MERCURY BLUEBAND 50HP THUNDERBOLT

Marley · Jun 8, 2003

Hi Folks, I live in Christchurch, New Zealand and have bought a Merc, 50Hp thunderbolt blue band motor and another one for spares (both electric start). The first one has serial no. 5844095 and according to the CLYMER manual ,which I have a copy of, was made in the USA (some were made in canada and australia). Any idea of its yr of manufacture?. I looked at some web sites shown in previous messages for the same question. But didn't get much "traction" in getting into them to find some dates. Is there anyone in the forum keen to tell me about some things you've learnt about the motor that would be useful for a first time user?. For example, before testing the motor I have got the oil in the gearbox changed (located in leg). Great site. Marley.

andrewkafp · Jun 8, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Try here http://www.marineparts.com/partspages/techhelp/images/TECH158.gif Reckon it's 1981-82 I'm told they are a great motor if you take care of them. Check some of my replies. Your's is a USA No (5+6) Australian nos were 8* (Mine is 8055598 #1980 Canadian were 7* Europe 9* The last Blueband was made in 1984 After that was a brownband Then Red Prior to 1979, they were called 500's not 50's Has your 50 got light and dark blue band with silver "mercury" and look like this ? http://us.f1.yahoofs.com/users/81724e9b/bc/DSCN1292.jpg?bcXuy4.AYxVi5Quv Yes .. This is a great site... The Americans like their Mercs and know a lot about them Some good members. Alcan, 12footer, rickl1dboat to name a few.

Marley · Jun 9, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Gidday Andrew, thanks for the quick reply. We are about to test the motor in the next few days and today spent a bit of time flushing out some of the old gearbox oil through the vent plug with some new. Should we have just totally drained all the oil first then add new. The old one looked good. Also there is no sign of o-rings or such with the vent screw and that bottom filler screw. Are the o-rings rubber or copper. Are they inside the motor and dont need regular service?. Can you buy this oil in bulk. Does it have to be Mercury type?. Regards Marley

andrewkafp · Jun 9, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

The seals behind both screws are hard to see because they and countersunk and sometimes clear or white. You will find them when you remove the screws probably still inside the seat. If you decide to refill or add, take out the top vent screw and then the bottom one. put the sueeze bottle in the bottom and squeeze until all the air bubbles come out the top hole followed by oil. Then put the scews back in. A small loss is OK. You need to use marine grade lower unit oil.Don't use SAE 90 car diff oil, it doesn't have as good properties. Unit will take less than 1 litre. You can buy in 4l qty. http://au.photos.yahoo.com/andrewkafp NB Is your motor as above ??

ledgefinder · Jun 9, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Use good gaskets on those upper & lower drain screws - grab some new ones from a dealer if they're at all questionable. ORings are fine, but the white nylon Evinrude/Johnson washers work fine on the Mercs as well. Bad gaskets are a common reason for water getting into the lower unit (bad, and worse if it's salt water). If new gaskets are hard to come by, you can put a little gasket sealant or silicon sealant on the screw threads for a quick fix. The impeller on those 50hp Mercs is relatively light-duty, I'd change it out unless you know that it's been done recently. Minimally, keep a close eye on the telltale flow until you do change the impeller. It's not a tough job on that particular model. Make sure you run fresh gas - old/dirty gas gums up the carbs. Lean carbs can burn a cylinder on a 2stoke. If it's been sitting, and the carbs haven't been cleaned (best idea, but a bit of a chore on those 50hp 4cylinders), minimally add about a 1/4 bottle of regular fuel injector cleaner to your first tankful of gas. The 500s idle well, but like to rev. Ideally, prop is so it turns just over 6000 rpm with the lightest load in the boat (just you alone). If it won't turn at least 5000 with the prop on there, don't leave it that way, or at least don't cruise full throttle.

Marley · Jun 12, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Hullo Re : Mercury Thunderbolt 50Hp 4 cyl, 1981-2 thanks to Andy and Ledgefinder for your comments. All other people are most welcome to comment as well. Just to keep you informed. We took the motor out for its first test run the other day. We found that the engine starts first time everytime. When we ran it for about 15 min we started to play with the controls to see what they all did. In doing so we turned the motor off. It would not start again. When in gear mode ( there is a throttle button you push on the gear stick) it started beautifully. But in neutral it would not. So we adjusted the throttle adjustment screw inside the motor. The motor idled ok but fast. THEN we noticed while looking at the throat of each carb (choke butterfly is visible)the bottom carb was spewing petrol out of it and the top one was dry. Bugger I thought!!!!. It was giving out tons of fuel , especially when revved up. Then we kept running the motor without the covers on and after 3o min all the petrol stopped running out of the mouth of the bottom card and it was all normal. WHAT HAPPENED?. I still have not put in 1/4 Bottle injector cleaner in the fuel ( which was brand new 96 octane lead free petrol with 1/50 Johnson Oil). If it is running should we leave it alone and just carry a fire extinquisher???. Regards Marley

tmcalavy · Jun 12, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Well keep a fire extinguisher aboard, but hopefully you won't need it for your carbs AFTER YOU REBUILD THEM. The float or needle valve/seat in your bottom carb is malfunctioning. That is why it urps gas...a very bad thing. Try this, get it running and watch that carb. If/when it starts urping fuel, tap a couple times with the hard plastic end of a screwdriver. If it then stops urping fuel, the float or needle valve is sticking. The carb rebuild is easy...kits cost about $18-$25 each (US). Hardest part is getting the carbs off to rebuild them. Takes time and patience. Or have a mech do it.

