1990 Johnson 200 - "normal" compression numbers?

[metriccrescentwrench]

I took a new to me '90 Johnson 200 out for the first time yesterday and it didn't run well at all. To top it off the overheat alarm sounded after 15 minutes so I idled back to the dock and put the boat on the trailer (the alarm stopped after a couple minutes of idling). It has a brand new water pump, and water pressure was between 20 and 25 psi at all times when running above idle. I didn't have a lot of time to troubleshoot it last night, but did do a compression check and the numbers have me a little puzzled.

On the port cylinders I got 80, 76, 72; and starboard cylinders were all 72. That seems low, but since they're all close I wonder. I realize different compression gauges will read differently, as a point of reference my gauge shows numbers between 110 and 120 on my '81 Johnson 90 HP.

 

[red boat]

Re: 1990 Johnson 200 - "normal" compression numbers?

Metric I would try a decarb with some seafoam and see if those numbers come up a little. They say comperssion numbers should be within 10% between cylinders.

 

[JB]

Re: 1990 Johnson 200 - "normal" compression numbers?

Those numbers are just fine for a big OMC V6. They are within a 10% span and all over 60psi, which is the low end of typical range.

 

[metriccrescentwrench]

Re: 1990 Johnson 200 - "normal" compression numbers?

Those numbers are just fine for a big OMC V6. They are within a 10% span and all over 60psi, which is the low end of typical range.

Thanks JB. That information definitely helps.

Red, I'll probably eventually go ahead and do a decarb, especially seeing as how I know nothing of this engine's history.

 

[metriccrescentwrench]

Re: 1990 Johnson 200 - "normal" compression numbers?

I've learned a bit more since my last post on this subject. I also had a cooling issue with this engine and just got the parts installed that will hopefully take care of that. Now that it will run without cooling problems (at least on muffs - knock on wood for running on the lake) I let it idle until warm, then checked compression. Numbers were a little different than when it was cold. Port side was 72, 70, 70 and starboard side was 62, 62, 62. (I always had assumed that compression would be higher when warm, but I think I've just proven that theory wrong.)

From JB's post (thank you sir) indicating that 60 is the lower range of what to expect I'm not too concerned, but it was curious how the two sides were so even, yet that much different from each other. Then I noticed that it looked like there are two head gaskets on the starboard head. I measured the thickness of each head gasket as best as I could with calipers, and sure enough the port side was 0.060" and starboard side 0.100". I'm guessing that can probably explain the difference in compression numbers, but I can't for the life of me figure out why someone would put a perfectly good engine together like that. So.... I'm going to put on 2 new head gaskets (btw, best price I could find from trusted online stores was at iboats) - I kind of wanted to take a look inside the cylinders anyway.

 

[daselbee]

Re: 1990 Johnson 200 - "normal" compression numbers?

Any reading less than 90 is not acceptable to me.

 

[tvtech]

Re: 1990 Johnson 200 - "normal" compression numbers?

Not sure if this helps. My 93 200 has the following compression readings

Port Bank top to Bottom
108
104
104

Starboard bank again top to bottom

110
115
110

Nick.