How to choose an old 2-stroke 150/175 Merc

[BWR1953]

I'm in "search mode" for a used 2-stroke 150-175HP Mercury, possibly 2, but just one at a time. I choose Mercury partly because I'm a fan, but also because the only repair shop in my area is for Mercury. Logistics is a factor for me.

I've been doing a broad search, a ton of reading and watching videos online. I'd get fired up about one year-group, then read that those were not good. Or some such. My local Mercury repair shop steered me away from a few as well. I definitely don't want anything from the 70s or early 80s. That puts me in the range of mid-80s up to about 2007.

One thing that I do in my research is to check parts availability, either aftermarket or OEM for a motor I find interesting. That can be a major factor. I was seriously revved up for a Merc XR4, only to find that a voltage regulator is $800! That was a bummer. From what I'd read, the XR4 was designed for bass boats (music to my ears!) and actually had an output of 170-180HP. Glorious!

I'd been interested in the 1990 year(s) EFI versions, but my repair guy said to steer clear because of electronics failures and parts availability.

And another factor for me is saltwater. I'm a bass angler, so don't go into the briny deep. This being Florida, there are loads of engines which are used in saltwater and owners always advertise them as "flushed and washed" after every trip. Uh huh.

Any suggestions on which engines may be best? Things to watch out for? Would an XR6 work? I've read that it's rated closer to 170HP as well

All help appreciated.

 

[Chris1956]

First of all, you want a V6 engine. The inline 6 engines are just too old and while a lot lighter, do not have the low end power of the V6.

The V6 engines have not changed a lot in mechanical design since introduced and are a proven design.

If you buy a motor older than 10 years, your shop may decline to work on it. In that case, you are own your own for repairs and maintenance.

Carb V6 engines usually have 3 two barrel carbs. They are not hard to rebuild and tune, if you have some experience with multi carb engines. Merc did make the Optimax direct injection 2 cycle engine. They are an order of magnitude more complex than a carb engine, but share most engine block components with the earlier carb motors.

In the early 90's Merc went to twin 20A voltage regulators which are much cheaper then the single 40A VR.

If you want a 175HP motor, buy one. They are simply high performance versions of the 150HPV6. Early V6 engines of 135-200HP used the 2.0L displacement blocks. While fine for the 135HP version, the 2.5L displacement blocks are better for the 150+HP engines.

 

[Chris1956]

One more thing. Some of the older 150HPV6 motors have the smaller diameter gearcase. I believe they are D/C by now. You likely want the larger diameter gearcase as I believe them to be more robust. Prop selection is also better as most of the 150HP and larger motors of all brands use it.

 

[BWR1953]

Thanks Chris. All good info.

I'm very lucky that my Merc repair shop does indeed work on the old stuff. It's a Dad & Son place, and the old man has a wealth of knowledge which he's passing down to his son. I have a good relationship with them and they've helped me a lot. They'll guide me through stuff and when I finally hit a brick wall, I'll take it in for them to service. Then get it back in 6 weeks or so.

Yesterday I read about the gearcase sizes. It seems the XR4 used the small one to help increase bass boat speed. It wasn't designed for larger, heavier boats, which therefore used the larger size case. My boat is 1300 pounds, the same as many of the bass boats of the 1990s. Do you know if the 175 had the larger gearcase?

 

[Chris1956]

I think (think) all the 175HP motors used the larger gearcases. I think the XR4 was the only V6 with the smaller gearcase.

The advantage of today's modular props is that one can switch props between engine brands with the purchase of a new hub kit, provided the props share a hub size. I have a '93 Merc 135HPV6 and a Johnny 150HPV6. I have swapped props back and forth between them. I am pretty sure I could swap props with my neighbor's Yammie 150HPIL4 s well.

 

[Faztbullet]

From what I'd read, the XR4 was designed for bass boats (music to my ears!) and actually had an output of 170-180HP. Glorious!

Most HP I have ever seen on dyno XR4 was a tad over 160hp at prop. The 2.5L XR6 is a detuned 200Hp with a lil over 170hp at prop. Merc never made a 200hp 2L engine but did make a SST120 full race 2L that was a 180+ at prop.

 

[BWR1953]

You guys are getting me chompin' at the bit for an XR6 now! There's one that comes with an old bass boat that I don't want or need, but it's several hundred miles away! And it's also had "some work" (larger jets plus exhaust work) done on it to further increase performance.

The seller says he's had the engine for 13 years and it's always performed well. It's still on the boat, which has a broken transom and that's why he's selling. The engine and transom don't look impacted, more like the engine wanted to rip the transom off!

 

[jimmbo]

The XR were Rated at the HP on the Decal. There is a 15% tolerance, but the main Difference between, an example, the Reg 150hp and an 150 XR2 is the Torque Curve of the Power Band. The XR2 had Beefier Midrange Torque, this was the result of different Exhaust Tuning and possibly slight changes to the Fuel Delivery Curve, and resulted in lower Fuel Economy. At the Top End the HP was within the 15% tolerance, and many non XR engines were up there too

FWIW Mercury did get the 2 liter engine to produce 200hp, during the Development in the early 70s(72 or 73), but it wasn't an engine that was much good as a Pleasure Boat Engine, made the old 150 Inline 6, which was a Cranky Engine, look real good in comparison

Here is a Pic of Ol Blue, the 1st V6 Prototype, on an Inline Midsection and Gearcase. The pic is inverted because the Motor was standing on the Flywheel

 

[Dukedog]

You guys are getting me chompin' at the bit for an XR6 now! There's one that comes with an old bass boat that I don't want or need, but it's several hundred miles away! And it's also had "some work" (larger jets plus exhaust work) done on it to further increase performance.

