Anyone ever build an outboard motor? Or know about compression?

I accidentally bought a 1978 Johnson Outboard 140hp for parts that turns out I can't use. Thing is, it looks really clean, like it might be worth saving. No idea why it was originally pulled off the water.  The motor spins, the starter works, the carbs are good, so I figured I would dig into it. The first step is a compression test, no?  The cylinders read 80, 100, 100, 110 psi.

Question #1: According to Johnson/Evinrude, a 1970s motor should be no more than 5% variance. Does that mean that this thing is a boat anchor and not a boat motor? How accurate is hooking up a gauge and cranking it over anyway?    

Question #2: How likely is it that the head gasket is bad, as compared to rings? Head gaskets seems to be a walk in the park, but I have never done rings and am not inclined to start. 

I have invested $100 in the purchase, and can get that back in parts. But a running 140hp motor can probably fetch me $1000. Or I can upgrade from 85hp, who doesn't want an extra 55hp? 

Does the compression on the "bad" cylinder change if you add a bit of oil to it?

Depends on how long its been sitting, if the rings are stuck, blah blah blah.  For the most part, the same questions you'd ask of an automotive engine

Headgasket is usually fairly easy provided its not a salt-water motor.  I've still got a fairly rare "shortblock" on my shelf somewhere of a case and rotating assembly that I was never able to get the bolts apart from.  Steel and aluminum don't like each other.  Thankfully Johnson/Evinrude generally were all stainless hardware by that point in time so it should be somewhat painless.  Still, be on the lookout for stuck bolts.

Personally, I'd spend the bare minimum getting it running, start using a slightly heavier fuel/oil ratio (that year should be 50:1, so go with 30-40:1) and put it on the water a few times and then re-do the compression test.

I'm a bit dubious about cold compression tests on an engine that's been sitting for a long time. 

Spray some penetrating oil into the cylinders, let it sit a a day, rotate it, spray more, let it sit a day. Then add a bit of 2 stroke oil, crank it a bit, let it sit for a few minutes, hold the throttle open and try again.It still won't be a hot compression test, but I think it might be a bit more accurate.

As for being a boat anchor, it probably isn't, but if it is broken, fixing it might be $$$.

Let's see what Curtis has to say.

Do you have a borescope?  The 80 psi cylinder is the one I'd be most concerned with, 110 - 120 psi is typical for 2 strokes of this era.  Those OMC V4 engines were pretty resilient but any 2 stroke that runs lean can result in poor oiling as a result.  If you can get a borescope I'd pull the plugs and take a look at the cylinder bores for signs of scoring.   If the bores look decent it could be the rings are stuck, there is a Yamaha product called "Ring Free" that has been recommended by some.  Sea Foam might be an option as well.  Either way you'd need to be able to start and run the engine on a hose with "ear muffs" to attempt to free them.

The cold compression test makes a lot of sense, this motor has been sitting for a very long time without any oil or Heat. Thanks a bunch for the advice comma I'm going to oil up the Cylinders and see what Happens. 

I've built quite a few and back when I did it for a living went to service school for all things OMC (Johnson/Evinrude). Rings could certainly be stuck on an engine that hasn't run in a while. I think the borescope would be a good place to start. OMC made a product called "Engine Tuner" that was basically solvent like Seafoam and I witnessed it making some pretty amazing difference at times.

 Also, if it's been in saltwater much, I wouldn't go very deep on repairs. Salt eats outboards and one that old would be bound to have lots of corrosion. On the other hand, inland engines around here sometimes have very little actual running time. Not unusual to see boats get used less than 50 hours a year...some way less.

I wouldn't recommend an overly rich oil mixture. Good quality (BIA certified TCW-3) oil at 50 to 1 is all you need. Bear in mind that the only time the engine really needed that 50 to 1 ratio was at wide open throttle. Later automatic metering systems mixed as lean as 150 to 1 at idle.

The 85-140 hp engines of the era were a well-engineered 90° Vee design that dates back to 1958 with some crazy iterations in early years. By 1978 the electronics were pretty solid. It was sad to watch OMC go down the tubes. Classic case of top heavy company that took it's eye off the ball.  Looked like Bombardier might resurrect  the brand but nope. I don't know what parts availability would be, I've been out of it for some time.

carbidetooth said:

I don't know what parts availability would be, I've been out of it for some time.

I could fully rebuild just about any 1950s Johnson/Evinrude tomorrow if I really wanted to.  I'd be surprised if parts are not available for a '78.  That's not even 50 years ago!

If i remember right, these v4 engines could get air trapped in the water jacket and it would make the top cylinder on 1 side run hot and cause issues. Is the lower PSI on a top cylinder?   Id say the motor is likely worth repairing. 

Mr_Asa said:

carbidetooth said:

I don't know what parts availability would be, I've been out of it for some time.

I could fully rebuild just about any 1950s Johnson/Evinrude tomorrow if I really wanted to.  I'd be surprised if parts are not available for a '78.  That's not even 50 years ago!

