Impeller Replacement discussion from iceout thread

MAXUM · 03-13-2012, 09:40 AM

Quote:

Originally Posted by Dave R

Those are great drives. The "floppy vane" impeller design change when they went to gen 2 was brilliant. I know some people hate changing the impeller in the drive, but it's a lot easier than changing the impeller on my engine in my Bravo 3 equipped boat. That Bravo pump is in an awful place to access and the impeller is only good for 2 seasons max. The only plus is that I don't have an oily mess to deal with when I change it.

I agree, matter of fact if you think about it, the basic design of the Alpha I has remained relatively unchanged since it's original design. A true testament to a very good design and having had a couple of these drives apart they are built like tanks IMHO. Yeah the impeller is kind of a pain to deal with having to split the drive but I use that as an excuse to also re-seal it to. I planned ahead and just pulled the drain plug in my stern drive so it should be fully drained by Saturday so less messy.

I was really surprised to see the bravo 3 has an external impeller and I think that's unacceptable it only lasts a couple of seasons. Good grief! Then again I've talked to several boat techs over the years that haven't had to many good things to say about the bravo 3. Thing is if you're paired up to a big HP engine or have a boat that really needs a duoprop setup your choices are limited to the Bravo 2 or 3.

No matter I'd take the Mercrusier any day over a Volvo.

Blue Thunder · 03-13-2012, 10:13 AM

Quote:

Originally Posted by MAXUM

I agree, matter of fact if you think about it, the basic design of the Alpha I has remained relatively unchanged since it's original design. A true testament to a very good design and having had a couple of these drives apart they are built like tanks IMHO. Yeah the impeller is kind of a pain to deal with having to split the drive but I use that as an excuse to also re-seal it to. I planned ahead and just pulled the drain plug in my stern drive so it should be fully drained by Saturday so less messy.

I was really surprised to see the bravo 3 has an external impeller and I think that's unacceptable it only lasts a couple of seasons. Good grief! Then again I've talked to several boat techs over the years that haven't had to many good things to say about the bravo 3. Thing is if you're paired up to a big HP engine or have a boat that really needs a duoprop setup your choices are limited to the Bravo 2 or 3.

No matter I'd take the Mercrusier any day over a Volvo.

Good idea to move this thread. I have had an Alpha Drive in the past on my 211 Liberator and was a Merc guy all the way for more than 20 years. Like you as a DIY'er I changed the impeller in the drive every 2 years.."just because". I now have the Volvo DP (11 yrs) and I have to tell you its the best thing going. The impeller is crankshaft driven and is much easier to change than the splitting the case method on the Alpha One. Volvo's cone cluthes are superior, IMO to the B3 drive mechanics. Just my opinion and to each his own.

MAXUM · 03-13-2012, 11:33 AM

Don't know that much about the Volvo's never owned one and have no desire to. Personal preference I guess, Merc's Alpha drive has been around for a long time and has a proven track record of being pretty bullet proof. Volvo on the other hand is a glorified OMC which let's face it didn't have a good track record. I understand the past few years Volvo really straightened out the SX drive units and they are supposedly pretty good. Dunno maybe that's true. There is no question the shifting in the Volvo is way smoother than the Merc.

I don't change my impeller every 2 years in the Alpha they last much longer than that. Matter of fact the new one I'm putting in is made of a new material that has a much longer life expectancy. It was DaveR that said his Bravo drive needed the impeller replaced every couple of years, and to that I say that's a poor design. I've let my Alpha go long enough, 9 years, it's time.

jrc · 03-13-2012, 02:08 PM

I had two boats with Bravo 3's and current boat has a Volvo-Penta Duo-prop. I'd like to say never again on the B3's, but you never know what deal wil come up. If you maintain them, they are nice handling drives.

The first one left me stranded at 370 hours, burned out the impellar. After that I change it every 200 hours. What a bear to get to that pump, especially on our small boat. Both boats had lots of issues with corrosion, not as bad as you see on the web but a lot of peeling paint. You absolutely must change to magnesium anodes in the lake.

Now with the VP, after four seasons I see just a tiny paint peel here and there. My mechanic is in no hurry to change the impellars, says they will last a lot longer.

Dave R · 03-13-2012, 07:52 PM

Quote:

Originally Posted by Blue Thunder

Volvo's cone cluthes are superior, IMO to the B3 drive mechanics. Just my opinion and to each his own.

All Bravo drives have cone clutches and shift in the upper gear case, just like VPs. Alpha drives use shift dogs rather than cone clutches and shift in the lower gear case, just like outboard engines.

MAXUM · 03-13-2012, 09:46 PM

I can't understand why Merc can't make an impeller on the Bravo configuration that doesn't last. That's poor engineering IMHO. I do wonder why they didn't use a similar design as the alpha which obviously is pretty much bullet proof.

Since my boat doesn't sit in the water for the season I don't have to worry so much about the anodes on my stern drive, although I do take them off every year and hit them with the wire wheel on my bench grinder to freshen up the surface on them. Seems like there is varying opinions as to what type of anode to use depending on the water you're primarily operating in, zinc, aluminum, or magnesium. Mine have always had zincs.

