Latest Wiki Addition M35 Engine Oberdorfer Pump Swapout for Sherwood

[Ken Juul]

The folks at the C36 site were kind enough to share with us this great write up about replacing the expensive Sherwood raw water pump with a much less expensive Oberdorfer.  On the M25 series engines the pumps are interchangable.  On the M35 series engines it involves a bit of surgery to pumps.  Nothing beyond the DIY level.  If interested take a look at in the engine, then cooling section of the Tech Wiki.

Thanks again to the C36 Assoc for sharing.

Link to the Wiki article:  http://www.c34.org/wiki/index.php?title=Replacing_a_Sherwood_Water_Pump_with_an_Oberdorfer

[Ken Heyman]

Ken,

Can you include a direct link top the write-up?

Ken

[Stu Jackson]

The article was published in the C36 IA "JibSheet."  The C36IA Message Board/Forum notes:  JibSheet is an E-Newsletter exclusively for C36/375IA members. A direct link doesn't work unless you are a C36IA member.  Nice of Ken Jull to "get" that copy.  It's the same text, so a link is unnecessary.  I've also made the URL in Ken's original post into a link (by highlighting the http and clicking on the URL button - sometimes it does it automatically, sometimes not).

And, the article is for M35 series engines.  

For M25 series engines, just remove your expensive Sherwood and slap the Oberdorfer right on, no base plate mods are required.  Model N202M-15.

I wanted to attach my PDF catalog for Oberdorfer pumps, bugt the file size was too large.

[Ron Hill]

Guys, Susan and D. Gill : Before I would jump on the Oberdoffer "band wagon", I'd do some checking with Westerbeke and ask:
Why did Westerbeke elect to put a Sherwood pump on their M35BC & M25XPB engines??? rather than an Oberdoffer??

It's a known fact that the Sherwood, pumps more water flow than the Oberdoffer.  Don't know the GPH number, but I believe it's substantial (x 2?).
 
I believe that the Oberdoffer is a "better maintenance made" (all bronze body) pump.

I can see a number of pros and cons on each of the pumps, but the water flow bothers me, in that the M35BC and M25XPB engines have a 3 " HX which is approx. 3 to 4 inches longer (added cooling) than the 3"HX on the M25XP engine!!
 
My thoughts until the water flow/Westerbeke question is answered.  The guy to ask is Joe Joyce Westerbeke Service Manager (or his asst. Russ Hagen)

[John Langford]

Nile Schneider from the C36 Association provided me with an update on his experience with the Oberdorfer raw water pump on his Universal M35B. I was concerned about water flow and maintaining the 160 degree operating temperature especially in the dog days of summer.

His response:
"I have not noticed any issues with the reduced water flow of the Oberdorfer from the Sherwood.  We put about 100 hours on it last season, with some long periods of motoring.  Temperature never gets higher than 160.   Maybe in the tropics with 88 degree water it might make a difference, but I doubt it.  Lake Champlain here in  Vermont got up into the high 70's last summer without any noticeable operating temperature changes."

I also asked for more details on altering the base of the pump to fit the available space on the M35B. He said:
"I used a metal cutting sawzall blade.  The bronze pump body is very easy to cut.  You could probably cut it with a hand hack saw in less than 10 minutes.  In retrospect it might be a good idea to start cuts by hand with a hack saw, so you have a little more control when using the Sawzall.  Just take your time with the Sawzall, especially when starting the cut.  I think I made 3 or 4 different straight cuts, to get the clearance.

The Oberdorder is a much superior pump.  My motivation was, it irritated the hell out of me to pay twice the price for a pump (Sherwood) that was not even half as good.  I had gotten dimensional drawings for both pumps and knew they were a physical match, except for the mounting flange.

You will love the all bronze body in salt water, which we plan on being back in a couple years.  When we leave I will modify another Oberdorfer for a spare, I don't want to ever get stuck having to use the Sherwood.   Now the Sherwood we had on our Catalina 30, M25 was a similar design to this Oberdorder and we never had a problem with that one"

I have an Oberdorfer on order and will provide a further update when I modify and install it.

[Stu Jackson]

We have an Oberdorfer.   We have a 3 inch HX, which I installed as a replacement for our orignal 2 inch HX on our M25.

We have all the water we need from our pump to keep our 3 inch HX keeping our engine cool and matching the engine temperature with the installed thermostat temperature.

The "inadequate" or "less water" claims do not apply to my engine.  Everything works just fine.

[noworries]

Great info... thanks for sharing... if my pump ever dies I'm doing this!

