Before you install the head, clean every head bolt hole in the block. Not a bad idea to run a tap through the threads to remove any gunk, at least use a clean old bolt to make sure the threads run free. Make sure there is no debris or fluid in the hole before installing the head. Follow the instructions about lubricating the threads and underside of the bolt head. Don't overdo it on the thread lube... a drop or two is enough, starting at the bottom thread.

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1987 W201 190D