If it is anything like a similar vintage Merc ('82), the parts are definitely available. But they may be expensive, rebuilt, or sitting in a marina across the country. If you have time to wait for a deal, you'll find it eventually. But if you just want to go and buy it as soon as is reasonably possible, it could get iffy. 

My evinrude 25 has 90-95 psi hot and runs fine.  Smokes but I do run heavy on the oil mix.  Put a new honda on this year.  Quieter, easier to start and no more fuel mix.  The tech at the store said 80 PSI motors will still run for years from his experience.

Mr_Asa said:

I could fully rebuild just about any 1950s Johnson/Evinrude tomorrow if I really wanted to.  I'd be surprised if parts are not available for a '78.  That's not even 50 years ago!

Even though the exterior appearance changed over time, it was common for OMC outboards to have basically the same mechanicals underneath the hood for many years.

stuart in mn said:

Mr_Asa said:

I could fully rebuild just about any 1950s Johnson/Evinrude tomorrow if I really wanted to.  I'd be surprised if parts are not available for a '78.  That's not even 50 years ago!

Even though the exterior appearance changed over time, it was common for OMC outboards to have basically the same mechanicals underneath the hood for many years.

Mmmmm.... eh.  Broadly true, but there are a few big caveats in there.

I've rebuilt a couple of them. One was an 80s-era 50-hp that I burned up. It got pistons, rings, and a gasket set. the other was a 1956 5-hp that I also burned up. It also got pistons and rings. Both were saltwater engines that had stopped up water passages. 

I would get the engine up and running for a couple of hours and retest the compression.

Parts used to be pretty easy to find and I bet they still are. OMC uses the same parts for a long time. When I rebuilt my 56 5-hp, the pistons for a 80s era 6 hp were the same. I would bet that the 140 uses the same pistons as everything from the 85 through 200. Sierra used to be the big parts supplier for engine parts. Parts used to be fairly cheap. Piston and ring sets were $35 in the early 2000s. 

The bearings will still be good. OMC uses needle roller bearings. If they were gone, the entire engine would be shrapnel. 

Look closely at the reed valves for cracks or chipped spots. They can and do fail. When they do, it's very hard on the engine. 

While you have it apart, pull the foot and change the water pump. 

If this is a saltwater engine, get a good torch and plan on replacing every gasket in it. I would also plan on painting it. The only way to get them apart is lots of heat. Like put tension on the bolt and heat it until it turns. It took me 3 days to get the powerhead off of the 50 I rebuilt. 

I have a 1975 Johnson 75 hp 3 cylinder. The lower unit gear case always filled up with water even though I replace the prop shaft seals several times. Eventually the lower unit seized up out here is Bum berkeley North Dakota, I couldn't find anybody who would touch it and they all told me to buy any engine out of the 80s (probably needs bearing and gears). So I did, a 1983 115 hp Yamaha attached to a 1983 18 foot aluminum boat. I would still like to find someone who would rebuild it close to my neck of the woods up to 500 miles away.

In reply to VolvoHeretic :

Likely not the prop shaft, driveshaft and the shifter rod (if not electronically shifted) should be the culprit.
Parts are out there, or you could find a full lower unit.
https://www.ebay.com/itm/314718151082

https://www.ebay.com/itm/256495010929

You should be able to find exploded parts diagrams for everything on here https://www.marineengine.com/parts/parts.php

In reply to Mr_Asa :

wow, thanks a million.

I fogged the cylinders with some oil a few times over the last few days, and the motor is definitely easier to turn over by hand. Checked compression and 3 cylinders went up by about 5% and one cylinder went down by about the same. Ugh

I think these old Motors are pretty robust and run regardless of compression differences, said the next step is to clean up the carbs and check the reeds and try to start it on earmuffs. If I can do that and get it to idle, I'll let it warm up and then recheck compression. If I find an obvious issue I'll rebuild the heads, it's just two plates and some gasket so it's not a big lift. That'll also let me look at the cylinder walls. 

I'm still waiting on a fuel fitting to be able to start the motor, but I picked up a cheap camera to look inside the cylinders. The cylinder walls don't look too bad to me, but hard to say. What I found more interesting is the difference between the pistons. One is so clean and lacking in carbon buildup it might be new, and one is pretty heavily blackened. The mystery deepens, did someone attempt a rebuild? Is one cylinder running rich and the other lean?  The investigation continues. 

I have a Johnson 90 HP V4 from 1983.  I haven't had any issues getting parts for it to this point (knocks on wood) but my parts guy at the local boat dealership retired and the new guy doesn't know squat about old stuff.  I've heard these things are all but impossible to kill.  Not long after I got mine, I had the head off on one side, and there was what I thought was some pretty severe scoring on the exhaust side.  I checked the compression years ago, and I don't honestly remember where the number were.  Maybe as much as 20% variance.  The engine makes good power, is easy to start, and runs pretty darn well.

I did source a lower unit, as mine would leak lube and fill up with water.  Given that this engine spent at least some time in salt water, I had no interest in trying to pull out and replace prop shaft seals.  Used lower unit cost me like 250, and it's holding the lube in.

Fire it up!  Just be sure to put a water pump kit in it before you do.