When did Merc switch from 7.5 to 8hp?

[ChrisAG]

I'm trying to get a little history on the 8hp I just bought. The seller said it was a 1990, but I suppose I'll need the serial number to verify (the motor is locked away at the moment).

How many "generations" of 2-stroke 8-9.9 hp motors have there been, and starting when?

 

[Texasmark]

Re: When did Merc switch from 7.5 to 8hp?

I had a red/blue band 7.5 that was a mid-late 1970 engine. It was one of Mercs slanted engines that they developed in the '60's. I had an '84 85 hp 4 cyl and as I recall that 7.5 design was still current when I bought the '84 engine. The slant engine idea was to keep fuel from puddling at the rear of the cylinders and to make it easier to get over logs and stuff so they just tilted the whole thing forward at the top....worked great.

I have a '97 Merc and '94 Mariner sales brochures and both have the 8 hp and these are different critters from what I had in styling....vertical mid section, horizontal cylinders.

I'm going to guess that the transition came about in roughly the mid to latter '80's.

Best I can do.

Mark

 

[Laddies]

Re: When did Merc switch from 7.5 to 8hp?

The first 8 HP was built by Mercury in 1986

 

[Texasmark]

Re: When did Merc switch from 7.5 to 8hp?

The first 8 HP was built by Mercury in 1986

Hey Bro thanks! Giving me some much needed credibility.

Mark

 

[ChrisAG]

Re: When did Merc switch from 7.5 to 8hp?

The first 8 HP was built by Mercury in 1986

Thanks - do you know when they next did a generational change; was it 1990?

 

[Texasmark]

Re: When did Merc switch from 7.5 to 8hp?

This is nothing more than wild-arsed speculation, commonly known as a Scientific Wild Assed Guess (SWAG).

I would assume that with the aforementioned modification, enough R&D and re-tooling $$ were expended that it will be many years before anything more happens, especially considering that you can do a weeks worth of average fishing on the 3.2 gallon remote tank; fuel efficiency (and noise too for that matter) were not a consideration. Besides, with the current EPA mandates $$ were directed to 4 cycles and 2's just had to hang onto what they had.....my opinion but probably true.

For the record (from the sales brochures), they had the old design cross flow combustion; not real fuel efficient, but cross flow provided very smooth operation with alternate firing twin cylinders (didn't really need fuel efficiency on these already fuel efficient engines of this size). Did have CD ignition, which coupled with 50:1 oil mix made for very nice and reliable fishing power. Optional accessories were a tiller handle, thermostat, electric starting, and 5 amp alternator battery charger (probably came as part of the electric start option).

What's really nice about them is a problem OMC had for years and what really divorced me from them, and that was their drive pin, commonly known as a "shear" pin as every time you got into the place where the fish were....windward side of timber or rip-rap, the prop would figure out how to find something to ding it'self on, break the "drive pin" and render you powerless......Merc, for all of my life, never had this problem as it had the slip clutch rubber bushing in the prop.....hit something, the prop stops but the engine continues, once cleared the prop reengages the propshaft automatically, and away you go.....doesn't get any sweeter than that. The other thing Merc had that OMC didn't was their slick/smooth frontal lower unit presentation, rather than the God awful stupid OMC gearbox with it's "snout" that stuck out in front of the lower unit/skeg and caught on every possible underwater obstruction....talk about a piece of crap!!!!!!!!!!!!!!!!!!!!!!!! Oh and then there was the problem of trying to seal this obomination to keep your gear oil just oil, not a water/oil mix....puke!!!!!!!!!

My 2c.

Mark

 

[ChrisAG]

Re: When did Merc switch from 7.5 to 8hp?

I think the 8hp was redesigned in 1990 to match the 9.9 - maybe they were both redesigned in 1990 - but I could be wrong.

Regarding OMC, I agree that the 6hp from the '60's - '70's had all the problems you describe. Not sure about the 7.5 or 8hp.

The OMC 9.9/15 from 1974-on had none of the issues you speak of, being modern designs with thru-hub exhaust, etc.

One observation, the 1990 Merc 8 is a little more refined than my 1978 Johnson 15, with some nice features like idle speed built into the choke knob and shifter integrated with the throttle. It also seems to idle better, but that may be due to having less hours on it.

 

[Texasmark]

Re: When did Merc switch from 7.5 to 8hp?

I think the 8hp was redesigned in 1990 to match the 9.9 - maybe they were both redesigned in 1990 - but I could be wrong.

Regarding OMC, I agree that the 6hp from the '60's - '70's had all the problems you describe. Not sure about the 7.5 or 8hp.

That's the ones I grew up with and the ones I was talking about. But, a point of interest. Since you have a current design apparently, have they done away with the drive pin and splined the prop shaft....meaning you now have the same convenience Merc has had for years? If so, great.

Mark

 

[ChrisAG]

Re: When did Merc switch from 7.5 to 8hp?

That's the ones I grew up with and the ones I was talking about. But, a point of interest. Since you have a current design apparently, have they done away with the drive pin and splined the prop shaft....meaning you now have the same convenience Merc has had for years? If so, great.
Mark

The 9.9 & 15 were the first "small" motors by OMC to have the splined prop shaft and thru-hub exhaust (starting 1974). The 20 and 25 took a little longer - maybe 1980 or so - when they decided to go with the same lower unit as the 35 for those models. Of course 50 hp and up were all thru-hub since the late sixties or early seventies.