Engine swap question - Merc 3.7 vs. 4.1

[stonyloam]

The 470 is counterclockwise, that is looking from the aft looking forward at the flywheel. So BOTH OF YOUR 470's are CCW engines. If you are looking at the front of the engine from the bow the rotor on the 470 crank or the harmonic balancer on the 250 would rotate clockwise. When determining rotation the convention is flywheel rotation looking from behind the engine. So if your props are different then the rotation is reversed in the outdrive.

 

[brodie123]

ok - a little hard to follow lol.

Both props are different. The stbd engine L4 rotates clockwise from looking from the bow to aft. The L6 I know also rotates the same way. I just don't have the port L4 to check - but sounds like from the prop setup I'm ok??

 

[stonyloam]

ALL 470's are CCW engines. Rotation is determined by the direction of the flywheel rotation looking at the engine from behind, not the rotor (or harmonic balancer) in front. Yeah it is a little confusing. You are OK! A little FYI http://www.ebasicpower.com/faq/rotate.htm

 

[brodie123]

lol - k. Thx!! Phew!!! lol

 

[brodie123]

Ok, the engine is installed (except out drive) and all ok 'except' how the exhaust manifold lines up. It's 'in line' just fine but even with the short bellow, the exhaust elbow cant go on as there is not enough space between the elbow and the exhaust tube.

I looked up and saw a riser kit ($300+) ugh, but also it's 3" high and I only have 2" clearance above the elbow. Double ugh. No way to be able to get more clearance without destroying the deck.

The exhaust tube is 2 pieces together with a straight rubber bellow in the middle. I was thinking of cutting one to give me the approx 2+ inches clearance I need. I haven't measured yet to see if that will clear (not hit the engine mount). Short of that, all I can think of is replacing the top piece of the exhaust tube with a shorter straight pipe or running a rubber pipe between the elbow and lower exhaust pipe.

Any suggestions? This is a tough one.

Thx

 

[EZDuzIt]

Hi All;

I have twin Merc 3.7 L4 165 HP motors in my boat (27' cabin cruiser) that give me constant grief. (One seized on me this weekend)

In our 19' boat, we have a 4.1 L6 165 and I really find it to be bullet proof - very happy with that one.

I scored two Merc 4.1 L6 165 HP engines a while back and want to replace them in the cabin cruiser.

I did a quick measurement and it appears that it will fit fine but wanted to post here before I invest in rebuilding them prior to the install.

I'm not sure about gear ratio or anything else I need to think about.

Any thoughts on this?? What will the difference be between the two motors? I'm hoping a little more torque??

Thanks!!!

This is a real grey area for me. My 1976 Apollo 17' tri hull has the 4.1L L6 and it's proven to be a fantastic marine engine. For being 48 years old on almost all original equipment, it has served us well. But my folks had a 1987 Bluewater 17' I grew up with on the water every summer had the 3.7L L4. That thing never let us down. It did go through starters til my dad put the "Crusader starter" on it. Never had another starter issue or many other issues with it for many, many years and hundreds of hours. Both engines are very reliable, rather economical on fuel, moderately easy to work on, virtually bullet proof and have parts readily available. If the L6's will swap in fairly easily, and since you already have them, I'd say do it. If you're going to have to reinvent the wheel to do the swap I'd say rebuild that L4. Bear in mind, the 4.1 L6 "GM 250 Iron Duke" got its name for a reason. They're tough as nails! I'd say fuel consumption on the 3.7 vs the 4.1 is very close but the 3.7 is probably marginally better.