1971 Mercury 500 50HP Thunderbolt Ignition

[dPride]

Hi all, got this motor for free from a friend who bailed on attempting to rebuild a classic Duo x15 1965 15' boat. Bought new solenoid, rebuilt the starter and replaced the fuel lines and she started right up. Have had no prior experience with any outboard engine so I wanted to see if it would turn over before I invested any more money and effort. Now that I got it to turn over and saw no pstream, am going to replace the water pump. New pump should be here on Friday.

Since I've got the lower unit off and prep'd for the new water pump, does anybody have any advice on anything else I should be looking at while I've got the lower unit removed?

Only problem I'm having right now is that I removed the Mercontrol to get the motor off of the boat and I reattached it before dropping the lower unit, the Mercontrol was sticking when shifting from Forward to Neutral, every other shift is ok so I believe this should be an adjustment of the cable (at least since this wasn't a problem 'til I touched it), but am unsure.

Any advice would be great!
Thanks

 

[Maxz695]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Take a peek at the Reverse Cam for the REv lock on the LU shifter shaft and see if it,s in good condition. Not cracked or too badly worn> be sure to put a bit of lube to help it shift better

 

[oldman570]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Work the control and make sure that you have put the cables back on the correct positions and have not reversed them. check the shifting slide bar for cracks or broken slide.Put grease on the splines of the DS before replacing LU back on the motor, do not put grease on the top of the DS.While LU is off place garden hose up on the water tube and turn water on to check for good flow from tell tail and exhaust tube asw they could be pluged and will need to be cleaned out. Old impeller chunks or mud dobber nest are easier to clean out with the LU off.JMO
Oldman570

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Thank you both, will definitely make sure to use both of your advice to the fullest. Should be back tomorrow or Saturday to let you know how it all turned out.

Thanks again for the advice.

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Hit a snag, tried to feed water from the water pump inlet up to test the tattle tale and no water came out of the tube at the cowl, water started coming back down along the side of the exhaust tube. I'm pretty sure this means I have a leak and need to take the cover off to access where the leak is. I tried feeding weed wacker line through both ends and am running into something about 1.5' in on either side. I have the Seloc 1406 manual but it doesn't show how to remove the drive shaft cover. Any links that might show some steps for removal? Or better yet a magic wond fix so that I don't have to remove it? Haha!

 

[emckelvy]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

This is normal circulation, water will enter the powerhead thru the copper water supply tube, circulate thru the powerhead then dump out the bottom of the block, into the exhaust tower. Your telltale is probably plugged, a good puff of compressed air will usually clear the line.

HTH & let us know if that doesn't work..........ed

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Hi Ed, borrowed an air compressor and pushed air from the small end at the cowl and am not feeling any air at the water pump end. To confirm I ran the weed eater wire through again and still feel the blockage. What are your thoughts? I've seen on some other posts that in some cases the tattle tale stays closed intentionally until the engine is at warmer operating temps, could this be the case here? I wouldn't think so since it's such an old motor.

I've got the new water pump on the lower unit, once I get this figured out I'll be good to go!

 

[Maxz695]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

My 1979 40 HP engine ran the water hoses through the fuel pump then to the tell tale remove the hose to the fuel pump and then run line through the arch in the fuel pump I have seen them tottaly clogged with dried sand a wire hanger works well to reem it out. If your 50 HP is like my 70 HP the hose to the TT comes off the upper part of the rear water jacket. If you disconnect that hose and have flow then it,s between there and the TT. If no flow there is obstruction between the Exhaust base plate and the rar cover. More than likely blown impellor fins

 

[oldman570]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

The water will come out the exhaust tube as it should and dose. If the weed eater string stops at the elbow on the exhausr cover or water jacket cover ao the head, then that is good. You can take the thermostat out an test it for opening up in hot water, as it should open when the water hits close to 145 degree temp. While doing the stat test replace the cover and test for water flow again thru the tell tail. As long as there is water comming out the exhaust tube in the midsection the stat might be bad or there is crud pluging the elbow for the tell tail. Removing the tell tail elbow and look for blockage there you might find that the hosing inside is packed with sand and mud that has been pumped into themotor and has setup like concret if the motor has set for sometime. If that is the case use the weed eater string , Blowgun before using anything metal to try to break it lose as you do not want to damage the threads in the housing plate. On some of the older motors there is no stat. If all is clear there the stat would have to open for water to come out the tell tail. Getting the water thru the tell tail should be done before replacing the LU and could save removing it again.JMO
Oldman570

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

"The water will come out the exhaust tube as it should and dose. If the weed eater string stops at the elbow on the exhausr cover or water jacket cover ao the head, then that is good."

