4.3 LX water in the oil...

[dubs283]

I’d wonder why the exhaust seats were hammered?

Exhaust system cooling water from a failed manifold/riser/gasket allowing water to enter the combustion chamber through the open exhaust valve

Would most likely account for a failed head gasket as well which could be the source of the water in the oil

 

[Swedefj40]

I’d wonder why the exhaust seats were hammered?
Low octane fuel?
Lean fuel mix?
Too much spark advance?
Boat is not reaching specified max rpm with current prop?
All those should be investigated to avoid a recurrence….

BTW I know some think that 87 octane fuel is fine but my old OMC Cobra has a sticker on the flame arrestor indicating that 89 octane fuel must be used or else the timing should be retarded a few degrees. Our gas dock sells only 93!
Anyway never had pinging or detonation running on 89 or higher octane. Marine engines are highly loaded all the time…

I always use 91 octane. Shop said that they were originally designed to use leaded fuel and they could be hammered because of the unleaded. They replaced them with hardened seats. My cruise speed is about 25 mph at 3800 rpm. She'll max out at the recommended rpm of 4600 rpm or thereabouts. So prop should be good.

 

[Lou C]

Don’t think the shop was right about leaded gas. Leaded gas was getting phased out starting in ‘72 all cars after that were set up for unleaded fuel. That 4.3 didn’t show up till 1985 and all cars ran on unleaded by then. So they all came with hardened valve seats.

 

[Swedefj40]

Well I got her buttoned up, primed the fuel and it started immediately. Initial timing was at 15° BTDC but it ran SO SUPER SMOOTH!!! Sounded like a different engine! Backed it down to 8° BTDC at 700 rpm and let it warm up. I then tweaked the idle A/F screws and set the idle to 700 RPM. She's not as smooth at 8° as it was at 15° BTDC but that's the recommended position. I shut it down and did another comp test and the readings were way better. 4 cylinders were @ 170 PSI, #5 cylinder was at 158 PSI and the lowest one was #4 cylinder @ 150 PSI. Oil looks perfect too! We'll get her in the water in the next day or two and check for leaks and go for a rip. Thanks for the help people!

 

[Lou C]

That sounds great! On mine whenever I've done the compression tests it is usually between 160 and 170.

 

[Swedefj40]

Well she's definitely got a little spring in her step now . Wife and I went out for a few hours today and it's got a little more get up and go and it also starts much better. Win win!