Impeller Replacement discussion from iceout thread

MAXUM · 03-14-2012, 08:09 PM

Another thought too, the alpha has the impeller placed right above the water inlet in the stern drive housing therefore the flow of water into the casing doesn't have to go far before it hits the pump. With a more "remote" setup on the bravo that impeller has to spin fast enough to create a decent vacuum to overcome gravity (right?) so it makes sense it'd need to spin faster. If that thing even momentarily runs dry I can see where that would seriously reduce it's live expectancy.

Dave R · 03-15-2012, 05:58 AM

Quote:

Originally Posted by MAXUM

Another thought too, the alpha has the impeller placed right above the water inlet in the stern drive housing therefore the flow of water into the casing doesn't have to go far before it hits the pump. With a more "remote" setup on the bravo that impeller has to spin fast enough to create a decent vacuum to overcome gravity (right?) so it makes sense it'd need to spin faster. If that thing even momentarily runs dry I can see where that would seriously reduce it's live expectancy.

The Bravo impeller needs to be able to handle suction head since it can be above the water line. The Alpha only needs to be able to handle pressure head since it's always operating below the water line. That's why they are different designs and why they don't use the Alpha design on Bravos.

MAXUM · 03-17-2012, 08:03 AM

I just went out into the garage and it's kinda raw and cold out. Hmm think I'll wait for it to warm up a bit before ripping my stern drive apart. If I'm not to messy I'll snap some pix of the job and post 'em.

MAXUM · 03-17-2012, 03:56 PM

So here's where we start.

MAXUM · 03-17-2012, 03:59 PM

And we move on to splitting the lower unit....

MAXUM · 03-17-2012, 04:04 PM

Disassemble the impeller housing. Kind of messy in there. Most of that is just crap that built up over time from being in the water. Keep in mind this boat does not sit in the lake for the season!

MAXUM · 03-17-2012, 04:09 PM

Clean everything up, clean the pump housing, insert new impeller bolt housing back together, replace o rings as needed, almost ready to go.....

MAXUM · 03-17-2012, 04:14 PM

insert inlet tube and it's ready to go back together. All in all took a little less than 2 hours to do and about 50 something in parts including the gear oil. Best part was firing the engine up after it was all done. Nothing says spring like the first time that boat engine runs!

jst_4_kiks · 03-17-2012, 08:18 PM

So much controversy over different types of impellars.

Alpha gen I = low volume, high pressure pump. Replace 2-3 years
Alpha gen II = high volume, low pressure pump replace 4-5 years or longer (depends)
Bravo = high volume, low pressure. 2-3 years
Volvo Penta = cross of Alpha 2 and bravo. 3-4 years (depends)

Belt driven pumps have good and bad qualities. Pump loads of water for cooling (ie big blocks 454, 502, 496, etc) belt driven also been on volvo penta for years. Some volvo sx drives have belt driven pumps on 3.0 & 4.3 engines.

Volvo impellars that are crank driven are very simple to replace. Can even be done with the boat in the water. I have done it numerous times. There is a small seal that rides on the end of the crankshaft that can wear out and cause a water leak. Some people have changed just the seal but I perfer to change the entire housing and not have to worry about the seals surface fit.

On all alpha 1&2, bravo impellars there is a date code molded into the rubber between the vanes. Its interesting to see that a gen1 impellar can sometimes make it 6-10 years sometimes. I don't see how, but it happens. Gen2. (Floppy vane) pumps last for a long time depending if you operate in a shallow sandy areas that cause wearing of the rubber edges and create uneveness in the housing. This will produce overheats and loss of water to cool the engine.

Basic information above. Can go on and on about the subject of impellars.

NoBozo · 03-18-2012, 03:03 PM

Quote:

Originally Posted by MAXUM

Disassemble the impeller housing. Kind of messy in there. Most of that is just crap that built up over time from being in the water. Keep in mind this boat does not sit in the lake for the season!

Thanks for the pictures MAX. I think I've learned something here.

It looks like the impeller is central in the SS housing...no offset. I always thought there was a wedge in the housing that would make each impeller blade flex/compress as it went over the "eccentric" wedge.

