TOPIC: 1975 evinrude 70hp help!

hello, I have a 1975 evinrude 70hp and looking to change the impeller and the lower unit oil. First off, what lower unit oil do I use on this guy? And to take off the lower unit, I disconnect the shift pin from the upper unit and I should be good to go right? there is no pee hole, but it looks like a good deal of water is coming out when I start it. is there a temp gauge I can add to it? thank you for your help!

First off, "good on ya" for wanting to do your own work and taking the time to do a little preventive maintenance on your motor Jon. One of the first things I do is buy a service manual for the new motor, it really pays for itself and helps with even routine jobs like this.

That being said, the normal routine for me is to pull the prop, disconnect the shift linkage, drain the lube, and drop the lower unit. There are several schools of thought on which gear lube to use, some folks do use regular 80W90 / hypoid gear oil, personally I run only Mercury or BRP (OMC) oil, synthetic blend. Maybe overkill, but gearcase rebuilds or replacements are expensive. Make sure you replace the little washers on the drain and vent plugs, they're inexpensive and good insurance that water won't get in past the plug when submersed.

Many folks use aftermarket water pump impeller kits without problems, but I believe it's worth the few dollars more for the O.E. quality pieces here. If the impeller vanes fail and spin on the hub, it only takes a minute to cook a perfectly good outboard. If the housing the impeller rides in has any signs of wear or "grooves", it's best to replace it as well. Even if just replacing the impeller, it's best to buy the kit that includes new rubber seals for the water tubes, bolts & washers, etc.. I always lube the housing the impeller rides in well with vaseline, makes assembly easier and protects the impeller from wear at first start up.

It often helps to have an extra pair of hands when re-installing the lower unit the first time, to help guide the water tube into position while raising the gearcase. After you've done it a time or two, you will learn little tricks to do this alone but it helps to have some assistance the first time through.

A water pressure gauge is a great idea IMHO, much more common than temp gauges on outboards. You can monitor the pressure in the cooling system that way, no pressure = shut her down!

Sorry to be so long winded, just a few thoughts your question brought to mind. Good luck, and let us know how it goes.

Hey MarkS thanks for the reply. I can't afford the hourly rates for these mechanics anymore...100 bucks an hr is crazy imo. I have done this a few times on my merc I/O but never on a outboard. Ill order one of those manuals, thanks for the recommendation. I was confused as to the oil to use...the type C stuff or just some 80w90 like u said. I guess the type C stuff is for electric shift motors so ill be going to use the 80w90. I have always used marine oil on the gear oil...to my understanding is the auto oil foams and this could cause excess pressure in the lower unit. I ordered those seals and just the impeller, hoping the housing is in good shape. But this winter I will replace everything with the kit for good measure. Do you pull the prop just so it doesnt freeze on or is it necessary in order to pull the lower unit?

thanks again for your help,
Jon

No problem, glad to help.

Do you pull the prop just so it doesnt freeze on or is it necessary in order to pull the lower unit?

The two biggest reasons I pull the prop is to;

A - check the propshaft for fishing line (it seems like it always finds it's way between the front thrust washer and the propshaft housing seal!), eyeball the seals, clean and lube the propshaft and

B - prevent damage to the prop while I'm wrestling the lower on and off. It's easy to ding the tip of a blade or nick a leading edge which would effect performance or possibly throw it out of balance. That can also wreak havoc on the bearings and seals in the gearcase, causing other issues you just don't need.

I may run the impeller a couple (2 or 3) years (depending on how much usage it gets), but I always change the gear lube and do prop service at least once a season.

If I may squeeze in here, theres one other reason to remove the prop and grease the shaft. A friend gave me a big boat with 2 mercs and one of the props wouldn't slide off. Think he hadn't used the boat for a few years and I had to use a short piece of wood and heavy hand sledg pounding around the hub area, took near an hour to remove it. At least I saved the prop:)
I have a 85hp rude and guess its about the same as the 70hp, so for myself I appreciate the long winded reply, lol

NOTE: I read that theres an additive in the marine gear oil that resists water and oil seperating, forget the word:( Mike Moore always used reguar Auto gear oil and had no problems, as long as seals aren't leaking its usable. His many motors out lasted him unfortunately.

Well Mark said it all so I can only add to make sure you have good lighting.

I forgot about the fishing line. Ill have to go check my merc now for that too.
g3bill thanks for the reply, I don't want to run into that issue ether and especially because saltwater makes everything harder to remove, ill make sure to pull that prop at lest once a season if not more.

Question for MarkS: have you ever installed a pressure gauge on one of these outboards? I have no clue as to where to start...looks like its just a brass T tapped into the cooling system next to the head...is it that easy?

g3bill: what year is your 85? does it have a pressure gauge or a tell tale?

jonthropology wrote:

Question for MarkS: have you ever installed a pressure gauge on one of these outboards? I have no clue as to where to start...looks like its just a brass T tapped into the cooling system next to the head...is it that easy?

My experience on the Johnnyrudes has all been on the V4 CrossFlow motors, but the principle would be the same. Here's a pic of the current set-up I'm running, T'd off to run a tell-tale and the pressure gauge just as you described;

Marks, nice work there. I plan to do the same, why did you chose to install it so low? and do you think I need both a tell-tale and a gauge or just the gauge? I guess its double security? Did you get the T in a kit or did you get it from the local hardware store?

above is a pic of my motor

Thanks Jon, I ran the 1/8" plastic tubing through 1/4" rubber hose to protect it, acts like a sleeve I guess. (Maybe overkill?)

why did you chose to install it so low?

That's where the factory put a boss for the tell-tale on this motor, I just T'd it off to run a gauge as well.

I just like being able to glance down at the dash (the gauge) and make sure everything is working as it should be.

I have a 73' and a 76'
On the 73' the telltale is the two exhaust relief holes.
You simply need to be skiing to see them.
Also if yours has an o-ring at the top of the drive shaft, make sure you grease the drive shaft splines and get the o-ring back in place.