merc crusier 3.7 lt engine knock

Hello like some feedback please, have a 88 well craft w/ a 3.7 lt engine had just purchased boat and had run it a few times and one day was at full speed and the engine started knocking loudly, changed oil & added marvel mystery to it and also removed cam cover and check all rockers and bumped engine & checked push rods all ok suspect lower end. also notcie engine oil pressure runs low and when @ crusingh speeds temp runs high but doesnt go in red, volt meter runs low hard pressed to get it over 12 i hear the charging system set up stinks on these engine (behind lower front pulley) and when the engine knock started found that after i use is and go to restart it engine wil crank very hard & slow as if battery is almost dead & sometimes wont start till engine has been sitting and have run with several know good batteries same thing.
so i am suspecting that when running engine gets hot causing piston drag and kocking is bad rods or wrist pins and slow crank result of piston drag matter of fact one day went to make sure battery terminals tight and the + was so hot to touch it burnt my hand after i had tried to get engine to crank.
so given this information and what i have been reading about the 3.7 is there a engine other than a 3.7 that would direct fit my 88 wellcraft and has anyone had these same symptoms as i am having with thier 3.7 and what did they fine? I also have a oppurtunity to buy a used 3.7 for $700 thinking it may be less exspensive that a re-build..
any input would be greatly appreciated the boat its self is in great condition its the FORD power thats killing me rather have GM.
Thanks people.

Re: merc crusier 3.7 lt engine knock

northeastguy3 said:

@ crusingh speeds temp runs high but doesnt go in red,

volt meter runs low hard pressed to get it over 12 i hear the charging system set up stinks on these engine

engine wil crank very hard & slow as if battery is almost dead & sometimes wont start till engine has been sitting and have run with several know good batteries same thing.

is there a engine other than a 3.7 that would direct fit my 88 wellcraft

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A new impeller may help

Yes it does Best fix is an alternator kit. Breezeworks has a good one

470 starters have a reputation for doing that. I changed to a permanent magnet gear reduction starter (part# 2-2591-DR-2) works fine and a lot smaller.

Nope.

Re: merc crusier 3.7 lt engine knock

It may have helped and could help the running hot but the engine knocks now as soon as you fire it up sounds deff lower end up to the top of the engine block I done hear good things about the aluminum block and cast iron head combo.