I'll try again: what to do about 1986 75 Mariner/possible low compression?

I'm not sure if this is posted somewheres in this forum but I tried to post yesterday and can't find it so, I'll try again.
Anyway, my 4 cyl 1986 75HP Mariner wouldn't start, so took it to marina. I have had it since new, always, winterized it and it always started easily and ran great. I only use it once a year or less. Most of the lakes in my area are electric only. Marina said it would start if lowered into water but not with hose hook up. They said it had low compression in top cyl. "Common for this engine".
I just wondering what I should do next. I'm going to check comp before I go any further but IF it is low in that cyl, what can I do. I'm guessing it should be over 100 lbs[?] and as long as they are relatively even, then I will look elseware. It is very clean with low hours. I have rebuilt several auto motors from my VW Beetle to my 67 GTO with excellent results, so I am not afraid to rebuild it if needed. I don't have a clue, can they even be rebuilt, if so, is it worth it, are there kits? Are there other things that would cause low compression other than bad rings/cyl that I might look at first? Is there a shop manual available and will it cover tear down and rebuilding?
Sorry for the rambling but I am looking for any help and suggestions.
Thanks and HAVE A GREAT WEEKEND!
Karl.

Definitely check the compression first and repost the results. I don't understand why they said it would start in the water compared to on a hose. The only thing the water does is cool the engine and lubricate the impeller. If it won't start at all then you need to troubleshoot the engine for good ignition, good compression, and good fuel delivery. Even if one cylinder was dead, it would still start and run rough. That 4 cylinder is a great motor, if the readings are a little low you could try to decarb it with some seafoam. This willl sometimes improve compression if there is a stuck ring. Obviously if it has a ring is broken, you will need to rebuild it or buy a used powerhead. There are kits to rebuild the engine, but a lot of times you can find a used powerhead in good condition for less than you can rebuild your old one.

this site will guide you to fix any start issue http://issuu.com/cdielectronics/docs/cdi_troubleshooting_guide_-_2012_1?e=2044661/2001100 Using it once a year is not good for the engine...they like to run alot. Do as thebubba stated. Powertune by Merc. is also a good product. Decarbon it and recheck the compression.

What do the spark plugs look like? If the top one is clean then there may be water intrusion or no spark. The rings can be checked by removing the exhaust plate. Remove the head to check the piston tops and the gasket...may be leaking causing the compression drop. More likely the rings are worn. But testing and examination will tell you what to do. Your experience will make the rebuild alot easier. Check ebay for a factory repair manual for the engine.

Remove the head to check the piston tops and the gasket...may be leaking causing the compression drop.

Click to expand...

Is that possible on a 4 cyl 75 Mariner?

I believe the 4 cylinder was a split-block "headless" - typical of most of the blocks that Yamaha made exclusively for Merc. You can still get a look inside by pulling the transfer covers (on the intake side) and the exhaust cover on the opposite side.

Just one other note here. You call it a 1986 75 horse 4 cylinder - can not be.

In mid 1985 the model was redesigned and returned as a 3 cylinder (block shared with the new 90 horse) - so at best it's an early 1985 model - that could become a big deal when trying to source parts - you want to make sure you are getting the right "stuff"....

Sorry...my bad; didn't realize it was a split case. Love the station wagon. Plymouth or Dodge?

My similar Merc 850 runs 150 pounds compression. (It's a really good block.) Anything less than 120 pounds is a weak cylinder (though still usable). If less than 100, however, the motor had to be torn down.

Jeff

I believe the 4 cylinder was a split-block "headless" - typical of most of the blocks that Yamaha made exclusively for Merc.

Click to expand...

Thats not a Yamaha designed block as that block has been made by Merc since 1969. According to Merc rep the way to tell if motor designed/manufactured by/for Yamaha is that it will have metric bolts in it. This is a lot of small engines under 25 hp . the 25hp chrome bore & Mercocil, late model 3 cylinder 40/50/60 loopers. small and big bore 70/75/80/90 hp 3 cylinder looper. the 4cylinder 100,115,125hp and 2000- 2003 4 cyl 4 strokes.

