compression

Joined
Aug 27, 2015
Messages
5
I have an early eighties 200hp Johnson we did the heads put it back together and have compression readings of 95 on the left bank and 75 on the right bank are these readings acceptable or do I need to rebuild the motor
 

1983 ercoa 21'

Chief Petty Officer
Joined
Jan 12, 2014
Messages
632
Welcome aboard
75 side is low .
are the heads the same part# ?
have you ran the motor to warm it up and check the compression?
what did the cylinder walls look like when you had the heads off?
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
The actuall number isn't so much of an issue, it's the difference between them that indicates a problem
 
Joined
Aug 27, 2015
Messages
5
Had the heads resurfaced new gaskets cylinder walls looked good also it was a cold compression test.have to check numbers on heads.I just purchased the motor for 300bucks
 

1983 ercoa 21'

Chief Petty Officer
Joined
Jan 12, 2014
Messages
632
All one sid being the low 75 would make one think maybe a head gasket but you have replaced it .
are you using a top of the line compression gauge?
I would find another gauge and retest.
if you have the same results I would fire it up on a decarb treatment on muffs to see if cleaning the carbon out would help.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Please post the part numbers of the heads on your engine. I purchased/ran a 1979 200 hp crossflow for a number of years, after complete overhaul. When originally purchased, it came with a set of 1983 324/325 low compression bathtub heads, the compression was initially 75-80 lbs at first startup after the overhaul. Once the engine got broken in, these low compression heads would make around 90 lbs compression. After removing them and installing a set of 457/457 stock 1979 heads, the compression increased to 110. With a set of high compression early 235 heads 872/873 heads, the compression ran 120. So, before you condemn the engine, check to see what heads you are running. Are they period correct? I've seen a lot of engines where one head was replaced and it was not a matching period-correct head. Make sure your head part numbers match the factory parts lists. Also, you can change compression easily with different heads.
 
Joined
Aug 27, 2015
Messages
5
I'm going to pick up the motor this weekend thanks to all the good advice. When I get there I will check the numbers on the heads since one bank was consistently lower I'm going with the head theory keeping my fingers crossed till I see the motor in person thank guys
 
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