Mercruiser 140 3.0L supplies

rlrobian

Cadet
Joined
Oct 14, 2012
Messages
29
Folks,
I'm not exactly new to boating but I just picked up a 1971 Glastron Starflite with a Mercruiser 140, I/O. The boat has sat idle for about 7 years. The engine is free, turns over, and has compression of 130, 130,125, 60 in cyl 1, 2, 3 & 4. Not sure why #4 is low, initial thinking is valve. Tested the ignition system and have a nice big blue spark coming from the coil and occasionally from one or more of the plug wires. So present plans for it is to replace, rotor, cap, wires and plugs with new.
My question, to this great body of knowledge, is where to source parts? Also can I get over the counter parts from my local auto parts guys for this engine. The engine was made my GM, then somehow modified by Merc I presume for the cooling. But how much is still GM stock and which engine do I tell the AutoZone guys to use for locating the parts?
Thanks
RL
 

ENSIGN

Lieutenant Junior Grade
Joined
Jun 21, 2009
Messages
1,179
Re: Mercruiser 140 3.0L supplies

You need to do a cylinder leak down test on the engine FIRST.There's no point in wasting money on a engine with only 60 pounds of compression in one cylinder.
 

rlrobian

Cadet
Joined
Oct 14, 2012
Messages
29
Re: Mercruiser 140 3.0L supplies

Thanks, I did a quick test. I squarted some oil in the #4 cyl. Did a quick compression test and got 90#. That is even a little more confusing. But with 3 of the 4 cyl right on the money after 7 years of sitting makes me suspect a stuck or burnt valve. Not ready to bail out on the engine yet, still testing.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Mercruiser 140 3.0L supplies

For an engine that has been sitting for a long time, get it running for a few minutes before you worry about the compression.
 
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