The seller says he's had the engine for 13 years and it's always performed well. It's still on the boat, which has a broken transom and that's why he's selling. The engine and transom don't look impacted, more like the engine wanted to rip the transom off!

can't go wrong with tha XR6 in my opinion... simple and very dependable (pre cdm ign.).. depending on year of tha XR6 as to which gear case it has... tha XR4 and first years of tha 6 had tha small case with 1.78 gears and tha only motors ta have a small case.. tha 4 being a tad weaker (smaller drive shaft, pinion and bearing) than tha 6... think tha 6 went to tha "normal" size case in '96/'97 maybe?.. maybe even '95?.. would be either 1.87's or 2 ta 1's dependin' on how it was ordered..... its been a minute!

take tha words "some work" with a grain a salt unless ya know tha guy..... bolt on's don't add much to this motor.. takes machine work ta see any real improvement.... lotsa folks do things to tha exhaust that makes it loud and gives a false sense of faster.... jmo

 

[racerone]

Very few people bought V-6 motors just to " baby " them.----Find an older one , rebuild it and use it for 20 years.

 

[BWR1953]

Very few people bought V-6 motors just to " baby " them.----Find an older one , rebuild it and use it for 20 years.

I won't be alive in 20 years. But thanks though.

 

[BWR1953]

can't go wrong with tha XR6 in my opinion... simple and very dependable (pre cdm ign.).. depending on year of tha XR6 as to which gear case it has... tha XR4 and first years of tha 6 had tha small case with 1.78 gears and tha only motors ta have a small case.. tha 4 being a tad weaker (smaller drive shaft, pinion and bearing) than tha 6... think tha 6 went to tha "normal" size case in '96/'97 maybe?.. maybe even '95?.. would be either 1.87's or 2 ta 1's dependin' on how it was ordered..... its been a minute!

take tha words "some work" with a grain a salt unless ya know tha guy..... bolt on's don't add much to this motor.. takes machine work ta see any real improvement.... lotsa folks do things to tha exhaust that makes it loud and gives a false sense of faster.... jmo

Thanks for the info!
Ah yes, the "louder means it's faster" crowd.

 

[racerone]

Often times older folks buy new stuff so they have warranty instead of worries.

 

[BWR1953]

Often times older folks buy new stuff so they have warranty instead of worries.

Absolutely! That's why I bought a new 2022 car in 2021 with a 10 year 100,000 mile warranty. No worries there. It could very well be my last vehicle.

But, I don't have $15,000-20,000 laying around to buy a new outboard.

 

[racerone]

Look around.-----Find a small shop that still rebuilds these things with a one year warranty.

 

[Faztbullet]

Peak horsepower was about 155 at a modest 5000 RPM. I had purposely kept the exhaust ports low for starters because it’s a lot easier to take metal off than to put it on. At some point later in the test program it was decided to up the port timing and see what she would do. We notched the piston leading edge to do this. The first cut produced 175 HP at about 5500 RPM and another gave 204 HP at just over 6000 RPM and still climbing. She really responded to exh port timing.

Ole Blue posts from designer

 

[BWR1953]

Ole Blue posts from designer. Peak horsepower was about 155 at a modest 5000 RPM. I had purposely kept the exhaust ports low for starters because it’s a lot easier to take metal off than to put it on. At some point later in the test program it was decided to up the port timing and see what she would do. We notched the piston leading edge to do this. The first cut produced 175 HP at about 5500 RPM and another gave 204 HP at just over 6000 RPM and still climbing. She really responded to exh port timing.

Oh my goodness!

 

[jimmbo]

Ole Blue posts from designer

That was an interesting Read about the Development of the Merc V6.



I remember reading how they made a V12, by placing 2 V6s kind of facing each other

 

[Texasmark]

I won't be alive in 20 years. But thanks though.

Neither will I.......thank goodness. I figure another 3-4 years and I will have had my fill of "The Golden years".

 

[stresspoint]

sadly i just sent all my old motors to scrap.

i have to say the one merk that stood out to me was a 135 mariner / merk 2.0, i used that motor on a lot of boats , it was still a runner when it was sent to scrap .the advantage was there was no need to worry about finding parts as there was never a need to get any in the 20 years i owned it., FWIW the head gaskets were still original.
compatible power against a 150 how i used it was not an issue.

only issue i ever had was if i left old fuel in it i would have to take the carbs apart and clean them. i even used the same gaskets several times when reassembling.

one thing to note if looking at older 175s is the drive shaft can rust up and get stuck in the power head , i believe ( correct me if i am wrong ? ) its because they did not make the shaft with quality stainless steel , later versions had better stainless and a spring pin that i believe was to help get the gearcase free if it was a bit rusted.