[Ron Hill]

Guys : Please do your engineering before you change raw water pumps from the Sherwood to the Oberdoffer.

Just remember that then early C34s (1986) had an Oberdoffer pump and a 2" heat exchanger ona 21hp engine.
Later (1987-1991) C34s usually had an Oberdoffer pump (some Sherwoods) and a 3" heat exchanger on a 23hp engine.
Even later C34s had a 3" heat exchanger, Sherwood pump on a 30hp engine.
The MKII C34s have a 3" heat exchanger (but a few inches LONGER), Sherwood pump for a 35hp engine.

So look at the engine/year of the C34 giving the advice.  A thought

[Stephen Butler]

Interesting topic.  We have a 1990 model, "dimpled-stern" C34 with a gold painted M25xp engine, a 3" heat exchanger, and a Sherwood pump.  A little bit of everything.  The PO swears that the boat came from the factory with this configuration.  As Ron says, do the checks and engineering before making changes and purchasing new parts.

[Mark Sutherland]

Hi Everyone.  I was on the phone with Corey at Depco Pumps yesterday.  I have a 2006 Universal M35B engine and was looking to replace my Sherwood pump with the Oberdorfer pump.  Up until now, the latest recommended Oberdorfer replacement pump that I've seen was the N202M-908.  Depco said this was the correct pump, but that it did not include the necessary modified plumbing fittings (apparently the original Sherwood fittings need to be modified to work with the Oberdorfer replacement pump on the M35B engine).  He said that part number N202M-837 is the same as the N202M-908, but it includes all of the needed modified fittings, gasket, etc.  The cost for the kit was $468.  I also bought the Impeller/gasket/O-ring kit OB 6593K ($47), Lip seals(2) OB 5463 ($21.85 ea), and Pump-block Gasket WB 302678 ($1,40).  Corey said that if/when the pump begins to "weep", it's usually the outer most (forward) lip seal (there are 2) so it's good to have a spare.

[Ron Hill]

Mark : There are two lip seals, one on either side of the weep holes.
The water lip seal is the one that weeps water and is the seal closest to the impeller side of the weep holes.  The other lip seal keeps oil in the engine and is on the engine side of the weep holes and it seldom leaks oil.

A few thoughts

[KWKloeber]

Before you install it, remove the cir-clip from the shaft and throw it away.
Bottom of page
http://c34.org/wiki/index.php?title=Why_do_some_of_our_engines_have_different_Oberdorfer_sea_water_pumps_than_others,_and_what_about_that_cir-clip_%22holding_the_impeller_on%22%3F

Smear a thin bit of SuperLube on the shaft to prevent it getting corroded/stuck, reinstall the impeller.

All, I caution that Corey is NOT the person to talk to about converting a B-series engine pump, to an Oberdorfer.  He sells parts not needed to install the 908 pump, plus the clips, etc, that we already have.  There is no problem re-using the Sherwood hose elbows.  It takes about 60 seconds with a dremel or hand file to make the "mod", below:




I've supplied about 30 of the 908s from US to Canada to Australia, currently $390.

I produced the 1st round flange clip-on pump and also a bolt-on alternate, for the B series -- showed it to Depco, they stole the idea and gave it to Ob and, miraculously, Ob came out with the same pump a year later.  What a coincidence?




Don't overpay for the kit -- don't ever buy the impeller kit, Depco charges you for a gasket you throw away!!!   Buy ONLY the cover o-ring and impeller separately.


The Kubota mounting gasket is better than the Westerbeke gasket (the "pump land" on those Kubota gear covers is actually for a mechanical engine hour meter.)

I don't normally do this, but I feel badly you got taken.  If you want one, PM your address I'll send you my free kit to install stainless studs and stainless nylock nuts instead of the bolts.  The studs stay in there so in the future you're not torquing bolts into the crappy gear cover metal whenever you remove/service the pump.

kk the pump guy

[KWKloeber]

Mark one thing I forgot to mention.  While you have the pump off, shine a flashlight into the gear cover to make sure there is a reinforcing ring on the fork on the end of the shaft.  They were not put on all B-series, pre-year-2000 engines are suspect.  p/n 48245 if your ring is missing.



k

[rmbrown]

Mark (and anyone else who's made the sherwood to oberdorfer swap!): 

Have you had any overheating issues now that you've got some hours under your belt?

Mike

[MarcZ]

2 seasons with Oberdorfer N202M-16 mounted om my M35(a), no issues. Normal operating temp is 160F (verified) just like it was with Sherwood pump.