1970 Johnson 20 hp throttle Q's

[AlTn]

Re: 1970 Johnson 20 hp throttle Q's

surfacing the head and replacing the head gasket along with decarbing the motor < see Top Secret Files > will be about the best you can get w/o pulling the powerhead apart...I saw a 15 to 20 lb. increase on a 9.9 doing this

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

There was some salt under the thermostat cover. The thermostat was actually jammed (against its own wall) in a sort-of open position.

I could get all head bolts but ONE. This one seems to be stuck pretty darn hard!!!


The top cylinder through the bypass cover.


The carburetor.


The other bolts that are rusted hard are the little ones on the bottom where the leg connects to the powerhead (I think).

 

[AlTn]

Re: 1970 Johnson 20 hp throttle Q's

heat the area that the head screw passes through < mapp gas has worked for me >...it helps to have 2 people on this operation, but not really necessary..if you get it to relax some, tighen it back up, loosen some more, etc...first time doing this you'll probably be surprised how long you have to heat it, but don't rush it. Despite your best efforts it may snap anyway, at least it's in an accessible area for drilling.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Will try.

I've managed to remove the little rusty bolts on the bottom which hold the powerhead in place. I haven't removed the powerhead assembly yet; I figured I would take the lower unit off first. I've removed 4 bolts, 1 large bolt and the lower bolt in the shift linkage (through the window). The lower unit moves by half an inch but won't come off. I'm afraid I may break something since it requires a lot of force. :S

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

This has really become the question whether I should move ahead or not and I veer towards the latter.

For every bolt that I can get out I find two bolts that are frozen. I don't know what I've missed, but I can't get lower unit off. I won't be able to open gearbox, too, since it has screwdriver bolts which are frozen. This engine has seen more neglect than I have imagined and I was surprised the gearbox had oil in it. Adding to that the Dead Sea in the passages and the need to replace a lot of parts including all gaskets and the definite need to remove the frozen bolts which would require the attention of a shop since I wouldn't do this precisely enough myself...

At least I know now what to look out for in used outboards. The maintenance checklist is there for a reason, no matter how old the engine is...

 

[AlTn]

Re: 1970 Johnson 20 hp throttle Q's

try wooden wedges between the lower unit and the exhaust housing to bring it down, it really doesn't need to come much farther before the driveshaft comes out of crankshaft/crankcase head....those screws holding the skeg onto the gearcase housing may be easier to heat and remove once you have the lower unit inverted

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

I maybe overreacted the other day.

The shift rod was stuck and I had to insert a screwdriver there and turn hard. The lower shift rod came out of the socket and I was able to remove the lower unit.

The reason I am worried about the gearbox is that after my futile attempts to remove the lower unit I may have broken something. I'm not sure. All 3 gears on the lower unit shift fine and when I rotate the driveshaft it behaves accordingly. But it's not extremely easy to rotate the propeller shaft (in neutral) and there's some rubbing noise coming from inside the gearbox - I'm not sure if it was there before. It's the same with and without the oil. It's like a little easier than turning a spoon in a sugar pot. I hope it's normal.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Success! I've removed the last bolt from the head, in the end penetrating oil did its job. I've removed the head, bypass covers and starter assembly, and of course I've removed the whole assembly from the base.





Now for the exhaust cover... It seems to me I should probably heat the exhaust cover, but will it work? It has these hard to work on slot bolts which are all stuck. I've read around here exhaust covers are the most neglected of them all.

 

[AlTn]

Re: 1970 Johnson 20 hp throttle Q's

good progress!..yes heat will certainly help....I'd suggest you remove anything in that area that heat will affect before you begin

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

I've found a really old flywheel puller that seems perfect, but the bolts are too short. Until I get longer bolts... I've noticed the flywheel doesn't move anymore. It rotates by half a degree, but something is stuck. (Pistons move by a little and the crankshaft rod moves also by as little as seen from below.) I haven't used a hammer or anything like that. The flywheel doesn't move even when I tighten the flywheel nut, I don't even have to hold it! Now I remember that I had that before to some extent where the starter would seem stuck for a moment, but not to that extent! The pistons are well lubricated. How could the bearings have gone bad with no abuse? A week ago, I could rotate the flywheel with ease.

Some more bolts came out of the exhaust cover but still half to go.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

POP!

One coil is cracked, the other's not. Probably one of them has been replaced during the motor's lifetime.
An inscription left by one of the previous owners says "FRAM" near the cracked coil.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

I got the magneto off and went on to crankcase.
I got to probably the last 2 hex bolts that hold the crankcase and I can't seem to find my hex set at this moment.
The moment of truth is going to be soon when I open that crankcase. It is worrying as the crankshaft still doesn't turn... Seems to be frozen shut!
I already have the powerhead gasket set ordered. My common sense tells me I also need to replace the coils. But first, I want to take a look at what the devil is going on inside!

