The Boating Forum - Can I use a stock Chevy 305 in my boat?

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Oct7brian
09-09-2005, 07:51 PM
Well after pulling my plugs I found water leaked into 2 of the cylinders due to the head not being sealed correctly. Since I need to swap out the motor can I use a block from chevy pick-up? They both are 305's and actually are the same year too. Plus the truck was owned by a older gentleman and barely had 40,000 miles when he was rear ended thus totaling the truck. Am I able to just swap the blocks and transfer over the head, intake, and exahust manifolds? I wanted to make sure before I started in on the project.


Oct7brian
09-09-2005, 08:49 PM
Anyone???

Bullshipper
09-09-2005, 09:03 PM
I did this with 350 chevies, and I used rv cams to develop more torque, high pressure oil pumps, balanced the pistons with a dyno to run hih rpms, and used a timing chain on one and a belt on the other to make them counter roatating, as I remember.

It worked.


autobaun70
09-09-2005, 09:04 PM
in most marine applications there is a significant difference in the profile of the cam amoung other things. In most cases there are also differences in the cooling setup as well. I know plenty of people that have done it, but a lot of them have blown their motors as well. I would think that you would need to completely swap all marine components from the old motor to the new, and replace any of these that aren't within spec.

bnip1
09-09-2005, 09:05 PM
You have a lot to consider. 1st: was the water intrusion from a head gasket or a bad riser/exhaust manifold? 2nd: will the replacement motor be fresh water cooled or salt water? 3rd: is the exsiting motor R/H or L/H rotation. The most important thing to consider with an inboard block is the condition of the marine stuff that is going on it.

juniorbaiter
09-09-2005, 09:11 PM
I was in the same boat so to speak years ago and after conferring with a friend who was also a Mercruiser Certified mechanic, he pointed out that marine engines had to be more beefy, with heavy duty components because they are under constant load. You can't cruise downhill with a boat. I would be very careful about not using a marine replacement block. You might be wasting valuable time, money and parts and have to do it all over again. I would check such things as cam duration, torque specs, horsepower,4 Bolt mains, marine quality gaskets, water pump, etc. Just my 2 cents. Good luck, Jim

Oct7brian
09-09-2005, 09:25 PM
Thanks for the imput. I guess I'll go the route of getting the used 305 and swaping everything over and replacing anything not within spec. Hopefully everything will go well.

Bullshipper
09-09-2005, 09:31 PM
Oct7brian - 9/9/2005 9:25 PM

Thanks for the imput. I guess I'll go the route of getting the used 305 and swaping everything over and replacing anything not within spec. Hopefully everything will go well.

I would look to trade the old marine block for a rebuilt one with a garantee. It will be hard for you to do this cheaper than that IMO.

Oct7brian
09-09-2005, 09:33 PM
Good idea I actually just ran accross a 305 Marine Block not to far from home. Happen to know if a 1980 305 is the same as a 1990? I left the guy selling it a message but I'm waiting to hear back

Lone Ranger
09-09-2005, 09:44 PM
juniorbaiter - 9/9/2005 10:11 PM

I was in the same boat so to speak years ago and after conferring with a friend who was also a Mercruiser Certified mechanic, he pointed out that marine engines had to be more beefy, with heavy duty components because they are under constant load. You can't cruise downhill with a boat. I would be very careful about not using a marine replacement block. You might be wasting valuable time, money and parts and have to do it all over again. I would check such things as cam duration, torque specs, horsepower,4 Bolt mains, marine quality gaskets, water pump, etc. Just my 2 cents. Good luck, Jim Have to diagree with your Buddy to a point on this.I had a 1979 Wellcraft Nova Offshore model,low and original engines.Had the water intrusion problem with one,long story short...Pulled the ORIGINAL Engine apart.....Consisted of:cast iron crankshaft....2 bolt main block...cast pistons...Hardly Heavy Duty!

Relaced with standard G.M. Mr. Goodwrench Long Block,put brass freeze plugs in it,already had Marine head Gaskets.I SHOULD have replaced the Camshaft as I lost 200 rpm's on top end.That was in 1994 or 95.Sold it to a Buddy of mine and it is still fine to this day.

OH,By the way,the $1200.00 Goodwrench Engines I put in had 4 BOLT main blocks,cast Crank and Pistons!

