305 mercusier motor

[kelloggs25]

I bought a 1986 four winns with a 305 mercusier motor..The motor was not winterize right and has a crack block..My question is if I buy a 305 car motor what do I have to change? Do I have to change the crank and rods and cam ect.ect? thanks..
I also want to add that I have ask a few question on Iboats and all of you are so helpfull..This has to be one of the best sites on the internet..A big THANKS to all that help us boaters

 

[Don S]

Re: 305 mercusier motor

Buy a 5.7 truck engine of the same basic vintage, replace all the core plugs with brass and add all the electrical and fuel system parts from the marine engine on it and you should be set to go.

 

[Bondo]

Re: 305 mercusier motor

Buy a 5.7 truck engine of the same basic vintage, replace all the core plugs with brass and add all the electrical and fuel system parts from the marine engine on it and you should be set to go.

Ayuh,... Agreed,... the 350 will give ya 20/ 50 hp more, at the same cost or less...

 

[Moose truck]

Re: 305 mercusier motor

Buy a 5.7 truck engine of the same basic vintage, replace all the core plugs with brass and add all the electrical and fuel system parts from the marine engine on it and you should be set to go.

Also, if you are mechanically inclined, swap the 350's camshaft to a marine grind. The truck's OEM power band is at an RPM higher than your boats.

 

[markheck1]

Re: 305 mercusier motor

Should he also use the circulating pump from the marine engine too? they have different impellers, correct?

 

[Bondo]

Re: 305 mercusier motor

Should he also use the circulating pump from the marine engine too? they have different impellers, correct?

Ayuh,... Correct... the impeller is cast, insteada stamped...

I don't think I'd worry 'bout the cam though,...
A truck cam is Sooooo close to a Marine cut, you'd never Ever know the difference...

 

[kelloggs25]

Re: 305 mercusier motor

Update: I went and bought a rebuilt 305 Camero z28 HO motor.. Now I have to change over all the parts..

 

[Bondo]

Re: 305 mercusier motor

I also want to add that I have ask a few question on Iboats and all of you are so helpfull..This has to be one of the best sites on the internet..A big THANKS to all that help us boaters



Update: I went and bought a rebuilt 305 Camero z28 HO motor.. Now I have to change over all the parts..

Ayuh,..... Great choice,....

Did ya miss the 350 truck motor comments,..??

I doubt the cam in that motor is very Marine friendly....

 

[kelloggs25]

Re: 305 mercusier motor

I only paid $200 for the motor..If I have to I will change out the cam..

 

[dingdongs]

Re: 305 mercusier motor

you could run your new engine on the ground to make sure all is well before fitting it in the boat just to make sure all is well if you haven't heard it running before with a few connections to the wiring and a small tank once the manifolds are assembled.remember the engine and drive will require an alignment bar to set the engine to the drive.available for $30 off ebay if you dont already have one.this will save the cush drive thats on the engine as they'ree not cheap and engine out again to replace.

 

[kelloggs25]

Re: 305 mercusier motor

No I have not had it running..I bought it from a friend of a friend..you know how that goes.. But anyways it looks rebuilt after i put boat in water if I have to change out cam it will only cost me about $150..So for $350 I have a rebuilt motor..I will Have this motor running before I put it in boat..Do I hook up a Postive wire to postive side of coil? thanks

 

[RogersJetboat454]

Re: 305 mercusier motor

Do I hook up a Postive wire to postive side of coil? thanks

That's the idea...
You are using a marine distributor, and not an H.E.I. distributor, right?
You may also want to take a look at what you have for head casting #'s on the new engine, as they may be something more suitable for higher RPM passenger cars then low end grunt like a boat needs.

 

[dingdongs]

Re: 305 mercusier motor

a hint on wiring for bench test;
5.7 Mercruiser Chevy 350 Engine running for the first time - YouTube

 

[thumpar]

Re: 305 mercusier motor

Make sure you use your original external parts like alternator and starter. Hopefully it will make power in a boat since it was meant for road power in a car. Watch the RPM's. Even if the engine can take it the drive might not want to spin that fast without coming apart.

 

[kelloggs25]

Re: 305 mercusier motor

Yes I am going to swap over all the marine stuff..Starter,Alt, and Intake Manifold...Can I use a bigger or smaller prop to make up for the rpm..Most boats rpm's are around 4500..lets say at top speed mine is 5500 can I use a bigger prop to make up for it?

 

[thumpar]

Re: 305 mercusier motor

That is pretty fast to spin the input shaft in an older drive. Boat engines are designed to make power below 5k RPM so the drive is not spinning like crazy. That is why everyone said to get a truck engine. Those make power at lower RPM and have torque that is needed.

 

[RogersJetboat454]

Re: 305 mercusier motor

That is pretty fast to spin the input shaft in an older drive. Boat engines are designed to make power below 5k RPM so the drive is not spinning like crazy. That is why everyone said to get a truck engine. Those make power at lower RPM and have torque that is needed.

+1^^^

The point is that the engine needs enough a** to get the boat out of the hole, and on plane. High flow heads that are designed to build power at higher RPM's are going to hurt this. What year Camaro did this come out of BTW? If it's a pre-'86 engine, the flywheel and coupler on your old engine may not be compatible.

 

[Bondo]

Re: 305 mercusier motor

Yes I am going to swap over all the marine stuff..Starter,Alt, and Intake Manifold...Can I use a bigger or smaller prop to make up for the rpm..Most boats rpm's are around 4500..lets say at top speed mine is 5500 can I use a bigger prop to make up for it?

Ayuh,.... That's the Next step, After ya got a runnin' motor bolted in,....

After it's in, 'n runnin',... Run it with the prop ya got,... It might already be the Right 1....

If it'll run at Over 4800/ 4900 rpms, go to a taller pitched prop to get the Wot Rpms down to 4600/ 4800 rpms....

 

[kelloggs25]

Re: 305 mercusier motor

I have most of the marine stuff swap over to new motor..Maybe this weekend I can start it..The casting numbers on the heads are the same numbers on both motors..I have the flywheel already on new motor..The motor came out of a 1986 Camaro

 

[RogersJetboat454]

Re: 305 mercusier motor

I have most of the marine stuff swap over to new motor..Maybe this weekend I can start it..The casting numbers on the heads are the same numbers on both motors..I have the flywheel already on new motor..The motor came out of a 1986 Camaro

The engine is most likely an "LG4" (GM RPO code). They were basically grunt motors that made respectable torque at low RPM's. Best spec's I can find for them in '86 is 165 Hp @ 4400 RPM, 250 Ftlbs @ 2000 RPM (as installed in a car with a converter and smog stuff). Compression ratio is a bit high for a boat at 9.5:1, so you may need to fiddle with timing and run mid-grade or better fuel.