VICTORY! You're right Charlie. The slight taper at the end was just enough to get the tap started straight and clean up those first few threads that were stopping the plug before.
The plug now goes in cleanly and stops just like it should.
I didn't put the petcocks on yet because I didn't have a wrench big enough to fit it.
Charlie, the plug is that size because the manifolds are reversible from left to right. Cooling water is fed to the manifold through a 90 degree hose barb screwed into the 3/4" hole in the front of the manifold and the plug goes in the back.
I'll probably clean up the hole in the other manifold so the new petcock had good threads to bite into. I'll try to get it buttoned up this weekend, but looks like rain will keep me off the water.
quote:
Originally posted by BillK
In my opinion the Pleasurecraft 302 and 351 were some of the best marine engines made. We had a 302 in our '79 Correct Craft - when I sold it in 1990 with 2000hrs for MORE than my father paid for it in 1979 it still ran perfect, only issue we had was a carb rebuild. It still had the original manifolds and risers. I have always boated in freshwater and I have never replaced a riser or manifold. Now, that said, in your case your are having a problem and 1. since you already have risers and 2. that is a great boat and irreplaceable engine I would 3. pony up and replace everything - that boat is a keeper! If you were not seeing the problem with the plug I would say keep boating, but the $80-$100k a new boat like that costs would make me replace the manifolds.
BillK you'll get no argument from me there. I am most definitely not a Ford guy. I've driven GM vehicles for most of my life. That being said, I am so impressed with how good of a marine motor the 351W is and am equally impressed with PCM's marinization parts.
I've been equally impressed with the build quality of this Supra. While tied to a dock, the boat took a hit on the starboard side from a PWC that had to be going at least 10mph. No structural damage whatsoever. She is a tough cookie:
The only reason that side was still caved in in the picture is because it pulled out the screws underneath the rubrail.
I may end up having other boats in my lifetime, but there is no way this boat will ever be sold. About 10 years ago, the colored gelcote was badly faded on the right side from being stored year-round in the sun. After many years of wet-sanding and buffing I gave in and had the red parts of it painted. Best thing I ever did and it still looks great to this day.
Thanks again to everyone here for their advice. I will renew my anchor and try to come around more as a show of my appreciation.
So I won't be in a hurry to get the boat fixed this weekend. I emailed the vendor and cancelled the manifold order but asked them to send the riser gaskets, easy drains, and one manifold gasket on. 
