Changing impeller - lesson learned
Thought I'd share my most recent mistake with the list in hopes of
preventing some of you from having the same experience, and tell you
about a great place in the Cocoa/Melbourne area of Florida for generator
service/repairs.
We're about to head out on a cruise from Florida to inland Canada,
estimating about 6,000 statute miles or so. Consequently, I wanted to
make sure the generator, an Onan MDKD 8KW, was in good working
condition, and since it has about 3700 hours and I have no idea when
maintenance was last performed, I thought it would be a good idea to do
a little preventive maintenance even though we run it only about 50
hours a year. Checked the fan belt and it needed replacing and was very
loose. Pulled the impeller and it was probably OK before I started to
pry it off the shaft; the blades were slightly bent and the new one from
Onan purchased the day before from Noah's Ark was at hand, so I lubed
everything up with some lithium grease (been doing that with every
impeller change on the main diesel) and put everything back together.
Started the genset and no water came out with the exhaust. Shut it down
and tried again. No joy. Removed the newly installed impeller and
salvaged the paper gasket (worth nearly it's weight in gold). Contacted
the owner of Noah's Ark by email and ended up sending him a couple of
photos of the inside of the impeller housing (he was concerned about
whether there had been a wear plate since the old impeller was about
1/16" of an inch wider than the new one). We discussed the problem a
couple of times by email over the weekend, and I sent him the exact
measurements of the impeller taken using a caliper. He emailed me early
Monday morning that he had the replacement.
When I got to Noah's Ark on Monday morning the replacement he had was
identical to the new one I'd purchased the end of the previous week and
that I installed and that hadn't moved any water. As we discussed the
matter and I explained how I'd carefully greased everything, Mike
commented that I should only use soap as a lubricant to get the impeller
to slide into the housing. He suggested that I try one more time and to
start by degreasing everything (I was getting a lot of experience
working in small spaces on things I couldn't see with tools that I had
to manipulate with my finger tips).
The grease wiped right out of the housing and came off the impeller
without a problem. I cleaned off the cover plate with turpentine to get
rid of the thin layer of grease there. Reinstalled everything, replaced
the fuel solenoid, started the diesel and - voila! Water came pumping
out with the exhaust.
Lesson learned: never grease the inside of an impeller housing! Mike
explained earlier that the only lubricant the impeller needs is water!
When I sent Mike an email to let him know that his advice was spot on,
he said he sees this mistake a lot.
Anyway, if you need Onan service in the Cocoa/Melbourne Florida area,
give Noah's Ark a call. I've heard other praises of their service, and
was impressed when Mike was willing to spend so much time with me over a
$30.00 item I'd already purchased from them.
FWIW, they have two new Kohler diesel gensets available at great
discounts; they bought them from the overstock of a large power boat
builder and can sell them at below dealer cost at $6800 each. Not sure
of the size.
--
<><><><><><><><><><><><>Mozilla Thunderbird<><><><><><><><><><>
Bob McLeran and Judy Young Manatee Cove Marina
MV Sanderling Patrick Air Force Base
DeFever 41 Trawler Melbourne, Florida
Blog: http://sanderling2011.blogspot.com/
Pics: http://tinyurl.com/yjx2vky& http://tinyurl.com/yhxjvas
I have always understood that you never use petroleum lubricants on
impellers. My westerbeke impeller comes with a packet of glycerin. I use
dish washing soap--dawn or similar- the suds in the exhaust is positive
confirmation of water flow.
murai.com]On Behalf Of Bob McLeran
Sent: Tuesday, April 19, 2011 6:51 PM
To: T-T&T List
Subject: T&T: Changing impeller - lesson learned
Thought I'd share my most recent mistake with the list in hopes of
preventing some of you from having the same experience, and tell you
about a great place in the Cocoa/Melbourne area of Florida for generator
service/repairs.
snipped
Lesson learned: never grease the inside of an impeller housing! Mike
explained earlier that the only lubricant the impeller needs is water!
