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1968 Johnson 3hp JHL-23M Overheating, Chirping at WOT

S

Swarlos

Regular Contributor
I've been working on this 1968 Johnson 3hp for most of this summer. Initially it wouldn't run so I rebuilt carburetor and fuel pump to get it running. I took it out today since I hadn't run it in a couple weeks so I took it out on the lake for awhile and I noticed some problems I was hoping to get help with. First of all after warming the motor up for 10 minutes or so I opened up the throttle slowly. The motor vibrates quite a bit and at WOT there is a kind of machine gun chirping. It's hard for me to describe, but if you were to pair a whistling noise along with the noise made if you hum into a fan, that would be in the ballpark. When I heard that I backed off to 3/4 throttle and it went away. After that I noticed that the cowling was hot to the touch so I brought the throttle down to headway speed and went back to the dock.

After taking the motor into the shop I noticed that there was some peeling paint on the outside of the head, especially around the bottom spark plug.

I did a compression test a few hours later, the top reading 60psi and the bottom reading 58psi.

I decided to take the head off to see if there were any blockages in the water passages, but while doing so I noticed some threaded holes on the top of the powerhead that looked like they were missing some bolts. I looked at the parts diagram and I can't find anything that corresponds to it. I'll try to post a picture of what I'm talking about.

While removing the head, there was a trickle of water that leaked out. I tried for a second to remove the head gasket, but it immediately started tearing, so I stopped there until I got a replacement head gasket and some help from the esteemed members of this forum.

https://ibb.co/7JnZm53
https://ibb.co/5Y1n3tc
 
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I replaced the propeller this season too. My first thought is that the noise is related to that. I didn't replace the Prop Clutch Ring even though it looked a little worn.

I would say the chirping noise is around 900 beats per minute.
 
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60 psi is borderline. I have no idea what the noise is. Also can't say much about your overheat concerns, but that motor does not look like it has been overheated. The threaded holes are relics of bygone days, not used on your motor.
 
So that spot where the paint flaked off near the bottom spark plug isn't discolored? I always thought the head was made of aluminum, but I guess if it's made of copper then that color is correct.

How hot can the cowling get before it indicates a problem? It's not so hot that I can't leave my hand on top of it, but it's borderline.
 
Swarlos said:
So that spot where the paint flaked off near the bottom spark plug isn't discolored? I always thought the head was made of aluminum, but I guess if it's made of copper then that color is correct.

How hot can the cowling get before it indicates a problem? It's not so hot that I can't leave my hand on top of it, but it's borderline.
Click to expand...

OMC coated their cylinder blocks and heads inside and out with a red dip material to prevent corrosion. Unfortunately, paint often peeled off of that red material. That is what you are looking at. Yes, the head is aluminum under the protective coating.

Your statement about the cowling mystifies me. That engine should totally destruct long before the cowling gets too hot to touch. Or do we have a word definition problem? I take "cowling" to mean the fiberglass motor hood. There are spots on the engine powerhead that do get too hot to touch, the flat exhaust cover on the side of the cylinder block, for one.
 
I definitely mean fiberglass motor hood when I say cowling. The flywheel is wide open on that motor with the cowling off so I'm not about to put my hand inside while the motor is running.
 
I'm thinking about taking the exhaust cover off too to clean it out, am I likely to need to replace anything other than gaskets between taking head and exhaust cover off? Also what torque should I tighten head bolts to?
 
If it is a saltwater motor, those 50 year old bolts have been in place for a long time and it's going to take some time and talent to remove them. What gas oil ratio are you using???
 
bobbyc said:
If it is a saltwater motor, those 50 year old bolts have been in place for a long time and it's going to take some time and talent to remove them. What gas oil ratio are you using???
Click to expand...

Strictly fresh water use, I already removed the head bolts, it wasn't very difficult and I didn't feel like I was in danger of breaking them. They are pretty rusty though, so I'm going to spend some time cleaning those up before I put them back on.

I've been using a 50:1 gas/oil ratio.
 
I pulled the exhaust cover off a little while ago. I noticed that the bottom piston seemed to have a little line of scoring or abrasion on the wall facing the exhaust. I'll link some pictures of head, exhaust cover, and things they revealed.

https://ibb.co/X3Rf1sJ
https://ibb.co/q9935hw
https://ibb.co/585z7R8
https://ibb.co/svkgprW
https://ibb.co/PWKL3Sj

I watched a video by Dangar Stu about how cooling water passes through an engine. I expected to see some kind of passageways to separate input water from the exhaust gases, but maybe I just misunderstood how things work.

Any advice for clearing the gunk out of the water jacket around the cylinders?
 
Don't get too zealous about the water jackets, You don't want to remove whatever protective coating that remains. Hey, it held up pretty well for 50 years, don't you think? Gently scrape or brush out the loose stuff. Hose it out with some WD-40 if you wish. The gasket surfaces are very nasty and need to be cleaned up. As I remember it, the only passage that commonly gets plugged up is the one leading horizontally from the top of the exhaust cover left side. Down deep in that horizontal passage is a hole that is only around 1/8" diameter----more or less. Eveerything else is plenty big for free flow.
 