I'm not saying the Merc rep was lying to you, and the process is quite convoluted, but in actuality, before the mid 2000's, while Merc assembled most of it's outboards in the US, the bare blocks were built in Japan and shipped over for final assembly on "most" models.

Alot of information that Merc would like to have kept from public knowledge came out a few years back when Brunswick co (Mercs parent) accused Yamaha of dumping outboards in the US market.

The whole mess went to court when the US government came in on the side of Brunswick, but in the process forced them to disclose their agreement with Yamaha in it's entirety.

In November of 1972 Brunswick and Yamaha bought equal stakes (38% each) in a Japanese motor mfg called Sanshin (prior to this Yami owned 60% of the company - it produced their powerheads). Sanshin originally had an agreement with Yamaha building outboard engines for them exclusively.

With Brunswick now in the picture (this is 1972), the agreement was amended - here's some of the wording directly from the court documents:

" A collateral or ancillary agreement gave Brunswick the exclusive right to sell Sanshin-produced outboards in the United States, Canada, Mexico (with some exceptions), Australia, and New Zealand. Yamaha obtained the exclusive right to the sale of Sanshin outboards in Japan. In the rest of the world's markets, Sanshin-produced Yamaha and Mercury engines could be sold in competition with one another. There were several other collateral agreements, which (1) barred Yamaha from manufacturing directly or indirectly the same or similar engines made by Sanshin or from purchasing any other outboard motors from other suppliers for resale, (2) limited competition between Brunswick and Yamaha in those remaining markets where both were permitted to sell Sanshin-produced motors, and (3) prohibited Brunswick from manufacturing any products competitive with those then produced by Yamaha, except snowmobiles."

What all that cross talk resulted in was - you have never seen, nor were you likely to see a "headless, splitblock" (aka jughead) Yamaha.

My 1986 Merc's powerhead and gears absolutely came "the joint venture plant" (which incorrectly get's referred to as "Yamaha" (especially by myself), who "was" the majority owner before Brunswick came into the picture").

The bolts are "not metric" because the motors were built to Merc spec and under agreement could not be sold to Yamaha, by Yamaha or anyone else for that matter.

Yes, some of the Mariner line was simply recycled Yamaha motors, built by Sanshin exclusively for Yamaha then sold to Brunswick's "Mariner" division under a separate agreement, and they did have metric components.

By the mid 1980's Brunswick was already pursing options with Tohatsu. Possibly sensing that things were going to fall apart with Yami, in the late 90's Brunswick started a "joint-venture" with Tohatsu which included building a gigantic facility in Japan. This resulted in the Optimax line (Merc) and TLDI (Tohatsu) and saw production of under 40 horse 4 strokes, plus the 25 horse 2 stroke and the single cylinder 2 strokes become nothing more than a Tohatsu with Merc paint/decals.

By the time 2000 hit, Brunswick has also set up shop in China to farm more of their production work overseas. Suzhou, China is now Merc's largest "production" facility.

For years, over 20, all of Merc's electrical/ignition components have been made at the Brunswick plant in Juarez, Mexico.

So the next time you see this "rep" perhaps he can arrange a tour of the US Merc facilities in either Fond-du-lac, WI, or St. Cloud, FL and point out the various milling machines and lathes used to "build" Merc motors. Perhaps he would have to provide a plane ticket to Japan or China to actually see that - because as the details of the court case showed, Merc has done little more than "assemble" outboards in the US for about 40 years...

Sorry, this is going to be long, and I apologize for hi-jacking this thread, but I really do have to expand on what I posted above. I do take a certain amount of pride in my knowledge of Merc's history. So to add to the above.

The whole process of who actually built what first came to light in 1981 when a minor spat erupted between Brunswick and Yamaha over the Mariner line. It was doing far better than Brunswick thought it would and was eating into their domestic sales of the “premium” Merc line – despite the fact that Brunswick wanted the line to help them go after OMC who was the dominant player in the US domestic market in the first place.

It was settled quietly and ultimately resulted in both the Yamaha/Mariner and Merc/Mariner line existing in the market place at the same time (for a while) and as the Yamaha models ceased production they were replaced with Merc’s “dressed” as Mariners.