Perfect, this is exactly the case, however I don't see anywhere on the motor, in the manual, crowleymarine.com or any other reference that shows any type of tstat for this motor. Haven't run anything metal through, just the weed eater. No worries, I'll be keeping the LU off until I know for certain everything's going to work properly, no rush.

Is it possible to narrow this down now to a clog in the line at the powerhead? The old impeller had none of it's blades left so it wouldn't be a stretch.

Thanks again all for your help, David.

 

[79Glastron]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

No thermostat is that motor. Remove the cowl and wrap. Follow the rubber hose, you'll find the blockage, pretty simple.

 

[oldman570]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

No vains left on the old impeller tells the story. Yes they are probly just what is causing the blockage and need to be removed. Removing the elbow at the motor will definetly help get the job done as the particals will have a bigger area to be blown out of. Using the air gun and blowing in the water tube and the hole in the exhaust housing plate will cause the particals to be blown out the all the openings. Then hooking the water hose to the Tell tail and the water intake tube should be done to flush any particals left in the motor out before replacing the LU on the motor. Just get as many as you posibly can out. Most of them will be fairly small as the hole in the waterpump plate is fairly small. You DO NOT want to remove the exhaust cover plate unless it is a last resort,as it can cause more trouble. Best of luck,
Oldman570

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Good morning, I removed the elbow at the lower cowl and traced the blockage back to the powerhead. I moved the cowl down so that I could fit a wrench and remove the plastic fitting from the power head and it broke! threads are stuck in the powerhead hahaha, I'm losing my mind. Any ideas how to get that plastic out of there? Will obviously need to replace the fitting, no biggie, I just don't have the experience removing broken pieces like this. It appears as though the blockage is just behind this fitting so once I get the broken piece out, I'll send some air and then water through from the water pump end and I'm sure it'll clear the blockage. I don't believe there's any easy way of removing the lower cowl from this motor, is there? This would make this work so much easier.

Thanks again Oldman570 for your help.
David

 

[oldman570]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Using a finshing nail as a punch chisle, grind a chisle point on a larger nail, you should be able to make groves in the plastic left in the exhaust plate and work the pieces lose and remove them with pointed twessers. Then a new fitting can be bought at a dealer to replace it. They use the nylon because of the meatle expansion from the heat is diffrent for alluminium than other metal and will leak when the motor gets warm. Cutting two groves accross from each other should get the job done or maybe you will need to cut a third between the two you have cut to get the pieces out. Try not to cut into the threaded area of the metal.There is not a easy way to remove the lower cowling as the power head has to come off to remove it. I have used a hole saw in a drill to cut a access hole in the cowling to get to the fitting area and pluged it with a plastic hole plug for auto use or a metal one used in electrical boxes. Several sizes are made and will give you room to do the work. Alot easier job than removing the power head or the plate as the bolts in them are very hard to remove and will usally break causing more trouble.New aluminium fittings that will replace the plastic can be bought at a lawnmower shop as the are used on some of the older fuel pumps on Kolher motors and are what I use. Works for me and looks good when done. JMO
Oldman570

 

[dPride]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

All done, fired her up and I've got the tattle tale working! Not the strongest stream but I anticipate that this is because of the rectangle flusher, it lets alot of water out. It is a solid stream though and doesn't cut out at all. I actually found a small Ryobi bolt extractor set at Home Depot that worked perfectly, (using the right size to not damage the threads on the black of course) found a new fitting at True Value and was on my way. Didn't even have to cut any holes in the cowl. Let her run for about 20 minutes, never idled out, never any smoke, shifts fine, throttles up good (didn't ever give it too much, didn't want to risk a runaway) and cables are good. I probably had the cables installed wrong after I removed the motor from the boat and that's why they were sticking, but hey, it's all fixed now. I'll post a youtube video in a couple days that I took from my phone yesterday.

Thank you all for your help, especially you Oldman570.

- David

 

[oldman570]

Re: 1971 Mercury 500 50HP Thunderbolt Ignition

Part of the fun of working on things that are in need of repair is the enjoyment of knowing that you can fix things and have a better understanding of how they work. Now all that is left is have all the required safety items and time to enjoy a new toy.
Best Of Boating,
Oldman570