Sunday, 12 May 2013

Oil Strainer

As I said in my previous post, I still have welding to do but it is time now for something quiet. 

This is the oil strainer banjo bolt out of the bottom of the oil tank. You will note that the strainer is conspicuous by its absence - only a scrap of solder remains:


A strainer is a simple affair made from brass mesh - I selected some from an eBay shop at 40 wires/inch to be suitable for filtering bricks, flies and sweet wrappers from the cold viscous oil in the tank.

Strainers are easy to make. Select a former to match the diameter of the banjo bolt - I used a piece of chromed tube intended for making clothes rails. Pass it through the hole in the tank, and measure the maximum length of the strainer. Subtract the length of the banjo bolt.

Cut a piece of gauze to that length with your snips, or use scissors. You need good quality snips - scissors are fine. Loose or worn snips will just allow the wire to slip between the shear blades. Cut the width to wrap around your former and add 3/8".


Fold up 3/16" or so at each edge, shown in the photograph above. One edge must go up, the other down, as shown in the first sketch below. Wrap the gauze around the former so the edges overlap, shown in the middle diagram.


Ease the folded edges over one another with your fingers, so they lock together like the last diagram.

At this point, check the strainer fits over the solder area on the banjo bolt. If it's OK, find a suitable mandrel (I used a cold chisel) that will fit inside and press the seam tightly together with something hard & smooth (like the shank of a screwdriver)


Now you need to make the end. Cut a disc of gauze, about 3/16" larger than the former you used to wrap the gauze. Lay the disc over the end of the former, and press it into something soft - you palm will do. This will raise the edges of the gauze around the former. You can finish that off with you fingers. The aim is to make a little 'dish' of gauze.


When you've finished, set it upside down in the strainer (raised edges upward)


This is how it looks all together:


Next step, solder it up. Start by taking the strainer off the banjo bolt again. Use a small torch to heat the large banjo bolt, with some Baker's Fluid in the solder recess at the top. Tin this area with solder when it is up to temperature. Use ordinary plumber's or electrician's solder for this job, there is no point in using anything stronger.

When this is complete & cool, mount the strainer back on the banjo bolt. Use a big electric iron and some more Baker's Fluid to reheat the solder at the top of the banjo bolt and it should flow happily into the gauze. Now, after the bolt has cooled move the banjo bolt in the vice so that the strainer is horizontal and the seam is uppermost. Take your soldering iron and run a small amount of solder right along the seam. 

When it is cool again, have a look inside the strainer and make sure it is clean. This area is for CLEAN oil and goes direct to the oil pump - you DON'T want any gobbets of loose solder in there!

Fit the end cap, and dunk it in some flux. Use the soldering iron to run a small amount of solder around the end cap, fixing it to the barrel of the strainer.

Let it cool, and wash the flux off.

And this is the finished article:


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