Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

[Merc-Moron]

Hi all,

I'm a fair novice when it comes to boat engines, and long story short I inherited an awesome old boat which has a Merc Thunderbolt 850 Blue Stripe, and from the serial number seems to be a 1976. This beast older than me!

I had it serviced (service sheet attached) and it was starting well, I left it for a few months while I got the trailer fixed up and then when testing it out the other day it just conked. I removed the side panel and found all this green corrosion and split insulation within the wiring.

I understand this may be something to do with the Stator also, and than I might be able to get one from CDI electronics?

I do plan on buying a service manual & parts list from the link in the stickys, but wanted to see if anyone could give me any advice. I haven't worked on outboard before, but I'm technically minded and really willing to learn from the ground up. I would love nothing more than to hear this beast open up on the open water!

I've (hopefully) attached some pics, but in case they don't work you can grab them from my page with these links:

http://members.iinet.net.au/~emass/Corroded Wires.jpg

http://members.iinet.net.au/~emass/Corroded Wires 2.jpg

http://members.iinet.net.au/~emass/Service Sheet.jpg

P.S. Thanks in advance to anyone who might help me out with where to start, books would be great! I'm really keen to start learning how to repair boat engines, and this forum looks amazing for info and legends of the trade!

All the best,

Merc-Moron

 

[Moody Blue]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

MM, those old Mercs are notorious for bad wiring. Mine is a few years older than yours so I'm not really familiar with the specifics but I will offer some general advice.

First thing to check is the compression on all cylinders. Not much sense putting alot of money and time into a motor with a bad cyl.

I noticed that no carb work had been done. That should be high on the priority list.

Appears as though the waterpump has been serviced, and that is very important.

You WILL need to replace most if not all of the internal wiring. Carefully check the big multi-pin connector that plugs into the motor as well.

Once all appears good, you should perform what is called a "link and sync", a procedure that correctly sets up the synchronization of the carbs and ignition system.

Lots of good info here on these forums. Use the search feature at the top of the page to find specific information. If you plan on keeping the motor, a good manual will be essential. A genuine factory manual is the best, but failing that, I would choose Clymers over Seloc.

 

[dwco5051]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

The cover for the fuel pump looks like someone smeared some sort of sealer on it to stop it from leaking. There is a filter screen behind this cover which should be cleaned now and then. The proper way to seal it from leaking is an o-ring under the cover. Get a couple of extras when you change it, you will need them later. I ran a motor just like this for about 30 years before it finally burnt a piston. Had 2300 hrs on it when the Hobbs meter quit working, ran it another 15 or so years.

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

I forgot to include the service sheet from what was done a year ago by a local marine repair center - I have added it to the original post or you can check it out here: http://members.iinet.net.au/~emass/Service Sheet.jpg

 

[redjmp]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Well it looks like your yellow/red wires feeding your rectifier at the bottom have shorted out. It also looks like the 4 wires from your trigger to the pack are rotten as well. Your stator and trigger may be still good otherwise. You may be able to splice in some good marine grade wire to replace the corroded stuff. But you may have fried the switchbox as well. More than likely it was your rectifier wires shorting out that caused it to die so I would start by replacing or wrapping some tape around them so they cant short as well as the 4 trigger wires and try firing it up. If it works under load, then at least you know that you don't need a switchbox. Then you can decide whether to fix or replace the stator and trigger , but they aren't cheap. If on the other hand, it doesn't fire up then on top of needing a multimeter and a spark tester along with a Dva just to properly test. Then you still might need a stator, trigger, switchbox, and rectifier adding several hundreds of dollars to the cost of just your shop manual. You'll have to ask yourself if its worth it to save such an old motor or whether you' be better off parting it out and getting some thing newer....

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

MM, those old Mercs are notorious for bad wiring. Mine is a few years older than yours so I'm not really familiar with the specifics but I will offer some general advice.

First thing to check is the compression on all cylinders. Not much sense putting alot of money and time into a motor with a bad cyl.

I noticed that no carb work had been done. That should be high on the priority list.

