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I have an 85 Merc 150 that needs a lower unit. From internet research, it seems that any merc lower unit from a 135 to a 200 from '78 to 2000 will 'bolt up'. However, there are also different gear ratios for those lower units/years. For example I know the 2 liter 150 (which I have) has a 2:1 gear ratio and when merc went to a 2.5 liter 150 (around '94?) they switched to a 1.87 gear ratio.

I have been told I could bolt up a 1.87 gear ratio lower unit but I would then need a new prop and it could potentially put more 'stress' on the engine. My already stressed 85 Merc does not need more stress!

I am looking for someone who can help sort this info out for me. Two basic questions:
1-what 'bolts up' to an 85 150hp merc?
2 - what are the gear ratios of those lower units that potentially 'bolt up?


Right now, I have a lead on an 87 175hp lower unit but I am not sure if this is a 2:1 gear ratio. So if someone knows the answer to that it would be a help too.

thanks
Graham

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Mercurys are really good in this regard; there is almost universal cross-compatibility between gearcase and motors through most of the model years since the 1980s.

Almost any gearcase of the appropriate shaft length will bolt up with your motor including 1.75:1, 1.87:1 and 2:1 gear ratio gearcases.

It is NOT true that a 1.87:1 gear ratio gearcase will put more stress on your motor if it is propped appropriately. With the taller gearing you will need to drop 2 inches of pitch to make this option work. HOWEVER, this does not mean it is a good idea to do this. The optimal gear ratio of a motor has a lot to do with the boast's potential top speed and weight. A taller ratio *might* be beneficial *if* you are running a very fast light boat. If your motor is on, say, an Outrage 18, I would stick with the 2:1 gear ratio.

I am fairly certain the 1987 175 HP gearcase is 2:1.

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Graham:

A word of caution based on painful and expensive experience, buy the lower unit from a reputable company that provides a warranty, and knows what they are talking about. I bought a used lower unit for a 175 Johnson from a member of another forum, he said it would "bolt right up". Bought it from him, had it shipped, replaced the impeller in it, took off the old lower unit, put the new one up in there, and there was a 1/2" gap between the lower cowling and the top of the lower unit. Took the new one back out, measured the shaft lengths, and the one that would "bolt right up" had a shaft that was 1/2" longer than the other. Once you get into the gut of the lower unit, you need some pretty special tools and expertise.

I've heard good things in the past about Crowley.

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I have a split cowl Merc 150 also, it's last year 1988. Tom's information is correct, you want the 2.0 original gear ratio.

It should look like this:

http://smg.photobucket.com/albums/v42...G_0352.jpg

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any idea if a mariner would work?

were the mariner/mercury the same each year?

.....perhaps and SEI lower unit is in my future!

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Mariner is the same as Mercury but with a different paint color.

What blacksmithdog said is true of the OMC motors; they many little changes over the years and the cross compatibility is not good the gearcases. I have heard several horror stories about the parts almost but not quite fitting together and damage resulting.

None of that is true of the Mercurys, which is why I said they are really good in that regard.

If you buy from a dealer you pay big bucks. Even the aftermarket SEI units are expensive, though they are nothing like a new OE unit.

I'd buy a used one, in fact I have. $400-$800 should get you a perfectly good 2:1 lower unit. I bought the counter rotating lower unit for one of my Mercury 150s for $500 and that price included the shipping. I also sold the standard rotation lower unit that was replaced for $500. It was flawless. Why pay more?

The Scream & Fly classified forum is a good place to shop for used Mercury lower units.

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tom-

can you recommend a good place or places to get a lower unit?

I am faced with paying $500 for a used one w/o any warranty from someone on craiglist or buying an SEI (with a 3 yr warranty) for $850.

I would be willing to pay $500 if I knew the lower unit actually worked!

Any resources would be greatly appreciated!

Graham

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As I said, I like the Scream and Fly classified section for lower units:

http://www.screamandfly.com/forumdisp...ower-Units

I'd be shopping craigslist too. Lots of good deals there.

If you buy used, you don't get a warranty but warranties don't mean much to me; they are really just marketing. I sure as hell would prefer a used factory lower unit to an aftermarket lower unit, especially if it was hundreds of dollars less.

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grahamh,

I have one still mounted to a 85 or 86 200 hp Mercury in good shape with no known issues for $250. What ever it cost me to package/pallet and shipping would be additional. I'm in the Savannah, GA area and freight cost should be reasonable. Shoot me an email if interested.

Bill

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numbber9-

do you know the gear ratio?

I guess my original question remains - does anyone have definitive info on hp/yr gear ratios for the larger merc engines.

thanks
Graham

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Graham,

I looked at a CD of Merc Manual and it is the 1.87. 175hp though 1988 will be 2.1.

Bill

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Bill (number9)-

can you PM me?

I am curious about this CD of Merc Manual. I am wondering if it could confirm some info I got from a guy at Merc.

I called Mercury today (and this may be the definitive answer) and they said all 2.0/2.4/2.5 liter lower units are interchangeable (ie they will 'bolt up').

When talking about 80's engines, the 135hp had a 2:1 gear ratio.
the 150hp had a 1.87:1 gear ratio standard but had a 2:1 ratio as an HD option. the 175hp had a 1.87:1 gear ratio as standard. I forgot to ask about the 200hp.

Would be interested to see if this is consistent with your CD.
g

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Shot you a PM...

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I believe I already pointed out that the gearcases will all bolt up because Mercury has maintained the interchangeability of the all the V-6 gearcases over the years.

Yes, the 135 used (and still uses) the 2:1 gear ratio.

The 2.0 liter 150s use the 2:1 gear ratio. The 2.5 liter 150s use the 1.87:1 gear ratio.

The 175s used both a 2:1 and a 1.87:1 gear ratio. Serial # 6618750 and below used the 1.87:1 and Serial # 6201969 used the 1.87:1 In 1990 there was also "Ski" 175 with that 2:1 gear ratio.

Most of the 200s and 225s use the 1.87:1 gear ratio, though the OptiMax use 1.75:1.

250s use the 1.75:1 gear ratio.

XR4 Magnum motors used a completely different gearcase and are not interchangeable with the other V-6 motors.