Why use an Oil Catch Tank?

Every internal combustion engine has pressure & blow-by gases in the crankcase & valve cover. Some engines do a better job of separating the oil vapours before reaching the PCV (positive crankcase ventilation) vents than others. Most engines don’t, sending a poor mix of oil vapour & waste gases out the PCV vent & in to the intake system. These vapours smother important (& expensive) sensors with oil & gunk (typically carbon deposits). In worst case scenarios, this gunk can build up on the valves affecting performance. On a smaller, micro level, oil vapours take the space of oxygen molecules altering air-fuel ratios & lowering the efficiency and performance of your engine. The simple idea is to trap the oil vapours in the PCV system before they have the chance to affect the intake charge. As oil mist & gases enter a catch can they are forced to flow through a series of filter / baffle screens. As the gases flow through these baffles, oil & gunk run down the baffles to the bottom of the tank & lighter gases reach the outlet tube at the top and vent to atmosphere via a filter. Without these baffles, only a fraction of the liquids are trapped by the catch can. A drain in the bottom allows the tank to drain captured oil back to sump (or drained off at regular intervals via a valve) where the oil is reused and any deposits are captured via the oil filter.
I hope this has been a useful blog for some one and if I can help in any way with your future custom modifying needs please contact us at www.flashcustoms.co.uk
Oil Catch Tank Design coming next

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VW Drive Shaft Shortening


Originally these drive shafts were made from high tensile steel and heat treated to handle the torsional (twisting) forces being fed through them. The customer was fitting a turbo diesel lump from a Golf into the back of a type 2 vw van similar to pictured below, and needed the original shafts shortening.

Once the drive shafts were cut in half with a grinder, the job of machining them down to size (length) was undertaken. As the steel shaft is High Tensile steel that has been heat treated to give it the correct properties it is quite hard as well, this means we have to slow the speed of the lathe down (approx 540 rpm). Now we can either use coolant when cutting or take smaller cuts with the tool and not use coolant. Either way it is not good advice to start without coolant and then turn it on whilst the tool is hot (during machining) as this does the cutting tip no good at all (fast change in temperature of the tip) and may dull or blunt the tip. The drive shaft halves were machined to length by cutting along the shaft to reduce the diameter as opposed to “facing” off the excess material, when cutting harder material this can sometimes cause the tool to bounce off the hard material and you end up with a radius on the end and not a flat faced off end.
Once machined to length I used a centre drill to pilot dead centre of the shaft in preparation for a drilled hole to accept a machined pin. The idea of this is to make sure that both ends of the shaft to be welded are pressed onto the centre pin in theory this means that each end is “centred” accurately with the other.
Final machining of a chamfer on both ends allows easy access to the “root”  (bottom of the joint near the pin) for a quality “TIG” root run.
When Machining is complete, shafts can be pressed onto machined centre pin and then set in vee blocks on a flat surface to ensure alignment; as we do not want any “run out” end to end once the shafts have been welded together.
Notice in the images above I have machined a doubler boss to add strength and material to the joint just as a precaution. The aim of this is to add additional strength to the joint area. I have stated previously that drive shafts are made from High Tensile Steel and then Heat Treated to “Temper” the material to reduce the brittleness and improve the resistance to torsional forces going through the shaft. Once cut and welded I have changed the properties of the material due to heat input from welding, this may well have changed the “tensile” and “torsional” resistance properties of the material; so this is now an unknown. In order to offset this I bulk up the material cross section around the joint as a “belt and braces” fail safe. Notice the heat affected zone (HAZ) areas around the joint (where the blueing of the material occurs). This you can see changes colour the further away from the actual heat input point (weld), showing that heat travels through the material and if looked at closely you would see a range of colours indicating that the heat reduces as it travels through the material away from the weld. This is typically known as thermal conduction. A point to note if welding aluminium you would not see the material change colour due to heat input.
Once a TIG root run has been laid in the bottom of the “vee” a capping run is completed (using a MIG welder) over to fill the joint. This was then sanded off smooth and level with a flap disc (left image) to allow for the strengthening doubler boss to slide back over the original joint. Before welding the boss into place the shaft was “eyed” up for run out simply by rolling over a smooth surface whilst watching for the ends “lifting” and “dipping”   Then the boss is slid in place (central over the original joint) the boss was then tacked in place and a nice “hot pass” fillet was laid around both ends of the boss (again using a MIG welder).
A couple of points to note:- welding the root is undertaken in a clockwise direction, heat input causes expansion, cooling will contract the material more than the original expansion. To reduce the amount of times the shaft heats up and cools down, immediately after “root” run a “capping” run is laid in the joint in the opposite direction to offset any contractile forces created by the “root run”. Again the sanding process adds heat to the welded area and hence keeps the area warm. Immediately then the boss is welded in place and the whole job is allowed to cool down. Completing the job like this means that less shrinking and expansion occurs and reduces the effects of the coinciding forces created.
Finally the shafts were then put in a lathe and the welds skimmed down to ensure a nice even weight of weld is left around each end joint, thus hopefully reducing any vibrations due to excess weight of weld causing an imbalance in the shaft.
Once complete the shafts were left to “air cool”, If I had cooled them quickly in water this may have led to cracking or brittleness in the joint. After these shafts will be painted and fitted to the custom engine swap.
I hope this has been a useful blog for some one and if I can help in any way with your future custom modifying needs please contact us at www.flashcustoms.co.uk

