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Old 08-22-2013, 06:18 PM   #1
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wanted 350 5.7 omc long or short block

Im looking for a motor to replace the cracked block in my 34 tolly. The motor is a 5.7 350 OMC
Any ideas would be great
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Old 08-24-2013, 09:24 AM   #2
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GO , not call your local GM dealer and get his parts catalog for a short block.

There will be dozens of offerings , one might be what you want.

For a complete running marine unit Jerries Marine services listed 350 with fresh water cooling for about $6000- $6500

http://www.jerrysmarine.com/

Otherwise talk to the local auto salvage folks as GM 350are really common and the scrap yard can decipher the VIN to get the real HD version.
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Old 08-24-2013, 01:31 PM   #3
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No idea where you live but almost guarantee there is a local machinist that rebuilds engines. That man has at least a few 5.7 liter blocks sitting in the back of his shop waiting for a new owner.

Your neighborhood gear head probably has one or knows where he can get one too. "Marine parts" bolt onto the basic block, nothing special about the block itself.

OMC is an engine marinization company, in your case they sourced the base engine from Chevrolet.
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Old 08-24-2013, 03:39 PM   #4
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Long blocks for that engine are almost a commodity. Google it and you will find lots of long block suppliers. You can also order from a GMC dealer (expensive) or your local auto parts store (not so bad). Expect to pay less than $2,000.

But the long block will be for an auto application. Likely the only difference in an automotive long block and one for marine use is the camshaft profile, which should be ground for torque, not rpm.

I wouldn't trust any of these guys to give me a marine camshaft. I would pull the one on my engine and install it in place of the one you get from the long block supplier.

And get a long block. The price difference, particularly if you have any concerns at all about the head, is trivial.

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Old 08-24-2013, 06:47 PM   #5
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Marine Tex. I repaired a cracked block last summer for about $30. Never pulled the motor - same 5.7 you have. Ground down the cracks about 1/8" with a diamond wheel. Globed on the Marine Tex and covered with a cardboard/duct tape bandaid. Works like a champ.
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Old 08-24-2013, 07:12 PM   #6
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Years ago I repaired a 454 with a freeze crack the same way, worked great.
(Get ready a lot more carefully for winter now)
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Old 08-25-2013, 12:31 PM   #7
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After my ancient (1977) 350 threw a rod and destroyed the engine I started with a low compression (regular gas) 350 (5.7) long block crate engine directly from GM. As I recall 15 years ago that was about $1400. I had compared the part numbers and except for the pistons, heads and cam the low compression model was the same as the higher power units. My primary activity was fishing (actually trolling) so idle characteristics were very important to me. I had cam data from a previous rebuild where I had sent the old cam to Crower for a regrind years before so I just ordered a Crane cam (Summitt) that matched it as closely as possible.

The hot rodders will tell you that you want a 4 bolt main (stronger and more $) but my original boat engine was 2 bolt as was the one in my 1974 Blazer. Not that I have any real exposure to it but I’ve never heard one of these things coming apart because of bearing cap issues. Guess I would try to duplicate what you have now.

I took the new engine home, replaced the cam, put in brass freeze plugs, installed a high volume oil pump, roller timing chain, and put on the marine windage tray and aluminum pan from the old engine.

The original engine was opposite hand rotation so using the automotive block involved a new prop and reconfiguring the velvet drive to turn the other way – as I recall this was just a matter of turning over a ring under the input shaft bearing.

She hit the WOT specs on the money.

The opposite hand rotation was also what drove me to the previous regrind by Crower vs replacement---I just couldn’t get the backward turning cam reasonably. Interestingly, the wrong way cam was turned by gears vs a chain so it turned opposite to the crank – or in the same direction as the automotive engine. The significance of this is that the original distributor also turned in the correct direction and didn’t need to be replaced.

My guess is that the backward turning engine in a single engine boat was an effort to keep the production numbers up to support the twin engine guys. I think the diesel guys just turn one of the engines around to avoid aggravating the torque issue. I don’t know if the gas guys are still building backward turning engines.

GM has been through several iterations of the 5.7 and you need to watch for things like dip stick changes (which side), single one piece rear main seal (good if you can get it), pan changes – where the pan meets the timing chain cover, intake manifold and valve cover bolting etc. I’m also not sure that the newer blocks still have all the old bosses and bolt holes for mounting things – engine mounts, fuel pump, alternator etc. As a general rule it would be wise to get an engine that is the same type and vintage as your old one and hopefully all the old accessories will still fit.

Good luck…..
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Old 08-25-2013, 12:48 PM   #8
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Just did a quick look at Summit and they offer Marine "built" crate engines. They are pretty reputable with the hot rodders. http://www.summitracing.com/search/b...-crate-engines

One other thing to watch with the automotive engines is head gaskets - if you are fresh water cooled you shouldn't have a problem but sea water could work over any metal head gaskets.
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Old 09-18-2013, 11:41 AM   #9
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Great news I fixed the old engine after removing the intake and finding the leak
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Old 09-20-2013, 10:15 PM   #10
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