1956 7.5hp Ring Replacement

[wbeaton]

I am in the process of tuning up my 1956 7.5 hp Evinrude. I did a compression test and found 75psi in the top cylinder and 70 psi in the bottom.

I have not yet pulled the head or decarbed the engine, which I will do before I even consider doing a ring job. I will also inspect the cylinders for wear and try to free the rings with penetrating oil to see if that helps.

Assuming, I need to replace the rings and the block doesn't need to be rebored what else do/should I replace when I have the crankcase open? Are the parts still available? I have two powerhead drawings. One is from a 1952 (which looks like my motor) and the other is in my Clymer manual (and doesn't look much like mine). The '52 doesn't show any connecting rod bearings or main seals while the Clymer does. Do these parts still exist? Can the originals be reused if I can't find replacements? This motor still seems to run well so I'd rather run it until it finally wears out completely then to pull it apart only to find out I can't get the parts to put it back together.

 

[F_R]

Re: 1956 7.5hp Ring Replacement

There are no replaceable rod or main bearings, nor top seal. However, there is a lower seal, which it may be well to inspect because if it leaks, water is admitted into the crankcase. That could be responsible for your slightly lower compression on the lower cylinder.

The lower seal is a spring loaded carbon seal assembly on the top end of the drive shaft. All that has to be removed in order to do a water pump job. Trouble is, people fail to replace the cork-like gasket and o-ring when they are in there....That is why they leak. Given enough time, the result is a destroyed powerhead when it throws a rod.

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

Thanks F R,

That is invaluable information. I am no longer concerned about opening the crankcase. I will also replace the lower seal when I do the impeller. You may have just extended the life of this motor another 50 years.

 

[DJ]

Re: 1956 7.5hp Ring Replacement

Why do want to take it apart? There is nothing wrong with those numbers.

Decarb it and go.

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

Is compression this low normal for these motors? I assumed the lowest acceptable readings would be somewhere in the 80's.

Compression in the mid-low 70's seems a little too low to me. I figured an old oil burner like this could get by with lower compression due to the high oil mix, but I'm afraid at these levels I'll soon start having low compression issues. So I thought why not do the rings if I need to since I'll have the powerhead stripped and removed from the outboard during the tune-up anyway? I don't want to do the rings, but I'd rather do them now while I'm doing everything else than to HAVE TO do them next summer.

 

[DJ]

Re: 1956 7.5hp Ring Replacement

I Have a 1957 model of the same engine. I don't think either cylinder in mine is 70 psi. But, it's been a long time. Plus, I'll bet mine has over 1000 hours on it.

70 is fine. Some models read in the sixties.

You're right though, a decarb is an absolute must. Those things used straight 30 weight motor oil when they were new. That can't have been good.

My suggestion is to replace the impeller, decarb it and enjoy it. It's a great little engine.

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

Sounds good to me, djohns19.

I'll hold off on the rings for now.

It is a great little motor. I use it on those small hard-to-access lakes here in Ontario so I need it to be reliable. I just picked up a carb rebuild kit, head gasket, new ignition parts and an impeller - all in stock. It'll run like new when I'm done.

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

I now have this motor apart and found that the lower seal is completely missing. All that is left is the spring and brass caps. This part is no longer available. Can I build a replacement?

 

[F_R]

Re: 1956 7.5hp Ring Replacement

It's made of carbon. Try sea-way.com

 

[F_R]

Re: 1956 7.5hp Ring Replacement

Are you sure it's obsolete? ishopmarine.com shows it discounted for $16.07. Part number is 303391. O-ring inside it is 303347 and gasket for the plate is 303355

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

Maybe it is only obsolete in Canada. I can't find a supplier here and my OMC dealer says they can't get one. I assumed it would be the same in the US. I should have tried US sites, as well. You folks have everything.

I'll try both those places. Thanks.

 

[samo_ott]

Re: 1956 7.5hp Ring Replacement

Where are you in Canada? My dealer here in Ottawa has all the 50's parts I have ever asked for but I have never tried for that specific seal. Try Laurentian Marine @ 613-526-5622

 

[wbeaton]

Re: 1956 7.5hp Ring Replacement

Samo, I'm in Hamilton.

Turns out it is still available. I took the part numbers given to me by F_R and the diagram of my gear case into the marina and they were able to find all the seals except the cork gasket in stock. Maybe the first guy I talked to didn't what to be bothered to look. When they ask the model number and I say 7520 sometimes they just look at me funny as if they can't believe that's the right number.