350 truck engine. What to convert to marine.

F

Fordiesel69

New Member
Nov 1, 2009
75
Erie, PA
Boat Info
Looking for Sundancer 245
Engines
Looking for 260HP
I need to know by tomorrow what I need to do if I plan to install a truck engine into an alpha one mercruiser. The old one is not fixable. Its a 350 chevy 260HP.
Something about flywheels, starters, and mounting ears I seem to read about is what prevents people from swapping.
 
Fordiesel69 said:
I need to know by tomorrow what I need to do if I plan to install a truck engine into an alpha one mercruiser. The old one is not fixable. Its a 350 chevy 260HP.
Something about flywheels, starters, and mounting ears I seem to read about is what prevents people from swapping.
Click to expand...

Hi: you will need to use many parts from the damage engine to make the one from the truck to be marine. its not a drop off. verify how much it will be to buy a remanufacture one. just dont use ( Rapido-Marine ) I personaly have a very bad experience. the engine block and heads will work also the intake manifold. if your engine runs on raw water use marine gasket. verify with a marine mechanic first before just to verified the parts you goin to need from the damage engine are good.

Good luck
Jorge:smt017
 
Plus all wires and connection must be spark proof and water tight remember you truck engine is designed for average 2500 rpm for long periods under fairly light load marine engines are designed around wot a 350 would be around 80% of 5000 rpms or so I think by the time your done you could install a remanufactured one for the same money also marine engines are against large loads all the time good luck
 
The mechanic that work on my boats for many years before he retired told me the torque and power curves are different. He said I would not get my boat on plane with an engine from an auto.
 
Ummmm, Not only what everyone else said, but Marine engines are usually cast thicker, stronger heads, thicker cams, heavier springs.....You really are setting yourself up for failure here with this one.
 
Something to think about is that though there are all the differences mentioned above (I can not confirm #5) and a few more most marine rebuilds are sourced from auto or truck applications and then machined etc due to the fact many boat engines are used in salt water, and not a preferred source of rebuild-able blocks.

What I know from my recent re power using a rebuilt 454 is that most of the following is different, gaskets (especially intake), starter, water pump (circ), cam, carb, internal clearance (piston to cyl, and even ring gap), freeze plugs, and even the intake manifold.

Not that you couldn't use auto on some of these, but while some just will not last as long (especially on raw water cooled in salt water) others can reduce performance, and some can be down right dangerous.

With all that said I have seen people use "spare" engines in their boat and they did work, but all either up front or later had to update to marine accessories.

I would not suggest using the auto parts on a boat engine for the reasons above, but if you have a perfectly good and nearly free truck engine that you could swap your marine acc's onto and can not or do not want to spend the extra $1300-7000 for a true marine engine the change in peak operating rpm's may not be as serious as the cost difference.

Hope I did not leave too much out, and that it helps too
 
Isn't there something to do with the cam profile as well? Overlap or something?

LK
 
I did this a few years ago using a car engine and converted to boat on my Sea Ray. The basic short blocks are the same. No difference in strength or block design. I would change the cam and water pump and then swap out the other "unique" marine parts (exh. risers, etc.).. the engine ran great with no issues. I worked on Ford marine Engines many years ago and most of the base engine specs. were the same between car and marine applications.
 
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One big difference not mentioned is the year of the boat and the engines year. 1986 and older have a 2 piece rear main seal and flywheel. 87 and up is a 1 piece. If you change this a new flywheel will be required.
 
well google the casting number on the block like I did 2 days ago and it pulls up 1985 truck or marine motor 4 bolt main. now it depends on what you consider the motor. the long block is the same except for the cam. the starter and alternator in marine applications have shielded brushes,to keep sparks from escaping. so take the cam out of the boat motor and since you have to pull the intake to do that use the intake and cam from the boat motor as well as the accsessories and bolt them to the truck long block and you have a marine motor. the blocks at least on the chevy motors is not cast any different. make sure the lifters stay in same order they came out and swap with the cam.
 
alwhite00 said:
Isn't there something to do with the cam profile as well? Overlap or something?

LK
Click to expand...

There are differences, but if it is a true truck engine they would not be as different as if it was a auto engine. Also by saying truck I do not mean a silverado either.

If it was me and money was tight etc I make sure the bottom end was solid, and then would opt for trying to change out the cam and related parts (an upper rebuild) because it would be a lot of improvement for a small amount of money.

I would also look to try and find a cam profile that was the same or similar to what is used in the 350 mag motors as these seem to produce good power with a nice power curve for most applications.

I believe overlap as well as duration and total lift can become more an issue when you get into performance engines, and even some of the true marine engines can be a problem due to reversion (the motor suking exhaust water back into the engine). I remember all kinds of problems with a HP500 in a Baja from this, and all the thousands spent by the original owner (actually someone I knew) on head work and repeated head gaskets etc did little for the problem. I know the exhaust set up was partially to blame as well, but a slightly smaller cam was the only thing that eventually stopped it from happening.

Still I do not think it would be a problem with the engine being discussed here.
 
I agree with mainstream that it might be wiser to install a reman engine. By the time you install a new cam either rebuild heads with the marine grade valves or get replacement heads change freeze out plugs and I think I would change crankshaft and conecting rod bearings if motor has over 30k. here is a link I found on a quick search http://repowercentral.com/Reman_350_5.7.html they claim $1295 for a 5.7
Good luck
 
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