Preparing the 2TG Block Deck Surface and Head
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Pictures and Text by: Michael Yount
It’s becoming apparent that finding a traditional composite head gasket for the 89mm overbore is likely not going to be possible. The good news is that Cometic makes multi-layer steel head gaskets for the engine in 8 different thicknesses and in a diameter to accommodate the 89mm overbore.
The not so good news is that Cometic require a quite smooth finish on the block and head in order for the gasket to seal properly. Easy-peasy for the machine shop – just order up a head/deck cut of “50RA” or better. Of course, the head and block must be completely disassembled which I want to avoid if possible.
Research plus experience tells me that with right “sanding block” I can likely solve problem right here at home. Turns out my bride has several pieces of granite countertop. Granite cut for kitchens is very smooth and flat. I used duct tape to tautly fasten sand paper to the piece of granite. I started with 150 grit – 220 – 320 – 400 – working up to 600. Two “tricks” – 1) the piece of granite ideally is big enough to completely bridge the width of the head, 2) you “wet” sand using oil as the lube. The oil keeps all the particles in suspension so tiny bits don’t go everywhere.
I worked slowly – about an hour for the head and two hours on the block. Vary motion – across length and width, mixing in circular and diagonal passes – and stop occasionally to wipe out cylinder walls/chambers so oil/debris doesn’t up where you don’t want it. I was very pleased with the outcome and believe it will seal with the Cometic. You get a sense for how smooth/polished it is by the level of reflection.
An add/edit — on first start, I had a couple of oil and coolant leaks that required the head to come back off. First time that has ever happened in over 50 years of working on cars. Nonetheless, it happened. I decided while I had the head off that I’d seek an even smoother finish on the head and block — so I used the same procedure described above, started with 600 grit and then went 800, 1000, 1200 and 1500. My thought at the time was “if that’s not smooth enough to seal the Cometic MLS gasket, I give up.” So far, seems to be sealing perfectly.