1989 70HP EVINRUDE COMPRESSION

PROFESSIO

Cadet
Joined
May 24, 2005
Messages
10
HI, I HAVE A 3 CYL. 1989 70HP EVINRUDE, WITH THE ENGINE WARMED AND THE PLUGS OUT, THE COMPRESSION WAS APPROXIMATELY 100 PSI IN ALL CYL. DOES ANYONE KNOW WHAT THE NORMAL RANGE IS (IS THIS LOW)AND WILL I EXPECT TO REBUILD THIS SOON? I WAS TOLD THAT 120-140 PSI IS OPTIMAL AND AT AROUND 100PSI IT WONT LAST TOO MUCH LONGER. ALL CYLS HAVE EQUAL PSI AROUND 100.
 

REELSPORT

Petty Officer 1st Class
Joined
Apr 14, 2005
Messages
235
Re: 1989 70HP EVINRUDE COMPRESSION

The book on it says that the amount of compression is not nearly as important as the consistency of compression between cylinders.<br />Since you have about the same of each cylinder that is a good sign and I would not worry about the amount so much. That motor might have low compression head gasket on it.
 

PROFESSIO

Cadet
Joined
May 24, 2005
Messages
10
Re: 1989 70HP EVINRUDE COMPRESSION

thank you for your quick reply. so then there is no particular psi number that becomes the turning point for rebuilding? since i am at 100 psi in each cyl now and i was told that that is roughly the minimum requirement, i was concerned that only a small amount of use/wear will drop it below 100 psi and give a hard start and ultimately force a rebuild. any idea how accurate this is?
 

REELSPORT

Petty Officer 1st Class
Joined
Apr 14, 2005
Messages
235
Re: 1989 70HP EVINRUDE COMPRESSION

I think that the 100 psi is on the low side but just run it for a while and see what happens. You might want to run a can of deep creep made by seafoam to decarb it and get any carbon away from rings that might help compression.
 

REELSPORT

Petty Officer 1st Class
Joined
Apr 14, 2005
Messages
235
Re: 1989 70HP EVINRUDE COMPRESSION

I think that the 100 psi is on the low side but just run it for a while and see what happens. You might want to run a can of deep creep made by seafoam to decarb it and get any carbon away from rings that might help compression.
 

Solittle

Fleet Admiral
Joined
Apr 28, 2002
Messages
7,518
Re: 1989 70HP EVINRUDE COMPRESSION

Not to worry - - If you had 1 cylinder at 110, one at 80 and one at 100 then you might start thinking about doing something. But if it starts OK and runs OK then the compression readings don't mean much.
 

John McFarlane

Petty Officer 2nd Class
Joined
Jan 14, 2005
Messages
116
Re: 1989 70HP EVINRUDE COMPRESSION

At the end of the day, how does the engine run? Have you noticed a change in performance? Is it using too much petrol? Is it unreliable?<br /><br />Leave well enough alone. If you worry enough you will invent a problem.
 

PROFESSIO

Cadet
Joined
May 24, 2005
Messages
10
Re: 1989 70HP EVINRUDE COMPRESSION

thanks for the info guys. i just bought this motor and am hoping to get a season or two out of it before any major work. i'll try that deep creep too, if i can find it!! <br /><br /> thanx again, rob
 

dajohnson53

Lieutenant Commander
Joined
Apr 28, 2004
Messages
1,627
Re: 1989 70HP EVINRUDE COMPRESSION

You can usually find both Deep Creep and Seafoam at autoparts stores. I've bought it at NAPA and Schucks, fwiw. Both Merc and Johnson/Evinrude - and I believe Yamaha - all sell comparable products, so their dealers will have something you can use as well. The FAQ has two methods of decarboning explained, one uses aerosol, one liquid.
 
Top