Appears as though the waterpump has been serviced, and that is very important.

You WILL need to replace most if not all of the internal wiring. Carefully check the big multi-pin connector that plugs into the motor as well.

Once all appears good, you should perform what is called a "link and sync", a procedure that correctly sets up the synchronization of the carbs and ignition system.

Lots of good info here on these forums. Use the search feature at the top of the page to find specific information. If you plan on keeping the motor, a good manual will be essential. A genuine factory manual is the best, but failing that, I would choose Clymers over Seloc.

Thanks very much Moody Blue for the advice, I do have a copy of the Owner's Guide & Maintenance manual, which seems to cover basic lubing / cleaning of certain areas, but it doesn't get into any of the meaty stuff like compression tests, carb work or link & sync. I'm currently on the hunt to buy a proper genuine factory manual and hopefully a parts list.

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

The cover for the fuel pump looks like someone smeared some sort of sealer on it to stop it from leaking. There is a filter screen behind this cover which should be cleaned now and then. The proper way to seal it from leaking is an o-ring under the cover. Get a couple of extras when you change it, you will need them later. I ran a motor just like this for about 30 years before it finally burnt a piston. Had 2300 hrs on it when the Hobbs meter quit working, ran it another 15 or so years.

Thanks dwco5051 I'll look into that proper O-Ring for behind the fuel pump. Awesome to hear that you ran a motor similar like this for so long. I'm sure this thing can rise again! P.S. What's a Hobbs Meter?

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Well it looks like your yellow/red wires feeding your rectifier at the bottom have shorted out. It also looks like the 4 wires from your trigger to the pack are rotten as well. Your stator and trigger may be still good otherwise. You may be able to splice in some good marine grade wire to replace the corroded stuff. But you may have fried the switchbox as well. More than likely it was your rectifier wires shorting out that caused it to die so I would start by replacing or wrapping some tape around them so they cant short as well as the 4 trigger wires and try firing it up. If it works under load, then at least you know that you don't need a switchbox. Then you can decide whether to fix or replace the stator and trigger , but they aren't cheap. If on the other hand, it doesn't fire up then on top of needing a multimeter and a spark teaster along with a Dva just to properly test. Then you still might need a stator, trigger, switchbox, and rectifier adding several hundreds of dollars to the cost of just your shop manual. You'll have to ask yourself if its woth it to save such an old motor or whether you' be better off parting it out and getting some thing newer....

Hey Redjmp, thanks very much for your info. I'm definitely up for replacing any & all the wires that are going bad. As a general question what's the best type of multimeter to pick up for this kind of work? There looks to be some good stuff on this site http://www.iboats.com/Marine-Electrical-Parts-Lights-Wiring-Batteries-Switches/dm/view_id.5 page. Maybe I should get some wire and tools etc from here. For a multimeter, just the standard ones from Tandy / Jaycar would do?

Sorry everyone for being such a novice, I'm super keen to keep this engine as I've already sunk a considerable amount of coin into it, I really want to get her going again! I understand it might cost a fair bit of time and money if things keep going wrong, but hopefully I'll learn a whole lot from the process and once she's going again it'll be worth it to hear it hum!

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

P.S. Hopefully I can send you all a case of beer one day to celebrate! Ha ha Thanks again.

 

[dwco5051]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Thanks dwco5051 I'll look into that proper O-Ring for behind the fuel pump. Awesome to hear that you ran a motor similar like this for so long. I'm sure this thing can rise again! P.S. What's a Hobbs Meter?

Hobbs is a genericized trademark for products generically called Engine Hour Meters

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Hobbs is a genericized trademark for products generically called Engine Hour Meters

Ah, great! Would I expect there to be such a meter on my Merc 850? Would be good to see how many hours it has actually done.

 

[72mtwain]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

not to hijack your thread but I have the same motor with the same wiring issues. I was wondering if someone knew what gauge wire the green + coil wires are and the trigger wires? I will need to replace them all.. Also I read that marine grade wire should be used?

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Great question and please feel free to hijack add to this thread if you like! I am seeing a friend this afternoon who has re-wired a 84 Merc and will ask him what he recommends and post back.