Dave R · 03-14-2012, 09:43 AM

Quote:

Originally Posted by MAXUM

I can't understand why Merc can't make an impeller on the Bravo configuration that doesn't last. That's poor engineering IMHO. I do wonder why they didn't use a similar design as the alpha which obviously is pretty much bullet proof.

The alpha pump would be too big to mount on the engine without affecting the engine package size because it is designed to run at a much lower RPM (lower than engine RPM). Slowing it down would require a huge pulley. The Bravo pump is really small and is designed to spin pretty fast (faster than engine speed) so it has a small pulley. The fast speed and compact design makes it necessary to have smaller and stiffer vanes. Those vanes just don't last as long as the floppy vanes in the Alpha.

MAXUM · 03-14-2012, 10:13 AM

Hard to get into the heads of the engineers that design these things, I suppose there is a legit reason why they did what they did. My initial guess is they need to pump a larger volume of water through those big block engines to keep the operating temperature where it needs to be. I wonder why not use a closed loop cooling system with some sort of heat exchanger unless it's just plain cost and weight prohibitive.

Dave R · 03-14-2012, 01:49 PM

Quote:

Originally Posted by MAXUM

Hard to get into the heads of the engineers that design these things, I suppose there is a legit reason why they did what they did. My initial guess is they need to pump a larger volume of water through those big block engines to keep the operating temperature where it needs to be. I wonder why not use a closed loop cooling system with some sort of heat exchanger unless it's just plain cost and weight prohibitive.

The alpha was used with a big block in the past so it moves plenty of water, it's just a very different pump design that moves much more water per revolution thatn the Bravo pump because it is turning at a lower speed. If you try to spin it really fast, the vanes will probably flex too much and make it cavitate.

Alpha impeller

Bravo impeller

Closed cooling is an option on most marine engines, people just tend not to want to pay for it. Either way though, you still need a raw water pump to pump lake water through the heat exchanger.

Edit: One other thing I wanted to note, I am pretty sure the Alpha impeller is a a centrifugal pump and the bravo is a positive displacement pump. The Bravo pump requires that the vanes be flexed substantially on every revolution, as they get squished, volume is lost between each vane and that forces water out of the pump. The Alpha pump, if memory serves, just flings the water out with centrifugal force. The vanes are not nearly as stressed.

Dave R · 03-14-2012, 02:41 PM

I was wrong about the pumps needing to operate at different speeds, some Alpha upper gear cases (1:1.65) have 24 tooth drive and 24 tooth driven gears (1:1 upper gear case ratio) so that means the pump operates at engine speed. Also, I looked at my Bravo pump and it has roughly the same size pulley as the crankshaft, so it operates at engine speed too.

I agree, they should change the design to use the Alpha impeller in the engine mounted bravo pump.

NoBozo · 03-14-2012, 07:09 PM

Quote:

Originally Posted by Dave R

I was wrong about the pumps needing to operate at different speeds, some Alpha upper gear cases (1:1.65) have 24 tooth drive and 24 tooth driven gears (1:1 upper gear case ratio) so that means the pump operates at engine speed. Also, I looked at my Bravo pump and it has roughly the same size pulley as the crankshaft, so it operates at engine speed too.

I agree, they should change the design to use the Alpha impeller in the engine mounted bravo pump.

I guess I'm a little confused. :..."some Alpha upper gear cases (1:1.65) have 24 tooth drive and 24 tooth driven gears".

SO: As you state.. 24/24 equals 1:1 .. I guess your 1:1:65 comment has me confused. Is the 1.65 gear ratio achieved in the LOWER gear case in the Alpha 1..? Just wondering..

NB

MAXUM · 03-14-2012, 08:00 PM

That's kind of an odd gear ratio, both of mine had/have 1:1.81

Maybe they change it depending on what engine it's mated with although my first boat had the 3.0L 4 banger and my current boat has the 4.3L V6.

Another thing, changing the speed of the impeller itself can only do so much, you can't pump any more water through the block once you hit critical mass, after that you'd be building positive pressure in the impeller housing.

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, 05:40 AM

Quote:

Originally Posted by NoBozo

I guess I'm a little confused. :..."some Alpha upper gear cases (1:1.65) have 24 tooth drive and 24 tooth driven gears".

SO: As you state.. 24/24 equals 1:1 .. I guess your 1:1:65 comment has me confused. Is the 1.65 gear ratio achieved in the LOWER gear case in the Alpha 1..? Just wondering..

NB

Yup, you got it. There's two sets of gears in an Alpha drive (any drive): upper gears that turn the rotation 90 degrees to vertical, and lower gears that turn the rotation back to horizontal. With a 1.65 drive, the upper gears are 24 and 24, the lower gears are 17 and 28. The final drive ratio is 28/17 or 1.64705...

