Sherwood Redux

[patrice]

Hi
I have the sherwood pump on my boat.
What fun did I had to remove the impeller while winterizing the engine.
Who would have that great idea to put the screw behind the cover ???
I just hope that the original design was for something else.

[Indian Falls]

I replaced my impellor underway due to leaving the thru-hull closed... it got so hot it changed the color of the paint on the cover.  It wasn't super easy but not all that difficult overall.  In four seasons, this is the only trouble I've seen with it.  This also appears to be the original pump on my engine.

So far I have seen no mention of making sure the impellor fingers all lean back in the proper direction.  They will not right themselves in this pump and will break off ending up in your heat exchanger.  I found a dozen of them when I opened the HX the first time.  I also found that 2 fingers on my first new impellor were leaning forward the whole season upon removal for winter lay up.  There is just no room inside for that finger to collapse and lean back at the same time to be righted. I always seem to have the enigma...

[Hawk]

Guys, Great discussion on pumps, particularly as I was warming up the engine last week to change the oil and while doing my engine running inspection saw quite a steady drip from the Sherwood weep hole.....
Frankly it has worked well for the last 6 years and longer but the testimonials here are less than favourable.

I am going to replace the pump...Oberdorfer or Sherwood? Am I correct that Oberdorfer has increased the flow capacity so that it is no longer an issue? Does it fit right in to place....I saw some people mention modifications?
Ron, you mentioned that you found the weak link on the Sherwoods...is that still an issue on the recently purchashed ones?
I may have the old one renewed by Depco.

Thanks fellas.

Hawk

[Stu Jackson]

Am I correct that Oberdorfer has increased the flow capacity so that it is no longer an issue? Does it fit right in to place....I saw some people mention modifications?

Hawk, please re-read this topic, especially replies #8 & 13 about pumping capacity.

Modifications to the Oberdorfer pump base are in the link to the wiki article for the M35 engine, not the M25 or M25XP.

You don't "redo" a pump, you replace the seals.  The first time took me all of 2 hours (it was cold and raining and I didn't wanna go out  ).  Like this:

http://c34.org/bbs/index.php/topic,6766.0.html

[Hawk]

Thanks Stu.

Reviewing the wiki article the Oberdorfer mod for the M35A is simple and the pump position looks the same as my M35. The M35B pump is positioned very differently and the mod is more than I would bother with.

Has anyone replaced the Sherwood with an Oberdorfer on a 1990 M35 engine? Looks like it is the same as depicted in the wiki article....

Scotty says at #13 that Oberdorfer changed the cam to increase delta so they pump 8 gpm...don't know what all that means but do we all agree there is no more issue about Oberdorfer's alleged inferior pump capacity?

Thanks guys...I only want to do this once (:

Hawk

[Ron Hill]

Tom : Most rotary pumps that I've seen have the interior cam to make the the inside cavity asymeterical, so I'm not too sure what Scotty is talking about??

Just be sure that the slot on any pump shaft matches and fits into the slot that drives it in the engine.

A thought 

[Hawk]

Thanks Ron.
Is there any way of determining whether the Oberdorfer pump shaft does in fact fit without buying and trying?
I'm leaning to simply replacing the Sherwood for simplicities sake. Maybe you've told Sherwood about the weak link and they've fixed it(:
Hawk

[Hawk]

...........and this I found on the ever open can of worms on flow capacity.....from Joe, I take it....year 2002.

http://sankaty.homestead.com/Universal_5432_rawwater_pump_cap.html

[Hawk]

Sorry to keep coming back to this issue but Oberdorfer shows specs for the N202M-16 that appears to be the model installed on M35 engines according to another site. It seems to say that at 2500rpms it is moving 8 or 9 GPM which I believe is in the Sherwood range, certainly not 3 GPM I've seen mentioned, although Scotty did say Oberdorfer changed their capacity to 8GPM.

http://www.oberdorfer-pumps.com/Spec_sheets/202M%20Series%204%20page.pdf

Also set out in the below link is the latest from Catalina Direct discussing the improvements to the Oberdorfer and the increased GPM capacity.......all apparently $150 cheaper than the Sherwood.

http://www.catalinadirect.com/index.cfm?fuseaction=product.display&product_ID=2361

I'm leaning to the Oberdorfer more for the avoidance of recurring leaks others discuss... with only a small mod for my M35 engine. I never frankly found changing the impeller on the Sherwood to be difficult but that was always at the dock.......the ober does look easier.

Tom

[Ron Hill]

Tom : Let me dispel some of the miths around these two raw water pumps.  I've rebuilt and have 25+ yrs of experience with both the Oberdoffer and Sherwood pumps.

There are two seals in each pump with weep holes inbetween them.  One seal keeps the oil in the engine and the other seal keep the water in the pump cavity.  
I don't know of anyone that has had to change an oil seal because oil was leaking from the weep hole; unless they screwed up the oil seal on an Oberdoffer while they were changing the water lip seal. You don't need to touch the oil seal on a Sherwood to change a water seal.

The water seal is usually the problem on either pump. The water seal failure rate should be about the same, except that the Sherwood does have more of a seal surface.
That seal in each pump is a piece of "rubber" compressing against a stainless shaft (that turns). The Oberdoffer rubber seal is about 1/16" wide while the Sherwood is about 3/16" wide.  Both are compressed, but in a different manner.

