The way to do it so you know your not going to skip any teeth on the cam gear is to use 2 vice grips to keep the chain on the cam gear sprockets at all times. Just put a vice grip on the left side of the sprocket, turn the crank till this vice grip is rotated to the right side of the sprocket, then take another vice grip and put on the left side, before taking off the right side, then keep repeating till the old chain is out. You could use this method to do it yourself, because there really isn't any way to screw it up if you always have at least one vice grip on the chain at all times. I don't think it's possible for the chain to slip off the crank, so you don't need constant tension on the old chain that's coming out.

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head