K-bike Oil Sight Glass Replacement

By John McClellan
January 1998

Replacement of the oil sight glass is not covered in the Clymer manual, so, based on input from various and sundry presidents, and my own experience, I performed the replacement as follows:

  1. Put the bike on the sidestand so that the sight glass is facing slightly upwards. If the oil level in the engine is no more than full, you shouldn't lose much when you remove the old sight glass. You may want to drain about half a liter out first, just to avoid running oil all over the cooling fins.
  2. If you have a hand-drill, drill a small (1/8-inch) hole in the sight glass. Drill slowly, taking care to remove the plastic cuttings (from the drill bit and the sight glass) frequently, so they don't end up in your oil pan. Drilling the hole may help prevent shattering the sight glass and creating loose shards during subsequent steps.
  3. Tap the sight glass with a standard (flat blade) screwdriver, using a hammer or mallet, to crack the sight glass. Avoid hitting it so hard that you drive the screwdriver into the sight glass' metal backing plate.
  4. Once you have a few cracks in the sight glass, remove as many pieces as possible with a needle nose pliers.
  5. The sight glass assembly includes a metal backing plate which is held near the sight glass with a gasket and a spacer (appx. 1/4-inch). The backing plate has holes perforating it to let the oil through. Take a 3-inch wood screw (appx. 1/8-inch diameter) and twist it a few turns into one of the perforations.
  6. With a claw hammer (or maybe a "WonderBar"), slowly pry out the sight glass assembly via the wood screw. You may need to put the wood screw in a second location to work out the sight glass. Also, use a small piece of plywood as a backing piece for your prying tool.
  7. Once the sight glass assembly is removed, check for debris in the area from which it was removed.
  8. Rub some fresh oil on the gasket of the new sight glass assembly and press it in by hand as far as possible. Seat the assembly the rest of the way using a large socket as a drift, or by tapping it in around its edge in a star pattern (as you would tighten lug nuts) with a large plastic bolt or similar special tool. The sight glass assembly will stand out about 1/32-inch above the engine casing.
  9. Run the bike a while and check for leakage.
When I performed this, it took me approximately 20 minutes. I hadn't done it before, and I took time to be careful not to allow debris into the engine. As always, your mileage may vary.

John McClellan
Arlington, Washington
'85 K100RT