Broke Spark plug threads, pulled head, scored cylinder?!

[BigB9000]

Year is 1969 Johnson 20 hp. I was working on the ignition system (new coils, points, condensers, wires) while rotating the flywheel, I heard some hissing by the cylinder head. Turns out it was the top spark plug. Went to pull it out, and the threads came with it.

Bought the new head

Then pulled the old one off, and found a slight, but noticeable scratch in the bottom cylinder.

Compression prior to breakage was 80psi even in both. Ran and sounded great. A little hard to start, and took a pretty strong arm to pull, otherwise fine.

Did I just waste $20 on a cylinder head, for a motor that wont last long?
As long as the head is off, should I clean pistons or anything?

Old gasket came off in one piece, should I buy a new one anyway?
Seirra make them? Johnson number is 306163, but I cant find it on iboats.

 

[bktheking]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

If compression is even as you state then it should run, it may get worse. Put a new gasket on it and run it, after all it's a 69 dude.

 

[kenmyfam]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

I'm with BK unless you want to pour a lot of time and effort into it.

 

[BigB9000]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

If compression is even as you state then it should run, it may get worse. Put a new gasket on it and run it, after all it's a 69 dude.

So use it until it breaks. sounds like a plan.

I got $70 into the thing too!

 

[14ftgrumman]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

I'd pull the powerhead and change out the piston. I'm not one to let things go from bad to worse just for the heck of it.

Price used outboards of this size. It is worth the money to repair it. At the very least, you will know the condition, not taking a chance on someone else's problem motor.

 

[milmat1]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

If compression is equal I would want to see the other cyl as well. And Make sure the motor is getting lubrication properly. But with that said, You would be suprised to know how many motors are running with scored/scratched cyls out there...It will likely run for years to come........jmho

 

[jonesg]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

Year is 1969 Johnson 20 hp. I was working on the ignition system (new coils, points, condensers, wires) while rotating the flywheel, I heard some hissing by the cylinder head. Turns out it was the top spark plug. Went to pull it out, and the threads came with it.

Bought the new head

Then pulled the old one off, and found a slight, but noticeable scratch in the bottom cylinder.

Compression prior to breakage was 80psi even in both. Ran and sounded great. A little hard to start, and took a pretty strong arm to pull, otherwise fine.

Did I just waste $20 on a cylinder head, for a motor that wont last long?
As long as the head is off, should I clean pistons or anything?

Old gasket came off in one piece, should I buy a new one anyway?
Seirra make them? Johnson number is 306163, but I cant find it on iboats.

Looks like it overheated, galled the threads on the sparkplug hole and they stripped out. But why did it overheat.
I'd pull the exh plates and check the rings too, the scratches came from something. And use new gaskets, air leaks cause loose sparkplugs when pre-ignition damages the sparkplug threads again.

Its worth fixing right but you need to look a bit deeper yet.

 

[rodbolt]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

you may wish to check parts avalibility, last one of that design I did,25 hp 1973 model. the rod bearings were NLA and I got the last set at Rons marine.
the pistons were avalible but the stocking number indicated they were going towards NLA.
if you need the block bored call Rons marine and equipment in portsmouth VA.
he has bored omc and others for about 40 years and I have used him for almost 20.
?PS delivers.

 

[BigB9000]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

I'd pull the powerhead and change out the piston.

Would the piston need changing? wouldn't you need to bore it/sleeve it or something? I'm pretty good at most external repairs, but internal knowledge is what I lack.

If compression is equal I would want to see the other cyl as well.

other cylinder is fine, nothing weird in there.

The top hole striped, and the cylinder scratch is on the bottom piston.

The paint isnt flaking at all, just old and faded. doesn't look like it overheated...

 

[kenmyfam]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

Check for spare part availability like Rodbolt suggests. Then make your decision as to what to do.
My further 2 cents

 

[BigB9000]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

0383476 PISTON ASSY., Std. Not Available

Well thats out. rings and everything else are still available.

Wouldn't the cylinder and piston need work? not just the piston?

 

[kenmyfam]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

0383476 Wouldn't the cylinder and piston need work? not just the piston?

To do it right....yes.
2 more cents !!!

 

[wilde1j]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

You're not going to use a std piston if it needs boring. At least.010 or .020 oversize. Bore needs to be measured and checked for round before selecting OS. I would check availability of OS pistons and rings.

 

[Tim Frank]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

You said that the motor ran great before you started working on it.
Did you have it for a while or is it fairly new to you?

The scratch....is it noticeable by feel or by eye?

If you had some good use from it, and the scratch is not "feelable" I'd clean any significant carbon off the pistons while you have the head off..slap the head back on with a new gasket, and enjoy it some more.

 

[BigB9000]

Re: Broke Spark plug threads, pulled head, scored cylinder?!

and the scratch is not "feelable"

Oh you can feel it. imagine getting a needle and putting a half inch scratch your cars paint job. thats what it feels like.

I have had it for awhile, but never had it in the water.
I have an 18hp power-head, maybe ill swap that over.