 

[kfa4303]

Re: 1970 Johnson 20 hp throttle Q's

yup, classic cracked coil syndrome, but you're right not to change it until you see what's going on inside. Good news is that you can get new coils right here at iboats for about $20 and they're 1000 times better quality than the original factory OMC versions.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Hey kfa, hows it going?

Just a quick update...

Crankshaft seems to rotate now and I don't know what caused it not to. I'm going to investigate.

 

[kfa4303]

Re: 1970 Johnson 20 hp throttle Q's

Hey Wolf. Glad you got it apart. It looks pretty good in there. Hopefully the binding was just a fluke, or something. Looks like the worst is over. Of course, now you gotta do the hard part and put it back together! Can't wait to follow the progress.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Hey Wolf. Glad you got it apart. It looks pretty good in there. Hopefully the binding was just a fluke, or something. Looks like the worst is over. Of course, now you gotta do the hard part and put it back together! Can't wait to follow the progress.

Ow!

The lower bearing (the rightmost bearing on that previous picture) was actually corroded to the crankshaft, that's why it did not rotate and I had troubles with the starter seizing sometimes before. I was able to get the bearing out and clean the shaft; the corrosion came from the internal wall of the bearing.

Crankshaft with the middle bearing still in place:



The pistons have mild yellow discoloration around the holes. Also, a nail catches in one streak in the bottom bore/cylinder. Here's a hi-res picture:



Now, I had 70 psi on both before dismantling. Are these pistons reusable? I will be using the motor only in summer months and not every day, but I want it to last and be reliable.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Umm...

A car repair shop technician said I need to definitely rehone the cylinders and install oversize pistons. He said that though it will start and run, it will not be an exceptional motor.

There is one place where a nail catches on the cylinder wall. Otherwise it is smooth to the touch, but scratches are visible to the eye.

I have no idea what to do. What do you people think? I am going more for general reliability than for speed records. I am thinking new rings would suffice.

 

[kfa4303]

Re: 1970 Johnson 20 hp throttle Q's

Hello again Wolf. Glad you found the reason for the seizure. Hopefully it's an easy fix. As for the cylinders, and I may get yelled at for this, I think if you only have the one scratch as described you'll probably be ok. You may want to get some new, normal sized rings now that everything is apart for good measure. I know my little 20 hp is pretty bulletproof and I highly doubt it has perfectly smooth cylinders. It's been rode hard and put up wet many times, has obviously overheated at some point and was dead as a doornail when I got it, but now it runs great and keeps on keepin' on. "Should" you get them rebored, yes. Do you "need" to get them rebored to have a nice motor, I doubt it. Either way, there are now cylinder police that will come and arrest you one way or the other. Ok let me have it guys. I'm sure others will disagrees, but I don't see the point of putting $500 worth of parts, effort and expense into a $400 motor.

 

[Wolf86]

Re: 1970 Johnson 20 hp throttle Q's

Hello again Wolf. Glad you found the reason for the seizure. Hopefully it's an easy fix. As for the cylinders, and I may get yelled at for this, I think if you only have the one scratch as described you'll probably be ok. You may want to get some new, normal sized rings now that everything is apart for good measure. I know my little 20 hp is pretty bulletproof and I highly doubt it has perfectly smooth cylinders. It's been rode hard and put up wet many times, has obviously overheated at some point and was dead as a doornail when I got it, but now it runs great and keeps on keepin' on. "Should" you get them rebored, yes. Do you "need" to get them rebored to have a nice motor, I doubt it. Either way, there are now cylinder police that will come and arrest you one way or the other. Ok let me have it guys. I'm sure others will disagrees, but I don't see the point of putting $500 worth of parts, effort and expense into a $400 motor.

Thanks. By the way, that's about what I paid last year for it.

Anyway, when I'll receive all the parts and I don't find anything drastic, I'm going to put it back together and see how it runs. I'll have to refresh my boat a little and the trailer when it gets warmer - can't wait, I love the sea. It shows 19 F right now and it feels like spring already, compared to temps down to -20 F we had a couple of weeks ago. The sea ice is already melting. Exactly a year ago I visited the nearby islands (a mile or two) by feet on ice and the ice roads were still open.

 

[kfa4303]

Re: 1970 Johnson 20 hp throttle Q's

Glad the thaw has started in the Great North. I'll bear that in mind. I was complaining about a bit of rain the last week. Spring has sprung here in North Florida. Flower and pollen everywhere, and temps are back to a civilized +75 F Keep us posted on the motor. I think it'll be ok. They're pretty tough.