Marine engine block versus Auto engine block

[JKEP44]

I am currently looking at changing the block on my 5.0L OMC. I just purchased the boat this past season and got it running only to find that someone had not done the proper maintence for winter and cracked the exh manifolds and to my supprise the block. I had no water in the oil and nothing to loose but a already bad block so I welded it and have ran it the rest of the season. I am no going to change it out in the off season and have read several posts about using automotive blocks versus marine blocks. As far as I can tell the block itself is the same as a 305 GM but I can't see everything inside of course. The price difference is fanominal! 50 bucks versus $700. Anybody's opinion with any experience would be greatly appreciated. KEP

 

[KaGee]

Re: Marine engine block versus Auto engine block

Everything is the same except the cam and the soft plugs. In saltwater, you need marine headgaskets. Your replacement block needs to be around the same year.<br /><br />You can reuse your heads and replace all the other stuff from your old motor. If you should find a 305 truck motor, the cam will be close enough so you would not have to change it.

 

[TilliamWe]

Re: Marine engine block versus Auto engine block

As Keith said.<br />But why you are at it, why not get a 350 long block? No substitute for cubic inches!

 

[f_inscreenname]

Re: Marine engine block versus Auto engine block

I hope you take the block to a machine shop before you build it. A $50 block, even from a junkyard is usually a anchor.

 

[Richard Petersen]

Re: Marine engine block versus Auto engine block

They are ALMOST the same. Read the GM marine specs. sometime. The engines use a Silicone steel mixture instead of plain steel. More rust resistant. Read their hype. Interesting.

 

[Bondo]

Re: Marine engine block versus Auto engine block

Read their hype

Ayuh,.............<br /><br />Hype it Is........<br /><br />As Long as you have the Right Vintage block,............<br /><br />Any Block will Work Just Fine..........

 

[JKEP44]

Re: Marine engine block versus Auto engine block

Thanks for the input everyone. I did actually plan on honing or boring the cylinders before rebuilding. It is good to know that this will actually work and is not taboo. I will probably use the original am if it is not worn very much. anyway, thanks again for the help.

 

[DHPMARINE]

Re: Marine engine block versus Auto engine block

If your block had cracks,and you welded them,and have no water in the oil,why are you replacing it? <br /><br />Other than that your motor is probably internally balanced,and some auto engines are externaly balanced.Different crankshafts.The flywheel may not fit.<br /><br />DHP

 

[JKEP44]

Re: Marine engine block versus Auto engine block

The reason that I am replacing it is I am a little nervous about running my boat and possibly getting stranded. I occasionally run it in salt water and will hopefully be making the leap out of the sound and into open ocean net summer. I don't plan on going more that a couple of miles out at the most but it makes me nervous to have the cracks in the water jacket on the only power plant on board. I guess the worst that could happen is they leak and the bilge pump has to run. I have two electric pumps (one auto one switch activated) and a manual backup. Its not like I would run out of ocean. It still makes me nervous though. Am I wrong for thinking this way and should just run the block that I have. I am pretty new to boating so give me your honest opinion.

 

[DHPMARINE]

Re: Marine engine block versus Auto engine block

Lets see who else spends two cents here.<br /><br />Not a problem to me,but we'll see what they say,.<br /><br />DHP

 

[trog100]

Re: Marine engine block versus Auto engine block

run it.. if it does leak u will only get water in your bilge.. the internal wall must be okay else u would have water in your oil.. no answer to that one except replace the block..<br /><br />and if u are really worried about getting stranded due to engine failure.. spend your money on a little outboard auxillary motor instead..<br /><br />trog

 

[JKEP44]

Re: Marine engine block versus Auto engine block

I have been looking at small outboards for an aux motor. My only question on that is would I have to make some type of mounting bracket or do they make mounting kits or what. The back of my boat is totally covered and right where one would clamp on there is a giant flip style lid that covers the back half of my engine. It is flush with the top of the boat. Could I make a bracket or something?

 

[KaGee]

Re: Marine engine block versus Auto engine block

Auxillery mounting or "kicker" brackets are available at here at Iboats. Usually good up to 15HP. Towing insurance is a good investment too.<br /><br />If your current engine runs well, I wouldn't worry about it. That weld could last forever, or last another month... who knows. As long as it's an external leak, even if it lets go while you are out, it should not affect your running ability. Running in salt or brackish water, if your trailer, you should flush the engine regularly with fresh water after use to prevent the salt corrosion from being an issue.<br /><br />Everything I have read here and elsewhere about SBC engines is the only differences between blocks mfg'd for boat and auto is the cam and soft plugs (which are brass in a boat). "Marine" engines also use stainless steel headgaskets. Like I mentiones, and Bondo did too, you have to make sure the replacement block is of the same vintage or year. That's easily confirmed by the casting # stamped on the back of the block.

 

[JKEP44]

Re: Marine engine block versus Auto engine block

Hey thanks to everyone for all of the help. I will probably hold off on replacing it since no one here thinks it will be an issue. I really like the kicker idea and will probably go that route. There are several really good ones at local dealers. Anyway, thanks again. Kep

 

[trog100]

Re: Marine engine block versus Auto engine block

i strongly suspect that the core plugs in my original mercruiser 3.0l engine are steel not brass..<br /><br />standing idly looking at the back of my engine recently i noticed that the top of the rear part of the engine.. the bit u could see above the flywheel was bone dry and had a light smattering of surface rust.. this rust extended evenly across the top of the engine rear and evenly across the core plug half visible above the flywheel.. <br /><br />i am pretty sure the one i could see was steel.. dont know about the rest cos the engine (except for the rear end) is all nicely covered in the original black paint..<br /><br />i did mention this to the mechanic stood next to me and he said steel core plugs were the norm..<br /><br />no wish to contradict anyone.. just quoting personal experience..<br /><br />trog<br /><br /><br />it also

 

[f_inscreenname]

Re: Marine engine block versus Auto engine block

You sound like me. I would not sleep well at night knowing that was like it is. Its going to be a long winter and the perfect time to make the change. Also you will have the time to build a "nice" motor and start off fresh next spring. My vote is to do it before it does you.

 

[DaytonaSlickCraft]

Re: Marine engine block versus Auto engine block

I think the center plug in the back of then engine is always steel, it keeps the cam from walking out the back of the engine. The ones on the sides and front should be brass. They do make them in stainless steel, but I've always heard just to use brass for marine use. <br /><br />Tom

 

[trog100]

Re: Marine engine block versus Auto engine block

so the rear one would not be exposed to the corrosive effects of raw cooling water then Tom.. ??<br /><br />trog

 

[DaytonaSlickCraft]

Re: Marine engine block versus Auto engine block

I don't think the rear one covers a water jacket. If you pulled it out and looked in, you would see the back of the camshaft. If you have raw water cooling on the inside of that plug, you have bigger problems. I'm not exactly sure why it's there, but it may be to facilitate cam bearing installation. Ther Merc 350 I have on the engine stand came with the steel plug from the factory.<br /><br />Note that I'm only referring to the center plug, the ones one either side should be brass.<br /><br />Tom

 

[JKEP44]

Re: Marine engine block versus Auto engine block

The plugs on the side of my engine are steel. I think this is where someone went wrong and caused the destruction of my block. If they had been brass they would have likely given up before the block did under all that freezing pressure. I was under the impression that that was the purpose of the freeze plugs so I don't know why even automotive ones would be steel.