Oct7brian
09-09-2005, 09:52 PM
Hmm now I'm not sure what to do just get the block and swap the cam and put all marine components on it hmmmm

Sleeper
09-10-2005, 07:23 AM
There is zero difference between a marine block and the same engine model auto block. The 2 bolt/4 bolt main issue is unrelated to it being marine or not. GM used both configurations through the years with the 4 bolt main engines being recognized by most as "heavy duty" and typically found in trucks and HO car applications. You will find both versions in marine as well.

What I do know is different between the same marine engine and it's automotive cousin is:

1. Camshaft; this is perhaps the most important difference and has caused the most dissapointment to those that went with a short block auto engine with the standard auto cam.

2. Carb; automobile carbs can spill fuel in a boat' bilge and are actually illegal although many try to save money and use them anyway.

3. Water pumps; the engine circulating pump needs to be marine if you are not FWC as they have upgraded (stainless) parts.

4. Freeze plugs; they are steel in auto applications and bronze in marine. Even if you are FWC the bronze plugs still offer an advantage from a corrosion standpoint considering how thin a freeze plug is.

5. Fuel pump; marine pumps do not allow a failed pump to leak gas in your bilge as an auto version would in your driveway.

6. Intake manifold; similar to the cam issue there are many variations of intake manifolds some of which are designed for the torque range requirements of marine use, some not.

7, Alternator and Starter on a marine engines are rated "explosion proof" not all auto ones are.

I had very good luck replacing a marine engine (350 GM) Volvo 260 HP application with a new short block but took some time researching cam and intake closely. Both are available after market to match your needs. I would not go through all that again and strongly suggest you go to the link below and buy a re-manufactured marine long block for $1600. Pull your engine strip it down, sand blast and paint all accessory brackets, buy new manifolds and risers, have the carb rebuilt and put her back together. If you do the work yourself you could get out of this for under $2500. Pay close attention to what you exactly get with the "long block" as it can vary between engine models. Good luck.

http://www.dougrussell.com/Products/index.cfm?fuseaction=ProductSearch&BrandName=Remanufactured%20Longblocks&SubCatID=8&Brand=75&Category=6

Bullshipper
09-10-2005, 07:56 AM
Good advice Sleeper, I forgot about the freeze plugs. This is the way to go, unless you have the scratch to buy a new fuel injected ingine.

chris V
09-10-2005, 11:49 AM
Sleeper - 9/10/2005 8:23 AM

There is zero difference between a marine block and the same engine model auto block.
http://www.dougrussell.com/Products/index.cfm?fuseaction=ProductSearch&BrandName=Remanufactured%20Longblocks&SubCatID=8&Brand=75&Category=6

I was under the impression that the actual nickle content of a marine engine was higher than an automotive engine. I have no facts for this, just something I thought from this or that.

where are you getting your information?

Sleeper
09-10-2005, 03:51 PM
Nickle content? Surely you jest.

:rofl: :rofl:

Marine engine blocks and their automotive sisters are exact twins. ;)

SeaCat22
09-10-2005, 07:28 PM
Mercruiser starts with a standard GM long block with brass freeze plugs and marine head gasket. Everything else is bolt-on marine accessories from your old one. I've put plenty of auto 350s in I/O boats (233 Formulas) and ran the tar out of them. The 305 has the same stroke but smaller bore. Good torque motor. Prop it correctly and don't run them lean. If you want more torque you can change the cam. Otherwise, save your money.

Oct7brian
09-10-2005, 10:36 PM
Well I picked up a 305 Marine Long Block this afternoon. All I got to do now is get the old engine out and swap over the heads, intake, well everything and make sure everything is sealed up well. Are there any pointers I should know when putting it all together or is it basically like building a auto block? I've built tons of car engines and never had a problem but since this is used for marine I wanted to ask to make sure. Also why would I need new manifolds and risers? If the current ones do not have any leaks what would be the point?

