Canon 100-300mm f5.6 front ring removal

Hi everyone,

 

I recently picked up this lens very cheap because it has some pretty significant fungus inside and I was hoping to disassemble and clean it but the front ring just won't budge. I am using a lens wrench and I have applied considerable force/torque but I have never experienced a lens ring being this stubborn.

 

Does anyone have any suggestions how I might remove this ring? Are their any techniques or lens-safe sprays or oils I could use to help loosen the ring? Like WD-40... but obviously not WD-40.

 

I have included an image of the front ring/element.

 

I appreciate any help anyone can offer.

 

This is my personal recipe for stubborn retaining rings. YMMV.

1. If there is locking paint, carefully remove it using acetone. I couldn't spot locking paint at my 100-300mm 1:5.6's retaining ring, though.
   
2. Carefully clean the filter thread using a drop of lighter fuel.
    
   
3. Use quality spanner wrench. Don't use the China ones. Micro-Tools has good ones but they are pricy.
   
4. Alternately apply loosening and tightening torque.
   
5. Carefully heat the front barrel of the lens. Use an adjustable heat gun, not your hair dryer.
   
6. Find a piece of round wood that fits the ring without geting in contact with the barrel or the front lens. Apply a few light hammer strokes just onto the ring.
   
7. Let a drop or two of thin oil soak between the barrel and the ring. Some cleaning required afterwards.
   
8. Be patient. Try again next day.
   

One more thing you may want to try. I read about this on a Large Format forum. Metal contracts when cold. Put the entire lens in a bag and stick in the freezer overnight. I tried this on an old large format lens I had and it worked.