'77 Johnson 70HP teardown - questions

[Thirsty Endgrain]

Hello, well as per another post down below I've recently purchased a boat with a motor (what could go wrong?), it was stuck in forward (and I couldn't start the engine) and found a frozen shift linkage rod. Currently rebuilding the lower unit now, waiting for seals.

On the the top: I had forced water up the pickup tube with a hose wanting to see if it would clear all of the passages and come down the drain side, but I wasn't sure if the thermostat would block the flow until the engine warmed up (which it won't do 'cause she won't start). No water ever came down the drain side so I assumed either the thermostat blocks flow, or there was a blockage. Got busy with wrenches this morning and well, what thermostat? It's completely MIA. Fun.

So I get even more curious and say what the heck, it's only like 30 bolts with a high likelihood of snapping in the head or block and I've had my coffee so let's do this. 30-ish bolts later (and only 1 snapped in the head! Was expecting worse) and I've got the thermo housing, head cover, and cylinder head off. I don't think they've seen the light of day in 43 years.

Water passages actually didn't seem in too bad of shape for what one might expect, I did see evidence of what *I think* was a melted impeller, picked all that debris out.

Did a cold compression test yesterday since I don't have the option to do a warm one, mind you I only wanted a rough idea.
Bottom - 80
Middle - 70
Top - 72
I think. Should have written it down. I know cold is innaccurate, but I wanted to basically see if any had a big hole in them.

There will be more q's and I appreciate y'alls time, but now that history's done onto my questions:

-Main one - There is some scoring on the top two cylinder walls, both in the same-ish location, intake side. I can feel the ridges with my fingers. I know that's probably.....bad? Pics attached. Bore cylinders and oversized rings? Are those even available? Is the block simply done?

-Is there a chance that scoring won't let the cylinder light a fire? Took about 10-12 chugga chuggas to get to gauge up to those numbers. I know I'd have to do a leak down test to see if the cylinder can hold compression, but I'm wondering if any of you more experienced can advise my best path forward.

-Since everything's apart I want to clean out the head and cover of the salts, is there a favored method of bathing/sonic immersion etc. to accomplish this? Completely new to outboards.

Well that'll get me started I think, thank you!

-Nick

 

[Thirsty Endgrain]

[No message]

 

[gm280]

Where are the pictures?

My original boat project did include an old (1976) 40 HP Johnson engine. And like you, had to tear it down (or up) :noidea: , and see everything. I had pretty good compression but glad I tackle the tear down first. Seems the lower main bearing and seals were totally destroyed beyond anything resembling a bearing or seal. I disassembled everything and cleaned, blasted every part and primed and painted back to new. I didn't install any new pistons but did use new rings and bearing and all new seals and water pump assembly.

If you care to see that project, click on the project link below.

But before doing that, pop a picture or three up for us to see what you are dealing with... :thumb:

 

[Thirsty Endgrain]

Sorry, technical difficulties with photos. Got it sorted. Wouldn't let me add to my original post.

Looked through your rebuild thread yesterday, looks like a fun project! I like to know what's going on inside before relying on something mechanical so I guess I'm glad I'm doing this, but honestly I just want to get onto the water...

 

[havoc_squad]

I like to know what's going on inside before relying on something mechanical so I guess I'm glad I'm doing this, but honestly I just want to get onto the water...

If you don't work on the stuff for a living, be prepared for a long duration before it's done if the motor is worth rebuilding.

It's been about 9 to 10 months before the initial tear down for me. Between life's curve balls, budget, finding a helpful machine shop for the work beyond your skill level, and motivational issues, it can drag on for a long while.

Keep in mind that OMC 3 cylinder outboards are very much more varied on compatibility, you may have a harder time tracking down a compatible used working lower unit as aftermarket lower unit options focus on the V4s and V6s.

Is that year model lower unit rebuildable? Yes, according to today's parts availability. It will just cost an arm and a leg in parts and labor.

Link to the lower unit compatibility forum sticky topic: https://forums.iboats.com/forum/engi...chart?t=359907

I would say if you can go up to at least 90 HP V4 90 degree crossflow motor (1982 to 1998) on your boat motor legal capacity, you might be better off finding one cheap one that is rebuildable instead of sinking the money in this one.

