Mercruiser MCM 140

D

deannaleanne

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I have a Mercruiser MCM 140 with a alpha 1 gen ll with a 1.65r. Im not sure about the prop. Is there going to be a problem with this combination? Also I replace the water pump and on the lower unit, there is a very small 1/16" tube that connects to the lower unit. This connection is directly net to the shifting arm. What is this for?
 
Don S

Don S

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Re: Mercruiser MCM 140

Is there going to be a problem with this combination?
Click to expand...

Yes, the gear ratio is wrong for the smaller 4 cylinder engine. The drive should be 1.98, not 1.65. The 1.65 is for a 6 cylinder engine.

there is a very small 1/16" tube that connects to the lower unit.
Click to expand...

Is it a tube, or a wire? There is a 1/8" ID hose near the shifter for the speedometer that plugs onto a disconnect fitting.
 
Bondo

Bondo

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Re: Mercruiser MCM 140

I have a Mercruiser MCM 140 with a alpha 1 gen ll with a 1.65r. Im not sure about the prop. Is there going to be a problem with this combination?
Click to expand...

Ayuh,... Welcome Aboard,... It's gonna be a slug with that gear ratio,...
It'll be lugging, 'n probably burn a hole in a piston in no time...

That tube is the pitot tube for the speedometer...
 
D

deannaleanne

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Messages
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Re: Mercruiser MCM 140

Thanks for the reply. The gear case has 1.65R, I am just wondering if someone changed the casing and used the proper gear ratio. Is this possible? I am going to count he the gear teeth just to make sure. Is it possible the prop is or can be adjusted to solve this problem?
 
Don S

Don S

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Joined
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Messages
62,321
Re: Mercruiser MCM 140

Is it possible the prop is or can be adjusted to solve this problem?
Click to expand...

Not really. Props have specific ranges where they work best, on a 3.0L that is between 17" and 21" pitch. In order to stay within that pitch range, and keep the suggested WOT rpm range ((Wide Open Throttle), gear ratio's are used.

To test your gear ratio, just put the drive in forward (engine not running) and turn the engine by hand until the prop turns 1 complete revolution. If the engine turns almost 2 complete revolutions for the props 1, then you have a 1.98 gear ration, if it take a little over 1.6 turns of the engine, then you have the 1.65 gear ratio.
 
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