Merc 500 ITS OVER Rest In Piece

[JGra]

I need all the old merc experts to chime in. I have aquired and old merc 500 thunderbolt (given to me). The motor is 100% complete and has no missing parts. The serial number on the motor is 2516298 whick I think makes this a 1969 model. It has been sitting on an old boat uncovered that was in a friends field for no telling how long. I would like to know if it is even worth the toruble, effort and money to try to bring the old girl back to life. I brought back to life an old merc 200 that was on a Jon Boat I had sitting for 15 years and it runs great today. This one seems a little more involved than the 20 HP

This is what I know as of now. I pulled the cowl off and just like the 20 hp all the wiring is in real bad shape. Looks like there is one complete internal harness that runs around the whole motor. Might be able to get one somewheres. I pulled the plugs and tried to sping the motor which it did freely. I seperated the wires as best as I could and put power directly to the starter ( I can hear you guys shaking your heads now) to see if it had any compression at all. The motor seem to have good compression with just holding a finger over the hole. I will put a gauge on it and get some better readings tomorrow. What kind of compression numbers am I looking for on this motor.I then put one of the spark plugs on the end of the plug to see if it had any fire. To my surprise it had fire to all 4 plugs.

Question? how would it have fire just by jumping from the starter. Does it not go thru the switchbox to fire the cyl's. Does this tell me that all the electronics are good?I have the controls for it but the external part of the harness was gone. I am decent with the tools. Spent 20 years as a ford engine tech but just leaning as I go on these outboards.

Well this had gone on long enough. Am I opening up a can of worm with this one. Even if I could get it up and running is there alot of issues with these model motor. All the advise I can get will be of great help. Thanks

 

[daveswaves]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I need all the old merc experts to chime in. I have aquired and old merc 500 thunderbolt (given to me). The motor is 100% complete and has no missing parts. The serial number on the motor is 2516298 whick I think makes this a 1969 model. It has been sitting on an old boat uncovered that was in a friends field for no telling how long. I would like to know if it is even worth the toruble, effort and money to try to bring the old girl back to life. I brought back to life an old merc 200 that was on a Jon Boat I had sitting for 15 years and it runs great today. This one seems a little more involved than the 20 HP

This is what I know as of now. I pulled the cowl off and just like the 20 hp all the wiring is in real bad shape. Looks like there is one complete internal harness that runs around the whole motor. Might be able to get one somewheres. I pulled the plugs and tried to sping the motor which it did freely. I seperated the wires as best as I could and put power directly to the starter ( I can hear you guys shaking your heads now) to see if it had any compression at all. The motor seem to have good compression with just holding a finger over the hole. I will put a gauge on it and get some better readings tomorrow. What kind of compression numbers am I looking for on this motor.I then put one of the spark plugs on the end of the plug to see if it had any fire. To my surprise it had fire to all 4 plugs.

Question? how would it have fire just by jumping from the starter. Does it not go thru the switchbox to fire the cyl's. Does this tell me that all the electronics are good?I have the controls for it but the external part of the harness was gone. I am decent with the tools. Spent 20 years as a ford engine tech but just leaning as I go on these outboards.

Well this had gone on long enough. Am I opening up a can of worm with this one. Even if I could get it up and running is there alot of issues with these model motor. All the advise I can get will be of great help. Thanks

Your motor has points and coil with condenser, it does not need anything other than being spun over to run. Sounds like its worth working on to me. But then I drove all the way to Chicago to buy a dead inline 6 150 block.:redface:

 

[blue90HP50]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

Congratulations JGra, you've got a beauty. Got my dads running after 22 years on it's side on dirt floor. Here is what I did to mine after reading many posts, and this will get you started(I'm no expert). Remove plugs and spray PB Blast or other lubricant in holes and tilt motor up, let set while parts are ordered and on the way. Suggest you order internal wiring harness, rectifier, impeller(waterPump rebuild kit), two(2) carb rebuild kits. External wiring harness/controls may be on E-bay(Can I say that here?). Don't mess with distributor and plug wires unless you have to. Replace all internal fuel lines.
Most likely the Switch box, distributor, and coil is OK. Have lower unit serviced and impeller installed at same time. Take pictures and make notes before disassembly of wiring harness. The battery is an integral part of the ignition system, therefore its not good to run without battery properly connected. I did not mess with the timing, as I have no boat. That's the extent of my advise. You can do this. PS: I replaced the timing belt, but probably was not immediately necessary. Others may differ or add to this accordingly. Have fun!

 

[JGra]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

Very good advise, thanks. What would be a good compression reading on this motor for it to run?

 

[JGra]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

Could somone tell me the part number for an internal wiring harness for a merc 500, serial number is (2516298). I think its a 69. It has a 6 pin plug on the side of the motor. I keep coming up with differant numbers. Just looking for the correct one

 

[sschefer]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I found two part numbers: 46905 and 38072. Both are NLA. I tried to cross it at Sierra but no luck. You'll save a lot of money if you just buy the wire and rebuild it yourself.

 

[Aqualift]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I have a 68 Merc 500 thunderbolt without the lower unit and I have run it via a battery and jumper cables and a set of smaller jumper wires with small alligator clips. From the battery, rig up the battery jumper cables to the motor with the positve going to the large red lead where it meets the starter solenoid. The negative to a good ground. Run one lead of the smaller set of wires from the positive battery post to the white terminal at the switchbox and the other one will act as your starter switch. Momentary contact from positive post to where the small yellow wire attaches to the solenoid. (If you don't have a remote starter)

 

[JGra]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I ran a compression test tonight with an old gauge I had. I am not 100% about the gauge but I got 90-95 psi on all 4 cyl. What do these motors require to fire.

