2001 mercruiser 305 alpha drive to couple year older 350 engine

[Devoman]

I have a 2001 305 mercuiser with a cracked block. I have a friend that has a running 350 mercruiser with the same lower unit but it’s just a few years older. If I reuse his motor and lower unit should it just be a straight swap? What should I look for or know if this will work?
Thanks

 

[alldodge]

Most likely it should be a straight swap being only a few years difference

 

[Scott Danforth]

as long as the 350 is a 1996 and newer, its a bolt in, align, mount drive and go type of thing

should be relatively easy assuming its a 1986 and up.

 

[Devoman]

Thanks for the quick reply! This is good to know. Sounds Ike it should be pretty straight forward. If I come across any issues I’ll add it here for others to know!
Thanks again!

 

[Devoman]

as long as the 350 is a 1996 and newer, its a bolt in, align, mount drive and go type of thing

should be relatively easy assuming its a 1986 and up.

So I was able to get some more info on the used 350 motor.
it’s an 89 350 motor. In your statement above you said as long as it’s 1996 and newer but at the end you said as long as it’s 1986 and newer. Can you confirm if we use our exhaust manifolds and just use the block and heads should that work? From what we could tell the bolt pattern of the manifolds looked the same at a glance.
Also I think we plan to just keep our lower unit and just swap the motors. Is there anything I need to consider with the lower unit going to a 350?

 

[Scott Danforth]

the exhaust pattern on an SBC has not changed since 1955

your 1989 350 is a turd compared to 1996 and later with the vortec cylinder heads. the 1989 motor is a flat tappet cam with open chamber heads. 1996 and later are roller cams with vortec heads. in fact the 305 your pulling out has almost the same HP as the 1989 350. it will work, you wont have more power. you wont have to worry about your lower.

make sure to use oil high in zinc for the flat tappet motor

you will need to compare flywheel size. the 1996 and later were all standardized on the larger 168 tooth flywheel

 

[Devoman]

Great info! Thanks Scott! Sounds like we will try to use this motor then.

 

[Scott Danforth]

Great info! Thanks Scott! Sounds like we will try to use this motor then.

make sure you use the old 1989 serial number and information then when buying parts. if you mix/n/match parts with the 2001 5.0 , make good careful notes

 

[Devoman]

So we are changing the drive coupler from the 2001 to the 89 motor and you are correct the flywheel is different and the rear main seal is a 2 piece vs one piece from the 2001 305. We noticed the bolt spacing on the older 350 of the rear main seal is also larger. We are going to check at the auto parts store to see if they have a 14" flywheel with 168 tooth that will mount on the 350. We moved the starter over and looks like everything should work. Just checking to see if there are any known issues doing this or is this exactly what we need to do. Thanks

 

[Scott Danforth]

a 2-piece rear main seal is 1985 or older.

 

[Devoman]

a 2-piece rear main seal is 1985 or older.

Well ok maybe we are wrong on that then? Im not a motor guy but my dad is and he thought that the 350 looked like a 2 piece rear main seal but maybe he was mistaken. We did do some research on the motor and the serial numbers showed it was a 1989 motor. I did the research because i didn't trust the guy that sold us the motor knew exactly what he had.
Could it be a one piece rear main seal with the larger bolt pattern?

 

[Scott Danforth]

look at the block casting number. not the serial number.

no, it can not be a one-piece RMS motor with a larger bolt pattern.

there are two crank patterns for an SBC. the 2-piece RMS and the smaller 1-piece RMS

 

[Devoman]

ok so sounds like this motor is older than we thought? So if we find a flywheel with the same bolt pattern to mount on this motor then we should be fine still? Also internally vs externally balanced flywheel matter?

 

[Scott Danforth]

ok so sounds like this motor is older than we thought? So if we find a flywheel with the same bolt pattern to mount on this motor then we should be fine still? Also internally vs externally balanced flywheel matter?

yes, the balance on the flywheel is more critical than you think.

are the valve cover bolts perimeter bolts or center bolts?

post the block casting number and we can narrow you down to see if the motor is at least only 40 years old

 

[Scott Danforth]

BTW, with the motor that old, it probably has 76cc smog heads on it, so its power at most would be about 210hp. which is less than the 5.0 you pulled out of the boat.

 

[Devoman]

Valve cover bolts are parameter bolts. Is the block casting number on the lower side of the block on each side or on the back side top of block?

 

[Devoman]

CFD
207
was on the block bottom sides on each side.

 

[Devoman]

BTW, with the motor that old, it probably has 76cc smog heads on it, so its power at most would be about 210hp. which is less than the 5.0 you pulled out of the boat.

This is going into a 20' open bow boat. Think it will be an issue with gettin gthe boat on plane or pulling skiers? Im not too concerned with how fast it will go as long as it will run good and pull tubes and ski's. This motor was cheap enough and i think i bought the boat cheap enough to have a decent cheap boat to play with.

 

[Devoman]

14019207 casting number

 

[Scott Danforth]

casting comes back as 1980-1985 crate motor