1978 50hp Mercury compression?

witty888

Cadet
Joined
May 12, 2013
Messages
6
Hi,
I have a 1978 50hp mercury that I am trying to bring back to life after being stored for over 20 years in a barn. I have done a compression test. I have been told that all cylinders should be within 10% of each other. My numbers are 125,128,105,130. The motor has no spark. Before I start buying electrical components, are these numbers good enough to contenue or should I quit while I'm ahead? The motor looks brand new inside and out. Seems like such a waist if it never gets wet again.

Thanks, Dave
 

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: 1978 50hp Mercury compression?

The cylinder with the low reading could just need a decarbing to loosen the rings up some. Lay it down and use a decarbing spray in all the cylinders and let it set for a day then run another compression test to see if the soaking worked. When doing the test, have the carbs in the WOT position and it very well can make a difference. JMO
Oldman570
 

witty888

Cadet
Joined
May 12, 2013
Messages
6
Re: 1978 50hp Mercury compression?

I probably should have mentioned that the motor was frooze up when I got it. It spent a week upside down getting a couple onces of karosine in the cylinders two times a day. It turns freely now. Do you think the decarb spray might still help?
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1978 50hp Mercury compression?

Any engine that I receive in a frozen condition gets disassembled for a thorough inspection. It is far to easy to get some rusty bearings freed up, only to have them come unglued a short while later with catastrophic results. Even if it was only the rings stuck to the cylinder wall causing it to be stuck, you can easily unstick the rings when disassembled. Freshen it up with new rings, gaskets, replacing any bearings that are questionable, and then you won't have to worry about it...
 

witty888

Cadet
Joined
May 12, 2013
Messages
6
Re: 1978 50hp Mercury compression?

Sounds like really good advice. I have never taken one apart that far. I only paid $75 for it. Maybe this is the one that I see what's on the inside.

Thanks a lot, Dave
 
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