Interesting that the Detroit Diesel shop manual in Section 5.6 that
deals with the Jabsco raw water pump says the following:
- Liberally coat inside of cam/liner with water pump grease.
- Insert impeller O-ring......Then push in impeller
I find it hard to understand why the grease would keep the pump from
pumping unless there was way too much.
Frank Burrows 79 43' Viking Piney Narrows Chesapeake Bay
. . . and interestingly enough, there's never been a problem when I
grease the inside of the housing on Sanderling's FL-135 (have changed
the impeller twice now) and before that on two FL-90s (changed the
impellers four times on each).
There was a coating of grease on the housing and on the impeller blades;
just a dab on a finger and that dab smeared around the housing.
Mike at Noah's Ark said that grease prevents the creation of friction
which is necessary to draw the water through.
Perhaps if the impeller is large enough (compared to the housing), the
grease doesn't matter. On the FLs I had to use a circular clamp to
compress the blades enough to get the impeller to fit into the housing;
not the case with the Onan - the impeller slid right in and the blades
were only slightly bent!
<><><><><><><><><><><><>Mozilla Thunderbird<><><><><><><><><><>
Bob McLeran and Judy Young Manatee Cove Marina
MV Sanderling Patrick Air Force Base
DeFever 41 Trawler Melbourne, Florida
Blog: http://sanderling2011.blogspot.com/
Pics: http://tinyurl.com/yjx2vky& http://tinyurl.com/yhxjvas
On 4/19/2011 10:23 PM, Frank Burrows wrote:
Interesting that the Detroit Diesel shop manual in Section 5.6 that
deals with the Jabsco raw water pump says the following:
- Liberally coat inside of cam/liner with water pump grease.
- Insert impeller O-ring......Then push in impeller
I find it hard to understand why the grease would keep the pump from
pumping unless there was way too much.
My lessons learned:
Using Vaseline, grease the spindle and the seal, and the screws that
hold the cover in place if you have NOT replaced them with wing nuts.
Use a tie-wrap to compress the blades for insertion.
Keep the old impeller (as long as not damaged) as a spare in a plastic
zip lock bag, coated with Vaseline to prevent dryness.
Keep only the last two impellers as spares for each engine.
On the intake of the fresh water / sea water cooler, see if you can
place a nylon mess (wide holes) to catch any impeller parts. Saves a
whole lot of work.
Replace impeller every spring, after having removed the last one while
on the hard...
With this practice in place, I was able to change out two defective
raw water impellers that failed within minutes of each other with less
than 40 hours on them each while on a marina approach at night with
guest on board. Could NOT make it to the marina as the temps were
rising really fast... Thank God each impeller decided to give up the
ghost about 20 minutes apart.
So, you may ask, after having changed one, why did I not shut down the
engine and go in single screw?
Because, having no idea what was causing the impellers to fail,
thought that if I was only to get a few minutes from the engines after
changeout, having two working would give me extra time to get pier
side, somewhere.
Wing nuts allowed me to to change the impeller with no tools. Vaseline
allowed me to grab the damage impeller and yank it out with hardly any
effort. The plastic mess? Caught all the big pieces from the failed
impellers on both engines.
And, the spares? They were "tacked" to the forward engine room
bulkhead. (Cannot claim credit for that... Old fart from winter
storage yard did that for me. Said it would become handy one day. Did
buy that man a beer or two after this "event.")
Lee
Izmir
[demime 1.01d removed an attachment of type application/pkcs7-signature which had a name of smime.p7s]
Keep the old impeller (as long as not damaged) as a spare
in a plastic
zip lock bag, coated with Vaseline to prevent dryness.
Great ideas Lee, but please forgive me as I would like to voice a desenting
opinion about this vasoline idea.
Jabsco, Johnson Oberdorfer and Sherwood have all told me to not use petroleum
based greases (vasoline is petroleum based) on impellers made for use in
water. Over time it will cause the material to disintegrate. Any non-petroleum
product (iquid soap, most synthetic greases, glycerin) is recommended by them.
