1969 Mercury 100 H.P. Thunder bolt lower unit

[downingd]

I recently aquired a 1969 Mercure thunderbolt outboard motor. The motor fired up and ran great after a easy repair to the fuel line connection. The problem is the water pump is not working. I removed the lower unit to inspect the impellers. After I put the lower unit back on the transmission was stuck in forward gear. The transmission worked fine befor I took off the lower unit. I think I can buy a rebuild kit for the pump and it should work fine. The transmission being stuck has me worried. Is there a certain way to put the lower unit back on? How can I get it to shift into nuetral and reverse?

 

[emckelvy]

Re: 1969 Mercury 100 H.P. Thunder bolt lower unit

Common mistake. The shift shaft is free to rotate quite a bit when the lower unit is in Fwd gear.<br /><br />The correct position for the shift shaft (if you plan on installing it with the remote control box in Fwd), is rotated counter-clockwise until it stops (while still remaining in Fwd gear). When you are at the correct position, any further rotation of the shift shaft in the CCW direction will shift the gears to Neutral.<br /><br />Some folks prefer to place the gearbox in Neutral when reinstalling, because there is a positive detent which Fwd gear lacks. However, you must ensure that the remote control box is also in Neutral.<br /><br />As you're installing the lower unit, you'll have to rotate the flywheel a bit in the clockwise direction to get the drivshaft to engage into the crankshaft splines. At around the same time the shift shaft is engaging the shift rod, so lots of fun there!<br /><br />I prefer installing with the L/U in Fwd gear, since moving the prop slightly in the Reverse direction will cause the driveshaft to turn, thus engaging the crank splines easily. <br /><br />Reverse rotation will have no adverse effect on a new impeller but you'd never want to rotate your motor in the wrong direction with a used impeller, as it could cause the impeller vanes to break.<br /><br />If you reinstall in Neutral it's good to have a 2nd person or long arms to turn that flywheel!!! <br /><br />You may find the shift shaft a bit hard to reposition with your fingers; if you're very careful, you can use a pair of Channelocks or similar, providing you cushion the jaws with duct tape etc to keep from tearing up the splines of the shift shaft. Grab the shift shaft and rotate CCW. It does help to spin the prop with your hand while manually shifting to the desired gear.<br /><br />BTW you definitely want to replace the impeller while you're in there; cheap insurance. I get great prices and fast shipping on parts at this site: www.boatfix.com<br /><br />Here's a search for genuine Merc replacement pump parts:<br /><br /> http://www.boatfix.com/bykeywordmerc.asp?textfield=47-89984&texttype=2&submit=Search <br /><br />And Sierra aftermarket ( 18-3017 for the impeller, 18-3517 for the entire upper pump kit including impeller):<br /><br /> http://www.boatfix.com/searchsierra.asp <br /><br />HTH & G'luck............ed

 

[bullfrogsierra]

Re: 1969 Mercury 100 H.P. Thunder bolt lower unit

hello,new to this site,hoping someone can help me locate a impellar spline key for my 68 100 hp thunderbolt,6 cyl.bought this boat a couple months ago,engine runs great but no water coming out of tell tale hole,so upon removal of lower unit,discovered spline key wasnt even in there,just a little roll pin looking thing.all help is greatly appreciated,i can be e mailed at lvela@lions.k12.ar.us. thanks again and have a great day.

 

[turtles11756]

Re: 1969 Mercury 100 H.P. Thunder bolt lower unit

the roll pin is the key .grease pin and drive shaft to hold pin in place slide NEW impeller down shaft make sure pin stays in place .bring (greased) impeller housing down press down on housing at the same time turning drive shaft clockwise and housing will slip right on over impeller.grease spines on shafts and make sure you have the lower unit in the same gear as the motor when re installing or your gonna have to start over. when it's all done correct the running motor will not feel hot to touch anywhere and water will stream out tell tale if the hose is not clogged