1970-something 85HP Johnson with a 'bad cylinder' question...UPDATED!

78Galaxy

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See most recent post for updated info/picture...


---------------
Hey all-

I first want to say hello, as I just bought my first boat this past weekend. I am glad that there is a forum on the web that addresses these types of issues, and perusing the past threads, it seems that everyone here is courteous and helpful. I'm glad to be a part of this community.

Now, to business...

The boat I recently purchased came with a 1970-something ('78 or '79, I think) v4 Johnson SeaHorse engine. It allegedly has a 'bad cylinder' according to the reputable mechanic who inspected the engine. I was specifically told that a cylinder has low compression, and 'must be replaced' at some point. I was told that the engine runs as is, but 'it will leave [me] somewhere, sooner or later - could be 2 hours, could be 2 weeks' if I run it (once again, according to the mechanic I was referred to).

Now, that being said, I was quoted $3,000 to fix the problem. Clearly not worth it. I called another reputable mechanic, and he said that his price would be about the same because the part needed to fix it is $2,100. The part needed escapes me, however, he deduced the part from the information I have stated above.

With that in mind, I have considered several options:

1) Get a membership with Sea//Tow or Boat US and just run the darn thing until it dies and subsequently buy a new engine after I get towed. (I won't be taking this boat out much farther than swimming distance of shore, by the way.)

2) Get an exact fix on what the part is, and try to locate it elsewhere for less money, then pay the mechanic to install it.*See footnote

3) Suck it up and try to find the $3,000 somewhere so I can pay to fix it (this probably would take longer than the remaining boating season to do, so I am not excited about this option).

4) Suck it up and buy a new engine. See #3 above.

5) Use a reputable 'independent' mechanic to fix the problem as is or install the replacement part that I procure. A close associate of mine has a shade-tree mechanic who he has trusted for years and who guarantees his work.

*If I do need to locate the replacement part, what degree of interchangeability am I looking at as far as 85HP engines? I.e., are the parts from a '78 and '79 85HP SeaHorse interchangeable? What about other years?

In any case, what are your thoughts?

Thank you so much! :D

James
 
Last edited:

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

I forgot to include...

Is there any more information that I should ask from the mechanic? Is there any information that would help form your opinions on this matter?

Thanks again-
 

R.Johnson

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

If the engine is low on compression, why? Is it a bad piston, and bore, or just a bad head gasket? Pull the cylinder head, inspect, and go from there.
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

If the engine is low on compression, why? Is it a bad piston, and bore, or just a bad head gasket? Pull the cylinder head, inspect, and go from there.

Now, if you'll excuse my unfamiliarity with the terminology, I was told that it has a 'bad cylinder.' Are you saying that a 'bad cylinder' could in fact be a problem with a multitude of things?

Thank you for the prompt reply, by the way R.Johnson!
 

iwombat

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

That's exactly what he's saying. Low compression can be a simple case of blown gasket, or stuck rings. It can also be a more complicated case of scored cylinder or burned piston.

$10 - $3000 fix depending on the cause.
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

That's exactly what he's saying. Low compression can be a simple case of blown gasket, or stuck rings. It can also be a more complicated case of scored cylinder or burned piston.

$10 - $3000 fix depending on the cause.

I understand that, but just to clarify;

I was told that the mechanic ran a compression test, and found one of the cylinders was running low compression. Because of this, he inspected the cylinder and told me that the cylinder itself was 'bad' and needed to be replaced. As in " I'm looking at the cylinder right now, and it looks bad. It should be replaced." I understand that a cylinder with low compression could be caused by many, many things, but in this instance, I was told that the actual cylinder itself was bad. Does that make any difference in reference to your posts, guys?
 

iwombat

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Not the best terminology since you don't "replace a cylinder". But, let's assume he means bore out the cylinder and replace the piston.

The only "part" you're going to be able to go out and buy yourself is a new powerhead. It needs to be disassembled, machined, and reassembled with new parts.

As far as interchange anything past '78 will swap. Give us a model# and we can be more specific.
 

JB

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

I would like to know exactly what "bad" means, James, and see the evidence of it.

I have heard outboard wrenches call a cylinder that is 20psi lower than the rest a "bad" cylinder, then fixed it with a decarbonizing procedure (I used water in those days).

Outboard wrenches have also been known, on occasion, to grossly exaggerate problems because they need the work.

Ask him for the exact compression numbers and let us know.
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Not the best terminology since you don't "replace a cylinder". But, let's assume he means bore out the cylinder and replace the piston.

The only "part" you're going to be able to go out and buy yourself is a new powerhead. It needs to be disassembled, machined, and reassembled with new parts.

As far as interchange anything past '78 will swap. Give us a model# and we can be more specific.

I don't mean to be gushing here, but I really do appreciate the help, guys. I get what you are saying, now. I'll try to get him to be more specific the next time we speak.

