Do I have 2 weak cylinders on my 140 Johnson?

[Jeff2012]

Hello
I have an 84 boat with 84 Johnson 140. Had the compression checked and results when standing behind the motor were 130( upper port cyl), 122(bottom port), 114 (upper starboard), 116 (bottom starboard).
Does anyone know what the compression should have been when this engine was new? Should I be concerned with the 114 and 116 cylinders?
Also what do you think these current compression numbers mean for preformance compared to when engine was new in 84? I was told from a guy who wants to buy my engine the new 140 in 84 was 140 lbs on all 4 cylinders and that now my engine is tired.
Thanks

 

[Joe Reeves]

Re: Do I have 2 weak cylinders on my 140 Johnson?

With absolutely no intention of insulting your intelligence, just in case you do not know how the cylinders are numbered. Notice that when standing in back of the engine, looking at the spark plugs the top starboard plug (#1) is slightly higher than the top port plug (#2) which is slightly higher than the bottom starboard plug (#3) which in turn is slightly higher than the port bottom plug (#4). So standing in back of a V4 engine facing the spark plugs, the cylinders are as follows:

2.....1

4.....3

Normal compression would be 100+ psi, usually about 115 or 125... BUT the readings should be quite close to each other. Your readings are:

#1 = 114
#2 = 130
#3 = 116
#4 = 122

You have a difference in psi of 16 between #1 (Top Starboard) and #2 (Top Port)... really not too bad for a 1984 model. The difference may simply be due to stuck rings, in which case there is a solution you can spray into the engine while running to hopefully free them, worth a try anyway. Unfortunately the name of that solution escapes me but I'm sure another member will be along shortly with that info.

EDIT 11:07 PM 08/31/12...... "Seafoam" is the solution as per other members replies below.

 

[boobie]

Re: Do I have 2 weak cylinders on my 140 Johnson?

I've always used BRP Engine Tuner and had good luck. There is a product called Sea Foam you can also try.

 

[emoney]

Re: Do I have 2 weak cylinders on my 140 Johnson?

I'm surprised he's still wanting to buy your engine if he thinks it's "tired". Seafoam it. I had one of these motors and they're good 'uns. Drank a little gas, but rock solid.