The US 8[SUP]th[/SUP] Circuit Court heard this initial dispute and ultimately retained jurisdiction over all future actions.

Fast forward to 1998 and Brunswick renews their expiring deal with Yamaha/Sanshin to continue providing powerheads up through the 2006 model years for Mercury outboards.

In 2003 the US government throws a 22.5% tariff on complete outboards AND powerheads produced abroad, So Sanshin informs Brunswick that the cost for their product will rise accordingly. The offshoot is that now Yamaha can import unimpeded to the US as long as the tariff applies to their own outboards and the cost of a Merc will rise because they are sourcing the majority of their powerheads “offshore”.

Brunswick sees this (the potential of a massive influx of Yamaha’s, at a time when their own prices will jump) as a breach of their original agreement, even though it was not specified in the “new” 1998 agreement, and takes Yamaha back to court.
Brunswick argues that Yamaha will “still be dumping” because ultimately they are raising the price of Merc’s production (new powerhead costs), so the playing field is not level.

Yamaha argues back that Brunswick doesn’t mind them “dumping” powerheads into the US market as long is Brunswick is the sole beneficiary of the deal.

Brunswick discloses that it has been sourcing it’s powerheads or key components from overseas suppliers since 1969.

(In 1961 Carl Kiekhaefer merged “Merc” into Brunswick and remained as the president of the division, initially called “Mercury Marine Division “Mercury”, until 1969. With his departure, Brunswick changed the name simply to “Mercury Marine” and started doing things “it’s way”)

(while there is no specific disclosure that Merc was getting powerheads from Yamaha/Sanshin before the “official” joint venture of 1972, it is certainly implied – probably began either just before or immediately after Carl’s departure)

The judge tells Brunswick to provide a list of all current production model Merc outboards that have powerheads manufactured outside of the U.S. (for the 2004 model year), since the tariff’s would not apply to previous model years, predating the tariff’s so that a better understanding of Brunswick’s position will become evident.

Although I cut off a bit at the bottom (footnotes), here is the table from the court docs. All motors with a “X” were built with powerheads provided by Sanshin or Tohatsu.

You will note that there are no Verado’s (personally have no knowledge of where they are actually produced (as opposed to “assembled” must assume they were either US produced or somehow were not affected by the tariff - or were on another chart that I failed to save and have since forgot if I ever viewed it).

This chart fully demonstrates the meaning of Made in the U.S.A. (with foreign and domestic parts)



While I have condensed the more than 1000 pages of jibberish going back and forth in court, if anyone is really interested the entire collection of documents is on file electronically (google search of US 8[SUP]th[/SUP] Circuit Yamaha Brunswick will allow you to find it). A few years back while doing customs work (midnight shift) for a logistics company I passed many long nights reading through the entire collection of documents and took copious notes and examples of some of the exhibits. While I have paraphrased or converted to “plain English”, I do not believe I have misrepresented the original transcripts in either form or content. If I have it was unintentional.

Well! THanks for the education, Graham.

It's all going into my Keeper File.

Jeff

PS: Didn't know I was running a Sanshin!

Yes, if you want a "real" Merc you have to go pre-1969, when Carl was at least still the president of the Merc division in Brunswick.

I suspect that his "retirement" had quite a bit to do with Brunswick's insistence that merc source it's parts "overseas" (the word "outsource" didn't exist in the late 60's).

Thanks everyone for all the help.
Maybe it is an 85. I bought the boat in Sept. 86 with this story for the dealer. It was originally sold in 1984 with a 40 HP that was "too slow". Then in Aug. 86, he went to a new 75 HP "Japanese" Mariner and was "still too slow". He added a stainless prop and then traded it in on what he SHOULD have bought in th first place[a 150 hp figerglass bassboat]. If my speedo is correct, it will do low 50s and that seems like plenty for me anyway. I'm not sure where to look for the serial # but at a real quick glance, there is a part on the engine dated 5/24/85, so should this be one of the last of the 4 cyl Mariners?.
The tow vehicle is a low milage 1960 Plymouth Suburban. Very reliable even on my long tows of 6 hrs+ to Canada and it gets around 17MPG towing.
Is there a manual for tearing down this motor, IF I need to go that route? Although it much smaller that my car motors and no back breaking bending over the fenders, there is a lot going on there. I would take a lot of pictures if I take it apart. Would it require specail tools that most auto mechanics don't have?
Thanks again,
Karl.

