Each and every engine has its own character, and sometimes the true nature of that statement is not borne out until Davin plops a bunch of parts on the machine shop bench at Thirlby Automotive. The Subaru EJ four-cylinder is one such example. Each and every piece of this engine has a special type of machining needed, but luckily nothing cracked up the team too badly—well, almost.

The block was the easiest of the group, as it was a fairly simple problem to address. When cutting and honing the cylinders, it required a bit of special care to not push the hone out the bottom of the cylinders. The way the casting is designed there’s an access hole for removing the wrist pins on the pistons, and that leaves a giant gap in the cylinder wall that is happy to catch a tool and ruin your day. The Thirlby team is used to this though and knocks out the block haves in short order.

Then it’s on to the heads, which require a modified drill press to remove the heavily angled and shrouded valves. Before removing the valves, Thirlby did a quick vacuum test to see how bad the valves and valve seats were, and the results were somewhere between good and bad. A few of the exhaust valves were leaky but not so bad as to cause alarm. What did cause alarm were the cracks in the heads. These propagate from the heat of the exhaust valve seat to the spark plug threads and can cause coolant leaks. Luckily, these heads are cracked but not so bad as to actually cause problems. You could call it luck.

Then it’s all just reassembly and precision setup. The process rolls quickly with the right tools and team, making it easy to see why Davin has one machine shop that he frequents with all of his projects. This Subaru should be rolling back into the Redline Garage shortly, and if you want to see how it all goes back together you’re going to want to subscribe to the Hagerty YouTube channel so you never miss an update.

Kyle Smith

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