Machining engines - if you don't get this right prepare for mechanical devastation

The junkyard build fad has people ripping engines out of crashed nuggets and slapping them into projects with barely a second look at the engine's health. This can be a huge amount of fun, but sometimes builds get spicier and you need to rebuild the engine. This means you need to visit a "machine shop", which is what I did for the supercharged 6L V8 I put in my '64 Pontiac build (CLICK HERE FOR THE VIDEO)

The start of any engine build is always “machining”, but what does that involve exactly? Basically, an engine relies on finely-measured tolerances and clearances to stay together as we wring as many duck-powers from it as we can, and this all starts with ensuring the engine’s block measures up the way it is meant to.

Engine blocks are cast in huge foundries and, if you muck around with old mass-produced engines, you’re likely to find that one particular block may measure differently to another from the same factory. There are sometimes problems with the casting process, or during the process of the block being machined at the factory for the first time the machines were minutely out of alignment. This won’t normally kill a stock production motor, but when you want to make double, or more, power than what it was originally designed for this can present expensive problems that end up with broken metal and tears of sadness. 

We headed out to Jenkins Performance Engines in Penrith to watch an iron block LS go through the process, from cleaning to being ready for Troy Worsley from Warspeed Industries to build it into a monster ready for boost.

James and Kurt from Jenkins took the bare iron block and sat it in their cleaning bath for a week, so the heavy duty degreaser could work free all the dirt and slime built up on it over the last 15 years. It was hosed off after a week being submerged, stuck in a hot wash machine, then blown out with compressed air.

The first step was to deck the block on an AZ Machine Tools SP1300M, which ensures the block is in alignment and will have good cylinder head sealing once it is all bolted together. The machine sees the tunnel is 90-degrees to the deck, so the deck height (where the cylinder heads bolt) and tunnel height (where the crank bolts) are measured and any problems with twists in the block or split bores can be identified, and a new block sourced (for common engines).

If the tunnel isn’t true this means your crankshaft can be under extra pressure from the block trying to deform it, which will shorten its life, so this is an important step. The CBN tip gives a high-quality surface finish the MLS head gasket needs to seal properly to the deck surface. All up there are five passes per-bank, and then all the passages are de-burred.

The next step is on to the honing machine, a Sunnen Cylinder King CV-616-D, which is basically a set of fancy, high-speed grinding stones that ensure the bore is straight and true as per-spec. The block is torque-plate honed with the main caps in and torqued-down to distort the block to how it should sit when assembled, which is a critical step when doubling the power of a production motor like this LS.

Checking the taper with a dial bore gauge is also key as most production blocks have a taper built into them, where it is tighter in the bottom of the bore. Kurt started with a set of roughing stones on each cylinder, moving to an intermediate and then a finishing stone, before ending on a plateau stone which improves run-in time by knocking down high-spots in cylinder walls. He machines off-cylinders to prevent too much heat distorting the block as he cuts fractions of a millimetre of material with each pass.

To finish off James checks the balance of the Texas Speed & Performance crankshaft intended to go into the motor. Some packages are sold as “fully balanced” but this might not be balanced as finely as your engine builder might like, and Troy wanted this TSP crank, custom Wiseco pistons and TSP con rods balanced to the absolute highest standard. James found the Wiseco pistons, TSP rods and TSP crank were all fine and ready to be put to work in the iron 6-litre LQ4.

Normally it takes around a fortnight to get your freshly machined, balanced parts back, ready to be washed up and assembled. This motor went to be line-honed at another shop after Troy fitted ARP main studs to it, and it would then go back to his shop for another 4-5 hours of cleaning before he’d start measuring all the parts in preparation of assembling it.

A huge thanks to James and Kurt from Jenkins for letting us follow them around their workshop for a morning and ask all sorts of silly questions about what they were doing and why. If you look closely at the below photo you can see how many engines are dotted around their shop, so we appreciate the time you guys took talking to us!