Maybe I'm thinking the bronze Jabsco belt driven pumps that I had on my old Yanmar diesel sailboat auxiliary.

NB

MAXUM · 03-18-2012, 06:24 PM

Quote:

Originally Posted by NoBozo

Thanks for the pictures MAX. I think I've learned something here.

It looks like the impeller is central in the SS housing...no offset. I always thought there was a wedge in the housing that would make each impeller blade flex/compress as it went over the "eccentric" wedge.

NB - if you look very close at the pic I took of the old impeller still sitting in the housing you will see that it is in fact not centered but slightly off center. Notice the fins towards the bottom are slightly more bent than the ones on top?
It's not huge but it's definitely not centered. I assume there is a reason for it although I can't tell you why it would be done like that.

An interesting thing to note. This is the first time this has been done, so all these parts were 9 years old. The impeller looked like new but and interesting thing that I noticed was the seal on top of the housing was showing some significant 'dry cracking' and I suspect that it wasn't to far away from leaking. I also noticed the replacement seal had a much wider 'skirt' on the bottom. where it squashes against the pump housing.

Kinda cool to see one of these things disassembled partially for those that never have.

Dave R · 03-18-2012, 07:42 PM

Nice job documenting the work. Ever pull your drive to check the alignment? It's shockingly easy (put shifter in forward, remove the speedometer tube, remove the rear trim ram shaft, remove the 6 nuts that connect the drive to the bell housing and slide the drive off). I have an alignment bar if you ever feel like checking it.

MAXUM · 03-18-2012, 10:55 PM

No never thought about it, is that something that needs to be checked every now and then? If the gears in the lower unit aren't disassembled then I would think everything should stay true. Boat has close to 300 hours on it now.

Dave R · 03-19-2012, 06:43 AM

Quote:

Originally Posted by MAXUM

No never thought about it, is that something that needs to be checked every now and then? If the gears in the lower unit aren't disassembled then I would think everything should stay true. Boat has close to 300 hours on it now.

It's supposed to be checked annually. Most DIYers don't do it because it looks like it would be complicated and/or it's hardly ever out of tolerance. Alignment is important for coupler longevity. When it goes out of alignment, it's almost always due to an issue with the engine mounts or the stringers. Having the drive off is a great way to check the bellows and the condition of the gimbal bearing and U-joints. It's also much easier to lube the drive shaft splines when they are out in the open, compared to laying on the engine reaching for the one of the zerks on the coupler.

There's some slick engineering on the Merc drives like the drive oil valves that close automatically when the drive is pulled. One valve prevents oil from leaking out of the engine compartment reservoir and the other prevents oil from leaking out of the drive itself. When the drive is re-installed, the two valves press against each other and open allowing oil to flow to and from the reservoir again.

MAXUM · 03-19-2012, 02:22 PM

Well I can say that getting to those zirks on the coupler is a total PITA. Good to know that alignment should be checked, maybe I'll put that on my list of things to do. I want to replace the gaskets in the top end of the outdrive at some point, just due to age more than anything else, it certainly doesn't have any water intrusion problems. probably should have done it when I split the case but didn't have the parts on hand do it. Eh put it on my list of things to do this fall for winterization. Ice is disappearing to quickly to think about doing anything other than spring cleaning, fresh wax and loading it up for the season. Looks like another year of being able to fish the entire lake come April 1st. Matter of fact at this rate the water temps should be warm enough for the fish to be a little more active than usual. All good stuff IMHO. Just not looking forward to paying to fill the gas tank!

