1988 Johnson 70HP 3 Cylinder, Compression and Alarm

[marcomputers]

Hi All,

I'm looking at purchasing what seems to be a clean 1988 Johnson 70HP VRO (disconnected VRO) outboard motor.

Went to look at the motor, we started it up and it ran good on the ear muffs, but only for a minute. Brought a compression tester from Autozone and removed all spark plugs per compression test thread, opened throttle and checked each cylinder. I was surprised to see the compression numbers come in at 85, 87, and 87. Thought they would be over 100.

Spark plugs were dark black when I removed them for the test, which based on the forms would indicate low compression or stuck rings, but it did seem to run strong. I'm obviously worried about the low compression.

The gentleman said that he didn't have any problems with it, other then that it sometimes was hard to start cold. He hasn't run it in a year or so, and it was still pretty cold (only ran for 1 minute) when we did the test.

The only other indication of anything strange was that on the part of the engine block where the ground for the battery goes, paint was peeling a small bit. Only in this location, however, and no where near the head or on other parts of the engine.

He's looking at selling for around $600, but can anyone advise if it is worth it, or what kind of cost will be involved with this engine in the near future based on my tests?

Thanks,
Mike

 

[bonz_d]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Well your low compression readings could also be the gauge as all 3 cylinders are very close. Could retest with another gauge. As to the price, if it's running and shifting as it should, not making any odd noises I think he's asking a fair price. In my area nonrunning parts engines are still fetching $300.00-500.00 depending on completeness and condition of the lower unit and whether there is tilt and trim.

 

[marcomputers]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Thanks Bonz.

If the compression comes in around 85-90 even with a different gauge, should I plan on replacing pistons and rings right away, or does it really matter if it still runs? My limited understanding is it is more important to have the engine running, and to have equal compression +/- 10%.

Some people say that under 100PSI, you're not going to have an engine that idles well under load, when actually on a boat.

It's a 25 year old engine, but I'd like to not have to pull it apart right away.

Mike

Well your low compression readings could also be the gauge as all 3 cylinders are very close. Could retest with another gauge. As to the price, if it's running and shifting as it should, not making any odd noises I think he's asking a fair price. In my area nonrunning parts engines are still fetching $300.00-500.00 depending on completeness and condition of the lower unit and whether there is tilt and trim.

 

[Bosunsmate]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

If that engines a looper i wouldnt run away just yet.
Is it on a boat?

 

[bonz_d]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Mike it is really kind of difficult to get a true impression of an engine sitting on a stand and running on muffs.

Because all 3 cylinders are very close is a good sign. Tells you that there isn't a damaged one or that there is a blown head gasket. It could also very well be that it has seen a lot of use and is worn out. Or that it has sat and the rings are stuck which by doing a decarb with Sea Foam or other product may improve that. A decarb is almost impossible on a stand with muffs.

Also how well was the engine turning over while doing the compression test? If it was turning over slowly that will also effect the compression readings. As that is seen requently on smaller outboards with manual rope starts.

Too bad you couldn't actually get it on a boat and test it as that would give a better indication of it's true condition. I would suggest making a low offer and go from there as at this point there is still no idea as to the condition of the lower unit. Is it shifting properly? Staying in gear? Metal or water in the gear oil?

 

[Bosunsmate]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Its a looper.
Take out the sparkplugs and see if there is any damage on the pistons or walls.Take a small torch with you.
Id also run it for a few minutes in a bucket making sure the guy didnt stop it after a minute as it overheats at idle. Make sure the water level is at least four inches above the anti-cav plate
As above check it shifts into gear and turns the prop ok. A quick shift is needed, a slow one will almost always make a crunching sound.
If all the above check out id chance my arm and buy it at that price and do the decarb as above

 

[bonz_d]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Also in this case because the engine hasn't been run on a boat and in that water you really need to determine if this seller is up front or feeding you a line. Talk more, ask questions, even stupid ones, repeat questions and see if the story changes.

Last fall I drove 6hrs round trip to buy an engine pretty much sight unseen. Before that I had many conversations with the seller to be assured what he was telling me wasn't BS. That engine is a 1983 Johnson 60hp 2 cylinder. He'd bought it to put on a 13' racing hull but after a couple outings he determined that that engine was too heavy for the boat and what he wanted to do with it. He still had that lil race boat along with another 18' Mirage tunnel hull with a modified 250hp Evinrude.

After getting that engine home and testing it I found it just as he discribed and is running wonderfully.

 

[marcomputers]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Thank you for the responses, I truly appreciate the advice.

I'll ask all of these questions, three different ways. Unfortunately the engine is not on the boat.

On the ear muffs, it shifted fine, but I do understand under load is different. He stated he did a decarb when he got the engine some years ago.

The seller did shut the engine down after a minute, as the engine emitted rapid, short warning tones - it was not a solid beep, which would indicate overheat. Went online to research this, and based on multiple threads this is based on him having disconnected the VRO tank, running premix, and not fixing the sensor. The warning tones for that engine specifically say that:

- Horn sounds rapid, short tones that vary with engine speed : No oil flow from pump

I plan to ask more questions surrounding why he removed the VRO (he stated it was because other's told him it was unreliable to run), check the wiring to make sure that he has disconnected the oil tank wiring properly, and have him run the engine longer on the muffs (5-10 minutes). If all goes well, I'll to make him an offer I can afford if I need to replace pistons/rings in the near future.

Mike

Also in this case because the engine hasn't been run on a boat and in that water you really need to determine if this seller is up front or feeding you a line. Talk more, ask questions, even stupid ones, repeat questions and see if the story changes.

Last fall I drove 6hrs round trip to buy an engine pretty much sight unseen. Before that I had many conversations with the seller to be assured what he was telling me wasn't BS. That engine is a 1983 Johnson 60hp 2 cylinder. He'd bought it to put on a 13' racing hull but after a couple outings he determined that that engine was too heavy for the boat and what he wanted to do with it. He still had that lil race boat along with another 18' Mirage tunnel hull with a modified 250hp Evinrude.

After getting that engine home and testing it I found it just as he discribed and is running wonderfully.

 

[bonz_d]

Re: 1988 Johnson 70HP 3 Cylinder, Compression and Alarm

Sounds like a plan. Try another gauge on your compression tester and see if it stays the same and look at how fast it's turning over.

Many have disconnected the VRO systems because some feel it to be unreliable. Some of which just may be because of poor maintenance.

Just today while surfin craigslist I came across a few late 70's and even a couple early 70's 70hp 3 cylinder engines that they were still asking as much so you might have a bargin there if all checks out well.

Good luck and let us know the outcome.