Well a few weeks ago I bought a shiny new cylinder head for my little Mitsubishi Triton truck. The truck was blowing too much smoke to pass a roadworthy certificate inspection, and it was annoying, so I was happy to shell out $1145 (about $800 USD) for a shiny new head that came complete with valves, springs, rockers, camshaft, new head bolts, gaskets, etc. I compared both heads side by side and they appeared identical, so I cleaned the gasket surface on the engine block, installed the new head gasket, spent another few hours installing a new timing belt kit and putting everything back on it. I finally fired it up and was rewarded with the "Farty Fart fart" sound of a leaking head gasket. Motherfcuker.........
What had I done wrong? I've installed heaps of head gaskets over the last 50 years and the only time I remember one leaking recently was on a CB750 that I was building for a customer who refused to pay to have the head skimmed, and it leaked oil, but apart from some of my cereal box gaskets that I made when I was a kid, that was about it. I scratched my head until the hair had disappeared in places. I ordered a new head gasket and started to strip it down again. I really wasn't confidant that I could fix it, which really pissed me off, but I couldn't understand what I'd done wrong?
I rode my K0 on Saturday and during the ride I had a minor epiphany. On the ends of the mating surfaces of the cylinder block there are hollow locating dowels that should fit neatly into matching recesses on the new cylinder head. I measured the recesses on both heads, and yep, the holes in the new head were ever so slightly smaller. As the dowels only protrude around 2-3mm above the head gasket, my guess is that the dowels fit (just) into the chamfers in the dowel holes in the head, But when I torqued the head down, the dowels couldn't go any further into the smaller holes, so even with the head torqued down it still had a poofteenth of a gap betwixt the head/gasket/cylinder block.
Yesterday I cleaned the remains of the ("used for 5 minutes") chinese head gasket from both surfaces, and even used a sanding block to make sure that there were no tiny rough areas or particles of poop that could come back to haunt me, and called it good. Using my drenel with a sanding drum attachment, I slightly enlarged the holes for the locating dowels at either end of the head and test fit the head onto the block without the gasket, and it was a nice fit now, with no “rocking”. I'd bought a spray can of Hylomar "Jointing compound" (gasket spray) just for a little extra insurance so I gave both sides of the new ($190....) Permaseal head gasket a squirt for some extra insurance and let it sit for 30 minutes or so before I dropped the head back on. The new head had come with a paper inlet manifold gasket which was useless and was buggered by the time I'd removed the head, so I cleaned the OEM steel gasket and gave it a spray of Hylomar for good measure.
I torqued the head down and started buttoning the engine back up again, but ran out of light (winter here) so gave up for the night. Lucky I did, as I'd just gotten out of the shower when the phone rang, and I had to go and rescue Spotty, who'd broken down on his way home from the coast. Today I stopped (paid) work early so I could get it finished in daylight. Much to my surprise, once I hooked everything up I turned the ignition key a couple of times to build up some fuel pressure, then turned the key all the way, and it fired right up, woohoo!
