Merc HP ratings

[Steeler]

Hi All

Anybody clued up on when Merc went from rating HP at the flywheel to rating at the prop please.

Steeler

[Noelm]

I think it was early 80's, but I cannot remember the exact year, a bit of googling would probably find it, I do believe they all changed at different times as it was something the manufacturers knew was coming and had years to do it, that way, old stock and so on could be used, some makes just changed HP to the next motor down like (say) a 115 became the 90, and the old 70 OMC appeared as a 60, so they had to change nothing but decals on certain models if they fitted in with the rating.

[Noelm]

maybe Huey could tell us exactly when OMC changed over.

[Steeler]

Thanks Noelm, the fixer one i discussed with you is a early 90's 100 4 cyl as opposed to the late 80's inline 6 115 i have now and am a little concerned if there will be a notable difference.

I have heard the general rule of thumb between rating at the f/wheel and prop is approx 10% so if Mercury changed there rating at this point of changeover then maybe i will not see a noticeable difference.

Still looking for a 125hp 4 cyl to bring back to life but seem rarer than hens teeth.

Steeler

[Noelm]

yeah, not too sure about the 125 4 cylinder, but from my experience (and someone can tell us otherwise) almost all the tower of power inline 6's seem to all perform about the same, regardless of what the HP on the cowling may tell us, I have onwed a 115, a 135, and a pair of 115's of different year models, and none of them seemed any better or worse then the other, my mate also had a 90 and it also seemed the same.

[Steeler]

Noelm

Just looked over a continuous wave forum about these 2+2 inline 4 merc motors and boy oh boy i thought our emotion inciting topics got heated.

The difference of opinion regarding rough idling being blamed on the actual 2+2 system and the opinion that you will never get an inline 4 crankshaft perfectly balanced being blamed for rough idling.All that conjecture was doing my head in.

Steeler

[Noelm]

yep, that system has been a bit of a mixed bag, but setup right, they seem to work a treat, a good fishing mate of mine had a couple of those and the only problem was trolling, at just the right/wrong revs, the second "stage" cut in and then you were going too fast, slow down and it cut out, but then too slow, but overall, the motors were setup by a good Merc man and never gave a seconds trouble with normal use. OH, and I see no reason an inline 4 will not be perfectly balanced, millions of cars are fine.

[Steeler]

I will have a crack at the inline 4 just wish i could find a 125 to give new life to rather than a 100.

Thanks for the tips.

Steeler

[Huey]

Hi, it all happened around 1983-1985 (86 model year) depending on brand and HP. Your inline 6 Merc is propshaft rated if that age and of course so if the I-4. When Merc did this change in the HP class, the I-4 offer more grunt the the old "towers of power" but a properly rigged I-6 did ten to go a bit quicker.

Mate if you found any I-4 in good nick, no matter what HP it would be a good project for you.

Cheers,

Huey.

[Steeler]

Thanks Huey

Thought that might be the case,i found a 100 4 cyl to play with that had a oil injection failure and at first look only appeared average on #3 the other bores and the pistons that came out of it looked fine along with the crank thank heavens as getting good blocks and cranks for things of that vintage are getting harder and harder to locate.

I am looking forward to having a play with one as my only past experience is with the older blues and browns.

As long as i don't let any white paint get onto it it should be a winner LOL,just pulling your chain Huey.I know you love your white ones.

Cheers

Steeler

[finga]

yeah, not too sure about the 125 4 cylinder, but from my experience (and someone can tell us otherwise) almost all the tower of power inline 6's seem to all perform about the same, regardless of what the HP on the cowling may tell us, I have onwed a 115, a 135, and a pair of 115's of different year models, and none of them seemed any better or worse then the other, my mate also had a 90 and it also seemed the same.
Oh goodo then matey.
Does that mean my old 90 Tower of Power is in fact a 135 Tower of Power??
It seems like it because it goes like the clappers with a lot of low down torque.
It's great on the Evans Head bar on the back of the 5m Bertie.

[Noelm]

I don't think they are really the same, but the difference in HP in those does not seem to change (or at least seem obvious) as much as some other motors, and yes, they did go, that's for sure, as long as you can find a good "man" to work on it for you, they will run like a swiss watch, especially at speed.

[Huey]

Thanks Huey

Thought that might be the case,i found a 100 4 cyl to play with that had a oil injection failure and at first look only appeared average on #3 the other bores and the pistons that came out of it looked fine along with the crank thank heavens as getting good blocks and cranks for things of that vintage are getting harder and harder to locate.

I am looking forward to having a play with one as my only past experience is with the older blues and browns.

As long as i don't let any white paint get onto it it should be a winner LOL,just pulling your chain Huey.I know you love your white ones.

Cheers

Steeler

Hi Mate, no offense taken, I like the Blue / White and Black ones(after 1980) that is and is why we have been selling the black ones since 1984 too.

Cheers,

Huey.

[BM]

Steeler,

Something else worth noting here is that the last of the inline 6 115 Mercs (1986) produced 138hp at the PROP. They were a very pokey engine.

Steeler, as you have probably read elsewhere the 2+2 system is nothing more than only 2 carbs with idle jets. All 4 carbs operate at about 1600rpm and as mentioned trolling can be an issue.

These are good engines although the early units (late 80's-early 90's) were plagued with electrical issues. Very common to have switchbox failure and stator failure. The retrofit stator was called the "Mars Bar" kit as the stator came with a black box about the dimensions of a Mars Bar.

The triggers were not prone to failure however.

Cheers

[Steeler]

Cheers BM appreciate the info.you have actually shocked the shite out of me with the HP at the prop on the last of the 115 inline 6's.

I have always had inline 6's and thought what the heck time for my next motor project rebuild and was thinking the next generation inline 4 would be a good'n to have a crack at.

Steeler

[Huey]

Good point about the ignition system, but have not seen any failures for years. If the engine you find has a black stator they were the problem childs, but if it has not failed by now chances are it will not. The new kit with some needing the "mars bar" adaptor run a Red stator so that is a dead giveaway it has been replaced.

Yes as I said to you in the PM, the 2 + 2 system can be tempermental and you need to have someone sync and link the system that understands what it going on. The latter ones were much nicer at low RPM than the earlier ones.

If you find one post a serial number and I can run it thru the system and see if anything pops up.

Cheers,

Huey.

[Steeler]

Thanks for the help and the offer Huey.I must need a life as i seem to get just as much fun out of playing with these things as i do actually getting to use one.Must have something to do with my inability to catch fish.

[BM]

Too true Huey, I have not replaced a stator in an inline 4 for maybe 2yrs now. One would think that its pretty much a non event these days as the failures should theoretically have almost all been replaced by now with the seemingly non (or less) defective replacement parts.

Steeler, depending on how long you plan to keep your inline 4 it may be worth whacking new pistons in her. Get a machine shop to measure up the bores and the pistons and if ok then just hone and re-ring it or, rebore it ($50/pot) and whack in some new pistons.

You can get good quality aftermarket pistons very cheaply. That's pistons, rings, gudgeon and clips.

Use a magnifiying glass to inspct all your roller bearings. Typically hardened roller bearings do not wear out and the only enemy they have is water.

Replacing all roller bearings would be quite expensive and typically unneccesary.

cheers