Dave R · 03-15-2012, 05:53 AM

Quote:

Originally Posted by MAXUM

That's kind of an odd gear ratio, both of mine had/have 1:1.81

Maybe they change it depending on what engine it's mated with although my first boat had the 3.0L 4 banger and my current boat has the 4.3L V6.

Another thing, changing the speed of the impeller itself can only do so much, you can't pump any more water through the block once you hit critical mass, after that you'd be building positive pressure in the impeller housing.

They use different gear ratios and different props for different boat/engine combinations. They range from 1.32 to 2.40. I'm guessing the 2.4 is popular with non-planing hulls like houseboats equipped with twin 3.0s. The 1.32 would work well on a small and light boat with high HP, like a Donzi Sweet 16 equipped with a 350 MAG.

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	#18
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	#19
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	#20
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	#21
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	#22
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

03-13-2012, 11:33 AM	#3
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Don't know that much about the Volvo's never owned one and have no desire to. Personal preference I guess, Merc's Alpha drive has been around for a long time and has a proven track record of being pretty bullet proof. Volvo on the other hand is a glorified OMC which let's face it didn't have a good track record. I understand the past few years Volvo really straightened out the SX drive units and they are supposedly pretty good. Dunno maybe that's true. There is no question the shifting in the Volvo is way smoother than the Merc. I don't change my impeller every 2 years in the Alpha they last much longer than that. Matter of fact the new one I'm putting in is made of a new material that has a much longer life expectancy. It was DaveR that said his Bravo drive needed the impeller replaced every couple of years, and to that I say that's a poor design. I've let my Alpha go long enough, 9 years, it's time.

The Following User Says Thank You to MAXUM For This Useful Post:
Blue Thunder (03-13-2012)

03-13-2012, 02:08 PM	#4
jrc Senior Member Join Date: Apr 2004 Location: NH Posts: 2,689 Thanks: 33 Thanked 439 Times in 249 Posts	I had two boats with Bravo 3's and current boat has a Volvo-Penta Duo-prop. I'd like to say never again on the B3's, but you never know what deal wil come up. If you maintain them, they are nice handling drives. The first one left me stranded at 370 hours, burned out the impellar. After that I change it every 200 hours. What a bear to get to that pump, especially on our small boat. Both boats had lots of issues with corrosion, not as bad as you see on the web but a lot of peeling paint. You absolutely must change to magnesium anodes in the lake. Now with the VP, after four seasons I see just a tiny paint peel here and there. My mechanic is in no hurry to change the impellars, says they will last a lot longer.

03-13-2012, 09:46 PM	#6
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	I can't understand why Merc can't make an impeller on the Bravo configuration that doesn't last. That's poor engineering IMHO. I do wonder why they didn't use a similar design as the alpha which obviously is pretty much bullet proof. Since my boat doesn't sit in the water for the season I don't have to worry so much about the anodes on my stern drive, although I do take them off every year and hit them with the wire wheel on my bench grinder to freshen up the surface on them. Seems like there is varying opinions as to what type of anode to use depending on the water you're primarily operating in, zinc, aluminum, or magnesium. Mine have always had zincs.

03-14-2012, 10:13 AM	#8
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	Hard to get into the heads of the engineers that design these things, I suppose there is a legit reason why they did what they did. My initial guess is they need to pump a larger volume of water through those big block engines to keep the operating temperature where it needs to be. I wonder why not use a closed loop cooling system with some sort of heat exchanger unless it's just plain cost and weight prohibitive.

03-14-2012, 02:41 PM	#10
Dave R Senior Member Join Date: Jul 2004 Posts: 2,985 Thanks: 246 Thanked 743 Times in 443 Posts	I was wrong about the pumps needing to operate at different speeds, some Alpha upper gear cases (1:1.65) have 24 tooth drive and 24 tooth driven gears (1:1 upper gear case ratio) so that means the pump operates at engine speed. Also, I looked at my Bravo pump and it has roughly the same size pulley as the crankshaft, so it operates at engine speed too. I agree, they should change the design to use the Alpha impeller in the engine mounted bravo pump.

03-14-2012, 08:00 PM	#12
MAXUM Senior Member Join Date: Apr 2004 Location: Kuna ID Posts: 2,755 Thanks: 246 Thanked 1,942 Times in 802 Posts	That's kind of an odd gear ratio, both of mine had/have 1:1.81 Maybe they change it depending on what engine it's mated with although my first boat had the 3.0L 4 banger and my current boat has the 4.3L V6. Another thing, changing the speed of the impeller itself can only do so much, you can't pump any more water through the block once you hit critical mass, after that you'd be building positive pressure in the impeller housing.

03-14-2012, 08:09 PM	#13
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.

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NoBozo (03-15-2012)

03-17-2012, 08:03 AM	#17
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	#23
jst_4_kiks Senior Member Join Date: Mar 2009 Location: Laconia NH Posts: 129 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

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NoBozo (03-18-2012)

03-18-2012, 07:42 PM	#26
Dave R Senior Member Join Date: Jul 2004 Posts: 2,985 Thanks: 246 Thanked 743 Times in 443 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	#27
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	#29
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!