Marley · Jun 12, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Thanks Tim, why won't a injector cleaner fix the problem? Just as a aside: My friend who saw the problem before and after reckons that it was a bit of carbon? or something that was in the way which when the engine cooled came away when we ran the engine again and was burnt up by the pistons. Is it possible?

tmcalavy · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Doesn't figure. How could carbon in your cylinders make your carb leak? The carb is upstream from the cylinders and any carbon they might hold. Injector cleaner will clean the carb passages, etc, but won't displace any grit large enough to impair the needle valve/seat. To get a carb completely clean and to replace a leaky/stuck float, YOU MUST REMOVE and clean the carbs.

jim dozier · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

You will even get a difference of opinion as to whether or not "cleaners" that you put in the gas will remove carb deposits either. Put me in the take it apart and clean it piece by piece with aggressive cleaners group.

steelespike · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

I believe your motor is designed to run on 87 octane, 96 is a waste of money. I have a 65 merc. 500 an older cousin of your motor. When the original owner bought it in 65 he told me it was the best motor Merc or anyone else had built to that point.And he was a strong OMC fan up to that time. I also had a 77 500 and loved it.

ledgefinder · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

I'm not saying cleaner will remove all carb deposits, & I'd agree that proper maintenance is to remove, dismantle & clean any carb that has sat for an unknown period. Same with replacing an impeller often, checking the gear lube every few weeks, etc.. Fact is, though, many people are simply not going to do it. People are telling me they paid $200 to $275 for carb rebuilds this year (and the $275 was for a 2 carb OMC 50hp!?). If the choice is between adding some carb cleaner to the season's first tank, or doing nothing, I'd suggest the carb cleaner. Best bang-for-the-buck, & it might actually get done.

ledgefinder · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

I'd see to the impeller first, unless you know for sure that it's been recently done. The 40-75hp Merc lower units have a relatively light-duty impeller, plus you have no overheat alarm on that motor. If the impeller goes, the first you'll know about it is when the motor seizes up. They're not hard to change on those. It might be fine, but I'd keep an eye on it until you change it, particularly if it's sat for a while. The overflow sounds like a sticking needle valve that has resolved itself. I agree with JimD & others completely that carb cleanings are a good idea if it's sat for a while, but if finances say it's one or the other, I'd do the impeller first. If you can, avoid full-throttle cruising until you rebuild them - maybe do the ones on your parts motor, then swap them in once they're done. The carbs on that motor are easier than the 1970-74 Merc 500s - which are brutal to get at. "John's Old Mercury" website discussion group is pretty good on Merc-only stuff, by the way.

jim dozier · Jun 13, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Steelspike I think they calculate octane differently down under (maybe they do reciprocals)

Marley · Jun 15, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Re: 81-82 MERCURY THUNDERBOLT 50HP BLUEBAND Thanks for the replies We fired up the motor and found that bottom carb was still normal. It is a good idea to sort out the suspect bottom carb but here like prbably what it is like in the US no many people want to touch a older motor like this. It also look complex to remove. I did not mention this before but our 80's motor supposedly had a $2000 recondition done to it ( when don't know). We bought it and a spare 1974 thunderbolt 50Hp motor for NZD$850 ( approx US$400 ). So I'm not sure it makes sense to throw hundreds of dollars at it. Probably doing it ourselves is the best bet. Just on a new line of questions. Our spare motor came with a hydraulic pump and ram. We've tried it out and found it pumps in one direction and not the other. I will follow the troubleshooting guide, but I am interested in peoples experiences with fixing these bits. I talked to a outboard motor dealer and he did not want to know , saying that these parts are really throw-away items. Our 80's motor does not have a tilt system, just two peumatic gas ? struts on both sides, supposedly to assist maual dropping of the motor and to counter the ensuing recoil when boats hit objects and the motor wants to recoil upwards. My question is if when fitting a tilt system ( with one hydraulic ram) can we keep one peumatic strut attached to the other side. I mean does the strut give too much mechical resistance when lighting and lowering. And there cause the pump to fail?. Regards Marley

ledgefinder · Jun 15, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

The carbs are different on your older (1974) motor, as is the ignition and starter. The lower unit is the same (I think). I think the midsection swaps over & not sure about the powerhead itself. Merc trim system wiring can be tough to figure out (for me anyway) - I'd just take your time and treat it as a challenge/puzzle. I'm guessing here, but I don't think you'd hurt anything setting it up with just one power ram. Probably just work more slowly/weakly. The system's don't go fast enough to generate much resistance from the 'shock absorber' units.

echozulu · Jun 15, 2003

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

hi marley, you cant just use one tilt cylinder because it wouldnt raise the engine evenly and bind up.....the knurled knob on the bottom of the trim pump is the manual release valve turn it counterclockwise and you get both up & down

Grant Manning · Feb 1, 2004

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

steelspike - We have a 77 500 serial number 4417206. First Merc we've owned. Would love to know about their reliabilty and performance. What are they like generally. I'm rebuilding following a reed valve blow up! Regards Grant Manning Sunshine Coast Australia

Clams Canino · Feb 2, 2004

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

To be short, they are the motor that made Mercury what it is. Bulletproof. The Volkswagon Beetle of outboards. -W

Originally posted by Grant Manning: steelspike - We have a 77 500 serial number 4417206. First Merc we've owned. Would love to know about their reliabilty and performance. What are they like generally. I'm rebuilding following a reed valve blow up! Regards Grant Manning Sunshine Coast Australia

Peter J Fraser · Feb 2, 2004

Re: MERCURY BLUEBAND 50HP THUNDERBOLT

Marley, I had one of those engines for 15 years. I am in Hamilton (N.I.). I have uncovered a lot of parts left over from that period which you are welcome to have if you give me a call on 027-4923674 days or 07-8494779 evenings. Peter

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