I'll get a model number the next time I speak to the mechanic - he currently has the boat. In the meantime, here's a picture of the engine - this may help:

164612oh0.jpg
 

jay_merrill

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

"Bad piston" is a generic term meaning that there is something wrong with one of your pistons/cylinders. Its sort of like saying that someone has a bad heart - which could mean clogged arteries, congestive heart failure, a hole between a couple of chambers, etc.

The apparent symptom of this "bad cylinder" is low compression. What you need to find out is what the cause of that symptom is. It could be as simple as a bad head gasket, or as complicated (and expensive) as a broken ring. If you actually have physical damage, about the only single part that might cost you $2,100 is the block or crankshaft. I could see a combination of parts costing that much, however. Another possibility could be that you need $900 in parts and that the rest would be in labor - OMC/BRP dealers tend to get about $70/hour, and more, in labor charges these days.

As was recommended (and it is very good advice), you need to determine just what is going on before you decide what the remedy might be. Changing a head gasket is not a big deal and, if you are mechaincally inclined at all, you could probably do the job yourself. You should first get a factory service manual and it can be obtained right here at iboats, as well as other places. In order to do this, you will need the exact model year - look for a plate on the motor with a bunch of letters with a couple of numbers interspersed. It may look something like this -

J85TCCF

The translation of this would be Johnson, 85hp, Electric Start with Trim & Tilt, 1988 model, Model Run F.

If you can't find a data plate on the motor, there will be a plug in the top of the block (its called a welsh plug) that will have a serial number stamped in it.

In either case, publish the number that you find here and we can help you identify the engine.

If the motor does turn out to need an overhaul, you might want to consider a used replacement powerhead or a powerhead rebuild shop, which should offer a warranty.
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Ask him for the exact compression numbers and let us know.

Will do, JB. So, the next time I talk to him, I will ask him:

-Compression numbers
-Model number/year of engine
-Why exactly the cylinder is 'bad' and what might happen if it goes untreated.

Anything else?
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Thanks for clarifying that with me Merrill, Wombat, and JD. I understand what you mean now.
 

jay_merrill

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Re: 1970-something 85HP Johnson with a 'bad cylinder' question...

Your motor does look like a 1978 or 1979. I think the model numbers may look a little different than what I just described. They may look something like this -

85TL79R

I didn't look up the translation again but I think this would be a Johnson 85hp with trim & tilt and a longshaft.
 

78Galaxy

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...UPDATED!

Well, he finally fixed it, and here's what I know...


-Compression numbers
-Model number/year of engine
-Why exactly the cylinder is 'bad' and what might happen if it goes untreated.

1. Compression numbers: 120, 120, 105, 110.
2. I have not gotten the engine code, but I will when I pick it up.
3. Allegedly, it needs a new ring, and to re-ring all of the pistons will cost me $3000.00, according to him. He says it is only a matter of time before it 'blows up.' Here is a picture:

deshaugreauxbob2ny0.jpg



Now, my questions are as follows (in addition to the questions in the first post):

1. If I run her gently, how long can I expect it to last? Is there anything I can do to prolong the life of this engine with the expectation that it will eventually quit on me?

2. Should I repower or repair?

3. If I repair, should I use my good friend's shade-tree mechanic who charges half as much and guarantees his work?

Now, I misunderstood the cost of the part - the replacement piston and rings should only run about $150-$250 - I will be paying for $3000 in labor, basically.

What are your opinions?
 

R.Johnson

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...UPDATED!

If you were to take the engine apart, you would find that the piston is also scuffed. I scuffed piston, and cylinder wall will not lubricate properly. The rough edges will break up the oil film, running it will only worsen the damage. When the engine is apart, the cylinder walls must be measured to see if they are in tolerance. You would have to add the reboring charge to the price, the cylinder shown will certainly have to be rebored. Reboring a 2 cycle is different in that the cylinder walls have the ports cut in, this means an interupped cut to the boring bar, and there must be a relief cut at the bottom of the bore, not all engine shops can handle that. You may have to send the block away to a shop that does 2 cycle work, I highly recommend that. As I recall, the flat rate manual lists about 15 hours to do this job properly, as a rebuild requires a complete rebuild of the carbs, water pump, and thermostats, gasket set, hoses, etc. The price can jump up in a hurry. If done by a shop, the price will far exceed the value of the engine. Even doing it yourself the price will exceed the market value. If done properly, you will at least know what you have. That call would be up to you.
 

ezeke

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Re: 1970-something 85HP Johnson with a 'bad cylinder' question...UPDATED!

The cowl on the motor is a 1978 model. If the engine is 1978, It is different than the 79 and up in important ways like mounting, crankshaft, and center main bearing.

Check the top of the starboard cylinder bank for the welch plug with the numbers on it, it is aluminum, round, convex, and about the size of a nickel. If you find the numbers, let us know what they are.
 
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