1971 Johnson 4HP...rebuild questions

[broadwayc]

Hello,

I just purchased a 71' Johnson 4 HP today. I knew when I bought it that it needed work but it's all original and I mainly bought it to put back together (as it's in many pieces) and learn how motors are built and how they work. It only cost me $55 so I figured it was a good deal for it's potential in working and teaching me a thing or two.

There are a few things that need some attention before I put it back together and hopefully these pictures load so you can see what I am dealing with.

First off, the major flaw is that the metal gasket has been broken off of the exhaust housing.(First & second pictures of the group). It is the part that attaches to the lower cover assembly (attached to lower cover in pic 3). Am i right about it being the top of the exhaust housing? The guy I bought it from told me I could just have it welded back on and it should work fine. An used exhaust housing would cost me around 100 bucks...not wanting to spend that if I don't have to.

There isn't any scoring in the cylinders (pic 4) but one of the pistons needs to be replaced and maybe the rings on the other (pic 5). Block/head looks great (pic 6). Magneto looks like it's in great shape (pic 7 & 8). Carb from what I can see looks excellent.

Besides a thorough cleaning, replacing torn gaskets and other small missing pieces....is there anything else I should be concerned with? Are there any parts that should automatically be replaced with a rebuild like this ie Fuel pump diaphragm, water pump impeller?

What cleaning products should I use for this task and should I be extra careful of anything?

I really appreciate any help you can give me. Thanks.



Sorry I just tried to load the pics and they were enormous...I'll try to get some smaller ones and post them in a few minutes.

 

[JIGGER]

Re: 1971 Johnson 4HP...rebuild questions

Hey man! I just sold a 4hp that I kept running for me to load the hours on. Few tricks Ive picked up on along the way. Pics would help but its a 2cly right. Has 2 coils and 2 points under the flywheel,single carb with a recoil and rap type start.

 

[1946Zephyr]

Re: 1971 Johnson 4HP...rebuild questions

Yes, I just rebuilt a 1970 4hp a couple weeks ago, so if you need any advice, I may be of some help. This one came in with a blown #2 rod and badly scored crank.

It has a new crank and new rods, so it's running great now. If you have troubl getting parts, let me know. I can help out.

Good Luck.

Leon

 

[broadwayc]

Re: 1971 Johnson 4HP...rebuild questions

Jigger and Zephyr, thanks for the responses. Yes Jigger I believe you are right...to be honest I don't know about the points under the fly wheel but there are two round black pieces under the fly wheel and it looks like one half of the under fly wheel is a mirror image of the other. Yes there is one carb with a recoil starter.

Zephyr, thanks for the help and I'm sure I will be posting again.

I did take a closer look at the parts diagrams on the internet parts sites and it looks like the metal plate on the top of the exhaust housing has snapped off somehow and the plate looks a little bent. I am thinking that welding it may be ok as it is mainly to connect the housing to the cover assembly, as long as it holds so the motor can be steered. Do you think this would be ok?

As far as other parts I need: One of the pistons will need to be replaced as well as the rings for both. I have seen regular "rings" and "set 30 rings" will I need two of each? wow they get expensive for the genuine parts...could I get them somewhere else for a lot less?

I think most of the other parts are here but I need a manual to be sure...do you have any advice on what brand manual to use?

Thanks again and I will try to post some pictures today or tomorrow.

Jake

 

[JIGGER]

Re: 1971 Johnson 4HP...rebuild questions

A couple things I found were by winding a rope around the flywheel spins the motor twice as fast as the re-coil rope. They were noted for weak coils making them hard too start and guys would rip up the re-coil. If you havent removed the flywheel and the head is removed you might want to see if itll spark each side. My unit was taken apart for the first time last year to change the out-put shaft that twisted off. Its chucked into the bottom side of your motor. Check it closely! The marina I get parts had a hole bucket full of bad shafts. If the splines on the block are worn you might want to think twice about rebuilding it. I J-B Welded mine and work good for the year or till you hit something and ruin your crank shaft. Also the water pump on mine looked like new after 30years.

 

[broadwayc]

Re: 1971 Johnson 4HP...rebuild questions

Jigger, yeah the fly wheel has been taken apart and I have no idea how to put the damn thing back together . Any manual recommendation?

