’87 Mercruiser 350 Magnum Replacement

[DTM]

I have a ’87 Mercruiser 350 Magnum in a ’87 Z-21 that I need replace. I found a small crack in the block, while I was changing the exhaust manifolds, which the previous owner had “patched”. It looks like the typical crack caused by freezing. The engine runs strong so I am thinking of just getting a short block or bare block and using the internals from the original engine.

I am wondering about using a “non-marine” block as compared to “marine-block”. I have worked on Chevy small blocks but am not familiar with any of the specific differences of a marine block. I am planning on keeping it rather “tame” as it only has an Alpha drive and I do need to replace that (yet…).

The engine is currently an open cooling system and, as I am using the boat is saltwater; I am planning to convert it to a closed cooling system when I do the replacement.

Any suggestions on how to approach these issues will be appreciated.

And if anyone has a block/engine for sale near the Atlanta, GA or Hilton Head Island, SC areas please let me know. I can travel a few hundred miles to get it.

[Greg]

I had a similar problem earlier this year and had to replace my engine. GM changed things around in '85,86, and 87. The flywheel and starter are different in those years. Be sure you stay with an '87 block or newer and your parts should bolt right on. You can check your casting #s at a website called mortec.com With closed cooling you shouldn't need the brass freeze plugs, but it wouldn't hurt. I considered buying a stroker sb from these guys. The price seemed pretty right. Performance Engine 888-770-4888. Good luck

[Rootsy]

there is no difference between an "automotive" and "marine" engine block, so don't fret that.

does the motor leak water internally? externally? or has the patch held? IF it is water tight you might just run her... but if you have the cash to spend take a look at the GM crate motors... the 350HO long block might be just what you are looking for and will give you 30ish more hp to boot... probably the least work intensive route...

as greg alluded to, you may possibly need the proper flywheel, coupler and starter if your current motor is a 2 piece rear main seal block vs the new 1 piece... GM changed to 1 piece in 87... doesn't mean that an 87 or 88 merc sbc is a 1 piece... with a little investigation on the motor you can decipher what you have...

J

[Greg]

Forgot to add this, I also dumped the stock merc intake and exhaust manifolds for some alum. parts. I went with Dennis Moore's exhaust and edelbrock intake. Took over 100lbs. of weight off. (similar to losing a fat midget out of the back seat)I also added Bennett sport tabs, its like driving a different (better) boat.

[gcarter]

For Closed Cooling see these folks;
http://www.oceaneastmarine.com/
My full system San Juan was only a little over $600.00 including shipping.
My Minx has an Alpha also. After installing the heat exchanger, I called San Juan and spoke to the owner (?). He asked me about the water temp where I boated. After telling him it might hit 88*, he suggested a transom pickup and a engine driven raw water pump. He said the drive pump impellor gets hot in warmer water, the vanes collapse and stop pumping. Then the heat exchanger has a hard time keeping up.
Fortunately this was something I had already done; http://www.donzi.net/forums/showthread.php?t=36014
When you look at the 5/8" dia. tube from the drive supplying water to your engine, it's pretty scarry.
That 1" pipe from the transom pickup sticking through your transom and the potential water it can supply is very reassuring. :wrench:

[MOP]

I have seen many cracked blocks in good running boats over the years, in salt they corrode shut and quit leaking. If it runs as strong as you say why not leave it alone until it breaks, apparently it is fine you would not have known had you not removed the manifolds. Keep the bucks in your pocket and go boating!

Phil

[DAULEY]

buy dr dans 454 price is right and just bolt it in

[Trueser]

I have a spare 1987 350 with 400 hours that you can have cheap. Everything but the exaust manifold/alternator/power steering. sitting on a pallet ready to ship.

If interested Trueser@comcast.net

Mike