Mercury 500 that has been running hot!

[Ricky_rich]

I recently bought this engine, and it appears to be a 67-69 model.
The previous owner had left the flush plug out when running the engine. So I guess the engine didn?t get any cooling. After this it lost a lot of power, still running but poorly.
I did a compression test, and here is the result. A bit low or?
1. 6.5
2. 7.0
3. 7.1
4. 7.5

 

[GA_Boater]

You need a different compression tester. Essentially you have zero compression with the tester used and the motor shouldn't be running.

You have to look inside the motor to what the cylinder walls and rings look like. Remove the transfer port covers and exhaust manifold cover/baffle to see the rings and walls.

 

[Scott Danforth]

I hope your readings are in bar, even then they are low. if so, you basically have between 94psi and 108psi

if they are in PSI, you are really really low.

 

[Ricky_rich]

Sorry guys, I'am living in Sweden and we use Bar over here. So this is the compressionnumbers in Psi
1. 94
2. 102
3. 103
4. 109

This is too low right? Is it the rings that first will be damaged if engine runs too hot?

 

[Scott Danforth]

Sorry guys, I'am living in Sweden and we use Bar over here. So this is the compressionnumbers in Psi
1. 94
2. 102
3. 103
4. 109

This is too low right? Is it the rings that first will be damaged if engine runs too hot?

usually the piston collapses or bores get scuffed. the only way to know is to pull it apart and inspect, mic the bores and mic the pistons.

however you may simply have stuck rings, so I would start with using seafoam or some other penetrating oil in the bores to see if that helps. let it sit a bit, then run the motor.

 

[GA_Boater]

Sorry guys, I'am living in Sweden and we use Bar over here. So this is the compressionnumbers in Psi
1. 94
2. 102
3. 103
4. 109

This is too low right? Is it the rings that first will be damaged if engine runs too hot?

No - I'm sorry, Ricky. I tried a conversion in case the numbers aren't PSI and went the wrong way. I hope I didn't alarm you.

Did you check compression with a warm or cold motor? Temperature can make a difference in readings.

Also, has the motor been unused for a while? Rings can stick from sitting unused, too. Follow Scott's advice about using some Seafoam or a fuel treatment to free rings.

 

[Ricky_rich]

No - I'm sorry, Ricky. I tried a conversion in case the numbers aren't PSI and went the wrong way. I hope I didn't alarm you.

Did you check compression with a warm or cold motor? Temperature can make a difference in readings.

Also, has the motor been unused for a while? Rings can stick from sitting unused, too. Follow Scott's advice about using some Seafoam or a fuel treatment to free rings.

I have actually never run the engine, bought it partly taken apart. But crankcase not taken off or apart. The previous owner didn?t fulfill the job, lost interest was the reason he told me, but you can never be sure. So now I have put it back together, and will try to start it someday soon. There is only a manual start, and I have to find a steady place to fix it when pulling the rope. The boat isn?t really ready to hit the water. Looks like Seafoam can?t be bought in Sweden, but I?ll find something similar, maybe WD40 will work?

 

[GA_Boater]

Sure you can find it in Sweden, but it's awfully expensive. http://www.envirosafe.se/webshop/vi...nt?prp=webshop/index/sea-foam-motor-treatment

There might a similar product available from a local dealer. Yamaha Ring-free is similar and Mercury has some fuel additives too.

 

[Scott Danforth]

WD 40 may work a bit. however you may need to tilt the motor (plugs up) to get such a light oil to creep where you want it. if you can find Yamaha Ring-Free or something similar, I would go that route.

 

[Ricky_rich]

WD 40 may work a bit. however you may need to tilt the motor (plugs up) to get such a light oil to creep where you want it. if you can find Yamaha Ring-Free or something similar, I would go that route.

I found a bottle of Omicron 636 in my garage, this oils has really good penetrating capabilities. So now the engine is tilted the way suggested and sprayed in plug holes.
I tried to pull the engine with plugs in earlier, it sure takes a man to start this engines by rope. :mad-new: The compression didn?t feel so bad when pulling...

 

[sutor623]

it sure takes a man to start this engines by rope. :mad-new: The compression didn’t feel so bad when pulling...

You ain't kidding brother!!! I had an older 650 4 cylinder with thunderbolt ignition, and MY GOD did it take everything that I had to get her to fire up. That and manual tilt/trim. After that motor I made an ode to myself that even my kickers will be electric start AND tilt/trim. Not worthing ruining a rotator cuff on a pull start. Rather do that with the cast net.

 

[Scott Danforth]

I found a bottle of Omicron 636 in my garage, this oils has really good penetrating capabilities. So now the engine is tilted the way suggested and sprayed in plug holes.
I tried to pull the engine with plugs in earlier, it sure takes a man to start this engines by rope. :mad-new: The compression didn’t feel so bad when pulling...

you should try pull starting one with 140psi in the cylinders. both hands on the rope, one foot on the transom and someone holding on to you so you dont end up in the water.