1991 300te. How clean should the lower block gasket surface be before installing a new headgasket? I have thoroughly cleaned the surface with brake cleaner, and a scotchbrite pad. Visually the only thing remaining are very slight stains here or there.

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You should be able to run your finger across the surface and not feel any bumps at all.

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How did you get the pistons that clean?

You should get the cleaning attachment for a dremel and clean them a little more so you can find hot spots.

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I used the flat edge of an exacto knife and scraped all the build up of carbon off. I would do two at a time when they had been rotated to tdc, making sure that when they were up I could not damage the chamber wall.