Regarding the head bolts, they were quite rusty when I removed them so I decided to soak them in vinegar to clean them up. After I brushed off as much rust as I could it looked to me like the threads weren't uniform for the length of the bolts. It looked like the threads were compressed or very close to the shaft of the bolt in some places. Is that something I need to worry about? I ran a die through all the threads, there were only a couple of spots I needed more than finger strength to run the die from end to end on the bolts.

The head bolts aren't available on the website as far as I can see, part # 0306418. They seem to be simple 1/4"-20 bolts that are about 1-1/4" long, so I may just visit the hardware store.
 
I'll bring one of the head bolts with me to the hardware store to make sure I get an exact match. Should I be worried about the bolts I have or just clean them up and put them back on?
 
I could use some advice on removing gaskets that have become one with the motor. The head gasket came off fairly easily and all in one piece, which makes me think maybe it wasn't the original gasket. The exhaust cover gasket however is another story. I got about 60% of it off in about a dozen separate pieces without a ton of trouble, but I'm having a really hard time with the last 40%. I heard that I shouldn't use scraping tools because they are likely to damage the aluminum, but I don't know how else I'm going to get the rest of the exhaust cover gasket off.

Edit: Wow that exhaust cover gasket was obliterated, could that have anything to do with the cowling getting hot?
 
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I suppose a scraping tool in the hands of Bigfoot could be a hazard. But I made a gasket scraper by grinding the end of a file to a not-too-acute-angled chisel shape 60 years ago, and have been using it ever since. Haven't damaged any aluminum yet (unless getting aggresivly stupid with it).

They make gasket release products now. I'm still old-school and haven't tried them yet. But someday----

Notice that exhaust cover is only cooled along one edge. The rest gets extremely hot. There's fire in there when running.
 
I think the noise I was hearing was from the prop, I replaced the prop clutch ring and it sounds fine now. Thanks for the help with the head and exhaust cover. I'm happy with how she's running.
 
Although you're happy with the way it runs right now... A couple things you may want to look into at some point down the road. In all of the above, I saw nothing about the magneto, however I may have overlooked it. At any rate...........
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(Replacing Regular Spark Plug Wires)
(J. Reeves)

If you also need the spark plug boots and the spring terminals that connect to the spark plugs, purchase them from your local dealership (OMC Part #581027). This includes one boot and one spring connector. Price is about $3.25ea.

Purchase whatever amount of spark plug wire you need. Be sure to purchase the kind that has a steel (or copper) twisted wire leading through the center of it....... not the carbon type plug wire that many automobiles now use.

Using your old plug wire, cut the new wire to a length about 3/4" to 1" longer. If you have no old plug wire, just make sure that the wire is longer than you'll need as you can trim the other end later.

The rubber boot, spark plug end.... With the wire cut to the length required, trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above. Holding the spring wire terminal, estimate where the prong should be inserted so that the spring will be flush against the exposed wire. Hold the spring terminal away from the wires end (sideways) and insert the prong into the insulation and into the center wire, then swing the spring terminal in front of the exposed wire portion (makes a tight fit for continuity purposes). Spraying the inner portion of the boot where the wire will insert with a small amount of WD40 makes the installation of the wire a easy project.

Now, the other end that slides into the magneto coil... Look into the awaiting hole of the coil and you will see a somewhat threaded tapered prong. Double check to make sure that the wire is cut to the length required (better slightly longer than shorter), trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above, then simply slide the wire into the coil so that the inner wire core of the wire is impaled by the tapered prong within the coil. That's it.... you're done.
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(Magneto & Driver Coil Alignment)
(J. Reeves)

To align the coils properly, have the metal vertical portion of the coil yokes aligned with the inside edge of the bevel that exists on the top portion of the aluminum seat upon which the coils sit. This creates the proper distance between the coils and the flywheel magnets. Faulty alignment creates friction and the yokes of the coils heat up, turn blue and expand.
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(Point Setting Of Magneto Models)
(J. Reeves)

Set the points as follows. Have the flywheel key aligned with the fiber rubbing portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.

NOTE 1: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key.

NOTE 2: Should the cam have the word TOP embossed on the top of it, that is a cam that could be installed upside down and this is simply telling you which side is up. It is not a position where one would set the points.
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I have a question concerning how tight the fit of the head bolt shaft should be to the holes in the head for the bolts to go through. I felt like there was quite a lot of play between the bolt shaft and the hole, I couldn't quite fit a 5/16" bolt through the holes, but there was room to spare for the 1/4" head bolts.

I saw fdrgator say that you should put gasket sealing compound on the threads, but should I put more on shaft itself to plug the gap?
 
No, don't worry about the clearance. That is ok, and actually made that way to give lots of room for corrosion to "grow" before it seizes. In other words, they acknowledged the reality that stuff happens.
 
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