replace 307 with automotive 307

casperfast

Cadet
Joined
Mar 13, 2017
Messages
18
I have a 71 Renell, just got it.... found out it froze this winter and cracked. I happen to have a same year 307 from a chevelle in the garage. what all do I need to change over. I was told they spin different directions. I was thinking swap heads, cam, oil pump, intake, water pump etc. it's a stronger. io. before all the negative comments begin about the drive, I don't need to hear it as my entire out drive is all new. thank you
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Howdy

Unless this is a twin engine boat it doesn't rotate in the opposite direction, it will be the standard left hand rotation. Your chevelle motor will work but need to change out the head gasket (composite), core plugs (brass), and use the carb, water pump, fuel pump, starter, alternator and ignition components from the boat motor

Since you need to replace the motor anyway, I would suggest getting a 350, more power and your stuff will fit on it. Need another carb and intake, but IMO will be better off.
 

casperfast

Cadet
Joined
Mar 13, 2017
Messages
18
awesome, that's what i wanted to hear. should I even worry about swapping heads? or just the gaskets? and don't I need to have the deck and heads machined if switching from compost to mls steel head gaskets?
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Auto's run using antifreeze, boats use raw water to cool. The head gasket will rust and fail if not change to a marine composite gasket. You can run the motor as-is but its taking a chance. No need to swap heads unless the boats are in better shape. Make sure to check flatness on head and block, just incase. If they are flat you should be good.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
the cam in the 307 from the chevelle may be a bit radical for the boat. nothing over 268 degrees duration on a flat tappet boat with wet exhaust

I would also suggest a 350. any 1985 or older 350 will bolt right in to the boat and use your existing flywheel, coupler, etc.

any 350 after 1986 can be used, however you will need a new flywheel and coupler

even the later vortec motors, however that is a specific vortec intake

if you want to use your motor or a bone-yard motor:
the gaskets need to be changed to marine quality (multi-layer stainless)
core plugs need to be changed to brass or stainless
the circularion water pump needs to be marine (brass impeller and stainless rear cover)
marine specific dipstick tube (goes to bottom of pan)
 

casperfast

Cadet
Joined
Mar 13, 2017
Messages
18
if the reason for changing head gaskets is corrosion and rust then I could just run a compost gasket correct?
 

casperfast

Cadet
Joined
Mar 13, 2017
Messages
18
No Title

is there a specific way I need to remove this to pull the engine, or just take the bolts aroind it off then slide off what I'm geussing is a spline, then pull engine?
 

Attachments

  • photo260544.jpg
    photo260544.jpg
    90.2 KB · Views: 1

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Remove existing core plugs (incorrectly called freeze plugs) and replace them with marine versions to avoid rust through.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
The drive is removed by removing the caps at the trunion. That is where the drive swivels up. Before you do that, disconnect the shift wires. Mark the orientation of the ball gears so you put the drive back on later in the exact orientation.

Disconnect the boot that goes around the intermediate housing.

Then pull the engine along with the intermediate housing after you have removed any cabling and wires like you would do with any other type of marine engine
 

casperfast

Cadet
Joined
Mar 13, 2017
Messages
18
awesome thank you. and should I have the drive on the hoist to remove or is it easy enough to man handle around?
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Been awhile since I removed your exact same drive. It's heavy so probably want a second set of hands, especially when putting it back on.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
I used to lower my stringer onto a block of wood under the skeg, undo the trunion caps and shift cable, and pull back to stand up. then bear hug it. then I got smart and would use a nylon strap and the cherry picker later on

if the ball gears are worn near 50%, time to replace them

I used to pull the whole boot once the drive was off when i removed my OMG motor. then as Bruce said, pull motor and intermediate housing as a unit
 
Top