Lone Ranger
09-11-2005, 07:44 AM
Sleeper.......Very informative info.! :thumbsup:

Sleeper
09-11-2005, 07:46 AM
If your manifolds and risers are in good shape then I would put them back on. I don't know how old they are and looks are very deceiving sometimes with manifolds. It's one of those "while you are there" theories that makes sense if the manifolds are more than 4-5 years old IMO, less if they are sea water cooled. If you have put auto engines back together you will be fine. About the only difference I can think of is gaskets. Obviously the manifold gaskets are pure marine. One thing to consider is paint. Unlike a car engine, a marine engine really needs to be protected and when it's in your shop is the best time to do it. I had a friend with one of those booth type sand blasters and that was great for all the brackets and small stuff that always look like crap on a boat engine. Getting a good paint job on the oil pan is very important if it is pressed steel because you will never get the chance again. I had to pull a V-8 once on an I/O because the steel pan had small pin holes in it. In that boat the pan was very close to bilge water all the time and it corroded from the outside, they are very thin. You can get stainless or cast pans but they are pricey. Some rebuilds come with good pans, some don't.


Good luck.

SeaCat22
09-11-2005, 10:55 AM
How much life do you want from this eng? Long life= big bucks in special parts and prep (fresh water cooling, oil cooler, hi-capacity oil pan, stainless parts, primer/paint, ect). Disposable eng=run the tar out of it, throw it away when it croaks. GM crate engine for $1500.00 or $800.00 rebuilt. Cheap throw-downs. Your choice.

chris V
09-11-2005, 01:57 PM
Sleeper - 9/10/2005 4:51 PM

Nickle content? Surely you jest.

:rofl: :rofl:

Marine engine blocks and their automotive sisters are exact twins. ;)

did it sound like I was joking ;?

I ask a question and ask for some facts to back up your answer, because someone else made the nickle( I think it was nickle content, it could have been some other alloy in the mix) content question, and all you do is give a few
:rofl:
:rofl:
and repeat yourself.

yep, that is real convincing. you may be 100% accurate, but a few facts sure would make it alot easier to believe.

Sleeper
09-11-2005, 07:49 PM
chris V - 9/11/2005 1:57 PM

Sleeper - 9/10/2005 4:51 PM

Nickle content? Surely you jest.

:rofl: :rofl:

Marine engine blocks and their automotive sisters are exact twins. ;)

did it sound like I was joking ;?

I ask a question and ask for some facts to back up your answer, because someone else made the nickle( I think it was nickle content, it could have been some other alloy in the mix) content question, and all you do is give a few
:rofl:
:rofl:
and repeat yourself.

yep, that is real convincing. you may be 100% accurate, but a few facts sure would make it alot easier to believe.



OK, actually I thought you were kidding. The facts are the facts and I really don't have to prove anything. I make a point of offering things on this forum that I know about. If I don't know, I don't post. Seems that lately a lot of folks want proof. If you want proof than go do the research. I am surely not going to scan in serial numbers of a 1986 Chevy truck with a 350 engine and a 1986 Volvo Penta 350 engine just for you. Get real. What proof do you want? This happens to be something that I know a great bit about. I have been in the marine business since 1979. But as a fellow boat enthusiast let me try to explain better:

The engine we are talking about (305 ci GM block) is a cast iron block made by General Motors for automotive use. Similar to the same issue is the 350 and 454 block made by GM that Volvo, Mercruiser, Crusader, PCM and others turn into marine engines. Those blocks are bought from GM in bulk by the various marine engine companies and then have some marine stuff done to them (I listed most of the difference above in this post). The actual engine block and the heads are pure OEM GM. The serial numbers will match right in line with their auto equivalents. You could go to Mr Goodwrench with the serial number of your marine engine and they could provide you a brand new block right from the factory. The casting itself is identical. Now, this isn't all about GM. Ford and Chrysler have provided many offerings of their specific blocks to the marine industry over the years as well. Seems like these days though, GM has the market share by a wide margin. The marine companies DO NOT MAKE THEIR OWN ENGINES they just make them suitable for marine use with varying degrees of changes. That said there is at least one marine engine that I know of where the block was actually cast by Mercruiser and that was the 470, an inline 4 cylinder, aluminum block made by Merc, it originally was made to develop 170 HP and later was pumped up to 190 I think. It was a good engine but very expensive to replace as it was all Mercruiser. If you look now at the major marine engine companies web sites, the newer blocks offered by GM in cars are now being used for marine conversions. Engines such as the 6.0 litre are right out of the auto line just as before. As the 305, 350 and 454 blocks go away so will they in marine engines. One of the curve balls that GM threw the marine companies recently is they stopped production of the counter rotation 350 CID engines. From what I know the counter rotation 350 is no longer being made so what is out there is what is left. The good news is that GM still casts 305, 350 and 454 blocks for auto and truck replacement thus even though you don't find those blocks in new cars today, the marine engine companies can still buy them, for how long is anyone's guess.

