Logo
FULL SITE MENU

Was I ripped off??

D

Denise99

New member
I recently purchased a small boat with a Mercury Magnum 40 engine. The seller started the engine and after a couple of starts it seemed to work fine: he said 2 of the cylinders have great compression (don't know what that means). I know nothing about boats or outboard engines so I trusted what he told me.

I never thought to ask him about an engine serial number and I can't find a serial number anywhere on the engine, and when I took the cowl off I noticed 2 of the spark plug caps were not fully pushed onto their plugs.
Did I buy a Mercury Magnum 40 or a pieced together Frankenstein engine with a Mercury Magnum 40 cowl??

I have enclosed a few photos of the engine....maybe someone can tell me what I bought just by looking at it :)
 

Attachments

  • 4170.jpg
    4170.jpg
    44.5 KB · Views: 25
  • 4169.jpg
    4169.jpg
    54.9 KB · Views: 27
  • 4168.jpg
    4168.jpg
    49.4 KB · Views: 26
  • 4164.jpg
    4164.jpg
    53.2 KB · Views: 30
  • 4165.jpg
    4165.jpg
    51.1 KB · Views: 33
  • 4166.jpg
    4166.jpg
    46.3 KB · Views: 34
Good compression means that the cylinder is healthy and sealing well. You want all the cylinders to have good compression near to what the factory-new specifications are. The readings should all be within like ten percent of each other. You use a compression gauge in the spark plug hole and crank the motor, looking at the highest reading on the gauge. You do that with each cylinder and compare the numbers. If all are within a few PSI of each other then you know the engine is pretty healthy. Any shop can do this test for a few bucks.

Oh and yeh that's a Mariner 40. Serial number should be somewhere on the transom bracket that holds the motor on the boat.
 
If the other 2 cylinders have low compression it means a rebuild is in order.----And before you ask this motor does NOT have a head gasket !----These are a wonderful motor if in good condition.----Best replace water pump impeller before your first fishing trip.
 
Thank you for answering:)...I don't know much about boats or outboard engines so I am learning as I go. I bought the boat on a whim thinking I'd take my boy out for some fishing.

How could you tell it was a Mariner 40??

The seller said it used to be fuel injected but it was taken out for some reason...
He said 2 of the cylinders had good compression - so now I know why only 2 of the 4 spark plugs were connected - it is only running on 2 cylinders not 4. Is this something that can be fixed?

I also primed the gas bulb and gas shot out of a brass looking screw on the right side of the top carburetor. Is this dangerous to operate??
 
This a a 2 stroke engine.-----It runs on 50:1 gas oil mix.-------It had automatic oil injection which was likely removed.-----It never had FUEL INJEECTION.-----It is a carbureted motor.----Time to get a manual.------Operator / owner manual.----Do some reading before you turn the key to start it.
 
Take it to a shop and have it checked out/gone over. It's gonna cost, but nothing free or cheap ever is.
 
Back
Top