So a week ago I took the boat out but when I started it I could hear a loud metallic ticking sound from the engine...My buddy also heard it as >Metallic< and a guy at the marina....It made me think of the time I heard a very metallic noise 2 years after I bought the boat, then had my Father and an engine builder buddy listen to it and concur that it was something metallic and then had the engine rebuilt...and no mechanical problems were found...I decided it was an exhaust leak- having found that exhaust WAS leaking past the gasket to one of the headers.
I could not hear the (Current)noise over the exhaust when in the garage and I wanted to search for it with a rubber hose as a stethoscope....I had been experimenting with exhaust mufflers made of ABS drain pipes and rubber adapters...I pulled the boat out of the garage and hooked up the mufflers, then the hose and ran it.....started searching for the noise but could not find it...was running the hose around the left rear part of the engine and suddenly felt air blowing on my hand...was near the exhaust hose....thought, "Wow....Do I have a hose leaking?" Then I found that one of the tiny "Freeze plugs" used to close off the smog-pump holes in the back of the head had rusted out. While GM had the smog pumps connected to the exhaust manifolds directly(In cars), Ford cast a passage INTO the head that ran the "Air" internally....The passages are open at both ends of each head, so you need a set of 4 plugs to complete an engine
If you hear a very metallic sound...Don't Panic and pull the engine! As far as I can tell, the fact that the Boat engine compartment is completely closed off at the bottom (Unlike car engine compartments that are open at the bottom) makes the sound more metallic rather than the sound we are all used to hearing in a car when we have an exhaust leak....
Not only check these plugs, but it may be smart to buy a couple so you are ready to change it out....If the old one has a hole in it, take a quality slot screwdriver and hook it behind the edge of the freeze plug thru the rusted out center, prop it against the edge of the hole in the head, and bang it with you fist relatively gently- it should start coming out....Have a socket(3/8") that will fit just inside the edge of the new freeze plug and drive the new one in. I used red(High-temp) RTV to help seal it.
This used to come in my shop when the plugs on the Mercrusier 470 that used a 460 head would blow out. Usually the rear one that was really hard to get to. The solution, cut a piece of 1/4" steel with a 3/8" hole and pack the hole with RTV then cover the hole with the plate. The front of the head can be used to make the pattern if the rear is too hard to get to. Easy and cheap permanet fix. The 3/8" threaded hole is close enough to make a tight seal.
Last edited by kenny nunez; 04-24-2017 at 11:11 AM.
Reason: Add another sentence
I had forgotten about the 470 MC 4 cylinder.....Someone told me to take a piece of rod and run it thru the head from end-to-end then weld it...But welding Cast iron is always a hassle. I have already hammered a plug in- The diameter was 43/64....But I have a line on some 11/16 brass ones- would really like SS. I'll get one of the brass ones and take it to my engine builder- He has a bunch of 460 heads so I can try it to see if 11/16 fits....I'll bring my big hammer!
The only one that I would have a problem getting to is the left front because it's behind the Alternator.....But I now have 3 spare plugs and a hammer in the boat tool box....