1974 Johnson 15hp compression readings?

[screwloose]

I'm looking at a used motor for my jon boat, its a 1979 Johnson 15hp tiller/manual start motor.
The thing looks clean, runs decent but a compression test shows only 108/109 psi.
The compression test was done with a rather new Snap On compression gauge. I had a neighbor go with me to check it out, he works in a new car dealership as a mechanic for over 30 years.
He seems to think its way low, he has an electric start 1980 15hp Johnson motor and his showed 143/145 psi on the same gauge. Both were checked by pulling the rope till the gauge stopped climbing.

The motor has a lot of new parts and has been run only in a lake according to the seller but I'm leery of why he wants to sell it since he just bought an almost identical Evinrude motor only a few years newer to replace it. He's got a repair slip from a local dealer for new coils, new breaker assembly?, new plugs, new water pump, new prop, and a new thermostat. The bill reads "revive motor from storage" He's looking to get the $685 they charged him out of the motor.
The motor looks super clean but the two main concerns is the compression readings being so much lower than my neighbors motor, and why he would go through all the repairs only to go buy another almost identical motor to replace it with.

Basically, if the compression is low, I don't care to bother with it. I'll find another, if the compression if fine, all else is minor.
It runs great in a barrel and seemed to run fine on the boat he had it on when I test ran it.

Is 108/109 psi low for one of these? Does it indicate a lot of wear?
Is our comparison between his 1979 15hp and a newer 1980 15hp legit or were there big changes over those years?

The model number is a 15E79E.

 

[JB]

Re: 1974 Johnson 15hp compression readings?

Both cylinders within 10% of each other, rope start. 108-109psi is fine.

 

[AlTn]

Re: 1974 Johnson 15hp compression readings?

in 1979 it would have come with CD ignition, no "breaker point" assembly, possibly someone has converted it back to points..I agree with JB as to the 108-109 psi being fine

 

[gozierdt]

Re: 1974 Johnson 15hp compression readings?

If you go to this article in "LeeRoy's Ramblings" (the best single source for info on these motors 1974-1992)

http://www.leeroysramblings.com/Johnson%209.9_15.htm

A little less than 1/2 way down, there are 4 pictures of different year motors. A 1979 motor should have the CD ignition module mounted on the port side of the cylinder block, as shown in the picture of the 1977 motor there (It's not real clear, but it's the black block and associated connector block right next to the spark plugs on the back of the block). If the motor you're looking at has points (like the picture of the 1974 motor), then somebody has replaced the original powerhead with an earlier one. One way to check this is to look on the top of the motor back near the head for a roughly quarter sized silver plug. On many motors, that plug is stamped with the original model number of the motor.

The compression figures are excellent for testing a rope start motor. Also make sure the telltale "pee" hole gives a steady stream of water, and that the cylinder head does not get too hot to touch for 10-15 seconds after idling for 5-10 minutes.

Is the new engine he got an electric start, or a long shaft? That may be why he's selling this one. But if it runs well on a boat, that's usually the acid test...

 

[boobie]

Re: 1974 Johnson 15hp compression readings?

Why does your heading say 1974 ???

 

[screwloose]

Re: 1974 Johnson 15hp compression readings?

The seller originally told me it was a 1974, but the model number and further investigation says its a 1979 model.
I tested two other 15hp motors in that same era, all gave me 135 to 145 psi, so to me that basically tells me his has a lot of wear.
The fact that he's not sure about the motor himself, and the fact that it may have points makes me think it may be made up from parts from prior years. The two motors I tested in comparison both had external coils bolted along side the cylinder head, the one I looked at for sale does not, both coil wires come from beneath the flywheel
Is it possible its a 1974 power head on a 1979 bottom section?
Either way I think I'm going to pass on it and find something newer. Maybe as the season here comes to a close more motors will come available.

 

[raczekp1]

Re: 1974 Johnson 15hp compression readings?

hi.
last year i did rebuilt 15 hp made in 1979, new rings instaled.after rebuilt i got 125ps/cyl.
but before i started to rebuilt compresion was 80psi/cyl
after rebuilt motor start first pull.

i got also 15hp evinrude made in 1996,compresion was 110/cyl.maotor also start first pull.run fine,

now i got 15hp motor as a rebuilt project.upper cylinder 110psi, bottom one 60psi(broken ring, but not scored cylinder)

so in my opinion 110 is fine.motor will be ok for few years.i think will start first pull also

 

[screwloose]

Re: 1974 Johnson 15hp compression readings?

The model number said 1979, the power head looks like a 1974. I think I did the right thing in walking away from this one, I passed on it and a guy down the road bought it.
It ran ok at first for him but died after he was a few miles from the dock, and wouldn't restart. It lost spark, and he later found it lost compression, after a tow back to the dock the compression showed as only 62/58 psi. It was pumping water fine, it ran cool after about 20 minutes in a barrel, so I don't think it overheated, but its toast now. The guy that bought it sort of bought it out from under me, he offered him more and it sold before I actually could tell him I wasn't interested. The seller had it listed at $750 on CL, this guy offered him $850 cash the morning after I looked at it. I was only really interested if I could have gotten it a lot cheaper, after seeing the mix matched years and all the unknowns, I wasn't up for the gamble. The guy that bought it came by here looking to sell it not running for cheap. I told him I'd go $50 tops with the idea of just parting it out, but he wanted $500 for it.
You have no idea how glad I am its not my problem now.

