Marine Engine Block vs Standard Block

[Rhathid]

Hello,<br /><br />I have a cracked block. I have a Volvo Penta 225, which is a 305ci GM engine. I want to swap the cracked block with a standard 305 block.<br /><br />Now, I know the obvious differences between Marine parts and auto parts, but I am assuming the block is pretty much the same with the exception of the cam.<br /><br />Is this true? I found a 305 block for a great price at a race shop. The guy can't sell it because everybody wants a 350 or better. So I was thinking of yanking my engine, swapping the block and cam, and slapping it back together with fresh marine gaskets and what not.<br /><br />Is this doable? I called a Marina trying to find out if I needed a single seal or double seal block and instead he told me the block wouldn't work as well. I don't buy that answer, I think he just wanted to sell me a reman.<br /><br />Thanks.

 

[Walt T]

Re: Marine Engine Block vs Standard Block

Go for it. Use marine head gaskets and brass freeze plugs.

 

[elpaso]

Re: Marine Engine Block vs Standard Block

a 305 block is a 305 block -<br />it will work - stainless gaskets-<br />brass freeze plugs - <br />The 305 was a good engine - builders<br />used them for years - good low end torque.

 

[Boomyal]

Re: Marine Engine Block vs Standard Block

Check cylinder to piston clearance. Marine engines, according to several piston manufacturers, require a little more tolerance than an auto. Two reasons: marine engines run under constant load. The other is that due to fresh water cooling there is a lot more expansion and contraction as the thermostat opens and closes.<br /><br />You can mic your existing block and compare it to the new one.

 

[f_inscreenname]

Re: Marine Engine Block vs Standard Block

You are right. There is only a couple differences. Brass freeze plugs, thermostat, maybe-head gasket, cam. While you have it apart there is no reason not to do a total rebuild. Go to Northern auto parts and get a master rebuild kit. You wont be sorry. You can also upgrade your cam, better pistons, better oil pump, double roller timing chain etc for a couple hundred bucks (2 or 3). Don't let anyone tell you there is any difference between marine and auto blocks, cranks, rods, pistons, heads etc. The all come out of the same factory. I bet if you find your cam specs for your boats 305 you will find the same cam was used in a GM truck of some kind. <br /> You may want to think about the 350. I am sure everything you need to replace on you 305 will be the same things that you need to change to make a 350 work. There is no reason not to do it. Buy a junk yard motor (you will pay the same for the 350 or the 305) + master rebuild (same price, 350 may be cheaper) = brand new, tailored to your liking (hi-pro/work horse) motor. Cheaper then you can buy a long block. Plus you would get the extra 45ci.

 

[Bondo]

Re: Marine Engine Block vs Standard Block

f_inscreenname is Right on the Money............. <br /><br />I'd put together a 350........<br />A Core Motor can be had for $100.00.......<br />Then take it to a Machine Shop,+ have them Prep the block....... Buy your Engine Kit for the Preped Block(Over, or Under Sized).........<br />Have them Assemble it For you.......<br /><br />Another thing, for another few Dollars, Have the Rotating assembly Balanced...............<br />Your motor will run Smoother, Longer.......<br /><br />The cut-off date for a 1 piece or 2 piece rear main seal is 1986........<br />1 piece is Pre-1986.....<br />2 piece is 1986 on.........<br /><br />Good Luck.......

 

[Northern Eclipse]

Re: Marine Engine Block vs Standard Block

Go with the 350, My 305 was replaced with 350 magnum in my Wellcraft it was a glove fit and the performance over the 305 was well worth it, I actually get better fuel economy with the 350 over the 305 due to a better hole shot.

 

[f_inscreenname]

Re: Marine Engine Block vs Standard Block

I forgot the cardinal rule (Thanks BONDO). The cheapest and best thing you can do for a marine motor is have it balanced.

