Mercruiser 140HP Engine Swap

[mariner1900]

Hi All! I have a 140Hp GM 4 cylinder Mercruiser, S/N 3826715, approx. '74 model. I am contemplating swapping this engine with a '91 model 3.0LX, S/N 0D612416, that I have in the garage. The question is what needs to be changed on the '91 model to fit as I believe the rear engine mount bolt centres have changed with the years as well as the flywheel. Can I change the flywheel and rear housing from the early model to the late model to fit the later model engine?

 

[Bondo]

Re: Mercruiser 140HP Engine Swap

Ayuh,.... The Flywheel Cover is No problem,...
The Flywheel,+ Coupler, I'm not sure...
The crankshaft bolt pattern changed along about that time, but I know not exactly when...

Either way,... It's Adaptable with Merc, or aftermarket parts...

 

[mariner1900]

Re: Mercruiser 140HP Engine Swap

Thanks for the info Bond-O. Back to work tomorrow so the engine change will be a project I do in 7 weeks time, when I get home after working on my other big toy. A 180 metre, 15,000 tonne cement carrier (ship) with a 10,000 HP direct reversing 2-stroke diesel engine with direct drive to a fixed blade propeller. Engine operates at 120 RPM.

I guess I will find out what fits and what doesn't when I go to do the change. Will get the new engine to fit somehow. Will be machining an alignment tool while I am on the ship for the next 7 weeks. (Thanks to I-Boats supplying the drawing).
Extremely expensive in Australia to buy any of the special tools or parts. Bunch of thieves over here.

Merry Xmas and Happy New Year to all!!

 

[fishrdan]

Re: Mercruiser 140HP Engine Swap

I'm not sure of the years, but the 140/3.0 differences I know of are:

- old has crank studs, new has crank bolts (for the flywheel)
- old coupler attaches to the studs, new coupler bolts to the outside edge of flywheel
- old/new couplers different
- flywheels are different sized, 12" vs 14"
- transom shield plate different
- Rear motor mount (flywheel cover) different
- starters
- manifold (there have been 3-4 different styles)
- carb, Rochester or Mercarb
- riser, one that goes straight back or 45% off to the side
- shift cable placement, transom shield, manifold, valve cover, plate above distributor

Hope this gives you some things to look at

 

[mariner1900]

Re: Mercruiser 140HP Engine Swap

Thanks fishrdan!! Have noticed or read about most of the differences that you have mentioned. The '91 model is a complete running engine and has the 45 degree exhaust riser.

Basically what I am hoping for is that the bolt/stud patterns for the flywheel and cover will be the same and I can do a straight swap and have the '91 engine sit straight on the old inner transom shield, with minimal exchange of other parts. I can get another inner transom shield but I believe that bolt pattern is different between the early and late models. As well I then have a dilemma with the reverse-lock valve.

Once I return from work, in 7 weeks, will pull engine and then will see what is what. At least I will have plenty of time to think and plan the exchange.