Velocette Venom Thruxton Oil Tank Return Tube

I thought that I would take the time to share a rather simple modification that I did to the return pipe inside the oil tank on my 1965 Velocette Thruxton.

Firstly, let me explain what this simple modification is trying to solve.  Here is the bike being assembled.  You can see the oil tank loosely hanging just below the carburetor.  These motorcycles use a dry sump oiling system, meaning that the bulk of the engine oil is held in this remote tank and fed in and back out of the engine from this tank.  The return line enters into the bottom of the tank and feeds into an oil filter chamber.  Once the oil is filtered, it then spills over into a larger chamber which is then fed back into the engine.

As I understand from reading and listening to the generous Velocette community is that this return pipe creates a restriction which is prone to clogging.  Below is a photo of the oil return junction that enters the oil tank.  The red sealing washer seals against the bottom of the tank, the threaded portion connects to the oil line and the rod (right) is inside the oil tank.  The oil enters the center of the thread portion and exits the side holes (one seen below).  If that were left as is, the oil would be feeding into the tank from the bottom and when idle, the full tank could feed back into the engine.  For this reason, the feed must come above the oil level.  This is done using the aluminum tube seen below.  It fits over the union just described. 

Below, one can see the tube being installed.  Note how little room is left for oil to pass.  Further, the fit between the aluminum tube and the steel union is not very secure.

The aluminum tube goes all of the way down to the second shoulder, leaving a very narrow passage for the oil to flow.  This is the area that can clog and cause oiling problems.

In my reading, I found that some clever Velocette owners are doing away with the center stud and letting the oil feed straight up the center.  So, I did the same.

Further, I opted to fit a more common paper oil filter.  The original Velocette filter is hard to get and I think a quick look at the photo below will be enough to explain why I did this (BMW filter above and Velocette filter below).

Off to the lathe to bore through some solid 1/2" aluminum rod that I had laying around.  The rod is the same outside diameter as the original Velocette aluminum tube. 

Here are all of the parts laid out and ready to install.  If you do not have the ability to make these parts and want to make this change to your motorcycle, a similar tube can be purchased from Groves (https://www.groveclassicmotorcycles.co.uk/GCM102-Oil-Tank-Filter-Tube-Assembly---Thruxton)

Here is the top assembly.  The side holes are where the oil will come out of the hollow tube, at the top of the tank filter chamber.  I used a little thread lock on the stud at the top of the tube to be sure that it does not come out  in the future when I undo the top nut.

Here is the bottom.  Note, the oil will no longer come out of the side holes in the Velocette fitting.  It will feed straight through and into the new tube.  I simply threaded the Velocette fitting to fit inside the aluminum tube (also threaded).  I used a little medium thread lock on this to be sure that it does not come apart when I unscrew the top.

I used a BMW OX 35 oil filter (BMW part number 11 42 1 337 572).

I did make a simple washer/spacer to make sure that the assembly put some pressure on the filter seals.  I don't know how I could own a Velocette without a lathe:)

The fun part is that it all looks original from the outside. 

Now to make some polyurethane grommets for the oil tank mount:)  The new replacements that I purchased are not even close to the correct size.

Lastly, the intention of these articles is to share my experience for the use of others working on Velocettes.  For this reason, please feel free to share comments, edits and suggestions to make this more accurate or clear.

Blaise