Compression on 83' 70hp Johnson

[smitty_bb]

I'm looking at buying an 83' 70hp Johnson, I did a compression test and the top cylinder was at 100 psi the middle was at 120 and the lower was 140. The motors sat up for a couple years and does not run. does the range from top to bottom sound bad? thanks for any help

 

[tashasdaddy]

Re: Compression on 83' 70hp Johnson

unless it is a really good deal, the numbers are out of line. could be just a head gasket. does it look like it has ran hot. any blistered or discolored paint. it is going to need some attention, carb cleaning and rebuild, water pump. what about spark, 7/16 blue spark. i would want the numbers with in 10% or each other..

 

[jay_merrill]

Re: Compression on 83' 70hp Johnson

I believe that "new specs" for that motor would be at 150 psi. The 140 value on the lower cylinder is good but the other two are not. The 120 isn't bad as an absoulute number but it is quite a ways off of the 140 value. The 100 psi reading is both too low and to far from the higherst value. As TD said, the problem could be minor and it could be major. Buyer beware!

 

[jtexas]

Re: Compression on 83' 70hp Johnson

140 on all three would be exceptional, 120 on all three would be fine, 100 on all three would be ok, just barely. but a difference of more than 8 or 12 lbs from best to worst says something's wrong. you might've did this already, but I'd test all three again just to rule out "operator error" ... otherwise I believe I'd want a peak inside the cylinders.