I guess I should have thought twice about rebuilding a motor...I could have bought a $4 puzzle from Wal-mart and had less of a headache as this motor will probably give me.

I am taking the exhaust housing to the welder tomorrow to get the top plate welded back on the rest of the housing. Once that's done, I can get my hands dirty. Should I clean the parts with anything special like Sea Foam Deep Creep?

Thanks

 

[JIGGER]

Re: 1971 Johnson 4HP...rebuild questions

You might want to take a couple pics of it. Itll help ya later puttin it together. Probably be a good idea checkin $$$ on the parts you think ya need and picking up a book. Also make sure the lower end oil isnt trashed. Black is ok but water and metal are bad!

 

[1946Zephyr]

Re: 1971 Johnson 4HP...rebuild questions

Once I rebuilt the one I did, it staterd on the third pull....if that. A good motor usually does.

I'm not exactly clear on your exhaust part. How did it get bent? Well, it may be cheaper to replace it, rather than fixing it. If a good welder isn't fixing it, then you may be wasting money.

If you want to clean the parts up good, then I would buy some carburator cleaner and soak them in it over night. They'll clean up nice and the welder can fix them properly.

As far as rings and pistons go, try Seaway Marine, up in Seattle Wa. They helped me with the stuff I needed. They should have what you need, in stock. Their number is 206-937-7373

Most likely they have your pistons and rings in stock.

 

[Rick.]

Re: 1971 Johnson 4HP...rebuild questions

Most of your parts will clean up fine with Varsol or paint thinner. Not sure if carb. cleaner will be good for painted parts. I have a 71 Evinrude and my friend has a 73 Johnson. Both are good motors but they both leak burned oil/gas back into the engine cover right at the base. Be careful that you replace the gasket or use a little sealer around that part of the job. They run fine but do get messy after being used and then laid down for transport. Enjoy your project. Rick.

 

[broadwayc]

Re: 1971 Johnson 4HP...rebuild questions

Thanks for your replies guys.

Zephyr, the broken/bent part is just the top of the exhaust housing which just connects the motor and cover to the rest. I don't think it will compromise the performance of the engine.


I sort of did a dry run putting the block together last night to see if there were any major missing pieces (still don't have the manual yet but I needed something to do). So far, I'll need a recoil spring for the rewind starter and probably a new rope, and a few minor pieces...no big deal.

Here is the headache. The Magneto looks to be in great shape however..there is a gold colored ring on the bottom of it. I am sure its just the support for the magneto itself because the screws that are still in it line up with the holes in the block. This is were it gets tricky for me. That goldish ring...is it supposed to be permanently attached to the underside of the magneto or is it seperate? If it's seperate, it sure is stuck.

I am asking this because the screws, that would go into the holes of the block to hold the magneto in place, are still in that ring BUT there is NO WAY to get to the heads!! The threads are hanging through the ring and the heads of the screws are between the bottom of the magneto and the support ring. VERY FISHY...and thinking about this made my brain hurt. Any suggestions?

 

[Don Hansen]

Re: 1971 Johnson 4HP...rebuild questions

I hope I posted this right. This guy has step by step pictures of how to rebuild a 4 hp. The only thing I don't agree with is his method of tightening up the magneto/amature plate. I made a brass washer out of shim stock to do that.

As you can see that brass ring your talking about is attached solid to the block. Below it is a loose aluminum ring that gets attached to the armature plate by the 4 screws he has indicated in the picture "Loosen the Magneto plate". This allows the magneto plate to rotate, and change the timing, as you advance the throttle.



http://shareaproject.com/pages/imageDetail,p,182,i,2526,00.html

Don H

 

[broadwayc]

Re: 1971 Johnson 4HP...rebuild questions

Don Hansen...you are the man! What a great site...thanks so much. He's working on what looks like the same engine as mine.

 

[Don Hansen]

Re: 1971 Johnson 4HP...rebuild questions

Glad the thread worked. I have a 1970 Evinrude 4 hp. That block design, first as a 3hp and then a 4 hp and with minor changes along the way, was built for something like 20 years or more. Good motors and easy to work on.

Don H