1958 7.5 Johnson AD 12 prop and shear pin

[SPK]

Hello,
I am new to the forum and am very impressed with the great information that I have been able to read. Recently I acquired a 1958 Johnson 7.5 hp AD 12outboard and am curious as to how the black hub in front of the propeller is properly removed to access the shear pin. Although my pin is not broken I would like to know how to get at if for future repair if necessary. I do not have a manual for this motor so I can't refer to any literature to help me out. As well I don't know what the pin is made out of or what size it is. I would appreciate any information that anyone would be willing to share with me about this motor besides shear pin information as I don't know too much about the motor as of yet. It seems to run fine and is in really good visual condition. I thank you all and look forward to your feedback.
Sean.

 

[Vic.S]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

Its retained by a cotter pin.. we'd call it a split pin in the UK

Remove that then it unscrews, I think

Parts catalog and diagrams HERE

Fuel mix for a 1958 model 20:1. Don't be mean with the oil as this engine has plain bearings ... no needle rollers.

 

[SPK]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

Thanks so much for the info. I may be incorrect but I have searched for a cotter pin on the black hub prior to my posting and can't seem to find any. I will look again but there doesn't seem to be any evidence of anything holding that black hub on there. I was wondering if maybe it is to be popped off or if it is threaded on perhaps with a reverse thread. Thanks for the reference manual notes. I will take another look to see what I can find. Maybe it is really tiny and I missed it.
Thanks again.
Sean.

 

[jay_merrill]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

The above description is accurate for a newer motor, with a drive pin. Yours works a little differently and has a shear pin.

You will notice that the black hub on your motor is rubber. It is held in place by a ridge molded into the inner side, which fits over the cotter pin. Pry the rubber hub off with a screwdriver or similar tool. When you get it off. wou will see the cotter pin and the shear pin, which is right behind it, may fall out. If the prop shaft happens to be oriented such that the shear pin holes in the prop shaft and propeller are horizontal, the shear pin will stay in place and you can just rotate the prop until the pin falls out.

The reason why your motor has a shear pin, is bcause OMC had not yet started using a system that included a rubber bushing between the inner and outer prop hubs. In the newer motors, that bushing is the weak link that is intended to tear, if you hit something.

You motor has a shear pin and a spring loaded link in the pinion gear that is inside of the gearcase. If you hit something, the idea is for the pin to shear and for the spring system to "give" a little.

BTW, take very good care of your prop, because you can't find then easily any more.



???

 

[SPK]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

Jay,
Thank you so much for your detailed information. I really appreciate the advice you have given me. Although nothing has been broken yet I did want to become aware of what to do in the event of a shear pin break. I will try my best to take care of the prop. I am sure they are rather hard to find and probably quite expensive. This motor is new to me so if you have any other advice for me I would be more than happy to read it and learn. Once again, thanks for your assistance.
Sean.

 

[Sargent Skiff]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

You've got a wonderful little motor, one of the sweetest running that OMC ever made.
Don't skimp on the oil. They were designed to run on a 16:1 mix and the plain big end bearings won't stand up to the commonly used 50:1.
Get familiar with your AD ( http://www.marineengine.com/parts/v...ntage-evinrude-johnson/377512/37751200001.htm ) and learn to do the maintenance yourself. They're a simple engine and a joy to work on. Lots of support here and at
http://www.aomci.org/cgi-bin/yabb2/YaBB.pl.

Parts are still easy to come by, including props, on ebay, etc.

Have fun.

 

[jay_merrill]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

I agree with SS that this is a great little motor. I'm a huge fan of the old " 2 cylinder magneto motors," from the 5.5hp models, right up through the 40hp motors. They are very simple engines and if they have been even reasonably well kept, they can last "forever."

I have been working on a pair of 1958 Evinrude Bigtwins that I own. Both of them have been sitting in my shop for about five years. They have not been run during that period and I didn't do anything special to them. The other day, I hooked a battery to them and fired both up - no fooling with the ignition, no carb rebuild, etc. Bam! Running in a couple of turns of the starters!

Not bad for a pair of outboards that are nearly 53 years old!



???

 

[SPK]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

Thanks so much for all of the input.
I have another question regarding the use of ethanol 10 in this older motor. What issues if any should I be aware of? The tank is the older style 5 gallon Mile Master. Should I be using a premium grade of fuel?
Sean.

 

[dvrdwn]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

I don't think it matters much about the grade 87,89 grade is fine. If it is at all possible to get gas with no alcohol, get it! The alcohol in the gas dose bad things to your motor. It will eat your fuel lines and clog your carb. in the states we can still find no alcohol gas. Hope you can too.

P.S you should put an in line filter on if possible.

 

[F_R]

Re: 1958 7.5 Johnson AD 12 prop and shear pin

The parts book specifies a part number 302333 "Drive Pin". It is 3/16" diameter X 7/8" long and made of Monel. Monel is an alloy of mostly nickle and copper. The point is, it isn't intended to shear. The prop doesn't have a rubber hub, but there is a shock absorber built into the lower unit to absorb bangs and whacks. Unfortunatly, those shock absorbers are now giving a lot of breakage problems. I suppose nothing lasts forever.