Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

[ajgraz]

Up in the air regarding whether to rebuild the powerhead on my 1978 Mercury 3cyl 70hp, or to find a replacement powerhead.

I see many more 65hp 3 cyl powerheads available than I do 70hp 3 cyl's. Far as I can tell they are largely (maybe entirely) the same as far as block, crank/rods/pistons, etc. Maybe transfer plate/fuel pump, cowling bracketry, electronics, etc. might be different and have to be transferred. Maybe the exhaust plate is different, too, more research needed.

So, who thinks (or knows!) if a 75-76 or so 65hp powerhead can be swapped onto a 77-79 70hp mid/lower?

 

[Faztbullet]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

It will bolt right up if you use the matching 65hp exhaust plate..............

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

Just what I wanted to hear...

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

Faztbullet,

Far as I can tell, a 1976 65hp powerhead is almost exactly the same as a 77-79 70hp. Probably is the same, they just upped the hp rating.

So what about the fact that a 74-75 era 65hp is distributor-based ignition. Would it be possible to easily retro-fit the whole CDI ignition from my 1978 70hp onto that powerhead?

 

[Maxz695]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

65 HP stator View attachment 168424 70 HP stator View attachment 168425 70 - 115 CDI Stator View attachment 168426 I don,t know if the 65 HP will accept the 70 stators and work with the flywheel The 65 seems to have only 2 wires coming out of the stator

 

[Faztbullet]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

So what about the fact that a 74-75 era 65hp is distributor-based ignition. Would it be possible to easily retro-fit the whole CDI ignition from my 1978 70hp onto that powerhead?

Sorry but no as castings are different,stator end cap is different as is carb and spark linkage. You do know that the late model 1984-1990 60hp is the same as the 70 only its prop hp rated where the 1978 was not.
http://for-sale.yakaz.com/60-hp-mercury-for-sale#lo=4&docid=0007mtn55k8jfpem

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

Sorry but no as castings are different,stator end cap is different as is carb and spark linkage. You do know that the late model 1984-1990 60hp is the same as the 70 only its prop hp rated where the 1978 was not.
http://for-sale.yakaz.com/60-hp-mercury-for-sale#lo=4&docid=0007mtn55k8jfpem

Not really interested in creating a Frankenstein motor.

OK, just so I'm clear what I'm searching for, bearing in mind that the (simplified) plan is simply to swap all the fuel system/carbs/choke, electronics/wiring/ignition, control cables, bracketry/cowling, etc., etc. from my 1978 Mercury 70hp 3cyl onto the replacement powerhead, I can use the powerhead from any of these "families" / "generations" of motor:

1976 65hp 3 cyl
1977-1979 70hp 3cyl
1980-1983 70hp 3cyl
1984-1990 60hp 3cyl

Is that right?

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

BUMP

Faztbullet, I really need to know if my list above is accurate, and in which cases I would need the exhaust plate from said motor/powerhead, also.

 

[Faztbullet]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

60hp........1984-90
65hp........1978-79
70hp........1977-1986
These years will allow you to swap over your parts with little/no modifications. The only mod would be fuel pump as they went to square pump in later year models..

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

60hp........1984-90
65hp........1978-79
70hp........1977-1986
These years will allow you to swap over your parts with little/no modifications. The only mod would be fuel pump as they went to square pump in later year models..

Thank you, thank you. Meant to pre-thank you in my previous but hit send too quick.

Got the transfer plate and fuel pump from current motor bagged, so I'm thinking that won't be an issue whatever year I find. Everything from 1977-1990 supposedly uses the same superceded transfer plate gasket (27-76862-1).

From what I can see, looks like later model exhaust plate to powerhead attachment just has one additional bolt in the back, and all 1977-1990 use the same superceded gasket (27-88451-1); so it looks like I can just skip that bolt (or drill my plate) and use my current plate.

My only remaining question then is, will there be any problem mating my 1978 driveshaft to a newer model crankshaft? My research indicates that the previous model cranks (1972-1979 p/n 4393A2, 1978-1979 p/n 6642A2, 1980-1983 p/n 7574A2) supposedly ALL supercede to the newest number (1984-1990 p/n 8839A2), so I gotta suppose there'd be no issue there--maybe just have to add the o-ring carrier at the bottom--what do you think?

 

[Maxz695]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

QUICKSILVER 27-88451 1 BASE gasket Is for the 79 You will probably have to use the exhaust baseplate from the engine you purchace if much older or newer. The powerhead kit I bought came with only one gasket and it wasn,t right for the exhast plate I have. They must have used it and sold the rest to me. 1979 70 View attachment 168891 http://www.ebay.com/itm/QUICKSILVER..._Accessories_Gear&hash=item35adc84670&vxp=mtr the other gasket looks like this View attachment 168892 QUICKSILVER MERCURY MARINE OUTBOARD GASKET, POWERHEAD TO EXHAUST PLATE 27-60317 http://www.ebay.com/itm/QUICKSILVER..._Accessories_Gear&hash=item43ad9919ff&vxp=mtr Manifold parting gasket GASKET 27-60286 http://www.ebay.com/itm/MERCURY-50-..._Accessories_Gear&hash=item25615732f7&vxp=mtr Exhaust gasket PN 27-38501 1 ML81View attachment 168895 http://www.ebay.com/itm/Mercury-Mar..._Accessories_Gear&hash=item53e4db7c21&vxp=mtr Cheaper --> http://www.ebay.com/itm/Quicksilver..._Accessories_Gear&hash=item1e4f7e5f68&vxp=mtr I have extra gaskets that are probably for a 65 HP Sending pics If you want them message me the address and I,ll send them View attachment 168896 I also have a bumch of O rings but I have to see what i,m gonna needbefore I know what I don,t need I believe there for a 650 or 65 HP I also have a 40 HP fuel pump that may be the same as the 65 HP http://www.ebay.com/itm/330793711966?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1586.l2649

 

[ajgraz]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

Hmm, supposedly that 88451-1 gasket would work for anything 1977-1990, although in your pic it doesn't seem to have enough bolt holes in the rear (to the right side in your pic) for the later years (at least according to the diagrams I saw)--maybe the one you're showing isn't the 1987 and up 88451-1 update that they all are supposed to supercede to, but the previous 76589, 78623 or 88451; the 60317 gasket is for 65hp 1972-1976 (head casting was apparently different on bottom in the earlier years, and for that I'd definitely need the exh plate)

Supposedly that 38501-1 gasket (between exh plate and mid-unit) is the same for all units 1972-1990.

Any case, I'm looking at a late 80's 60hp powerhead that supposedly includes the exh plate, I'll let you know what happens.

 

[Maxz695]

Re: Can a 1975-76 65hp powerhead be adapted to a 1977-79 70hp motor

oK i I put pics of the extra sets of waterpump gakets and the fuel pump gaskets (Wont fit mine) same as a 40 HP fuel pump. In any case it,s not worth listing these on ebay and i can,t use them so if you want them just give a holler