Did you manage to track down a repair manual or parts list for the '76 Merc 850, if so where from?

Thanks, ...and lets get these puppies roaring again!

Wooo!

Happy Weekend everybody!

 

[backyard mechanic]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

My thoughts were that this engine had seen the bottom of a saltwater lagoon somewhere and was resurrected for a quick sale. Call me a skeptic but this one deserves a lot of "looking". Wires are one thing; internal bearings another. Sure looks like a dunker to me.

Any history that may confirm or even deny that?

 

[72mtwain]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230543127406&viewitem= . This is the repair manual I bought, so far has been pretty good. No luck on parts list yet.

 

[ONERCBOATER]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

ok hope i don't get barbed for bringing a merc 200 20hp from 1978 into this, but they are similar engines and wiring. yesterday I was happily mounting my engine (somehow that didn't sound right) on the transom, I got the steering cable in, and the 55gal drum under it, and thought I was al ready to go, then just before I hooked up power to her i noted a green wire that the insulation was all crackly around upon further inspection and intentionally flexing that wire and a few others i found that the insulation on most of the wires was less than acceptable and that it had green corrosion on it under the failed jacket/insulation.
This evening when i get off work, by the romantic glow of the fluorescent shop lights I will be chasing ea and every one of the wires and replacing it with shiny new wire, my preference is silicone jackets and I think that is the way i intend to go here. 8yrs ago I had this issue with a force engine a 125 that sat out here in the SW desert and had its wires baked in the heat, what I did for that one worked to this day without issue (i dont have the boat anymore but the guy that bought her from me is still happy with his farce 125).
All wires that you can remove completely and replace from end to end do so, the wires that go into sealed units are the biggest headache....as you cant pull them off and replace them, what i did for those was trimmed them short and replaced them with new wire by soldering and using self sealing heat shrink to protect them. A lil bit of epoxy was then used on the damaged area of wire where it went into the component to insulate and isolate it from the other wires, then the group of wires as they came out was epoxied in place by essentially building a new boss around it so as to protect the wires from being pulled out. it was a lot of work, but the bright side is it is a long time repair.
You must pay special attention to getting the heat on and off the wires as fast as possible when soldering them as I do not know how heat sensitive the components are inside the modules. Also remember to use real lead solder and it must be rosin core. also from my exp it is best to use the smaller diameter solder as it seems to melt better and easier. Hope this is of some help to you.

Oh i noted that they suggested marine grade wire, that I am unfamiliar with, what i have always used was either silver or copper wire with a very high strand count as it survives vibration and movement well, and as thick a jacket as i could get. I would love a link to the marine grade wire and or an explanation of the difference between automotive and marine wire....or what is different with marine wire as I may well have missed something there.

Sean

 

[ONERCBOATER]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

one thing i forgot to mention is if anything shorted out and is failed such as voltage regulator etc... you will still have to replace it. I myself have more time than $$ so I generally attempt less expensive fixes 1st, but if you have a component that has failed it can take other components out as it goes, so please use prudence.

Sean

 

[Moody Blue]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

MM, there are a number of very good on-line parts libraries and exploded parts diagrams for your motor. All you need is the S/N of your motor.

Try here

dougrussell dot com
maxrules dot com
crowelymarine dot com
mercruiserparts dot com

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

I have just acquired a service manual and it's detailed as all get out! I have also sourced a CDI replacement wiring harness from a local supplier but it's $225.00 AU. There is one for about $160 on boats.net but they won't ship OEM parts internationally.

Since all the wiring may have to be replaced, is the internal wiring harness a good starting point?

Also, i think I will need some proper tool to get the flywheel off.

P.S. Friend is going to help me do a compression check, now that i have the manual.

Onwards and upwards!!

Will keep posting here with updates and photo's as I get them.

 

[Merc-Moron]

Re: Mercury Thunderbolt 850 Blue Stripe 1976 85hp Green Corroded Wires (Photos)

Have sourced the flywheel removal kit from Ebay. $50 w/ shipping.