1985 Merc 90HP - Will 115 Block bolt right up to it?

[ZigZaggin]

Concept idea - I have my 90HP running perfect and am very happy with the performance. However, knowing that this motor and the 115HP are basically the same and that the 115 HP is just ported a little differently etc, my question is this... If I have access to a professionally rebuilt 115 HP power head, will it bolt right on to my existing 90HP motor chasis? I'm pretty sure that it will but would like to know if anyone has done this and how it went? I'd like to have that 115 block sitting under my 90 cowling Not anything I'm looking to do right away but am thinking about it maybe next year.

Thanks in advance for your info.

-zig

 

[oldgradywhite]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

I belive it will if you have the whole power head and carb ect on the new 115 block.

 

[emckelvy]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

The block bolt patterns are identical. You will of course want to replace your ADI (Alternator Driven Ignition) 90hp powerhead with another ADI powerhead. Not that you couldn't use an older (from around '72-on) distributor-fired block on your mid-section, but there'd be quite a few things to change if you did.

A 90ADI-for-115ADI powerhead swap would entail no more effort than any R&R on the existing powerhead, except you'll get a lot more performance from the 115hp prop-rated 'head which was close to 140hp at the crankshaft! It oughta be a screamer, the later-style 115's ran real hard.

You'll definitely want the carbs that came with the 115hp though.

HTH...........ed

 

[Texasmark]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

Other thing is your 90 has a 2.3:1 gearbox and the 115 sits atop a 2:1. If you have this engine mounted on a light, fast, boat, you may have a problem finding a prop with adequate pitch. I run a 24P on my 90 and for that engine on my boat I'd estimate having to go to a 26P or so and that would have to be a special order from a speed shop or something like that.......$$$$$$ I had a hard enough time finding the 24P. Now the larger gearboxes (4 3/4" I think) like are on the V engines have all kinds of high pitched props, but not for this smaller diameter (4 1/4 I think) box.....course, thinking aloud, Merc/Mariner makes a hot dog 150 that has as an available option, this smaller gearbox with a 1.78:1 ratio. Merc might make some special props to fit that which would fit your lower unit, but probably not as with a 1.78 ratio at 6k rpm, a 24 would be moving forward mighty fast. Might check it out however.

If the boat is a low performer, then it won't be a problem, but you can expect a 2-4" increase in prop pitch over your current one to keep the rpm's outta-da-red.

Mark

 

[Faztbullet]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

90 has a 2.3:1 gearbox and the 115 sits atop a 2:1

The 1985 90/115 have same gear ratio... The 2.3:1 are for inline 4 cylinders and the Xr4/6 series V-6 cases will not bolt up as the rear 2 studs are spaced different, it can be made to work with a few mod's.

 

[Texasmark]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

The 1985 90/115 have same gear ratio... The 2.3:1 are for inline 4 cylinders and the Xr4/6 series V-6 cases will not bolt up as the rear 2 studs are spaced different, it can be made to work with a few mod's.

We've had this discussion before. I vividly remember sales brochures back in the days of the towers that talked about the 90 and 115, which I bought. I remember them talking about the "torque" of the 90 and heavy loads and all that and I'm sure I read that it had a 2.3; but that was a long time ago. If you have the manual then I can't argue with that.

Also, the 2.3 carried over into the 3 cyl 90's also; I have one of them.

Mark

 

[Faztbullet]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

The "Inline 4/6"engines use a different unit than what you have. The "bigbore" 3 cylinder(70-90hp) and 4 cylinder(100-125hp) lower units are what I call "metric" units. This unit design(metric) is also used on the 4 stroke engines and Mercury even made them for Honda for a couple of years and the 2.3:1 ratio is used in several other engines also.

 

[ZigZaggin]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

Thanks for all the info fellas. I will probably end up doing this. I found a "professionally" rebuilt 115 powerhead (1985) and the reman shop did tell me that the bolt patterns, lower unit, etc are all identical between the 90 HP and 115 HP. I do wonder though if the exhaust is the same? Seems to me that the mgaphone and exhaust housing would be different but maybe not? Anyway, the question about the lower unit beint 2.3:1 vs 2:1. There is no difference in the lower units on these Inline 6 motors. Both the 90 and 115 use the 2:1 gear ratio. I have a 17ft lund that runs about 40 mph at 5200 rpm with a 17 pitch prop. Im thinking the 115 might get me up closer to 50 with the right prop. I fish in Walleye tournaments on the Mississippi and it would be a real hoot to blow past some of the older retired guys running Verado setups Thanks again for the info everyone... except for the guy talking about 3 cyl stuff?

 

[sschefer]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

Just a quick note about reman's. Make darn sure you get a good guarantee and document the break-in meticulosly. Check the company history or if it's a friend with a motor egging you on, pass on it and keep the great running 90.

Make sure it is a reman and not a refurb or you might just be buying an old engine with new paint and within spec tolerances (might be on the bottom end of spec).

Be careful, I've been hearing some pretty nasty stories but I won't mention the companies because I can't fully determine fault.

 

[ZigZaggin]

Re: 1985 Merc 90HP - Will 115 Block bolt right up to it?

I see that Clams Canino is selling them on Ebay as well. Any feedback on his re-mans/overhauled 115's? The one that I found is a little more expensive than what he is selling them for and has the same 90 day warranty.