ADDING AFTERMARKET PARTS

Welcome back to Project Superjet, where we have now got our ski back from the sprayers and it’s looking pretty cool we think. But before we start work on the ski itself we’ve got to look at what aftermarket parts we need for the engine and pump unit.

CHOOSING THE PARTS

First off, we have decided that we want an aftermarket high performance head fitted to the ski to give it some serious performance gains. So we called Chris and Lisa at Air Time Products (ATP) to see what they had available.

Right from the word go we wanted the ski to be the perfect recreational ski, so we decided that at this stage we wouldn’t be putting on a Factory B Pipe (maybe at a later stage me thinks).

This got Chris scratching his head. He said that their Snake Heads were designed only to be fitted with an aftermarket pipe and not the standard one. So it was back to the drawing board, quite literally, to start designing a head that was compatible with the standard exhaust pipe.

Rather than me trying to explain to you the process of how you get from a block piece of aluminium to a finished head, it’s better I hand you over to Chris and Lisa who will explain how CNC machining works and talk you through the process of manufacturing our head.

OVER TO CHRIS AT ATP

Since launching Air Time Products five years ago, we made the decision to invest in a CNC (computerised numerically controlled) machining centre so that production of our aftermarket parts could be brought in-house. This was closely followed by a CNC tool room lathe so that we had tighter controls on quality and consistency, as well being able to upgrade, revamp, change, improve and produce custom one offs to larger batch parts.

More recently the machinery has been added to. In the early part of this year we took delivery of a CNC production turning centre, with a “C” axis and “live tooling”. While we currently manufacture true girdle cylinder heads (Snake G2), the Project Superjet head is different, because we have to make it to fit with a stock OEM exhaust system so therefore is non-girdled. The head will not need a girdle as it does not have an aftermarket exhaust system.

We will need the use of two CNC machines for this - one CNC VMC (vertical machining centre), which will be used for the head shell and O-ring groove on the domes, and one CNC Production Turning Centre, which will be used to produce the domes.

As this is the first time we’ve been asked for a head to fit with a stock exhaust system a new design was needed. Using our CAD/CAM drawing program we created the design, which is the program that will be fed into the machine. We need to tell the machine what to do using tool paths. This means programming which milling cutters to use and where, at what spindle speed, what depth and speed of cut to take and where to finish.

MANUFACTURING THE HEAD

Next we need to place the block of 6082 T6 aluminium into the machine and clamp down in the vice. This is aircraft grade aluminium and of a slightly higher grade than most commonly used by aftermarket companies. The next job is to reference the machine with height gauges. Referencing is required so the machine knows where the block is in relation to the machine bed and spindle. The tolerances we work to are usually 0.01 mm. But the referencing must be perfect otherwise there is nothing stopping three tons of spindle smashing through the machine bed.

As the program has already been sent over to the machine via the network, we are ready to close the doors and press start. The machine will begin cutting, following the program code given, the milling cutters will go to work then automatically retract and change over to the next tool required. The ATC (automatic tool change) is a huge time saver in manufacturing.

Now the machine has finished the topside of the head we now need to turn this over for the underside to be done. Again this will require re-referencing and the second part of the program will need to be sent over via the network.

FINISHING

The new head is now finished on the machine along with the special exhaust bracket mounting. The head now requires finishing, so we clean it off to remove the machine coolant before it can be finished. This head is going to be anodized black satin/matt finish.

First, we polish it. This is done in a small sealed room as polishing aluminium is a really dirty job that creates a black greasy deposit during the process. We use a floor mounted polishing spindle with various polishing mops and grades of compound to achieve the required finish e.g brushed, mirror etc. Most ATP parts are mirror finished before they are anodised.

FOR MORE, BUY THE AUGIST ISSUE OF JET SKIER&PW