 

[Rhathid]

Re: Marine Engine Block vs Standard Block

Thanks for all the info.<br /><br />I didn't think a 350 would get better mileage. My typical run is 45 minutes solid up ro down the river, or over an hour straight into Lake Erie.<br /><br />I'll definitely get it balanced, there's a shop right down the road that can handle that.<br /><br />Now, I'm thrown here on the seals. The block I found, I was told, has a single seal. So what I am reading here is that I need a double seal?<br /><br />Could anybody explain what the deal with the seal is? I get that there are 1 and 2, but why does it make a difference? I rebuilt a 350 for a Trans Am when I was in high school, 2 seal. Then I rebuilt an '88 5.0 for a Cougar, that was a single seal, so based on what I remember, I don't understand why it makes a difference. Does it have something to do with the jack shaft?<br /><br />Thanks

 

[Bondo]

Re: Marine Engine Block vs Standard Block

Now, I'm thrown here on the seals. The block I found, I was told, has a single seal. So what I am reading here is that I need a double seal?<br /><br />Could anybody explain what the deal with the seal is? I get that there are 1 and 2, but why does it make a difference? I rebuilt a 350 for a Trans Am when I was in high school, 2 seal. Then I rebuilt an '88 5.0 for a Cougar, that was a single seal, so based on what I remember, I don't understand why it makes a difference. Does it have something to do with the jack shaft?

"I rebuilt a 350 for a Trans Am when I was in high school, 2 seal. Then I rebuilt an '88 5.0 for a Cougar, that was a single seal, so based on what I remember" <br />Right Idea, But We're talking SBCs, Not Pontiac or Ford.....<br /><br /> "So what I am reading here is that I need a double seal?" <br />That's Unknown to Me.... You Haven't stated what Year your motor Is........<br /><br /> "Does it have something to do with the jack shaft?" <br />No, Nothing at All........<br />It has to do with the change in the Production Run at Chevy.........<br />When they went from a 2 Piece to a 1 Piece , the Flywheel Bolt Pattern Also Changed, along with the Block,+ the End of the Crankshaft........

 

[Rhathid]

Re: Marine Engine Block vs Standard Block

I see.<br /><br />I was just letting you know that I've worked on the two and didn't see how it tied in. That makes more sense now.<br /><br />I have to get out to my boat, it's been in storage for 2 years. All I know at this point is 1988 Volvo Penta 225 (305ci). That's what is labled on it.<br /><br />So from the sounds of it I'll need to find a different block.<br /><br />What else should I find out to get this done right?

 

[Bondo]

Re: Marine Engine Block vs Standard Block

1988 Volvo Penta 225 (305ci).

That's a 1 Piece Seal Block............<br />(1986 or Newer)<br /><br />I'd Still build a 350cid..............

 

[John Carpenter]

Re: Marine Engine Block vs Standard Block

The reason you want the "correct" year block is so that your sheet metal (oil pan etc.)will bolt up. There is no reason not to go with the 350...it is free horsepower. Fuel consumption will likely be better with the 350 as the engine does not have to work quite as hard.

 

[Rhathid]

Re: Marine Engine Block vs Standard Block

And with a 350 block I can use my existing heads?

 

[Bondo]

Re: Marine Engine Block vs Standard Block

And with a 350 block I can use my existing heads?

Yes............<br /><br /> But, <br /><br />They have a Terrible Flow Rate.....<br />And, with the Small Chambers, You'll need very Low Compression Pistons to stay in a Usable Compression Ratio range...........

 

[f_inscreenname]

Re: Marine Engine Block vs Standard Block

When you buy a junk yard motor they come with it.

 

[LubeDude]

Re: Marine Engine Block vs Standard Block

There is absolutly no way I would do this without putting in a 350. They are just too cheap to buy. You should be able to get a running one for $200-500. depending on miles. Parts are cheap, the only expence you will have other than that is machinework. Of course you will have to reprop when you are done.

 

[elpaso]

Re: Marine Engine Block vs Standard Block

If this is an older boat ? - and to keep<br />it cheap and easy - to understand what<br />you are dealing with - go to <br />propowermarine.com - FAQ - small block chevy -<br />print it out.

 

[John Carpenter]

Re: Marine Engine Block vs Standard Block

ElPaso...good link and good advice. Anyone interested in re-powering with a small block Chevy needs to go and read that article. Buying the correct block goes a long way towards an inexpensive & hassle free swap.<br /><br />It is true that you can make just about anything work...but being able to use your existing intake manifold, oil pan, valve covers etc., saves a few hundred bucks. On the potential flywheel problem, I think you just have to have the correct engine...don't think you can just swap the flywheel, but may be wrong on that. This also depends on whether you have MerCruiser, OMC, or Volvo as some of the manufacturer's changed drive couplings over the years also. Your drive coupling MUST bolt to the flywheel eh?<br /><br />Also, if you didn't buy the boat new, don't assume that the engine is original. There is a code cast into the top of the block that can be used to determine the year of the casting.