Impeller replacement and key pin 1984 7.5 Merc

[Auckland]

Replacing the impeller on my motor. How do you get the key pin to stay in place while putting the water pump housing onto the drive shaft? Does the hump on my key pin face in or away from the drive shaft?

Thank you,

Randy

 

[kdegru]

Re: Impeller replacement and key pin 1984 7.5 Merc

Replacing the impeller on my motor. How do you get the key pin to stay in place while putting the water pump housing onto the drive shaft? Does the hump on my key pin face in or away from the drive shaft?

Thank you,

Randy

Randy: I just did an impeller for the first time on my 1985, 7.5hp Mercury. The hump on the key faces away from the drive shaft. In other words the flatted side of the key mates against the flat of the drive shaft. You will need some thick sticky substance to hold the key in place on the drive shaft while you install the impeller. I usually use thick bearing grease to do these kind of jobs but you could also use a little contact cement if the shaft and key have been degreased first. My impeller was completely in pieces when I got into the pump. Make absolutely sure you get all the pieces out of the pump and water path. Compressed air helped me to do this.

 

[Auckland]

Re: Impeller replacement and key pin 1984 7.5 Merc

Randy: I just did an impeller for the first time on my 1985, 7.5hp Mercury. The hump on the key faces away from the drive shaft. In other words the flatted side of the key mates against the flat of the drive shaft. You will need some thick sticky substance to hold the key in place on the drive shaft while you install the impeller. I usually use thick bearing grease to do these kind of jobs but you could also use a little contact cement if the shaft and key have been degreased first. My impeller was completely in pieces when I got into the pump. Make absolutely sure you get all the pieces out of the pump and water path. Compressed air helped me to do this.

Kdegru,

Thanks for your reply. Been working on trying to get this key on for the past 3 hours. It is like putting a round peg in a square hole. My impeller was in pieces too, everything seems to be clear. Thanks for the input on what side the key should be facing. Any other ideas on how to get the key in place. I appreciate it!

Randy

 

[emckelvy]

Re: Impeller replacement and key pin 1984 7.5 Merc

Randy, one thing that'll help you is to take a Magic Marker and scribe a line on the driveshaft, above the water pump, to the centerline of the flat spot on the driveshaft. Make sure the impeller key is centered on the flat, and you'll know exactly where the key is when you're inserting the impeller into the pump.

Some folks like to take a couple of very small tie-wraps around the impeller, such that it'll just drop down into the pump cartridge without interference from the impeller vanes. Then just slice-off the tie-wraps afterwards.

Another method is to align the impeller keyway with the key, and turn both driveshaft and impeller clockwise at the same time you're pushing downwards on the impeller.

Such that the driveshaft and impeller stay aligned all the time you're pushing the impeller into the pump. Eventually the impeller keyway will engage the key; then give the driveshaft a bit of a "wiggle" while continuing to push downwards on the impeller. Should go right in!

Usually takes a few times to practice & get the feel for it, 'cause many times you'll get it just a wee bit out of line and push the key away. But when you get 'er just right, it'll go right down. Did 7.5 a few weeks ago and was pleased when it went right down the first time, instead of giving me a fight! Nice when they do that.

Once the impeller is fully into the pump body, spin the driveshaft clockwise (as viewed from the top) and make sure it drives the impeller. That way you'll be certain the key is properly engaged.

Slap 'er together and you're back on the water! Be sure to use some waterproof marine-grade grease on the gearcase mounting studs, that'll ensure the L/U will always drop right down instead of getting seized.

Don't forget to grease the driveshaft and shift shaft splines, but be sure to wipe off any grease that gets on the top of those shafts. A little grease on the copper water supply tube helps it to slide into the rubber pump cover grommet.

HTH.........ed

 

[Auckland]

Re: Impeller replacement and key pin 1984 7.5 Merc

Randy, one thing that'll help you is to take a Magic Marker and scribe a line on the driveshaft, above the water pump, to the centerline of the flat spot on the driveshaft. Make sure the impeller key is centered on the flat, and you'll know exactly where the key is when you're inserting the impeller into the pump.

Some folks like to take a couple of very small tie-wraps around the impeller, such that it'll just drop down into the pump cartridge without interference from the impeller vanes. Then just slice-off the tie-wraps afterwards.

Another method is to align the impeller keyway with the key, and turn both driveshaft and impeller clockwise at the same time you're pushing downwards on the impeller.

Such that the driveshaft and impeller stay aligned all the time you're pushing the impeller into the pump. Eventually the impeller keyway will engage the key; then give the driveshaft a bit of a "wiggle" while continuing to push downwards on the impeller. Should go right in!

Usually takes a few times to practice & get the feel for it, 'cause many times you'll get it just a wee bit out of line and push the key away. But when you get 'er just right, it'll go right down. Did 7.5 a few weeks ago and was pleased when it went right down the first time, instead of giving me a fight! Nice when they do that.

Once the impeller is fully into the pump body, spin the driveshaft clockwise (as viewed from the top) and make sure it drives the impeller. That way you'll be certain the key is properly engaged.

Slap 'er together and you're back on the water! Be sure to use some waterproof marine-grade grease on the gearcase mounting studs, that'll ensure the L/U will always drop right down instead of getting seized.

Don't forget to grease the driveshaft and shift shaft splines, but be sure to wipe off any grease that gets on the top of those shafts. A little grease on the copper water supply tube helps it to slide into the rubber pump cover grommet.

HTH.........ed

Ed,

Thank you for all the great suggestions. I sure could of used you over here today to help me with mine. After 5 hours of messing with it I called a local guy who said he would put the water pump and impeller on it for $65. Leaving on vacation on Saturday and who knows how long it would of taken me to get the key pin on.

Is there anything else I should know about reattaching the lower unit? I know I need to make all tubes are lined up when reinserting the lower unit and to pull up on the shaft and turn the prop shaft left to engage it in the forward position and to engage the lever in forward so the splines will match up.

Thank you for your help. I will make notes on this so when I change my impeller next time I will know what to do.

Randy