Menu Close

Oil Sight Glass Replacement

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

Oil Sight Glass Replacement

By Andy Newell
July 2005

I’m a formerly certified tech who changed careers in 1997. The easiest way to change a K bike sight glass:

  1. Wait for the next oil change.
  2. While bike is on center stand, with oil filter plate removed.
    Lay down on LH side of bike with a flashlight and a screwdriver at least 12″ long.
  3. Look up into the engine through the oil filter hole, from ground level from the left side of the bike.
  4. Look at the light coming through the existing oil window.
  5. Position screwdriver carefully on the center or in one of the ribs that let oil into the glass.
  6. Tap out the oil window with a long screwdriver using your HAND ONLY.
  7. The seal will fall out and a new one is easy to install.

From my experience, I would suggest a very light coating of clear sealer, (same stuff used for timing covers) and waiting 24 hours for the sealant to sealant to cure BEFORE putting in the new oil.

Using the technique of sealing and not putting any fluids in until the next day, was one of the best decisions I ever made as a tech. It virtually eliminated comebacks for oil/water pumps and timing covers.

Try it, you might like it.

Andy Newell

Leave a Reply