Parts availability is a lot better/easier to find, especially when it comes to used lower units available and new lower units.

Avoid OMC/BRP FICHT motors like the plague. Some of the critical parts are no longer made.

 

[flyingscott]

Parts not available for a 3 cylinder OMC looper?????? C'Mon!!! Your motor is not a great candidate for repair ,the lower unit and the powerhead are shot. Around me that motor would go to the junk man and pay itself off in scrap.Go find a running 1980 and up 3 cylinder because it will be cheaper than rebuilding that anchor. The 3 cylinder is a far better motor than the crossflow V4.

 

[Thirsty Endgrain]

Is that year model lower unit rebuildable? Yes, according to today's parts availability. It will just cost an arm and a leg in parts and labor.

I ordered parts for the lower unit that came out to about $100. Is that considered too expensive to rebuild? And all of the seals were available. I get that it may not be ideal, but I'm trying to work with what I have.

Parts not available for a 3 cylinder OMC looper?????? C'Mon!!! Your motor is not a great candidate for repair ,the lower unit and the powerhead are shot. Around me that motor would go to the junk man and pay itself off in scrap.Go find a running 1980 and up 3 cylinder because it will be cheaper than rebuilding that anchor. The 3 cylinder is a far better motor than the crossflow V4.

Why is the lower unit shot?

The powerhead though, yeah I don't quite know what to do. This sucks. Boat was sold to me under the pretense that all it needed was gas. I'd never buy another motor again without seeing it run, and doing a comp test. I already knew that, but I let my excitement get the better of me. Lesson learned.

Ok so path forward though. Bad idea to throw new gaskets in, and get it all back together, given the condition of those cylinder walls?

I know different folks will take different paths based on their capabilities and financial fitness, I'm not particularly in the position to drop money on a new motor, so I'm wondering if it's worth my time and money to have this block bored etc. So that scoring is too deep (seemingly)?

Appreciate the advice!

 

[flyingscott]

It is a 77 motor that will cost you around $1000 to rebuild if you do all the labor except boring. Save your money and find at least a newer powerhead. A used powerhead will save you money. Your compression is quite bad.
What do the bearings and gears look like in the lower unit? Especially the upper pinion bearing. Was there water in it?

 

[Thirsty Endgrain]

It is a 77 motor that will cost you around $1000 to rebuild if you do all the labor except boring. Save your money and find at least a newer powerhead. A used powerhead will save you money. Your compression is quite bad.
What do the bearings and gears look like in the lower unit? Especially the upper pinion bearing. Was there water in it?

Points all taken, with gratitude. Lower unit oil was creamy, still trying to get those monster snap rings out to finish pulling the lower unit internals, if I can get my modified long needle noses to give me better luck tonight, I'll have more info on that. All bearings so far have looked in tact with no signs of excess wear.

Trying to find a powerhead as you're suggesting, and I'm still trying to decipher what is meant by interchangeability of powerheads with my lower unit. Are there newer model powerheads that would drop in on top of my lower unit, fit in the existing engine cover etc??? Please excuse what are probably common knowledge questions, I'm learning here, and I appreciate everyone's help.

 

[Thirsty Endgrain]

Further down my options rabbit-hole: Still trying to determine what powerheads are compatible with my unit.

OEM gasket, adapter to plate p/n 0321796 - superseded by 0331016

Via crowleymarine factory fitment guide it fits:

Johnson
70HP - 1974-1985
75HP - 1975-1985

Evinrude
70 + 75HP - 1975-1977, 1980-1985

So are those my options for my powerhead search? Will call some places tomorrow to see what they say, but I'll be off the map for a few days so if I don't respond I'll get back to anyone's replies after the weekend...

Edit: Would this be a direct swap onto my lower unit please say yes and have it be true? Price is right. Need to ask some questions, but it seems to cross reference with my above year ranges. And from the reading I've done, Johnson = Evinrude? And would I gain a whole 5 ponies to boot?

