kant explain wrote on 2023-11-19, 06:00:
My old 90/91 LeBaron had a Mitsy 3.0. Good engine but for the blown valve stem seals. If I sat at a light for at least 30 seconds I'd drive away with a wad of smoke behind me.
I ran one of those motors for 10 years in a Voyager, and found out it was a three part thing. Yes, the valve guides could drop on earlier 3.0s, yes the valve stem seals got bad with age BUT... the stock PCV system failed to remove vapors/pressure from the heads when the engine was warmed up.... and it didn't happen however long you had the hood up in the driveway staring at it.... only with the hood down... because the top PCV hose would get hot, soften and suck flat... sealing off the head... then having lower pressure in the exhaust ports at some points in the cycle the mist, vapors and any oil clinging to the valve would get sucked down into the exhaust port and burn off there. So even if your seals were done, guides were dropping, if you replaced the top PCV hose fat plastic bit with a metal tube or better plastic part, then you'd change it from doing "Red Arrows/Blue Angels smoke on, go!...." at lights where you'd lay a trail for a whole block to just a one cloud puff, about washing machine sized on an old engine with the other troubles, but still a hell of a lot better. You could then further reduce this by running penzoil or motomaster "High Mileage" oil which cleaned up the head a bit and swelled up the old valve stem seals, and you'd be down to just a basketball sized puff. <<< which is still what a "rebuilt head" with fixed valve guides and new viton seals will do if you don't fix the PCV hose.
So full fix you could do on the vehicle, without pulling heads, was, use the rope trick to stop the valves from dropping, take apart the valvetrain, springs off, use compressed air to pop up any slipped guides. Groove the guides and circlip them, fit new viton valve stem seals, reassemble with springs and lifters, new gaskets on the rocker cover.... AND.. fix up the PCV line and then finally you'd have a fully smoke free 3.0.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.