Magnum 350

N

Norman45

New Member
Apr 6, 2009
35
Cape Cod Mass.
Boat Info
1983 Sea Ray 260 Sundancer
350 Mag
Engines
350 Magnum
I knew that the engine was hydralocked when I bought the boat. I have tried everything that I can think of to turn the engine over with no luck.
Pluggs out (nothing bad on them)new starter (the original just did not turn well) changed worn batterie cable to the starter. Ground cable is good and has good batteries. I used a drinking straw to saturate the cylinders with PB blaster, let it sit and do its work for a week and I still cannot turn it over.
I tried a breaker bar on the crank pulley and even tried turning the flywheel while the starter was out. Verified that the prop was free and not stuck in gear. The oil level was about 2 quarts high on the dip stick with no signs of water. I imagine that the water is at the bottom of the tank.
I also pulled the valve cover on the starboard side and did see that the oil was just a little murky. My thought at this time is that the main bearing or connecting rod bearing are fried. Is there something else that I can try before pulling the engine?
Also if needed, can I swap this engine with an 89 GM built 350?
All comments welcome.:huh:
 
If you tried a breakerbar and it doesn't move, pulling the engine is probably the right thing to do as you're gonna have some work ahead of you to get this thing working properly. I've generally found that buying a rebuilt engine is preferred over trying to rebuild one once you've reached this point. Curious about one thing though.. if you think there's water in the oil, why haven't you already drained it and replaced it? I bet that you anticipated having to pull the engine and saw no reason to throw good oil into it?
 
as in many threads here I will reitterate...car engines are different than marine
putting a "GM" 350 in would be a temporary repair at best
many differences....many
 
You are correct about not wanting to waste the good oil. I had wishful thinking and only a little time. I am not surprised about the final outcome, just wanted to share a little.
 
I should have clarified, the engine that I want to install is a GM marine 350 built to 350 HP by GM
 
Norman45 said:
I should have clarified, the engine that I want to install is a GM marine 350 built to 350 HP by GM
Click to expand...

Make sure it has a marine cam - automotive cams (esp high performance ones) have too much valve overlap and can cause water ingestion. Also, if you are replacing an early 2 piece rear main motor with a later 1 piece unit there is differences in the flywheel.....
 
Wow you guys are tough. Of course you have to pull the outdrive (unless you have about 10" clearance at the front of the motor)
This is not my first rodeo
 
moparlvr4406 said:
as in many threads here I will reitterate...car engines are different than marine
putting a "GM" 350 in would be a temporary repair at best
many differences....many
Click to expand...

I'm in the process of rebuilding mine. Regarding differences between automotive engines and marine, the only thing I've noticed is brass freeze plugs and of course a different cam. That's all I've noticed, am I missing anything?
 
Ok, apparently people stick to certain words that they read, so let me clarify.
I am not putting an auto engine in my boat. The question was and still is, what is the difference between the 350 Magnum and a 350 GM Marine engine?
 
The bearings are different as well as water pump starter and alternator to name a few.
 
Norman45 said:
Wow you guys are tough. Of course you have to pull the outdrive (unless you have about 10" clearance at the front of the motor)
This is not my first rodeo
Click to expand...
we weren't attempting to be tough...just sharing experience
this website IS some peoples "first rodeo" and some get in over their heads and make bad decisions..such as putting in a car motor...from a lack of experience and information
your first post was a bit unclear stating it was a "GM" motor as opposed to a marine engine .
I don't think anyone was trying to bust your balls over it ...just sharing info.
good luck in your project.
 
in going from a 260hp ?? to a 350hp I would have concerns with the drive being able to handle the extra horsepower without breaking...
but this may not be an issue :huh:
 
Thanks guys, your input is certainly appreciated and I do understand about all viewers.
The last drive the engine was mated to was an Alpha one aftermarket and seemed to do fine.
My big question is will the intake manafold from the Magnum fit my other engine?

Other than the intake and carburator set up I am satisfied with the rest of the engine components.
 
It may or may not fit.
The 89 motor probably has center bolt valve covers. Although the intakes look the same, the ones that bolt on these motors are different than the ones that bolt on to the older style (pre 87?)motors with the heads that have the valve cover bolts around the perimeter.
On the 89 motor the angle of the center bolt holes is different than the earlier ones.
You might have to get the right intake.
 
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