Johnson raw water pump just won't prime - new impellers

[ianat182]

One more possible answer is the raw water filter of the Vetus type leaking air into the system and destroying the suction/vacuum where the lid has been cross threaded, or hasn't been sealed with a grease or vaseline smear on the threads.
I check my filter every time I return from sailing because of previous weed (and baby mussel growth in the inlet piping),and it is much easier to tighten and loosen for this maintenance task. Have you also checked for a delaminated pipe here?

ianat182

 

[andygc]

For goodness sake! The OP said that the old impeller works. Therefore, it's an impeller problem.

If there is a gap between the impeller and the back of the pump chamber or between the impeller and the cover plate, air will leak and the pump won't prime. 0.2 mm is plenty of space for air (and water) to leak through. Either the new impeller is the wrong one for the pump or the pump is worn and the old impeller is the wrong one for the pump.

What else could it be?

And then I read timmfive's posting and looked at his other posting - which explains that there are two impellers

Old Pump: Johnson Pump F4B-902, 10-24509-02. Impeller Johnson 810B.
New Pump: Johnson Pump F4B-903, 10-24509-01. Impeller Johnson 810B-1. (no paper gasket)

Old pump Inner chamber diameter: 50.2 mm. Diameter to cam: 48.25 mm.
New pump Inner chamber diameter: 50.0 mm. Diameter to cam: 46.00 mm.

Try clicking here

 

[steve28]

are you ordering it for a 2gm20 pump or for the f4b pump, the pump on the 2gm has a round coverplate.
What im getting at is you could be ordering an impeller for a 2gm pump and the f4b one isnt the standard pump.


looking quickly i think you need 09-810B-1

steve

 

[nimbusgb]

Stupid idea but how about knocking up a temporary faceplate out of perspex?

 

[timmfive]

yeah, i wish i had measured the depth of the pump housing on both the old and the new pumps to see if any discernable difference
(ie: distance from the inside of faceplate to the inside of pump housing. you can clearly see in photo that the old pump had dark oxydized markings on inside of pump housing... indicating to me, in hindsight, that the impeller wasn't sealing on the inside of the housing.)

and also wished i had measured the two impellers diameter and depth
oh well... tried my best.

 

[savageseadog]

yeah, i wish i had measured the depth of the pump housing on both the old and the new pumps to see if any discernable difference
(ie: distance from the inside of faceplate to the inside of pump housing. you can clearly see in photo that the old pump had dark oxydized markings on inside of pump housing... indicating to me, in hindsight, that the impeller wasn't sealing on the inside of the housing.)

and also wished i had measured the two impellers diameter and depth
oh well... tried my best.

---

The yanmar GM's with the Johnson pumps are YEU engines the last of the GM range before the model change (European manufacture) if you buy a standard impeller replacement they are wrong. Also the impellers come in two varieties half inch shaft (12.7mm) and 12mm shaft also there are slight differences between the YEU - GM Freshwater cooled and raw water cooled pumps.

The good news is that the Johnson raw water pumps are only £180 brand new from the dealer (marine power, et al.) as opposed to the jabsco at £300/400, or for new bearings and seals are less than £10! - i have the bearing numbers if you need them, we have a 3GM30FC-YEU (you can tell if yours is the YEU by looking for an E on the engine plate near the number.

Some people replace a Jabsco pump with the Johnson pump as there less than half the price as a replacement (though the dealers don't tell you this!). There is no difference in the mounting so you can get Johnson pumps on the older GM' engines.

The Johnson pumps also have the o-ring seal, far superior to the paper gasket. Make sure your oring is properly seated.

Datasheet and diagram for the Johnson Waterpumps for the GM raw and Fresh YEU ENGINES ---- >>
http://www.depcopump.com/datasheets/johnson/10-24509-01.pdf