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1980 Mercury 80 HP 4 Cylinder

L

lovethatblackmotor

New member
"Water pump impeller failed bu

"Water pump impeller failed but motor was shut down very quickly. Impeller replaced. Bottom 3 cylinders 150 pounds compression and spark plugs look like new. Top cylinder 135 pounds compression and slight coating of grey flecks on spark plug. Motor starts and runs like always. Questions (1)Can I run this without further action, and (2)What are the chances that work will have to be done to that cylinder...and if work is required, what would it involve and is it something that a mechanically inclined person can do themselves? Thanks in advance for any help!! BW PS - There is a fin (or pieces of a fin) from the old impeller in there somewhere. Should I be concerned about that, and is there anyplace I can open up easily to get them out?"
 
"Bob, rule of thumb - as long

"Bob, rule of thumb - as long as all the cylinders are within 10% of each other, they are ok - so 150 to 135 is within the limits.

OMC/BRP (Johnson/Evinrude) has even taken that a little further and they consider 20% difference to be "within spec".

If/when the time comes to tear it down and rebuild (or re-ring and hone or bore out the cylinders), yes, someone that is somewhat mechanically inclined can do about 90% of the work required (I always use a machine shop to bore or hone cylinders and recommend any home rebuilder do the same - they just know what they are doing).

The piece of impeller may be a point of concern since if it hasn't "passed", could cause a clog resulting in an overheat which could fry the engine.

If you can back flush the engine with the lower unit off that will often clear the water passages, or compressed air can do it if it's stuck in the water tube, but sometimes it will call for more drastic action such as pulling the powerhead or removing water jackets or heads - just depends what you have lodged where..."
 
Thanks Graham...there obviousl

Thanks Graham...there obviously was some "damage" to that top cylinder (from what was found on the plug). Can/should compression be my only indicator of whether to use it without further intervention? BW
 
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