1972 Cobalt Ski Boat

[haulnazz15]

Re: 1972 Cobalt Ski Boat

Was OMC an option in 1972?

 

[Andy3]

Re: 1972 Cobalt Ski Boat

You're right, it could be an OMC. I didn't know exactly where to post, as I am new to all this. I will have a chance, hopefully, this weekend to investigate further and determine what setup I have.

 

[Bondo]

Re: 1972 Cobalt Ski Boat

You're right, it could be an OMC. I didn't know exactly where to post, as I am new to all this. I will have a chance, hopefully, this weekend to investigate further and determine what setup I have.

Ayuh,... What color is the motor,..?? the drive,..??

 

[Don S]

Re: 1972 Cobalt Ski Boat

 

[Andy3]

Re: 1972 Cobalt Ski Boat

It is definitely the Mercruiser. Man that OMC thing looks scary!

 

[Don S]

Re: 1972 Cobalt Ski Boat

It is definitely the Mercruiser. Man that OMC thing looks scary!

LOL, to borrow a word from Bond-o, . Ayuh .......

 

[Andy3]

Re: 1972 Cobalt Ski Boat

I'm a little worried about one thing. Reading other posts in this forum about winterizing. I haven't a clue what was done before I bought it. Is there any way to check to see if my block is cracked anywhere? I would hate to do a lot of work, take it to the lake all excited, all to find out the block is cracked.

 

[Don S]

Re: 1972 Cobalt Ski Boat

Isolate the block from the exhaust manifolds and risers, and pressure test the engines cooling system. Should hold pressure with no leakage.

 

[Bondo]

Re: 1972 Cobalt Ski Boat

Isolate the block from the exhaust manifolds and risers, and pressure test the engines cooling system. Should hold pressure with no leakage.

Ayuh,... 15lbs is plenty, 'n overnight is a good Test...

 

[Andy3]

Re: 1972 Cobalt Ski Boat

Had just a couple of minutes to look at the boat today. pulled the dipstick out and it looks milky. So, water is getting in the oil. So, this can be caused by a number of things including, blown head gasket, leaking exhaust manifolds, or cracked block, right?

 

[Bondo]

Re: 1972 Cobalt Ski Boat

Had just a couple of minutes to look at the boat today. pulled the dipstick out and it looks milky. So, water is getting in the oil. So, this can be caused by a number of things including, blown head gasket, leaking exhaust manifolds, or cracked block, right?

Ayuh,... Of course a cracked block,... cracked intake manifold,...
Possibly exhaust manifolds, but atleast 1 sparkplug will be water soaked, maybe more than 1..
Headgasket,..?? not so likely... possible I s'pose,...

 

[Andy3]

Re: 1972 Cobalt Ski Boat

Gonna start the disassembly process this week, as I have time. Plan on getting the heads off. Do you think at that point I will be able to tell where the damage lies? Also, the link you gave me to download the manual, the download takes forever and freezes before it finishes. Any ideas?

 

[Andy3]

Re: 1972 Cobalt Ski Boat

Couldn't get the download to work, so I bought a Seloc manual and it arrived Friday. First thing I did was remove the drain plug from the port exhaust manifold, and rusty water came running out. I'm assuming thats not a good sign. Bought a gallon of Acetone to test them with. I'm assuming that'll be enough for both?

 

[Bondo]

Re: 1972 Cobalt Ski Boat

First thing I did was remove the drain plug from the port exhaust manifold, and rusty water came running out. I'm assuming thats not a good sign.

Ayuh,.... That's the water from the water jacket that surrounds the exhaust cavity...
If it were empty, That would be a Bad sign, as it'd have leaked off somewhere....

My Best guess for where yer gonna find yer cracks are,...
Under the Intake, or Inside the block, opposite where the block drains are on the outside of the block...

Why aren't ya doin' a cooling system pressure test Before ya tear it down,..??
Ya can't do it Later...



Btw,... I just downloaded, 'n viewed the manual...
It took 6 minutes, on cable...

 

[Andy3]

Re: 1972 Cobalt Ski Boat

I thought that since there was water in the oil, that there had to be a crack somewhere. Took the plug out of the starboard manifold, and it was dry. With the little bit of daylight I had this evening, I removed the port side exhaust manifold, and was able to shake out large thick scales of rust. The hoses I removed that run to the manifolds were kind of rusted on. Seems to be a lot of rust.

 

[haulnazz15]

Re: 1972 Cobalt Ski Boat

I thought that since there was water in the oil, that there had to be a crack somewhere. Took the plug out of the starboard manifold, and it was dry. With the little bit of daylight I had this evening, I removed the port side exhaust manifold, and was able to shake out large thick scales of rust. The hoses I removed that run to the manifolds were kind of rusted on. Seems to be a lot of rust.

Well if they are the original manifolds, you will have a lot of rust. It's what iron/metal does when exposed to water/air. I replaced my original 233 manifolds last year during my rebuild and was also surprised at the amount of rust and carbon buildup inside them. Of course they had never been pulled and had 700hrs on them over the course of 40+ years. I still highly recommend replacing them (and the risers) as well as the thermostat housing/hoses. To me, it would just be a problem waiting to happen. If you have to get a rebuilt engine due to the water in the oil, it would be a mistake to use the old manifolds and risk ruining a new motor.

 

[Andy3]

Re: 1972 Cobalt Ski Boat

The elbows at the rear of the manifolds appear to be in good condition. The thermostat housing appears pretty corroded and flaky where the hoses connect. I know I'm jumping ahead of myself here, but other than the cooling setup, is there any difference in this engine (1972 302 Ford V-8) and a 302 in a Ford pick-up truck? Heads the same? Distributor?

 

[Andy3]

Re: 1972 Cobalt Ski Boat

Compression check results:

#1 - 120psi
#3 - 120psi
#5 - 120psi
#7 - 120psi

#2 - 150psi
#4 - 105psi
#6 - 90psi
#8 - 90psi

 

[Andy3]

Re: 1972 Cobalt Ski Boat

Also, thermostat was 160. Is that correct? Removed valve covers and found milky slimy rusty stuff. Heads are stamped 351. Were 351 engines installed with the mercruiser 888 as well? Anybody have any interpretations on those compression readings?

 

[haulnazz15]

Re: 1972 Cobalt Ski Boat

The heads are stamped 351, you don't likely have a 351w engine as 302's and 351w's shared heads for many years. The only main difference in the two blocks is the increased deck height on the 351w to allow for the longer piston stroke. In any case, it looks like you've got a pretty significant issue with lower than optimal pressure on 3 of the 4 cylinders on that bank.