1970 Mercury 80hp - Recommendations for compression testing

J

Jefduro

Recruit
Joined
Aug 14, 2013
Messages
1
Hi everyone,
I'm new to the forum. I recently was given a 1970 Sabre Craft Raider as a project for my son (10) and me. It has sat outside for 6 years with no long term storage procedures performed on it. The lower unit needs to be repaired because it had an ice blow-out so I have taken that off of the powerhead. Now I want to do a proper compression test on all cylinders. Given that it has been sitting for 6 years I'd like to inject some oil into each cylinder before I start pulling on it, in hopes of loosening any seized rings and just providing a general lube for it's initial testing.
Can anyone recommend a proper oil to put into the cylinders via the spark plug hole that won't cause issues later when I need to try and start the engine.

Thanks for your help!
 
E

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: 1970 Mercury 80hp - Recommendations for compression testing

WD40, Marvel Mystery Oil, just about any light oil will do, even TCW-3! Just be sure you don't try cranking the engine over with the spark plugs installed, after spraying with oil. It might have a tendency to hydraulic lock!

When you're doing the compression test, be sure the throttle is wide open. You want the cylinders to take in the max amount of air, to develop proper compression. All spark plugs should be removed for the compression test.

Since the motor will only crank-over in Neutral, when you shift to Fwd the shift interlock will disrupt power to the starter solenoid.

To crank over the motor in gear, run a jumper from the battery-side of the starter solenoid to the small terminal post on the solenoid which has a yellow wire attached. Use caution around the prop when you do this, since it's gonna turn!

Also be sure the ignition is off before jumping the solenoid.

HTH.............ed
 
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