mercruiser 165hp straight 6 engine swap

[josh42177]

I bought an old 1971 cobalt boat with a 165hp mercruiser straight six. Turns out the block is cracked. I found a running chevy 250 locally and it looks like a relatively easy swap. I just don't know about the drive system. Can anyone help me out?

Can I take the motor out without removing the shaft and the outer part of the drive (sorry I don't know boat lingo for these sterndrive parts)? What I mean is can I just remove the bell housing bolts and the front motor mount and slide the whole thing forward on a hoist?

 

[Scott Danforth]

no, remove the drive, you have to do it anyway to check alignment. it is actually much easier to remove the drive, pull the motor. total time is about 45 minutes to an empty bilge. fighting with the drive in the way adds about 2 hours to the motor removal process, about 2 hours to the installation process and you still have to remove the drive to check alignment.

as for your running 250, you will need to replace the core plugs with brass and replace the head gasket with a marine head gasket. then use all your bolt-ons from the marine motor

circulation pump
alternator
starter
distributor
fuel pump
brackets, etc.

 

[Bt Doctur]

you also need to see if the front motor mount ears are there

 

[josh42177]

no, remove the drive, you have to do it anyway to check alignment. it is actually much easier to remove the drive, pull the motor. total time is about 45 minutes to an empty bilge. fighting with the drive in the way adds about 2 hours to the motor removal process, about 2 hours to the installation process and you still have to remove the drive to check alignment.

as for your running 250, you will need to replace the core plugs with brass and replace the head gasket with a marine head gasket. then use all your bolt-ons from the marine motor

circulation pump
alternator
starter
distributor
fuel pump
brackets, etc.

Wow, thanks for the info... I have the head off the old motor with the intake and everything still attached, so I guess I'll swap that if I need a new head gasket anyway. Curious, what's the difference between a marine head gasket and a standard one?

 

[josh42177]

you also need to see if the front motor mount ears are there

I think they are there. You guys are great, thanks for all the info.

 

[Bt Doctur]

If there not there you will have to adapt inboard mounts

 

[Scott Danforth]

Wow, thanks for the info... I have the head off the old motor with the intake and everything still attached, so I guess I'll swap that if I need a new head gasket anyway. Curious, what's the difference between a marine head gasket and a standard one?

back in the 70's and 80's, the head gaskets on a marine motor were stainless cores where the automotive ones were simple steel. now most are MLS stainless, however not always.

raw water cooling causes rust (both fresh water and salt water)

boats dont run antifreeze unless you have a heat exchanger.

 

[josh42177]

back in the 70's and 80's, the head gaskets on a marine motor were stainless cores where the automotive ones were simple steel. now most are MLS stainless, however not always.

raw water cooling causes rust (both fresh water and salt water)

dont run antifreeze unless you have a heat exchanger.

Scott, You seem pretty knowledgeable, so I hope you don't mind me asking.... Do you know if the Mercruiser 2.5l will bolt right into the same mounts and bellhousing as the mercruiser 165hp (chevy 250)? I see a deal on Craigslist on an actual marine motor.

 

[Bondo]

Do you know if the Mercruiser 2.5l will bolt right into the same mounts

As I said in yer other thread,....

Welcome Aboard,.... Nope, it ain't,.....

 

[Scott Danforth]

Scott, You seem pretty knowledgeable, so I hope you don't mind me asking.... Do you know if the Mercruiser 2.5l will bolt right into the same mounts and bellhousing as the mercruiser 165hp (chevy 250)? I see a deal on Craigslist on an actual marine motor.

Even if it did, the 2.5 is a dog compared to the 4.1 liter. While the bolt pattern is the same on the flywheel housing, the mounts are in a different location and the drive has different ratios