I do have a line on a cheap 9.5hp that runs fine, and those are lighter yet. That motor has 115 on both cylinders and starts first pull, he's selling it because he bought a brand new four stroke with electric start. I'll get to try it too before I buy it too. He wants $350 for it but has receipts for a new water pump, new plugs, new points and coils, and a new prop and lower unit reseal job at the dealer. They also rebuilt the carb a year ago.
He's bringing it over and we're taking my tinny out on the river fishing this week, so I'll get a good idea what it runs like first hand.

Its a lot cleaner but a year older and a different style motor. I also think I like the lower profile, even though its less hp.

 

[raczekp1]

Re: 1974 Johnson 15hp compression readings?

dont take this 9.5,its not good construction,
look for 9.9/15 hp.its much better motor and parts is plenty around

 

[screwloose]

Re: 1974 Johnson 15hp compression readings?

Why is the 9.5 not a good design?

I sort of like how low it sits on the transom.
From what I found online, they made this motor for many years.
The one this guy has is from 1973.
It seems like every newer motor I've looked at is either big money or needs big repairs.
I looked at one this morning that the guy said ran fine but it had no compression on the lower cylinder and the lower unit had a huge hole corroded right through around the lower water intake. To me a motor like that is junk. I'd rather have a clean older motor than an abused later model.

 

[starcraftkid]

Re: 1974 Johnson 15hp compression readings?

I never heard anyone say the 9.5 wasn't a good design before.
I own five of them and really like those motors. They're far easier to work on than the newer 9.9, they're lighter, and they're plentiful.
Personally I see far more clean old 9.5hp motors than I do 9.9hp motors from the later years.
Just off hand, a few advantages I've seen is that you have a far simpler pin style prop, an easy to work on carb, you don't have any expensive electronics to fail, and they can be had for a lot less cash.

I own a few newer motors too, but my go to motor in the 10hp range is my 1973 Evinrude 9.5hp.
The 9.9 does make a bit more power, but it weighs more too. On a very small boat, the 9.5 is the better choice.
Neither hold up well in saltwater if you don't flush them and keep up on maintenance.
One very annoying feature about the newer motors is the location of the upper mounts, I've had to replaced the upper mounts on every one of my 9.9/15hp motors at one point or another. My 9.5hp motors are basically all original.

If there's a design flaw in the 9.5hp, I too would like to hear it. So far all of mine have been just fine.

 

[raczekp1]

Re: 1974 Johnson 15hp compression readings?

http://www.leeroysramblings.com/OMC_9.5.htm

in my opinion its trouble make disign.they dont look nice

9.9/15 were made over 30years, and parts are still avilable

 

[screwloose]

Re: 1974 Johnson 15hp compression readings?

Well, I got the chance to test run the 9.5hp today, we took it out in the river and I ran nearly 5 gallons of gas through it over the course of the day. It ran great, starts easy hot and cold, and looks half decent as well.
After we got back he asked if I wanted it, I hesitated and he dropped the price to $250, I said $200, he said sold and I own the motor. The way I see it is he's the original owner, he sold his boat and no longer has a use for it so I didn't get the impression he was trying to just dump a bad motor and it ran flawlessly all day.
I actually like the low cowl design, it didn't once get in the way of casting, it was easy to tilt, and its light. It wasn't fast but it had no trouble getting my 14' aluminum Sears boat up on plane with my 300lb self plus his roughly 200lbs sitting up front. The prop seemed a good match too, if it even matters on such a small motor. He also gave me a brand new spare prop, new in the box from OMC, plus the manual, owners manual, and a baggie full of spare prop pins, and other spare parts, including two new water pump impellers and one complete new water pump.

For what I have in it, if I get a year or two out of it I did just fine. If a good 15 or 20hp comes along, I'd still probably keep the 9.5hp just for use on 10hp limit lakes here.
The first thing I noticed was that the 9.5hp is a lot quieter than the 9.9/15hp, but that may have a lot to do with how low the motor sits, meaning that most of the noise is behind the transom not above it.

All in all it seems like a good design to me, with the biggest plus being its light weight and low cowl. I can carry this thing by the grab handle like a suitcase all day. It'll probably see more use on my 12' boat than on my 14' boat but I took the 14 today since there was two of us.

 

[starcraftkid]

Re: 1974 Johnson 15hp compression readings?

It sounds like you got a great deal on that motor.
They bring double that in the spring around here.
I wouldn't sell any of mine for any amount though.

If the only issue with the 9.5 is the way it looks, I don't see where that would even come into play on an old aluminum boat.
I don't much care what it looks like if its reliable and gets me to the fish and back again.