Now in the high performance market such as the big, ocean go-fast boats there are some unique engine casting made by the like of Merlin and others. Those are very specialized race bred engines that pump out huge HP, not to be confused with the standard offerings we see as pleasure boaters.

If you need some sort of verification to what I am saying just write down your engine's casting number and then go to a good book store. In the engine section there are books that will cross that number to auto models it was used in. As to the nickle content it may be that you misunderstood someone regarding a marine part versus the block itself? Nickle is used in stainless steel in varying degrees depending on the grade of stainless. Some marine water pumps have stainless parts which are required especially if the engine is raw water cooled.

Oct7brian
09-11-2005, 09:51 PM
Sleeper - 9/11/2005 7:46 AM

If your manifolds and risers are in good shape then I would put them back on. I don't know how old they are and looks are very deceiving sometimes with manifolds. It's one of those "while you are there" theories that makes sense if the manifolds are more than 4-5 years old IMO, less if they are sea water cooled. If you have put auto engines back together you will be fine. About the only difference I can think of is gaskets. Obviously the manifold gaskets are pure marine. One thing to consider is paint. Unlike a car engine, a marine engine really needs to be protected and when it's in your shop is the best time to do it. I had a friend with one of those booth type sand blasters and that was great for all the brackets and small stuff that always look like crap on a boat engine. Getting a good paint job on the oil pan is very important if it is pressed steel because you will never get the chance again. I had to pull a V-8 once on an I/O because the steel pan had small pin holes in it. In that boat the pan was very close to bilge water all the time and it corroded from the outside, they are very thin. You can get stainless or cast pans but they are pricey. Some rebuilds come with good pans, some don't.


Good luck.

Thanks for the advice I went the route of sand blasting the whole block today and painting it. Looks awsome!! The pan was actually in really good condition but I agree I wouldn't want to have to pull the engine again just to replace the pan.

chris V
09-12-2005, 09:20 AM
sleeper
thanks

that is exactly what I was looking for

I wasnt saying I didnt believe you, but when you here 2 different theories about a topic, additional info help weed out "Iheard from this guy" stuff

I run an outboard.

please keep in mind, I havent been around that long, and I dont know you personally, so a few facts, make life a little easier.


I understand that most engine comp purchase gm or ford blocks and rig them, I just always thought that GM had a marine division, and even though the blocks were the same configuration, I thought they were made different.

once again I am not disputing you, I was just looking for "the facts maam, just the facts"

dogboy
09-12-2005, 01:52 PM
the was a show on cable tv (a novelty for me) that stated exactly what sleeper says above

the basic block has marine components added to it, a different label slapped on it and bingo..... a marine engine

bakehard
05-21-2014, 10:25 PM
Hell yeah! Don't listen to crap like Sleeper is saying by paying $1400/$1600 for a marine small block. You could buy 14 to 16 running 305's for less than that. Run them until they blow, deep six them and throw another one in. Swap whatever you want before you throw the old one overboard! What a bunch of nonesense with the marine motor crap! BTW... If it spins the wrong way, just change the prop. How hard is that?

eheath
05-22-2014, 03:41 AM
Really, 9 year old thread.

SeaJay
05-22-2014, 04:09 AM
Before THT you would have to resort to some forms of organized religion to bring the dead back to life!

Lately, THT posters seem to be doing this as a regular occurrence.

Lone Ranger
05-22-2014, 06:03 AM
I was under the impression that the actual nickle content of a marine engine was higher than an automotive engine. I have no facts for this, just something I thought from this or that.

where are you getting your information?

Back in the 60's,early 70's the Hi_performance small blocks Chevies had higher nickel content cast iron,If the Block casting number ended in "010" from what I remember.. Standard duty Marine Engines are Car/Truck Engines with Brass Freeze Plugs,Marine Head Gaskets and Camshafts!

bakehard
05-22-2014, 07:54 PM
Really, 9 year old thread.
Well what are you doing here then, dopey?



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