston crown, making a new hole in the front of the case, aligned axially with the original removal hole in the back of the case.  Don't go too deep and hit the venturi.  Blow off the chips and support the engine on a wood block, nose down.  Use a brass or steel drift pin to drive the wrist pin back out of the case, through the original removal hole.  Use lots of heat and oil, and start with small taps from a light hammer.  The object is to get the wrist pin to move with only the least force necessary.  Now hot tank it again, and get the rest of the varnish out.  The new hole should be deburred before reassembly, but the sleeve will seal the forward hole just like it did the rear one.  A really stubborn one can take a week or so of intermittent heating and persuasion.  Tom H.

Hi ,

The heat/oil treatmrnt worked so/so ...

The wrist pin pads are non-existent , though , so I will make some .
The wrist pin is siezed to the con rod , but is free in the piston through holes , so I will try a roll pin punch on it (with a bit of heat) and see if it will move .
If I have to make a new pin , what Rockwell hardness should I be looking for and what type of steel should I use ?

Thanks for all the help .

Rob K.

Hi Rob

Rather than make one  you should be able to use one from a OS FP 35 or 40, you can grind the ends  down if it is too long, and reuse the  pads from it.
However if you have to make a wrist pin you can use  01 tool steel, heat it cherry red after sizing and drop it in motor oil. I then clean  and polish the pin so it is shiney, make sure you clean it with thinner or acetone immediatly before you put it in the oven. I use one with a window and a light in it, The part will  start to turn straw color and blueish stop the heat at this point.  If you have a  Rockwell C  hardness  tester  it will be around in the mid to high  50s  I don't have a tester  but a borrowed one  I use to test my parts showed  C 59

Regards
Randy