57 Johnson 18hp rebuild questions

[Hanr3]

Yep, I own a 57 18hp Johnson that doesn't seem to be running properly. Top speed varies between 6-8mph pushing my 14' boat and me.

I have the owners manual, am mechanically inclunded, but could use some troubleshooting help.
Point me in the right direction. #-o

 

[Pappy]

More information would be helpful here.
Compression? What exactly is the engine doing? Is your top speed 6-8mph or are you varying that much? Are you running the engine on 24:1 fuel/oil ratio?
Give us more information and we can better help you.

 

[jasper60103]

Agree^^^. Start with testing compression and spark. Compression testers can be borrowed (free) from some auto part stores like O'reilly or Autozone. Spark testers are cheap (~$6-7). Let us know if you need help performing these tests.

 

[ultra353]

probably running on 1 cylinder, check for spark

 

[Hanr3]

I'll check everything posted once i get back into town and keep you posted.

 

[MacDaddy21]

Once you test compression, go ahead and rebuild the fuel system. Get a rebuild kit for your carb, and one for your fuel pump, and all new fuel lines, and a new inline filter to go between the fuel pump and the carb. When you rebuild the carb and fuel pump, disassemble both parts completely, and soak all metal parts in a gallon container of Chem-Dip. Then rinse with water and dry them, and then re-assemble with your new parts. If your motor is running to begin with, but just lacking some speed and power, it is highly likely that it is fuel related.

I rebuild old Mercury's so I've been around plenty of them with this issue. One as old as yours is probably in need of a new/rebuilt fuel system. The jets in the carb can get clogged, and after enough time the liner of the fuel line can start deteriorating and bits and pieces of it will clog up the fuel inlet on the carb bowl which restricts the flow of fuel. Most carb rebuild kits come with new gaskets and seals. Generally the float and needle and seat are sold separately. Everything is cheap, and shouldn't cost you any more than $30. Fuel line from any auto store is fine to use, just get the right size. Its been awhile since I've done a Johnson, but I don't think the last one I did came with new jets in the rebuild kit. I think the majority of the jets on older motors are pressed in. Try to check the jets for clogs. Generally you can get a small pipe cleaner brush or piece of wire and run it down the jets to remove any debris after it has soaked in the Chem-Dip for several hours. Harbor Freight sells a little brush kit for cleaning their HVLP paint guns for less than $2, and that is what I used to clean my jets, and other fittings on my carb and fuel pump. Hope this helps.

 

[Pappy]

Once again, more information would be nice. Even though you replied you still havent said what the engine is doing/not doing!!
Second, a ton of misinformation.
One - your engine is not equipped with a fuel pump unless someone converted it to one so don't bother looking for it.
Two - you have no fixed jets in your carburetor. Both the low and high speed mixtures are fully adjustable
Three - OEM carb kits come with all necessary gaskets, seals, float, needle & seat, etc,. Off brand kits do not.
Four - You do not want to install any filter between the fuel pump and carb. That would put it on the pressurized side of the system for one (dangerous) and would allow debris to enter the fuel pump (if you had one) and keep one of the umbrella valves open for two.
Once again, if you will take the time to give us a run down on what the engine is doing we can short cut a cure for you.

 

[Hanr3]

Sorry for the delay, I was out of town all week for job training.

This week I'll test compression and spark.
Here is a quick history since I have owned the motor, on my 3rd year of ownership.
Replaced both coils, points, spark plug wires, spark plugs, basicaly replaced all components in teh electrical system.
Rebuilt the carb, and bought a 2nd carb, rebuilt it too.
I don't have the original quick connects at teh gas tank to teh fuel hoses, however I run teh hoses straight to the tank. I did rebuilt the gaasket ont he gas tank. The tank holds pressure and doesn't leak. I replaced the fuel hose with a larger diameter hose and the vacuum hose is smaller in diameter.
I timed the engine to the carburator linkage per the owners manual.

Observations-
The engine appears to be running properly, however it doesn't seem to hit high rpm's. I did have a rubber bushing in the propeller break free on the river bottom, the engine rpms went way up. Almost seems like the engine wont get to high rpms due to load.
That being said.

I can start the engine in one or two pulls, with a routine and both hands. Routine being, place in nuetral, turn trottle to high (as high as it goes while in neutral), push the primer, and pull the chock out (partially if warm, and fully if engine cold or its cold outside). Once the engine fires and runs, push choke in, shift her into forward and away we go.