 

[daveswaves]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I ran a compression test tonight with an old gauge I had. I am not 100% about the gauge but I got 90-95 psi on all 4 cyl. What do these motors require to fire.

It will run with that compression number, ideally it should be over 110, but as you say you are not sure of your gauge. Seafoam will likely improve those numbers, sounds like you have a project/

 

[rspar]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

I had some wiring on my 71 merc 800 that the insulation was off I just covered it with liquid electrical tape seem to be fine. You probably should change the old style fuel lines. Mine sat for ~20 years or so and started right up. Mine has the electronic ignition though.

 

[JGra]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

The harness on this motor is to fas gone to do any of that. I am trying to find another harness for it now. This is a thunderbolt eng that has a stator and a switch box. I assume this is an electronic ignition also. I am going to replace the harness, clean the carbs and check the fuel pressure regulator and see if I can get it to fire off. If it does I am going to go through the whole motor and replace all the fuel lines and really go through everything. Just want to make sure it will at leat run befor I dump alot of dollars it it.

 

[JGra]

Re: Merc 500 Should I Even Attempt This

Re: Merc 500 Should I Even Attempt This

Found a set of used internal and external harness's that are in good shape from the same year enging. Cleaning the carbs this weekend.

 

[JGra]

Re: Merc 500 Making Progress I Think

Re: Merc 500 Making Progress I Think

Well I got everything together and I think I making some progress on a mortor that has been sitting in a field for the last 20 years. I started with replacing all the fuel lines, fuel punp kit, removed both carbs and tear down and clean, replaced all plugs, replace starter solenoid and replaced internal harness. I tried to put some fuel to it tonight. The eng turned over great but would not start. Pulled the plugs and they are all getting fire. The new plugs looked still brand new and looked like they had not gotten any fuel. I added some fuel into the cylinders and put the plugs back in. Turned the key and it started and spiited and sputtered and then cut off. I pulled them out again and added a little bit more fuel and tried it again. It started right up and ran decent for about 8 seconds. Any thoughs about the fuel problem. carbs were not that bad when I had them apart. Needle and seats move free. I heard alot about reeds, could these be a problem. Could use a little advis before I move on.

 

[RaScLeS]

Re: Merc 500 Maiking Progress I think

Re: Merc 500 Maiking Progress I think

prime the bulb as you crank it ? or as its running

 

[JGra]

Re: Merc 500 Maiking Progress I think

Re: Merc 500 Maiking Progress I think

I will try that, I will also try to squirt some premix into the carbs. It was getting dark so I quit after it fired with putting some premix into the cylinders, will try again tomorrow.

 

[daveswaves]

Re: Merc 500 Making Progress I Think

Re: Merc 500 Making Progress I Think

Well I got everything together and I think I making some progress on a mortor that has been sitting in a field for the last 20 years. I started with replacing all the fuel lines, fuel punp kit, removed both carbs and tear down and clean, replaced all plugs, replace starter solenoid and replaced internal harness. I tried to put some fuel to it tonight. The eng turned over great but would not start. Pulled the plugs and they are all getting fire. The new plugs looked still brand new and looked like they had not gotten any fuel. I added some fuel into the cylinders and put the plugs back in. Turned the key and it started and spiited and sputtered and then cut off. I pulled them out again and added a little bit more fuel and tried it again. It started right up and ran decent for about 8 seconds. Any thoughs about the fuel problem. carbs were not that bad when I had them apart. Needle and seats move free. I heard alot about reeds, could these be a problem. Could use a little advis before I move on.

Sounds like you are almost there. Instead of putting fuel in the cyl, squirt it in the carb throats. Your carbs are dry and until the engine runs for more than a few revolutions the fuel system will not wet out. Make sure your squeeze bulb is installed the right way around, there will be an arrow on it, should point towards the carbs, not towards the fuel tank. Full choke to start, fast idle lever up if you have that style of control, battery fully charged.

 

[JGra]

Re: Merc 500 Making Progress I Think

Re: Merc 500 Making Progress I Think

I am going to try that when I get home. It was getting dark and I did not have a spray bottle last night. Its hard to get to the carbs with that front engine bracket there. I am hoping I can spray thru the holes they give to to adjust the mixture right into the carbs. If I have to I wil take the bracket off. I do have a fast ilde lever on my control and a push button switch on top for a choke. I just hope the reeds are not bad. I dont know if I want to dig that deep into the motor.

 

[JGra]

Re: Merc 500 Making Progress I Think

Re: Merc 500 Making Progress I Think

Well I think its time to put the old girl out to pasture. I did manage to get her running but once running the powerhead had a really bad knock to it. Might be why she was put up in the first place. Still had good compression and spark. I guell I will either sell it as a parts motor or part her out. Thanks for everyones help.

 

[daveswaves]

Re: Merc 500 Making Progress I Think

Re: Merc 500 Making Progress I Think

Well I think its time to put the old girl out to pasture. I did manage to get her running but once running the powerhead had a really bad knock to it. Might be why she was put up in the first place. Still had good compression and spark. I guell I will either sell it as a parts motor or part her out. Thanks for everyones help.

Before you call the glue factory try one more thing, buy 4 new spark plugs and install them, try again. The plugs might fire outside the engine but under compression one could be failing. It is quite common and the engine will knock like crazy if one cyl is not firing. Its worth the couple of bucks for plugs to be sure.

 

[mercuryverado]

Re: Merc 500 ITS OVER Rest In Piece

Good luck with your 500! I think I have the exact same one as yours! The '69 500 is truly a great motor. I have never had a single problem with mine... it has been the best one I have ever owned.