1974 Crestiliner 302/351 mercruiser swap

[mcuhan]

First time poster long time reader and student! Thank you.

Recently restored my grandpa's 1974 Crestliner C995 Crusader that had a Ford 302 188hp in the 888 drive train. Decided to give it a motor upgrade and found a 1975 Ford 351 in 233hp package with same drive. Here's what I did.

1) 351 came from working boat. Removed motor and kept everything in tact including flywheel cover, drive coupler and shift plate. I did not remove the gimbal assembly from this boat.

2) Removed 302 from my boat. Leaving only gimbal assembly.

3) Everything lined up beautifully putting 351 in my boat. Wired up and mounting was very easy. Even brought over the power steering and power steering cooler from 302 to 351 and that went fine.

4) CANNOT get the drive all the way on. Alignment bar seems to go in all the way and motor properly aligned. The drive gets to within a half inch before it binds. If I use the nuts to suck the drive tight, it's binding the crank and the motor won't crank freely. It will crank but the load is so great it won't start and eventually starter/solenoid get too hot.

5) It doesn't matter which drive I use, either the one from 302 or 351, the results are the same.

6) Removed gimbal bearing to test and drive still doesn't go on all the way so I'm not sure it's an alignment issue.

7) Mercruiser lists the following drive couplers between the 302 and 351. #59826A1 for all 302 and some 351s. On some 351s, it goes to #59826A3 My experience with part #s tells me this is probably an insignificant difference.

8) The 351 came from a 1975 Formula Thunderbird 25'. Thinking my difference could be in thickness of stern and/or gimbal housing.

Any ideas greatly appreciated. Been stuck on this for a while and 302 about to go back in.

Matt

 

[Bondo]

Ayuh,..... Welcome Aboard,..... examine the flywheel covers very closely,.....

I've found various differences in 'em, that I didn't know existed,.....

 

[mcuhan]

Solved - think it was a combination of the following;

1) Y pipe was wider between 302 and 351 making the exhaust bellows hard to line up and impacting rear height and overall alignment.

2) Original starter motor bendix wasn't working. Starter kept staying engaged. Therefore making it hard to turn over and crank when drive was on. Think this is where most of my binding was.

3) Shift plate differences between my 302 which had power steering vs 351 plate that didn't. Makes it easier to clear the power steering hoses for mounting and alignment purposes.

4) Wasn't securing the rear mounts tight enough upon initial lowering of the motor.

5) Old O-rings on the drive shaft. making it hard to suck into the gimbal bearing

So for you kids at home wanting to know if you can swap a 302 and 351, it can be done. Picked up 45hp going from the Mercruiser 188 package to the 233. Now time to re-prop and consider going to the four bbl manifold and phase two of the project.

Matt

 

[Bondo]

it can be done.

Ayuh,...... Glad to hear it was a success,.......