Compression- last year I checked it. One piston maintained around 105psi. The other wouldn't. I pulled the head off and found a small chunk of the piston wall missing, filled that in with JB Weld and a new gasket. The piece missing was no wider than my finger nail, and about 1/16" deep, it was located at teh very end of the piston wall.
Last fall I torn up my shoulder doing a one hand start. The rip cord stopped while pulling, and I ended up with a partial tear in my rotator cuff muscle, and a torn bycept muscle. Has surgery this summer to fix them both. Now its a two handed pull start. IF I use my other arm, I cant pull it fast enough to fire and run.

Like I said earlier in this post, Ill chek compression, and spark this week. Would you like to video in a barrel too?

Correct, no fuel pump. Still the two line gas tank.

Maybe related, maybe not. There appears to be a plastic idle adjustment on the tiller handle that is broken off.

 

[Pappy]

There is no idle adjustment on that handle.
As far as I can read, the only issue you are having is from the hub in your propeller.
Take your prop to a dealer and have them send it off to be re-hubbed. You will then have your top end performance back. You are definitely on borrowed time with that prop if you leave it as is.
You should be running no less than 24: fuel/oil mix in that engine, are you? Those engines are non-replaceable and should be run on nothing but the proper mix.
You never mentioned what your current compression is on the damaged cylinder. The mark at the edge of the piston may be indicative of a broken ring that caught a port, broke, and got caught between the combustion chamber and the piston before exiting the exhaust ports. What is your current compression on that cylinder?

 

[Hanr3]

Alright, finally had time to work on the engine. Only took 5 months. #-o

Yes, 24:1 fuel /oil mixture.
Compression-
Top piston maintians 65ish psi,
Bottom piston maintains 110psi.
I own a compression tester, and yes I removed both spark plugs prior to testing either of them.

Top piston spark plug is cleaner than the bottomw, but has carbon build up too,
Bottom piston spark plug show signs of burning.

I rebuilt the Carb last year and replaced both fuel line, cleaned the fuel filter. No fuel pump, dual line pressureized system. I also replaced the fuel tank gasket and I know if holds pressure.
I still had problems and bought a used carb off ebay and rebuilt it too. Same issues.

Replaced the coils, condensers, adjusted gaps, replaced points, and adjusted gaps, replaced spark plug wires, and replaced spark plugs too. Basically I replaced everything on the ignition system, from the coils to the plugs.

 

[Pappy]

Pull your cylinder head first and see if the head gasket is blown, possibly into the adjacent water jacket. We can then go from there.

 

[Hanr3]

Replaced teh head gasket last year. Still getting low compression on one piston.

My thinking is a broken piston ring.
The low compression piston holds 60 psi, and did all night long.

 

[Pappy]

Okay, at this point the engine will have to be disassembled and rebuilt in order to bring the compression back into spec. Good news is that the engine is and will be a workhorse for you for many years if you pursue this.
All gaskets are available through a local dealer for the rebuild. Havent checked on the hard parts lately but surely they can be sourced easily. If you are hesitant about doing the work yourself there are members of the www.aomci.org that may live nearby that would be more than willing to spend some time with you and help you through the process.

 

[Hanr3]

Thanks Pappy.

Rebuilding it doesn't bother me and I look forward to it. Thanks for the link.

What I lack is knowledge about specific things to watch for, tips, and tricks, or more importantly things I need to pay particular attention too, like orientation of critical parts, etc.

Hard parts, which hard parts should I replace?

 

[JFDBasser]

Hi hanr. I just picked up a 58 10hp rude. Found TONS ofinfo on the iboats board. Cool motors. Do you have the pressure tank?

 

[Hanr3]

Yes, I have a pressurized tank. I replaced teh gasket on the tank last year too. I know it holds pressure, actually the whole fuel system holds pressure all day/night long. I unscrew the gas cap slightly after Im done fishing to replieve the pressure and leave it loose until my next trip. When I unscrew the cap, I hear a swoosh as the pressure escapes. Kinda cool actually.

Thought about convertering to a fuel pump, but it works so I dobut I will mess with it.

 

[Pappy]

By hard parts I mean parts other than the flexible gaskets and so on. No way to know what you need until you get into the engine. When pulling the crankcase halves apart note that there are two tapered locator dowels that must be driven out. Easy to do but some folks never know they are there.

 

[Hanr3]

By hard parts I mean parts other than the flexible gaskets and so on. No way to know what you need until you get into the engine. When pulling the crankcase halves apart note that there are two tapered locator dowels that must be driven out. Easy to do but some folks never know they are there.

What the purpose of driving the pins out?

 

[Pappy]

When assembling the crankcase halves those pins are used to exactly align the halves for proper bearing fit and wear. On reassembly you will barely snug up the fasteners then drive the taper pins back into the block and begin initial torquing of the crankcase fasteners.