What compression is good for 1983 Johnson 70 Hp?

[My Limit]

I'm thinking about buying a boat with a 1983 Johnson 70 HP. I have a compression test kit and want to test this motor. I know that I want the numbers to be within 10-15 PSI of each other or the lowest to be 90% of the highest. <br /><br />What I don't know is what is the acceptable range for this motor? Does anyone have any specs on that? <br /><br />Thanks,<br /><br />My Limit

 

[Paul Moir]

Re: What compression is good for 1983 Johnson 70 Hp?

Welcome to Iboats!<br /><br />There are no published specs. OMC never did it and I think I appreciate why. Compression tests are absolutely affected by many variables. The temperature of the engine, altitude, and the tester itself all play a great roll. Even having the throttle plates open vs closed has a small effect.<br /><br />So, the answer is simply over 90 psi (generally speaking) and much more importantly no more than a 10% variance between cylinders. That said, the triples usually came in well over 100 psi, around 120-140 by most people's gauges and environment.

 

[Marauderk]

Re: What compression is good for 1983 Johnson 70 Hp?

My 77 has 130 to 132 on all three if this helps

 

[My Limit]

Re: What compression is good for 1983 Johnson 70 Hp?

Thanks alot guys! I'm really glad I found this site!

 

[Chinewalker]

Re: What compression is good for 1983 Johnson 70 Hp?

My 1980 punches the gauge over 140 with about a 3psi variance...<br /><br />- Scott

 

[REELSPORT]

Re: What compression is good for 1983 Johnson 70 Hp?

My 1969 55hp has 135 on each cylinder.

 

[TPD211]

Re: What compression is good for 1983 Johnson 70 Hp?

My 1993 88 SPL (V-4) says 128 in each cylinder, 1-2 psi defference, with throttle open, cold engine.

 

[Bradg]

Re: What compression is good for 1983 Johnson 70 Hp?

I have the same engine and it's 120-125.