Outboard top cylinder getting hot

[Dawnraider10]

Hi everyone, I have a Johnson 2 stroke 50hp 1983
I have noticed the top cylinder gets hot and bottom cylinder remains cool
The engine idles ok , I did a compression test on both cylinders readings at wot, top 120 and bottom 150 not to sure if they are ok. I have changed the water pump and water is strong through the tel tel and through the mid section. But still gets hot I am worried I have damaged the rings on the top cylinder. What I find puzzling is the top cylinder not been cooled
Any advice please
Dave

 

[jimmbo]

Welcome to iboats

A 30 PSI difference is not Good. Time to remove the Exhaust Cover and look at the Pistons for scoring, and to check for tension on the Rings.
BTW, on a 2 Stroke, you don't need to do the WOT thing when doing a Compression Test

 

[Crosbyman]

possible internal blockage any fins/parts missing on the impeller ??

tell tale is not always cooling water.... just an indicator the pump is pumping

salt water or lake water engine ??

checked thermostat ?? ,,, pull cyl head look-see cyl head and water jackets for crud build up

 

[racerone]

Lucky for you if motor has a blown head gasket.-----Remove head now to inspect.-----Tell tale water does NOT go through the engine block.

 

[Dawnraider10]

Thank you for all your replies
I will start to remove head ect what are the signs of a damaged head gasket? I havnt striped down a outboard before any pointer to look out for
Wont be able to check t stat untill I remove the covers
The motor has been used in salt water I never put in the water yet its my first boat hopefully I can get it sorted.
I will start the strip down tomorrow (Sunday)
Thank you for all your support

 

[jimmbo]

Signs of bad Head Gasket? Low compression is one, Water the Cylinder is another, When you remove the Head, the gasket itself might reveal the failure, but the Head and Block can sometimes also reveal the leak. You will need to check the Head for Warpage, and should Lap it to ensure a flat surface.
Been used in Salt water? That can make removal of Bolts and Screws a Challenge, don't be surprised if some break, hopefully with enough of the bolt/screw sticking out to grab on to it with Visegrips. A bit of Heat from a Torch, and it can usually be extracted. If not, then a Tread Repair Kit will be needed

 

[racerone]

A 1983 head will be warped.----They all are warped after 20 years , so a 40 year old head needs resurfacing.

 

[909]

Try removing the thermostat, and clearing the passages with water pressure or compressed air. A properly functioning thermostat assembly creates necessary restriction to adequately cool the top cylinder. You can also retorque the head bolts to see if your compression improves.

 

[tphoyt]

Did you use a temp gun on the heads? Just curious what the numbers were?

 

[Dawnraider10]

What should the torque be on the cylinder bolts? trying to find a service Manuel but cant find one that covers my engine. I did find one covering 1980 50hp would that do.
In answer to heat on top cylinder just felt it with my hand and it was hot to the touch

 

[racerone]

A 1980 model is the same.----I think 240 inch lbs comes from memory

 

[Dawnraider10]

A 1980 model is the same.----I think 240 inch lbs comes from memory

 

[Dawnraider10]

Good day everyone just a update I have removed front water jacket to find no t stat or spring and no poppet valve this motor must have had one. Could this be why the engine was getting hot. The other thing I noticed was the bolts were not very tight and all csme out with ease. Looks like someone tried to fix this motor on the cheap.
The water way around the head looks clean very little build up will give it a good clean any tip what to use
Do I need to remove the head now or the exchaust cover plate
Thanks Dave

 

[909]

Yes. See post #8

 

[racerone]

When motors overheat the head bolts usually end being loose.-----If an owner insists on running a motor after an overheat with loose bolts the head gasket fails.------Take the head off now.-----If there is no scoring then refacing the warped head and a new head gasket might be the fix.-----Just more proof that these fine motors are ruined by folks who simply do not maintain them.-----But at $120/ hr at many shops , many folks are scared to get proper help!

 

[saltchuckmatt]

Somehow I doubt the motor had 150 psi when it left the factory floor but maybe....a used motor should not test to 150. Something feels wrong with your test.

That being said, sounds like you have crud in your head. Remove head and check. Someone knew it had a problem and tried fixing it by removing the t-stat....a poor way to fix. If the pistons and cylinders look good than resurface the head by putting some sand paper on something really flat (I use a flat piece of granite) and do figure 8 patterns with your hand until the surface is flat again. New head gasket and see if your numbers improve

By the way, don't break the bolts, it's a major pain. Apply a small amount of pressure and if they don't spin, heat the head bolt and let it cool to shock it. You may have to do it many times over the coarse of a week to relieve it....I also use "cold spray" to cool it.

Patience is best here.

 

[Dawnraider10]

Head is now off no bolts snapped I think I have found the problem, top cylinder looks like a small piece of the piston has broken off

 

[racerone]

???----Those left the factory with 150 PSI or even a little more.----Time to tear it down for at least 1 O/S piston / rings.-----As per post #4 it was not your lucky day.----Bottom cylinder also suffered !!-----Make it 2 new pistons.----In my opinion it is worth fixing if you do the work yourself.-----But I would also tear down the lower unit for inspection reseal.----Be a shape to invest beer tokens in the powerhead and have lower unit issues a month later.----Lower units on those are not robust and can be scary expensive to repair.

 

[Dawnraider10]

Thanks for all the advice so far you all have been very helpful. The next hurdle is stripping down rest of engine, this I have never done, I will remove the power head next weekend any advice what to do first I will be ordering a workshop Manuel thank you once again

 

[racerone]

You will need a puller ( 3 bolts ) to take off the flywheel.----And a 12 point 5/16" thin wall socket for the rod bolts.