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BMW MINI Alloy Race Tank Fabrication

I was asked to manufacture a 5 gallon tank for a customer building a BMW Mini race car, after discussions about size fittings baffling etc a fag packet sketch was produced in order to make the job.

I started with 1.5mm thick NS4 Aluminium sheet, plastic coated 1 side. Once dimensions were worked out I decided to complete as 2 pressed panels. Panels were marked out using tape measure, engineers square and fine tipped marker pen.

Once marked out the sheet was cut using a hydraulic guillotine for speed and accuracy, de-burring panels before proceeding reduces chance of cutting yourself whilst working with the sheet. Fold lines were marked on the panels but, before folding the strengthening swage lines needed to be put in – this I completed using a standard manual swaging machine, after which folding the 2 panels on a Box Pan Folder was completed. Results as shown –


Main body complete and ready for assembly, however I need to add filler hole, fuel pick up, return and breather hole, this will be completed in due course with a drill, hole saw and drill bits before tacking up.

Splash pan was manufactured again using 1.5mm NS4 aluminium and again marked out from sheet cut out using a guillotine and bench knife before pressing on the trusty box pan folder to the correct degree for the corners to meet up.

Once formed up to a square splash pan with a flat base I used a hole saw of 41mm diameter to cut a hole in the centre of the base for the filler neck to welds into. The filler neck was tig welded from the back of the into the base of the splash pan during welding the pan corners up, After welding the main body a drain stub was welded to the splash pan to drain away any spillage during topping the tank up.

Before assembling the tank, I used an electric hand drill to cut all holes in the tank body as required, this then means we can ensure a totally clean tank inside as we do not want swarf or aluminium dust inside the tank once complete for obvious reasons.


Tank foam was added to fill the tank to reduce fuel slosh before the 2 halves of the tank were assembled. Some adjustment was needed using clamps and small wedges to ensure that a neat outside corner joint was tacked up all round the edges to be joined by welding. If the set up is accurate a neater stronger weld can be produced and even penetration can be achieved, thus reducing chance of leaks or fractures. A good joint set up is also critical for speed of welding and aesthetics – e.g. weld will be a more even corner fillet if joint is tacked up correctly. So its worth spending a little for time and effort to get this part of the job right.

You will notice that I have already added fittings before set up of main tank body again to reduce chance of tank contamination.  

Using a coin tor score plastic coating reduces chance of scratching panel when removing plastic around areas that have to be welded. Aim is to leave as much plastic coating on the tank during manufacture to reduce scratch marks. Once complete it can all be removed.


Safety is a must when welding, you may have noticed in some images I have a fire extinguisher to hand should anything untoward happen, I wear TIG gloves and work overalls (fire retardant are best) and a quality air fed (& filtered welding helmet).

TIG welding produces a quality weld (dependant on welder skill, set up, gas flow, torch angle, torch aim etc), I aim for a nice even regular ripple effect and whilst welding tanks with outside corners a nice small “teardrop” effect in the bottom of the root, which tells me I am achieving a nice even bead of penetration – essential to ensure you get a strong, leak free joint.

Picture of completed tank, ready for pressure testing, which I do using a battery powered pneumatic pump, connected to one of the pipe stubs whilst blanking off the rest. Once under pressure ( a couple of bar is sufficient) the welded seams are brushed with soapy water whilst I look for a steady stream of small bubbles indicating a pin prick of a hole in the weld. As with all tank caps, aluminium or stainless steel it is a good idea to put a small amount of copper grease on the threads which helps prevent thread “pick up”.

Hope that this post may of been some help to you or at least an insight into building a race tank in aluminium.

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What is a “SWAGE” in sheet metal work ?

What is a “SWAGE” in sheet metal work ?

A “swage” is a recessed or raised area of material (a bump or a dip) put into sheet metal components typicaly to strengthen the panel.

The swage is made by 2 matched dies – one a “male” and one a “female” these are used on what is known a “swaging machine” where the sheet can be placed in between the dies and pressure is used to clamp the sheet and “roll” it through the “dies” producing the bump or dip. Usually other shaped dies can be swapped onto the machine to produce various shapes of form to strengthen, shrink, stretch or even add decorative patterns to sheet panel work.

See example of swage below and also a typical manual swaging machine.



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