Cracking heads! Our Impreza engine heads to the machine shop

by Hagerty
6 September 2022 2 min read
Cracking heads! Our Impreza engine heads to the machine shop

With Hagerty’s Subaru Impreza WRX ‘bugeye’ body condemned to the crusher last time out, it’s really the engine that’s now the focus of the latest Redline Rebuild project.

That’s the most interesting part anyway, and with the 2-litre flat four heading to the machine shop, it’s a good time to inspect its condition following a lifetime of presumably quite hard use.

And, as you’ll have gathered from the title, the cylinder heads are both cracked – though it’s not quite as problematic as it might seem. While there are indeed small cracks between an exhaust valve and the spark plug hole in both heads (with another crack beginning to appear in the second cylinder in one head), it’s at a place where the aluminium is relatively thick.

The worry, of course, is that a crack could let coolant into the combustion chamber, or combustion pressures could force oil, air and more into a coolant passage. But as you’ll see, a pressure test has given the heads the all-clear.

There’s still work to be done on both the block and the heads, and you’ll see exactly what the machine shop does to both in this video. With that work done, host Davin then begins the process of reassembling the heads – explaining just how the valvetrain goes together, the concept of valve lash, and how to adjust the clearance with shims.

It’s already satisfying seeing honed, cleaned up and correctly-measured pieces go back together, but if you want to see where we’ve come from, then head here for previous Redline Rebuild videos. You can subscribe to Hagerty’s YouTube channel here, too.

Read more

Buying Guide: Subaru Impreza Turbo (1994–2000)
See-through cylinder demystifies the four-stroke process
Hagerty’s next engine rebuild project is… a Subaru Impreza WRX

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