1983 140hp V4 Johnson compression test...

[dfrants]

This is the 99.6 c.u. model. what compression should it have? the one I found the guy says it runs great, pulling the kids tubing and all that but he said three cylinders have 110psi and one has 90psi. would a motor with these numbers even produce 140 horse power?

 

[Joe Reeves]

This is the 99.6 c.u. model. what compression should it have? the one I found the guy says it runs great, pulling the kids tubing and all that but he said three cylinders have 110psi and one has 90psi. would a motor with these numbers even produce 140 horse power?

No, sure wouldn't. Besides... that indicates a 20 psi compression difference between the highest and lowest cylinder reading which in turn indicates powerhead internal failure. Suggest you pass that offer up.

 

[oldboat1]

ed.

 

[boobie]

Agree with Joe !!

 

[oldboat1]

^^I do too. Only question I have is what you (dfrants) are into -- don't recall from prior posts. If working on the motor for the guy pulling his kids, he may be satisfied with whatever power he has (for as long as it lasts). The motor needs a rebuild to produce 140 ponies. If you are buying it with a rebuild in mind, hard to say what would be best. If you are looking at it as a runner, I would definitely pass (like suggested).

 

[dfrants]

I was looking to repower a 17' Nitro Bass Boat. How would a "newer" Johnson 115hp, say a 1988 model compare with the older 1978 140hp?

 

[interalian]

The 'newer' 115 is about the same power as the 'older' 140. They switched from flywheel rated hp to prop-rated in the mid-80s.

 

[Joe Reeves]

The 'newer' 115 is about the same power as the 'older' 140. They switched from flywheel rated hp to prop-rated in the mid-80s.

Strange.... I've also heard this statement from other technicians. I think it strange because I have a vivid memory of my early years with OMC of a 1962 Johnson film commercial of a 1962 40hp Electric Shift model, and one of it's strong selling features was that the horsepower was rated at the propeller. This feature was used at that time against the Mercury Corporation whose horsepower was measured/calibrated at the power-head.... puzzling!

 

[interalian]

Strange.... I've also heard this statement from other technicians. I think it strange because I have a vivid memory of my early years with OMC of a 1962 Johnson film commercial of a 1962 40hp Electric Shift model, and one of it's strong selling features was that the horsepower was rated at the propeller. This feature was used at that time against the Mercury Corporation whose horsepower was measured/calibrated at the power-head.... puzzling!

It's been bandied about here for so long it's become gospel (or interwebs wisdom), and repeated. Now, who actually knows for certain?

 

[dfrants]

found some literature from OMC from 1984. "All Johnson models horsepower ratings: All ratings are BIA brake crankshaft horsepower rated in accordance with standard BIA 310-78."