I guess it would help if I included this:

https://www.ebay.com/itm/173362595014

 

[flyingscott]

You do realize that ebay listing is for just an empty block ,which you would still have to put your parts in and rebuild. look elsewhere. I would.recomend staying with a 70 hp

 

[racerone]

There is no way that block on E-Bay would end up on my work bench.----Overheated junk I think.----The 60 HP ( prop rated ) up to 1988 is also an option for you.

 

[Thirsty Endgrain]

Local shop wants $115/hole to rebore. ~$500 for the parts to rebuild. So for the parts and labor for upper and lower units, as you described above, I'm in about $1k. Would I really be crazy to drop $1k into this engine to get it into a fresh state?

I understand the point of getting a newer ('80's) unit in there, though I can't find one currently (and there's a certain amount of uncertainty in something that old and used). I would love something a bit newer, and 4 stroke, but darn those are $$$$. Even a good used '70's-'80's 70-ish hp engine is quite expensive.

So, this thing lasted 43 or so years up to now, and in my mind I can give it fresh bores, pistons, bearings etc etc and probably eek out a decent future for it, at least foreseeably. Barring of course catastrophic thrown rods and other things like that.

So, I think I'm going to at least pull the block off and apart, check condition of the crankshaft, and get into the lower unit gears to asses their condition. Depending on what I find, go from there.

I also don't want to waste time or money, and I know many of you here have enough experience to know when to just call it, so as always, appreciate any advice for my situation.

 

[Doh]

Sorry, technical difficulties with photos. Got it sorted. Wouldn't let me add to my original post.

Looked through your rebuild thread yesterday, looks like a fun project! I like to know what's going on inside before relying on something mechanical so I guess I'm glad I'm doing this, but honestly I just want to get onto the water...

I would move on. Scuffing on 1 cylinder, ingestion in another (looks like Ring Exiting marks) and LU problems.

If the unit has Trim/tilt, Salvage is worth more than the motor running anyways.

 

[Thirsty Endgrain]

Call me dense if you will, but I'd like to understand why it's a bust to rebuild this thing? If I can over bore it and get new pistons and rings in there, new gaskets all around, freshen the LU, etc etc for around $1000; whereas it's about 4x-8x that much for a decent slightly newer engine, that I just don't have the money for right now, it's really unreasonable for me to consider a rebuild? I'm truly not trying to argue against experience, but I am curious why it's seemingly such a bad idea?

If a rebuild is a bad path forward, what would you do in my shoes? Where would I go about looking for a decent used engine in the 70hp-ish range, aside from CL or eBay? What is a decent price to expect to have to pay?

Thank you.

 

[racerone]

What is your location ?-------Not all areas are the same with respect to good used engines with warranty !

 

[Thirsty Endgrain]

I'm in the bay area, CA.

 

[Thirsty Endgrain]

Ooooooooooookkkkkkk so after a few busted bolts and broken extractors and some head scratching and youtubing and wrench turning and severe questioning and beer I stripped the thing down to the block. I know everyone's saying so far to let it go, and I appreciate all input and time, I just wanted to get he block into the machinist to see what they say, and if they deem it salvageable. If it is I think I'll have them re-bore it. Looks like rebuild kits are available from .010"-.040" over.

Not seeing any reasonable and good shape powerheads available anywhere, locally nor ebay and all else. If the machinist deems it done I'll go from there.

Another question: is any light able to be seen through the reed valves bad light? I've got about 1/64" of light in maybe 4 of the valves, wondering if that's too much.

Also, I don't know what the heck caused all of the scoring in the cylinders/pistons, was trying to do a little forensic investigation now that everything's apart. There are some little missing scraps of aluminum from the block, very small pieces near the base of the cylinder where the meeting of block and cylinder sleeve occur. But I wouldn't think tiny bits of Al could do the kind of damage seen?

How do I determine if the crankshaft is in serviceable shape?

Well, this is my progress report. I think I had more questions but, like I said, beer.

 

[Thirsty Endgrain]

[No message]

 

[racerone]

Journal for #2 cylinder looks to have water damage.------What do the main bearing surfaces look like ?----Post some more pictures of bearing surfaces.------Bearing surface of #2 rod.-----As I see it so far that would go to the scrap pile here !!