One of the most common parts missing on used engines is the sight glass tube, probably because they are easily broken if
precautions are not taken to protect them. Replacing the tube is actually quite simple.

How To Change a Sight Glass Tube

Step 1: Determine the length of tube required.

Remove the jam nuts with a 5/16" wrench and measure the opening of the port in the fitting, and the distance between the ends of the fittings.

The standard distance between the fittings is 1", some fittings have smaller openings than the 1/8" diameter of the tube. In this case a 1" long tube is required as the tube sits between the ends of the fittings.

For units with openings larger than 1/8" a 1 1/8" long tube is required as the ends of the tube sit inside the ports in the fittings.

If one has the tools and talent it is often possible to bore out the smaller ports to use the longer tube as this is a better system.

Order sight glass tube

Step 2: Prepare tube for insertion.

Remove one of the gaskets, slide one jam nut on to the tube with threads toward gasket, Slide the second nut on to tube in opposite direction. Replace the second gasket.

Step 3: Insert the tube.

If you are using a 1" long tube locate the gaskets even with the ends of the tube, place the tube between the ends and snug up the jam nuts, do not over tighten.

If you are using a 1 1/8" long tube slide the bottom gasket about 1/4" from end of tube, locate the top gasket 1/16 of an inch from the end. Drop the tube into the bottom fitting and raise it until the top gasket meets the fitting, snug the top jam nut. Holding the tube carefully slide jam nut and gasket down and snug up jam nut, do not over tighten.

Replacing a Sight Glass Unit

Occasionally an engine may be missing the entire sight glass unit, the condition and size of the threads in the boiler should be checked before ordering a replacement.

If the threads look good upon examination it is easy to check the size by simply unscrewing the safety valve and trying it in one of the bushings, if it fits the threads are standard Weeden 1/4 -32.

If the bushings are missing or the threads damaged new bushings will have to be ordered as well and soldered in.

When installing the unit it is advised to use a product such as Loctite 565 to seal the threads.

Thread bottom elbow into bushing on boiler so that port is facing up. Prepare sight glass tube as per instruction at top of page, insert tube into port and let it drop down far enough to be able to thread top elbow into bushing so port faces down. Center the tube and snug up jam nuts, do not over tighten.