Put the engine in, then connect the RV oil lines, then put the lower half of the pipe in. Make sure you have EVERY piece of the rubber bushings for the two mounts. Thread the address almost all the way in. Then smear the joint with Cooper rtv, make sure the copper ring is there. Then install the upper half and snug the screws, put the clamp on around the pipe and make sure the joint is aligned and tighten. If all looks good tighten it all.
If you put the pipe on first you'll need to connect the rv oil lines before you install the engines, so you'll need to remove those from the boat. You'll also need to put the port engine in first then the starboard. To me it's too much work. I do it all piece by piece.
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