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Old 09-09-2005, 07:51 PM
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Default Can I use a stock Chevy 305 in my boat?

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.
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Old 09-09-2005, 08:49 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

Anyone???
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Old 09-09-2005, 09:03 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-09-2005, 09:04 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-09-2005, 09:05 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-09-2005, 09:11 PM
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Default RE: Can I use a stock Chevy 305 in my boat?

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
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Old 09-09-2005, 09:25 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-09-2005, 09:31 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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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.
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Old 09-09-2005, 09:33 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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
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Old 09-09-2005, 09:44 PM
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Default RE: Can I use a stock Chevy 305 in my boat?

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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!
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Old 09-09-2005, 09:52 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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
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Old 09-10-2005, 07:23 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

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/...=75&Category=6
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Old 09-10-2005, 07:56 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-10-2005, 11:49 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

Quote:
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/...=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?
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Old 09-10-2005, 03:51 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

Nickle content? Surely you jest.



Marine engine blocks and their automotive sisters are exact twins.
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Old 09-10-2005, 07:28 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-10-2005, 10:36 PM
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Default Re: Can I use a stock Chevy 305 in my boat?

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?
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Old 09-11-2005, 07:44 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

Sleeper.......Very informative info.!
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Old 09-11-2005, 07:46 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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Old 09-11-2005, 10:55 AM
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Default Re: Can I use a stock Chevy 305 in my boat?

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.
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