TOPIC: Johnson 70 hp, good or bad?

I know this isn't much info, but here goes. I'm considering swapping out my 64 Mercury 65 hp for a different motor. The Merc runs ok, but if I keep it it will need a fair amount of repairs (wiring, lower unit seals, etc, and when done it will still have some quirky transition model problems such as lower unit gear ratio being too high, and very limited availability of correct replacement props.

To make it short, a local has a 15 foot tri hull for sale, running condition with several accessories I could use plus a better trailer than I have. His ad says it's powered by a 70hp Johnson. Now, I've been resisting even calling him (already have two boats that need work) but I'm losing the battle. If I go to look at it, are there any particular items I should be watching for, besides rotted powerhead wiring, or water in lower unit? I mean, are older Johnson 70s prone to any special problems like cracks in the head or block, transmission troubles, stuff like that? If I go to look at it, I'll return with more info about the year of the motor. From his photo in the ad, it looks like a smaller powerhead model, not a V-4 like the old Super Sea Horse 75.

Lastly, are these older Johnsons a problem to find parts for? In the past I had great luck online with finding OMC parts for a stern drive I had but just wondering...

If it has an electric shift lower unit I would avoid it, sometimes they work well but if water gets in you are in for a pile of trouble and parts are almost impossible to find

If it is s 70 HP, it will be a 3 cylinder inline from 1974 or later. It will be mechanical shift (the last year for electric was 1973 and that was a 65 HP). They are very good motors subject to the same issues any motor is; Bad fuel, bad oil & overheating if neglected.

Thanks. I did some more searches after I posted and learned a bit about the 3 cylinder "looper" motors. They sound pretty good. I might go take a look at the rig this weekend.

Update: I called the guy and he has sold the rig. Darn, it sounded like the motor was in much better shape than my 64 Merc 650. His was a 1981 70hp 3 cyl and he said it ran like new. Oh well, that's the price I pay for procrastination.

If you continue the search, the 70/75hp triples are not just good motors, they're VERY good motors. I've had several over the years, and still have my 1980 Johnson 75. Great power, very good fuel economy (especially compared to your older Merc 65) and good parts availability.

Thanks Chinewalker. Something for me to keep in mind. I'm lucky, my old Merc 650 is still in running condition. But I know it's tired and needs work. On the good side, it's a magneto motor so no complex electronics. I'm going up to the lake next week for a test run to see if the doel-fin I installed last fall helps with the cavitation I'm getting on take-off with my new prop. If it still cavitates, I'll talk to the prop shop about getting it cupped. Beyond that, it will be decision time as to whether I keep this rig or not. Good used motors are pretty scarce in this area. That's what I get for being a lifelong boater living in the desert southwest.

That's a beautiful old Glasspar!

A cupped prop may help with your ventilation/cavitation issue.

The fin will give you more stern lift, which will help you plane out better. Dunno if that will stop the ventilation, those things act differently on different hulls.

One thing that would definitely help with a ventilation issue would be a 4-bladed prop, if you could find one with low enough pitch for your 65hp on that big Glasspar.

Comprop is still making their composite 4-blade props, and Solas has a good selection of pitches for their 4-blade aluminum props.

www.comprop.com/mercma.html

www.marineengine.com/parts/boat-propellers/catalog.html?http://www.marineengine.com/parts/boat-propellers/index.htm

Note if you use the propfinder at marineengine.com, you'll have to enter a different HP than your 65, the program only goes to newer Triple 65hp models. Just plug in a 75hp or 115hp and it'll pull up compatible props.

Here's a good deal at iboats for a 13-1/2" dia x 15" pitch:

boatpropellers.iboats.com/Solas-Amita-Propellers/1413-130-15/

13" pitch: boatpropellers.iboats.com/Solas-Amita-Propellers/1413-133-13/

HTH.......ed

Thanks Ed. The cavitation is severe on take off, and once the boat gets moving and the bow comes down, it hooks up like it should. With the doel fin installed plus moving some ballast to the front, I'm hoping to find a cure.

One thing I've learned, with much help from Joe Poole of Ferguson-Poole Marine, is that the 64 650 is something of an odd mix of old and new designs. The lower end was really meant for an 850 motor and was geared a bit high at 2 to 1. This meant that with the smaller 65 powerhead, they had to go with a smaller diameter prop (12.5") Add to that the use of a "different" thrust washer setup and changes in blade design and cupping, and it gets pretty hard to find the correct prop with the pitch I need. Merc later changed to a different lower end gear ratio of 2.3 to one. This makes the particular combo I need even harder to find since production of my setup was a short run. With enough trial-and-error I could find the right combo, but I'm trying to keep costs under control. Sort of...

Oops, I've wandered pretty far from the J.E.G.O. subject matter, so my apologies.

Norm, your motor has a square shoulder on the propshaft, which fits the old-style thrust spacer.

Merc used to sell a pipe-type of spacer that fit snugly around the propshaft, and butted-up to the square shoulder. Then, you could use the new-style, flat thrust washer which would fit the new-style props. Gives you a much wider selection of props.

I bet Joe could tell you the part number of that spacer, heck, he's probably got one! Or you could easily make one out of suitable tubing, all you need is a sleeve/washer combo that is the same combined length as the old-style thrust spacer.

You could also retrofit a 2.3:1 lower unit to your old 650; with a few mods, it'll bolt right up. This does work great on the little 650 but also is a good mod for early Inline Sixes.

Craigslist is a good source of motor parts and I bet you could find a good deal on a later 650 parts motor with 2.3:1 gears.

BTW the 4-cyl 66-c.i. 800, 850, 85hp, 80hp, & 75hp models all carried a 2.3:1 gearbox.

Send me a p.m. or start a new thread in the Mercs section if you'd ever like to explore further.

Happy Boating..........ed