To remove the self contained water lip seal in an Oberdoffer you'll need to drive out the seal's brass casing out of the pump body, by removing the oil lip seal first to get to the water lip seal.  Care must be taken during removal NOT to score/scratch the inside wall of the Oberdoffer pump body.  Because the brass body of the lip seal is a compression fit and a scratch can/will cause a leak.

To remove the water seal on a Sherwood there is no need to touch the oil seal.  The water seal is partially assembled and you compress the sides of it's metal seat and pull the old assembly directly out.  The new assembly is coated with "Permatex" and tapped back in place.

I've always found that it is easier to just change a spare pump if I note a water leak and rebuild the leaking pump at home.  It can be done on the boat, but it is are many times easier at home.
Pump change:
 
Sherwood - Remove the pump housing, removing the 3 bolts (they are in backwards to my liking) and move that housing with the hoses still attached out of the way.  Then remove and replace the pump body (2 bolts), align the impeller and replace the pump housing, tighten down the 3 bolts and it's ready.

Oberdoffer - First thing is to remove the inlet and outlet hoses and move them out of the way.  Back off the 4 nuts that hold the pump to the engine.  Reinstall the rebuilt pump with the 4 nuts amd reattach the two hoses and it's ready. (You might have to remove the 2 - 90degree nipples from the old pump and reinstall on the new pump; if you didn't already have a set on the spare pump.)

It's straight forward to change out a pump unless you are working over a hot engine (outside temp in the 90s), the black flys are biting your legs and your 1st Mate is telling you that there is too much sail up and she can't handle it anymore -- Otherwise it's an easy task!!   (that really happened!)

From watching my exhaust water for 23 years with one and 3 years with the other, I can assure you the Sherwood pumps more water.
The argument should not be - does the Oberdoffer as much water as a Sherwood?  
It should be - does the Oberdoffer pump enough water to adequately cool the M35(30hp) and M35BC(35hp) engines??  

A whole bunch of thoughts, but it's your boat.


 
 

[Hawk]

Ron,

Thanks again for the detailed info.
The ultimate question you posed is important for my m35. According to Catalina Direct and Oberdorfer as set out in the links to my last post above, the Oberdorfer pumps 9 GPM at 2500rpm. Catalina Direct says the pumps have been changed/improved.
I know you've seen less from the Oberforfers than your Sherwoods. Could it be that you had the older model Oberdorfers?

Thanks,
Tom

[Ron Hill]

Hawk : I had 2 - 202M15 Oberdoffer pumps, just like 99% of the other owners of M25XP engines. 

What I'd suggest is that you call Customer Service at Oberdoffer Tel. (315)437-0361 and ask them the difference in the gal/hr of their -15 and -16  202M pumps.  I'm going to guess that they are nearly the same?

Then call Sherwood regarding your G908 pump - don't have their number handy.
 
That way you can do your own research and stop depending on someone elses opinion. 
That's the only way you can be satisfied that you are making the correct decision !!

A thought

[karista]

Hawk : I had 2 - 202M15 Oberdoffer pumps, just like 99% of the other owners of M25XP engines. 

Ron!
I am now considering  switching to the Oberdorfer N202M-16 pump from the Sherwood. My engine only has about 1300 hrs, yet I am on my 4th Sherwood Pump (2 new and 2 rebuilt by Depco) These Sherwood pumps are a 25 year old design with no improvements made and at $400+ are way overpriced compared to the Oberdorfer.
Question: In your opinion having owned 2, is the Oberdorfer a more reliable longer lasting pump? Is the Oberdorfer a direct fit on a 25MXPB? If. not what is required besides a new gasket and Screws?

[DarthOccam]

That way you can do your own research and stop depending on someone elses opinion.  
That's the only way you can be satisfied that you are making the correct decision !!

Good advice, which I unfortunately recently had occasion to heed.  The Sherwood G908 pump on our M35B engine failed at about 160 total engine hours.  Like many have noted above, I've been frustrated with the Sherwood:

• Pump body rusts
• Water seal prone to early failure, especially when used infrequently
• Pain to change the impeller
• Replacement and maintenance is more expensive than the Oberdorfer

Enough issues that I was willing to consider the Oberdorfer as a replacement.

Randy Sherwood and Niel Schneider did a nice write up on modifying the N202M-16 Oberdorfer so that it fits the M35B, so the main question was whether it pumps enough water to adequately cool the engine.  Part of the confusion is that the current model ("N"202M) pumps more than the previous model. The "-15" and "-16" part of the part number means 3/8" and 1/2" fittings, respectively.

According to page 44 of the Universal Operators Manual for the M35B engine, it requires 8 GPM at 3,000 RPM.

[attach=#]

The N202M-16 puts out somewhere between 9-10.5 GPM at 3,000 RPM, depending on how it's installed.

[attach=#]

Subjectively, it seems to spit out a comparable volume.  A sea trial was successful, with the temperature rising and stabilizing normally.  I'll continue to monitor it this season, but I'm considering it an improvement.

[Stu Jackson]

Just to match Ron's thoughts about Sherwood pumping volumes, I'll repeat myself:

"If an Oberdorfer pumps enough water to keep your engine cool, what's the question?"