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Author Topic:   Right Prop for 1974 Evinrude 85HP V-4 on 76 Newport
Jholmes105 posted 08-19-2002 09:57 PM ET (US)   Profile for Jholmes105   Send Email to Jholmes105  
I have a 1976 Newport with a 1874 Evinrude 85 HP V-4 engine. I am just wondering if anybody has any experience with this setup and finding uot what would be the optimum prop size? How do figure the correct size in aluminum vs. stainless?

Thank You

pamlico posted 08-20-2002 03:24 PM ET (US)     Profile for pamlico  Send Email to pamlico     
When it comes to cost,... Stainless will cost twice as much as Aluminum.

Aluminum has some advantages,....if you hit a sand bar or some other hard object under the water, the aluminum prop tends to absorb the shock and at times bending one or more of the blades are breaking them off.

Stainless does not instead,....the force is absorbed in the lower unit. Possibly damaging the gears in your lower unit.

But stainless tends to last longer over time, long as you don't hit anything. A small ding can be easily taken out with heat and a brass hammer.

Alunminum tends to chip and break off,...causing a heavy vibration and power loss in acceleration.

As far as the prop size that you need; you need to find the RPM range of your motor. For example my otboard is rated 5000-5600rpms. You will want to install a prop that will get you as close to the top of your operating range (which mine is 5600rpms) without going over.

andygere posted 08-20-2002 05:58 PM ET (US)     Profile for andygere  Send Email to andygere     
'79 Montauk 17, '79 Johnson 85 hp. I run an aluminum 13.75 x 17 prop, which is ideal for this rig: Good holeshot, no problem with heavy loads and good top end (38 mph).
Dunk posted 08-22-2002 01:28 AM ET (US)     Profile for Dunk  Send Email to Dunk     
That 74 is smaller block V4. She's 92 cubes instead of 99.6. Really doesn't have the punch of the newer engines. I'd look around for 13 3/4 x 15" alum OMC prop to try before investing in a SS wheel. I ran a 76 85hp Johnson for 2500 hrs on a 16'7. She would turn a 15" at 5200 at about 40mph. She was also a small block. If you can twist the 15" alum then go to and buy a 15" Stiletto. You don't want to twist that engine over 5200 on a steady diet. The carbs are small and she will run lean above that rpm.
Jholmes105 posted 08-22-2002 07:17 AM ET (US)     Profile for Jholmes105  Send Email to Jholmes105     

Where is the best place to get a Tachometer for that engine? Where does it plug in? Would you suggest a Telefelx aftermarket style or to stick with OEM? I really appreciate all of your help. The Evinrude 85 runs very smooth and strong on my Newport. It only has a documented 189 hours on it from the ORIGINAL owner of 28 years!!!! It is amazing how smooth the engine is for a 1974! Thank you for all the help. Dunk, I am going to check what is on there now, I think it is a 13 3/4 with a 15" Pitch. I will check today and let you guys know.

Thank you,


jimh posted 08-22-2002 10:14 AM ET (US)     Profile for jimh  Send Email to jimh     
You can use either an OEM or an aftermarket tachometer, depending on your preference.

If the engine does not have a plug or fitting to connect to, it is simple (on most outboards) to find the proper connection point.

Having the engine propped correctly is important, but on the other hand I would not run a 25-year old engine at its maximum rated RPM for too long.

andygere posted 08-22-2002 12:04 PM ET (US)     Profile for andygere  Send Email to andygere     
My '79 Johnson 85 hp is turning 5000-5100 rpms at WOT with the prop noted in my post above.

Here are a few keys to long life of old motors (in my humble opinion). Be meticulous with your fuel: Use a good quality spin-on water seperating filter; Be a little generous with the pre-mix (get at least 50:1 in the tank, 49:1 even better); Use a decarbonizing treatment (OMC etc.) in every tank (keeps the rings on the pistons) and use fuel stabilizer in every tank (keeps varnish out of carbs, helps prevent burnt pistons); Change the water pump impeller before it needs it and watch the pee stream regularly; Don't run the carbs dry after every use (fuel stabilizer protects carbs, and pistons will stay oiled); Run the motor regularly and winterize it if it will be out of service for a few months. This is not a comprehensive list, but just a few things that seem to have made a difference for me.

andygere posted 08-22-2002 12:04 PM ET (US)     Profile for andygere  Send Email to andygere     
By the way, I learned most of these tips from members of this forum.
Dunk posted 08-22-2002 02:24 PM ET (US)     Profile for Dunk  Send Email to Dunk     

Look under gauges then under OMC. These guy's are selling OMC tachs for 30 bucks. It will connect right to the gray wire coming out of your wiring harness near the key switch.

Jholmes105 posted 08-22-2002 04:26 PM ET (US)     Profile for Jholmes105  Send Email to Jholmes105     
I want to thank all of you guys for all the advice. Andy, I am generous with the oil when I mix the gas. I always thought a "little" extra lubrication could not hurt anything but the plugs and I would rather replace a fouled plug than rebuild a motor. I love the other tips you gave me and I am going to begin following them. I will start to run fuel stabilizer in each tank. I will be changing the water impeller at the end of this season.

Dunk: Thank You for the link to Surplus Unlimited. I will be ordering a tachometer this afternoon.

JimH: I usually run about 1/2 throttle to cruise on this motor. It just seems to work effortlessly and run so nice at this spee/RPM's. I am looking forward to getting a tachometer to check the performance.

Thanks to all!

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