03-17-2012, 03:56 PM	#4
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	So here's where we start. Attached Images

03-17-2012, 03:59 PM	#5
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	And we move on to splitting the lower unit.... Attached Images

03-17-2012, 04:04 PM	#6
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Disassemble the impeller housing. Kind of messy in there. Most of that is just crap that built up over time from being in the water. Keep in mind this boat does not sit in the lake for the season! Attached Images

03-17-2012, 04:09 PM	#7
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Clean everything up, clean the pump housing, insert new impeller bolt housing back together, replace o rings as needed, almost ready to go..... Attached Images

03-17-2012, 04:14 PM	#8
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	insert inlet tube and it's ready to go back together. All in all took a little less than 2 hours to do and about 50 something in parts including the gear oil. Best part was firing the engine up after it was all done. Nothing says spring like the first time that boat engine runs! Attached Images

03-14-2012, 08:09 PM	#1
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Another thought too, the alpha has the impeller placed right above the water inlet in the stern drive housing therefore the flow of water into the casing doesn't have to go far before it hits the pump. With a more "remote" setup on the bravo that impeller has to spin fast enough to create a decent vacuum to overcome gravity (right?) so it makes sense it'd need to spin faster. If that thing even momentarily runs dry I can see where that would seriously reduce it's live expectancy.

03-17-2012, 08:03 AM	#3
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	I just went out into the garage and it's kinda raw and cold out. Hmm think I'll wait for it to warm up a bit before ripping my stern drive apart. If I'm not to messy I'll snap some pix of the job and post 'em.

03-17-2012, 08:18 PM	#9
jst_4_kiks Senior Member Join Date: Mar 2009 Location: Laconia NH Posts: 130 Thanks: 25 Thanked 15 Times in 11 Posts	So much controversy over different types of impellars. Alpha gen I = low volume, high pressure pump. Replace 2-3 years Alpha gen II = high volume, low pressure pump replace 4-5 years or longer (depends) Bravo = high volume, low pressure. 2-3 years Volvo Penta = cross of Alpha 2 and bravo. 3-4 years (depends) Belt driven pumps have good and bad qualities. Pump loads of water for cooling (ie big blocks 454, 502, 496, etc) belt driven also been on volvo penta for years. Some volvo sx drives have belt driven pumps on 3.0 & 4.3 engines. Volvo impellars that are crank driven are very simple to replace. Can even be done with the boat in the water. I have done it numerous times. There is a small seal that rides on the end of the crankshaft that can wear out and cause a water leak. Some people have changed just the seal but I perfer to change the entire housing and not have to worry about the seals surface fit. On all alpha 1&2, bravo impellars there is a date code molded into the rubber between the vanes. Its interesting to see that a gen1 impellar can sometimes make it 6-10 years sometimes. I don't see how, but it happens. Gen2. (Floppy vane) pumps last for a long time depending if you operate in a shallow sandy areas that cause wearing of the rubber edges and create uneveness in the housing. This will produce overheats and loss of water to cool the engine. Basic information above. Can go on and on about the subject of impellars. __________________ Marine Technician - Learning Something New Every Day PM with any questions about marine repair

The Following User Says Thank You to MAXUM For This Useful Post:
NoBozo (03-18-2012)

03-18-2012, 07:42 PM	#12
Dave R Senior Member Join Date: Jul 2004 Posts: 2,985 Thanks: 246 Thanked 744 Times in 444 Posts	Nice job documenting the work. Ever pull your drive to check the alignment? It's shockingly easy (put shifter in forward, remove the speedometer tube, remove the rear trim ram shaft, remove the 6 nuts that connect the drive to the bell housing and slide the drive off). I have an alignment bar if you ever feel like checking it.

03-18-2012, 10:55 PM	#13
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	No never thought about it, is that something that needs to be checked every now and then? If the gears in the lower unit aren't disassembled then I would think everything should stay true. Boat has close to 300 hours on it now.

03-19-2012, 02:22 PM	#15
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Well I can say that getting to those zirks on the coupler is a total PITA. Good to know that alignment should be checked, maybe I'll put that on my list of things to do. I want to replace the gaskets in the top end of the outdrive at some point, just due to age more than anything else, it certainly doesn't have any water intrusion problems. probably should have done it when I split the case but didn't have the parts on hand do it. Eh put it on my list of things to do this fall for winterization. Ice is disappearing to quickly to think about doing anything other than spring cleaning, fresh wax and loading it up for the season. Looks like another year of being able to fish the entire lake come April 1st. Matter of fact at this rate the water temps should be warm enough for the fish to be a little more active than usual. All good stuff IMHO. Just not looking forward to paying to fill the gas tank!