Before I knew this, I used to lub impellers, often with vasoline, when
installing them and never experienced a failure because of it. But, now that I
know different, I've stopped.
Storage of impellers coated with petroleum based products is a little
different story though, as they sit coated with the stuff for much longer
periods, often years.
As far as keeping used impellers for spares, I have a little different take on
this... if it isn't good enough for continued use, except in emergencies, it
isn't good enough for a spare. I always keep new parts for spares, cycle them
into use and replace the now-in-use spare with a new part.
Now, if I was selling my boat, I wouldn't waste my money on buying "new". I'd
keep the "old, used" parts so I could provide a nice a nice inventory of
"spares", without having to spend the money. This concept might be something
that folks looking to buy a boat might want to file away in the back of their
mind, as they will probably run into situations like this.
Rubber spares are degraded by UV, ozone and often heat, so I keep parts like
this sealed, usually in plastic baggies, although some more enterprizing
individuals, with more space and money than I have, will vacum seal parts.
Metal products (think injectors) rust (think on the inside), so items like
this I keep wrapped in an oil saturated rag, and, if additional protection is
needed, then wrapped with cardboard. As to injectors, I also pop-test them
yearly (unless they get cycled into use within this time frame) to renew the
fluid inside them. If metal items are kept in plastic, often even if vacum
sealed, condensation occurs, causing or accelerating rust.
Rudy
Briney Bug, Panama City, Fl
I take the same approach to spares - keep a set of new spares onboard, use
them when scheduled replacement is due, and replenish the spares stock with
new parts. Used parts that are removed go in the trash. Any failure while in
service gets repaired with new parts from the onboard stock. Keep in mind
that if you repair with used parts, it's a temporary measure and you need to
do the repair again with new parts shortly thereafter. Personally, I like to
repair things once, not twice.
On Apr 20, 2011, at 8:00 AM, Rudy and Jill wrote:
Keep the old impeller (as long as not damaged) as a spare
in a plastic
zip lock bag, coated with Vaseline to prevent dryness.
Great ideas Lee, but please forgive me as I would like to voice a
desenting
opinion about this vasoline idea.
Jabsco, Johnson Oberdorfer and Sherwood have all told me to not use
petroleum
based greases (vasoline is petroleum based) on impellers made for use in
water. Over time it will cause the material to disintegrate. Any
non-petroleum
product (iquid soap, most synthetic greases, glycerin) is recommended by
them.
Before I knew this, I used to lub impellers, often with vasoline, when
installing them and never experienced a failure because of it. But, now that
I
know different, I've stopped.
Storage of impellers coated with petroleum based products is a little
different story though, as they sit coated with the stuff for much longer
periods, often years.
As far as keeping used impellers for spares, I have a little different take
on
this... if it isn't good enough for continued use, except in emergencies,
it
isn't good enough for a spare. I always keep new parts for spares, cycle
them
into use and replace the now-in-use spare with a new part.
Now, if I was selling my boat, I wouldn't waste my money on buying "new".
I'd
keep the "old, used" parts so I could provide a nice a nice inventory of
"spares", without having to spend the money. This concept might be
something
that folks looking to buy a boat might want to file away in the back of
their
mind, as they will probably run into situations like this.
Rubber spares are degraded by UV, ozone and often heat, so I keep parts
like
this sealed, usually in plastic baggies, although some more enterprizing
individuals, with more space and money than I have, will vacum seal parts.
Metal products (think injectors) rust (think on the inside), so items like
this I keep wrapped in an oil saturated rag, and, if additional protection
is
needed, then wrapped with cardboard. As to injectors, I also pop-test them
yearly (unless they get cycled into use within this time frame) to renew
the
fluid inside them. If metal items are kept in plastic, often even if vacum
sealed, condensation occurs, causing or accelerating rust.
Rudy
Briney Bug, Panama City, Fl
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