1974ish Johnson 70hp powershift 2 question.

[davidmbv]

I’m considering picking up a 14’ ski barge powered by a 70hp Johnson. I think it’s a 74 or 75 based on the gold painted lower and the cowling. The cowling has a badge indicating 70 Powershift 2.
Any advice about the reliability/performance of this era OMC 70hp? It looks to be well maintained but planning to do the usual checks, compression, lower oil check, spark.
If the price is right I may just buy sight on scene because the boat is worth what he’s offering. I’ve seen a few of these 70’s come up for sale cheap locally also so could always repower the skiff .
Thanks

 

[jimmbo]

It is 50+ yrs old. They were good engines in their day, and were quite versatile, and offered good Fuel Economy. Were they Perfect? No, they had their share of Problems. They were producing almost 1 1/2hp per cubic inch, and propping was critical if you wanted a long engine life as overpropping often led to Detonation issues. Parts are beginning to get more difficult to find.
Powershift II was a Hydromechanical Shift System, it used Hydraulic Pressure to make the Shifts quicker, but was needed mainly to be able shift Out of Gear. In order to make the Clutch Dog Teeth and Mating Surfaces on the Gears last longer before wear required replacement, OMC machined the contact Faces with a Bevel that kept the Dog in place with reduced ability to jump out. However that made it more difficult to shift out of Gear, hence the Power Assisted Shift.

 

[davidmbv]

Thanks for the info! I’ve only worked on early OMC 25hp 22ci motors. How reliable is the ignition on the 70’s of this era? I like the points magneto because they always seem to run once set up right.
What should I be expecting to go through to make it a runner that won’t leave me stranded? The lower unit was apparently rebuilt several years back . I’ll still plan to change gear oil and impeller, check seal.
Besides checking for corrosion/cracked wires/grounds, carbs (cleaned/rebuilt/synced) anything else to go through? Assuming spark and compression is good…
I’ll plan to pick up a service manual but this will be my first “big boy” to restore/run.

 

[jimmbo]

Well, like any Electronic Ignition System, it is reliable until it quits working. Keep in mind it is 50+ yrs old, and replacement parts can be difficult to find. While the earlier versions of this Motor did have Points(still Electronic though), by 74 they were Breakerless.
There are 3 carbs, and that means 3 Carb Kits,
A Check of Ignition Timing(Max Advance). It should be fine, unless someone has messed with it. Don't worry about Idle Timing, that is what is adjusted to set the Idle Speed, and will vary. There is a Pickup Timing Spec, that pertains to the amount of Advance the Timing has, at the moment the Carbs start to open from fully closed. They are supposed to be fully closed Prior to that Timing Spec.
If the Carbs are removed for cleaning, then a check and possibly an adjustment, to insure the Carbs and Spark are in Sync with each other. It is called a Link & Sync. It would be explained in a Service Manual. Speaking of Manuals, forget most 3rd Party Service Manuals, they are usually only good for the Out House, and I don't mean for Reading. Get the Evinrude/Johnson/OMC Manual for that Motor.

 

[racerone]

post actual compression values here.

 

[davidmbv]

Well, like any Electronic Ignition System, it is reliable until it quits working. Keep in mind it is 50+ yrs old, and replacement parts can be difficult to find. While the earlier versions of this Motor did have Points(still Electronic though), by 74 they were Breakerless.
There are 3 carbs, and that means 3 Carb Kits,
A Check of Ignition Timing(Max Advance). It should be fine, unless someone has messed with it. Don't worry about Idle Timing, that is what is adjusted to set the Idle Speed, and will vary. There is a Pickup Timing Spec, that pertains to the amount of Advance the Timing has, at the moment the Carbs start to open from fully closed. They are supposed to be fully closed Prior to that Timing Spec.
If the Carbs are removed for cleaning, then a check and possibly an adjustment, to insure the Carbs and Spark are in Sync with each other. It is called a Link & Sync. It would be explained in a Service Manual. Speaking of Manuals, forget most 3rd Party Service Manuals, they are usually only good for the Out House, and I don't mean for Reading. Get the Evinrude/Johnson/OMC Manual for that Motor.

Great thank you!