Yes, Seloc's makes a fine manual (covers a number of motors) for about 30 bucks in either printed or on-line format.

Mercury Outboards 40 - 115HP, 1965-1989 Repair Manual


​It's available from this site and other marine dealers.

Just checked compression. #1 is at 90-100 lbs and the rest are at 150 lbs, so it looks like I have to do some work. Where would you start?

At the beginning (sorry, couldn't resist).

Personally, I would pull the exhaust manifold (cover) - that will give you a look at, at least part of the piston and cylinder.

You remove the manifold and it's gasket, then pull the baffle and it's gasket. Both gaskets should be replaced if you remove the cover/baffle, but they are a normal stock item for Merc and only go about 5 bucks a piece.

You can rotate the flywheel, with the sparkplugs out, and get a pretty good look at the cylinder(s), plus the rings (on one side) of the pistons.

Ultimately you are probably going to have to split the block, but I would still remove the exhaust first so you have some idea what you are getting into.

If you don't see "much" you can also pull the transfer port cover on the other side, and it's gasket (in stock, about 3 bucks for the gasket). The ports are smaller and you will see a little less than the exhaust side, but will give you a look at the other side of the pistons/cylinders.

If you need/plan to do a rebuild I would suggest that you do it "properly". You could maybe get away with fixing the one cylinder, piston rings etc, and it might last fine OR you could end up tearing it open again in a year or two.

IF you plan on keeping the motor for more than a year or two, personally I would get a rebuild kit. They come in different degrees of completeness - some have gaskets, seals, rings, some bearings - other also include pistons, and yet others also have the rods and other bearings additional to the basic kit.

For your motor they would generally run in the 600-1000 buck range.

You may have to get the bad cylinder bored - the machine shop can/will advise on the condition of the other cylinders - at minimum I would have the other honed. Most shops charge about 50 bucks a hole (whether they bore or hone) - so count on maybe 200 bucks of machine work.

Then you have to try and track down the "cause" of the bad cylinder. If you do a rebuild I personally figure you may as well do the carbs as well (the number one cause for toasted cylinders) plus a full water pump kit (the number two cause for toasted cylinders).

At this point you might be thinking "is it worth it" - only you can ultimately decide that.

I personally liked Merc's 4 cylinder models - lot's of guts.

A new 75 horse is running about 8000 bucks now.
A used one of that vintage, running, might run you 2K (and you could end up in the same predicament in a year).

For, probably at worst, 1500 bucks (and with a bit of looking, 1000 bucks) you can have a "like new" motor that will be good for another 12-15 years at least, even if you run it alot.

Of course, you would have to do most of the work yourself to get it done in that price range.

Since you have this motor since new, and assume you haven't abused it, I would say it's the perfect candidate for a rebuild "if it needs it"....

After reading all the great replies and thinking about it for a while, although I can't afford it, I think I'm going to tear it down. I'm thinking, reguardless of whats causing the low compression, I'm either going to have to tear it down or junk it and it won't cost me anything to tear it down. I'm waiting on a shop manual then I'll have a better idea what all is involved and what I will need to do with the head. I know my machine shop can do the block but depending on how the heads work, may not be able to do them. I am sort of looking forward to rebuilding it.
Again, thanks so much for all your help. Unless I suddenly come into money, it may be a while before I can start but I will be back to this forum then.
I've had this boat/motor for 27 years and have had MANY tow vehicles over that time. Maybe some of you might find some of them interesting. Most of you might appreciate my 69 427/400HP Vette, so I am including a few picts of my tow vehicles.
Thanks again,
Karl.

I do not beleive there is a cylinder head on an 86 4 cylinder Mariner.