What should I beware of in restoring a 1979 4hp Johnsons Model 4BR79Donohnson

[Monte NZ]

A friend of mine has been given the above motor which has been lying out in the weather and looks very scruffy.
I have offered to see if I can get it operational again and as I am not familiar with that model, wondered if there can be any particular problems with this series.
I’m familiar with the 3hp series of the 1950 -60s which are great motors, but what I have seen of the part list on Marine Engines.coms website, this engine is quite different.

Any help would be much appreciated and many thanks in advance.

Monte nz

problems with this model 4hp.

[frankr]

Well for one thing, the reeds are on the wrong side of the reed plate. Just kidding, that’s the way they are shown in the parts list. But not really.

True, there are many differences over the 1960’s models as a result of evolution, but none are really troublesome. I guess the biggest difference is it has CD ignition. No problem if you are familiar with it. It is the same system as used on many other motors of the era.

On the other hand, the side recoil starter is gone. That should make a lot of people happy.

The biggest drawback as I see it, is it is in New Zealand. But you guys seem to work wonders with those salty motors. I applaud you.

[fleetwin]

Yes, this 79 model is full of needle bearings everywhere…So, using 50:1 is not an issue, there are no plain rod bushings/bearings to worry about. That being said, I’m not sure this isn’t a bit of overkill on this small engine though. These engines tend to be a bit more noisey, due to a loose fit on some of the needle bearings… The CDII ignition is overkill also…
I didn’t see the pictures, did you post some? Maybe my computer is tired…
In any event, I surely would not pull the powerhead apart, not necessary unless there is obvious piston cylinder damage or rust to the bearings. If you want to have a better look, pull off the intake manifold and peek inside at the rods…But, I would certainly pull off the head and the exhaust cover…These engines have tiny water passages that plug easily. The cooling systems are a little more complicated than the older ones also.. Some of the cylinders have rubber restrictor plugs, etc. I would have to review a parts list to remember, but am pretty sure the head gasket is a little different also…
Pull the gearcase, do the water pump assembly complete. Please be sure to replace the driveshaft upper oring and lube the splines generously with OMC moly lube. Post more pictures, don’t know why I can not see the ones you have posted already…D

[billw]

I’d like to second what Fleetwin said about the tiny water passages. I guess if there was one thing I had to pick about “particular problems” with those motors, it would be the tiny water passage between the cylinder water jacket and the exhaust cover passage.. It is tiny on purpose, to let the motor run warmer without a thermostat. But it gets plugged up. If the engine should overheat, the first place I would look (after the pump service) is this passage. You just take the exhaust cover off, clean it out and you’re good to go, usually. Also like Fleetwin says, they are noisier than plain bearing engines; but they are okay. (And I would rather have the side recoil!! Just my opinion!)

Long live American manufacturing!

[Monte NZ]

Many thanks Frankr,fleetwin and billw for your very helpful posts.
First of all Frankr, your comment about New Zealand is true, in that we have a lot of salty motors unfortunately.
Being no more than one and a half hours from the sea at any point, means that there is a very good chance of our motors being run in the salt at some stage. Salt corrosion in our motors is a real headache.. …especially the old ones, and thanks for your applaud comment……..yes they can certainly be a bit of a challenge!

In reply to you fleetwin,I didn’t put up any photos……..that’s something I have yet to learn! This will be my first experience of working on a CDI motor. Interesting that you and billw mentioned the narrow waterways which makes me think that this motor could be well and truly gunked up

I will certainly take your advice onboard…….much appreciated

Thanks again
Monte NZ

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