1981 Johnson 35 Compression

[111torrance111]

I just picked up a 1981 35 hp Johnson outboard, the overall condition looks ok, but I have a compression question. 3 pulls per cylinder resulted in 75Lbs and 80Lbs. I think the 5 Lbs differnce is Ok, but how low can the compression be before you recommend a rebuild?<br /><br />And what do I give up by having low compression, I assuming top end speed?<br /><br />Jerry

 

[wilde1j]

Re: 1981 Johnson 35 Compression

Pulling over by hand is tough ... 75 to 80 psig should be fine. When compression gets too low, max power is reduced. BTW, 5 psig delta is fine ... up to 10% variation is allowable. Just use it and enjoy.

 

[111torrance111]

Re: 1981 Johnson 35 Compression

Thanks Wildeone...<br /><br />I haven't acually started it yet, I'm just makeing sure I know what I'm doing first. I do have a manual, but it generic for motors from 2 HP up to I think 75 HP. It's sure makes it hard to find what your looking for when they cover so many differnt engines.<br /><br />Once I try to start I may have more question to come.<br /><br />Thanks for the help.

 

[OBJ]

Re: 1981 Johnson 35 Compression

111...did you keep pulling till the press gage stopped going up? Did you have both spark plugs out and the spark plug leads across a spark tester...this is just to protect the ignition system components.<br /><br />I don't think just three pulls is going to tell you the real compression....unless it's zero.

 

[111torrance111]

Re: 1981 Johnson 35 Compression

I had both spark plugs out, but I didn't have the leads going to a tested.<br /><br />However I did put a little only in the cylinders over night and tried starting it up today. it seems to run fine.<br /><br />I changed the gear case oil which was dirty, the water impeller seems ok as I get plenty of water traveling through the engine.<br /><br />The last thing to do is test it in the water....<br /><br /><br />Thanks/Jerry