Gasket....Yes or No?

Sep 25, 2008
464
Catalina 30 MKIII Varuna Boat Club
Hi everyone,
I'm looking for some experienced advice. I have a 1997 Universal M25XPA. I am changing out the old Sherwood raw water pump with an Obendorfer. Both pumps mount exactly the same way using a mounting ring on the pump that mates against the block. The ring is held in place with bronze clips that are mounted to the block.
My question is, since neither Sherwood or Obendorfer provide a mounting gasket when you purchase the pump but, a gasket is available if you hunt for it; is the gasket necessary in the first place? The mounting ring is polished brass.
I have had several opinions including: No gasket needed since there is no pressure there......Blue gasket bond is all that is necessary....You must have a gasket.
Who to believe?
 

Tom J

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Sep 30, 2008
2,301
Catalina 310 Quincy, MA
I use the gasket if I have it on hand. If not, I order a couple and put one on next time. It doesn't seal anything, just less metal to metal contact. Now that I have the Oberdorfer, though, I don't take the pump off the engine as much.
You might want to check the wear marks on the driven end of the shaft of the Oberdorfer. If it looks like the shaft needs to go deeper into the driving shaft, leave the gasket off.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Both pumps mount exactly the same way using a mounting ring on the pump that mates against the block. The ring is held in place with bronze clips that are mounted to the block.
My question is, since neither Sherwood or Obendorfer provide a mounting gasket when you purchase the pump but, a gasket is available if you hunt for it; is the gasket necessary in the first place? The mounting ring is polished brass.
Do you have studs sticking out from the engine? My ObeRdorfer is mounted with four studs. The gasket is provided by the engine "side" not from the pump manufacturers. For my M25 I get them from a Kubota tractor dealer for pennies on the $ compared to Universal prices, but you get them from the engine dealer.

The goop is Permatex Ultra Black and I still used a gasket on the pump side.



IMG_20181110_114339.jpg
 

capta

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Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
If that is a shaft driven pump, then most likely there is oil in there to lubricate the shaft bearing, which will leak out w/o a gasket, when the engine is running and the oil pressure is up.
I don't have a Universal, but if the parts are interchangeable w/Kubota, then my Onan, which uses a Kubota engine, definitely needs a gasket. And no goop.
 

Ward H

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Nov 7, 2011
3,645
Catalina 30 Mk II Barnegat, NJ
I also agree with Capta.
The Oberdorfer pump for my M25XP came from depcopump.com. Mounts just like you describe. They supplied the gasket with the pump, along with the two mounting clamps and machine screws. IIRC, the gasket was in a small, thin, manila envelope with "Small Parts Inside, Do Not Throw Away" stamped on it.
 
Sep 25, 2008
464
Catalina 30 MKIII Varuna Boat Club
Thanks Ward. The pump did not come with a gasket, but I did buy one from Discount Marine only because it was so cheap. Just trying to determine the best route.
 
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Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
If I go with no goop, do I need to wet the gasket first?
No, dry fit. I recommend putting it on the pump body and then installing. Least that's what I did before I needed the goop for a completely different reason, too long to get into here (involves epoxying in a new stud). I don't know about your situation without the studs. Got any pictures? I'm always trying to learn. But the gasket goes on dry.
 
Sep 25, 2008
464
Catalina 30 MKIII Varuna Boat Club
No, dry fit. I recommend putting it on the pump body and then installing. Least that's what I did before I needed the goop for a completely different reason, too long to get into here (involves epoxying in a new stud). I don't know about your situation without the studs. Got any pictures? I'm always trying to learn. But the gasket goes on dry.
I do have a photo of the Sherwood from the front of the engine looking left. It shows the side of the pump and the mounting ring against the block.
Raw Pump 2.jpg
 

Tom J

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Sep 30, 2008
2,301
Catalina 310 Quincy, MA
Thanks Ward. The pump did not come with a gasket, but I did buy one from Discount Marine only because it was so cheap. Just trying to determine the best route.
You can't go wrong with using the gasket. The first time I rebuilt my Sherwood, the kit didn't come with the flange gasket. I re-used the old one for the time being. I finally sourced them through the Universal dealer. I have never re-used a gasket before, certainly not in a critical area, but I if I remember correctly, there was a seal on the driving shaft and a seal on the pump shaft, so the gasket didn't seem critical. Maybe someone who has worked on replacing the pump on the M25xba or b recently could confirm this or not.
 
Last edited:
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
there was a seal on the driving shaft and a seal on the pump shaft, so the gasket didn't seem critical. Maybe someone who has worked on replacing the pump on the M25xba or b recently could confirm this on not.
Tom, yes, there are two seals. But they are within the pump body and when they go they leak to the weep hole on the pump to tell you that a seal has gone bad and needs to be replaced.
The gasket keeps the engine face and pump flange tight and avoids the oil dripping out between the two faces.
Two different things with two diff3erent purposes.
I photoed my pump engine face earlier in this thread and have done so a few times since I learned how to replace the seals 15 years ago.
Here's a Kubota tractor gasket on my Oberdorfer:
IMG_20181110_114347.jpg


And here's the pump mounted:
IMG_20181110_115502.jpg
 

Tom J

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Sep 30, 2008
2,301
Catalina 310 Quincy, MA
Tom, yes, there are two seals. But they are within the pump body and when they go they leak to the weep hole on the pump to tell you that a seal has gone bad and needs to be replaced.
Thanks, Stu. My pump is like the one the OP pictured on his M25xpa. Mine is a M25xpb, and has the same circular flange and is held in place by two small clamps, no studs. The flange does not match up with the flat face on the engine. The pump can be rotated to orient it for clearance with the alternator, etc. My question concerns the opening on the engine block where the driving shaft is located. The flange on our pumps is not secured well enough to provide a tight seal, and I am pretty sure there is a shaft seal on the driving shaft at the opening in the engine block, but I can't swear to it. I think the OP brought up the question because like many of us M25xpa/b owners, the need for the gasket is not very evident.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
I think the OP brought up the question because like many of us M25xpa/b owners, the need for the gasket is not very evident.
Tom, I understand, and which is why I asked for a photo, because I do not have personal experience with that "other" pump mounting method. I admit I have never seen one, and the side photo that was posted frankly doesn't help me understand how it works. It also appears that my application does not reflect any help at all for the OP because the pump mounts are vastly different. Liker I said, I'm always up for more learnin. :)
 
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Tom J

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Sep 30, 2008
2,301
Catalina 310 Quincy, MA
I'm not very computer literate, Stu, so I don't know much about links, etc. But in the M25xpb manual, pg. 55, it says:
12. Mount the pump to the engine taking care that the end seal and gasket are in place. Do not tighten the pump mounting screws, just finger tighten.
14. Start the engine in idle; this will allow the pump to align itself with it's drive shaft.
15. Stop the engine and tighten the pump assembly mounting screws.
From this, I would say the flange gasket should be installed. The parts breakdown for the engine does not show the gear assembly in detail, so I still don't know what is at the pump mounting face.
Of course, this mounting procedure might be specific to the M24xpa/b, since the mount is not as precise as one with studs.