20HP MERCURY THUNDERBOLT

[remant333]

HAD MY 20HP OUTBOARD IN SHOP. HAD NEW CARBEURATOR AND SEALS and new water pump PUT IN. MECHANIC SAID GEARS LOOK FANTASTIC. WHEN WE GOT IT BACK IT RAN GREAT FOR ABOUT 15 MINUTES. IT WAS VERY FAST. THE NEXT DAY IT STARTED MAKING A GROUNDING NOISE IN TOP OF MOTOR and it lost power. It still runs, but not with the same power that it had. mecanic said he will take flyrod off but it may be bearings in top part of motor. Can that cause it to make grinding noise and loose power??<br />Thanks,<br />Robert

 

[Chinewalker]

Re: 20HP MERCURY THUNDERBOLT

It's not unusual for the upper bearing cap to loosen as the bolts will sometimes back themselves out if the lockwashers aren't used or if they're not Loc-tited. Take a peak under the flywheel and see if there's an air-gap between the bearing cap and the motor block or if the bolts look loose or missing. If the upper portion of the motor is wet with oily fuel it's a good sign that the cap is loose, or an upper seal is shot. It's also possible the flywheel magnets are loose and one is rubbing the armature. Localize the noise and you'll likely find the cause of the problem....<br />- Scott

 

[remant333]

Re: 20HP MERCURY THUNDERBOLT

Thanks Scott for your reply.<br /><br /> Of all the thing that you mentioned that could be the noise problem which one would cause the motor to lose power when throttle is still wide open?? thanks again, robert

 

[Chinewalker]

Re: 20HP MERCURY THUNDERBOLT

If the upper sealing area has loosened up and the cap is loose, then it's possible it's sucking in air there instead of through the carb. This could be causing a lean condition. The grinding noise could be caused by the armature hitting the flyhweel. It's fairly easy to see if this is the case - pull the cowling off and look up under the flywheel (red part that moves when you pull the starter cord). If the upper cap (held on by four 5/16" coarse-thread 1/2" head bolts) is loose, you'll know it by the bare aluminum showing and likely a lot of oily goo all over the top of the powerhead.<br /><br />Pull the spark plugs out and slowly pull the motor over, listening to where the grinding noise originates from. Localize a bit more and let us know what you find...<br /><br />- Scott

 

[remant333]

Re: 20HP MERCURY THUNDERBOLT

Scott, thanks again for your patience and your expertise. Will be getting the motor back tomorrow from the mechanic who says he didn't really look at the problem because he wasn't sure he could find bearings to replace what he thinks is the noise. Anyway, i will get back to you after I follow your instructions, thanks again

 

[remant333]

Re: 20HP MERCURY THUNDERBOLT

scott, by the way this is a 1973 merc 200 thunderbolt,20 hp, my son posted the first posts, thanks again

 

[Chinewalker]

Re: 20HP MERCURY THUNDERBOLT

Mercury doesn't make bearings, people like Fafnir, Torrington, etc. do. That said, pretty much any bearing in your motor can be gotten over the counter at a bearing store, usually cheaper than through a Merc dealer. With the exception of a couple of proprietary bearings, they're all readily available...<br />- Scott

 

[remant333]

Re: 20HP MERCURY THUNDERBOLT

Hello Scott,<br /><br /> Picked up the boat last evening and found out the mechanic didn't even look at it. To begin with I had him replace a ground wire which he did replace but left it very loose which is a no no from the point of what a ground represents. I started the motor and began checking the wires coming from the power pack and the insulation on these wires is beginnig to fall off. I noticed too that the power pack seems to be very soft, almost like putty. Anyway, while motor is running i tried to find the noise which seems to be around the flywheel . I pulled the plugs as you said but could not detect any noise when turning the motor over as the noise comes and goes. So, I noticed while motor was runing that the wires from power pack leading up to the flywheel area when wiggled affects the noise as well as the rpms. I wiggled these two wires and sure enough the motor sputtered and turned off. I put the boat in the water ,started it up and took off with myself and son in the boat and it ran almost too fast for the weight in the boat. I went back and picked up mama as well and the boat was not able to plane with her added weight, though it did plane initially with all three of us in the boat. The noise went away but then came back again.<br /><br />The mechanic said the power pack was fine as was the coils ect, but the wires are frayed and the insulation is falling off. I intend to take off the flywheel and look at the magnets and coils around the armature, especially where the wires from the power pack hook up. It seems to me I need to change out this power pack? do you agree?? If so, where is the best place for me to look for one? thanks again for your help, will keep you posted on what i find.