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Old 20-03-2021, 04:22   #1
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S Bishop, re: Yanmar 3QM

I have a C&C 39 with Yanmar 3QM series engine. Just forward of the impeller is a threaded hole that is weeping water when the engine is running. There is nothing in the hole. Is this a sign of problems to come or should there be a screw in this hole. I donít understand why itís threaded if itís meant for weeping.
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Old 20-03-2021, 04:25   #2
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Re: S Bishop

Welcome to the forum, Sbishop. I expect someone with knowledge of that engine will be along shortly.
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Old 20-03-2021, 04:28   #3
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Re: S Bishop

Actually, it woould help if you posted with the engine, something like "Yanmar 3QM weep hole" to attact those pesky Yanmar specialists.
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Old 20-03-2021, 05:49   #4
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Re: S Bishop

Greetings and belated welcome aboard the CF, Sbishop.
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Old 20-03-2021, 06:02   #5
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pirate Re: S Bishop

If it is just behind the plate top centre..
Yes, there should be a screw in there.. its a bleed hole.
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Old 20-03-2021, 07:54   #6
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Re: S Bishop

If the weep hole you describe is closer to the pulley, that would indicate a leak from the shaft seal, suggesting time to rebuild the pump.
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Old 20-03-2021, 15:13   #7
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Re: S Bishop

Actually, the threaded screw hole is on the bottom side and aft of the impeller. Itís not the scrub screw shown in the photo. Iím afraid youíre right in that itís a sign that the water pump seal is leaking. I just donít understand why itís threaded with no screw in it. Im afraid if I put a screw in the hole Iím going to eventually force water into the engine. A new water pump is awfully expensive. Thinking it may be time to re-power. These vessels originally had the atomic 4. Whatís is everyoneís opinion on what engine for re-power.
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Old 20-03-2021, 15:27   #8
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pirate Re: S Bishop

Quote:
Originally Posted by Sbishop View Post
Actually, the threaded screw hole is on the bottom side and aft of the impeller. Itís not the scrub screw shown in the photo. Iím afraid youíre right in that itís a sign that the water pump seal is leaking. I just donít understand why itís threaded with no screw in it. Im afraid if I put a screw in the hole Iím going to eventually force water into the engine. A new water pump is awfully expensive. Thinking it may be time to re-power. These vessels originally had the atomic 4. Whatís is everyoneís opinion on what engine for re-power.
In that case remove the pump, strip it down and replace all the seals.. not a difficult job, cheaper than a new pump and way cheaper than a repower.
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Old 20-03-2021, 15:43   #9
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Re: S Bishop

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In that case remove the pump, strip it down and replace all the seals.. not a difficult job, cheaper than a new pump and way cheaper than a repower.
+1

This alone does not justify engine replacement.
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Old 20-03-2021, 16:03   #10
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+1

This alone does not justify engine replacement.
Had this happen to me only it was not a drip but a jet of water.. pulled into the anchorage at Cascais and went ashore to visit the Chandlers in the hope of a kit..
No joy and a couple of weeks wait if ordered.. went back to the boat, removed the pump and stripped it down then went back with the leaking seal which was the one behind the impeller.. eventually after searching through the boxes of washers I found a tap washer the right bore and just fractionally smaller than the total outer circumference so I bought two..
Went back to the boat, installed one and reassembled and fitted the pump back in situ and started the engine.. no jet of water but a steady dribble..
Removed and stripped down pump again, dried everything throughly then smeared Sikaflex around the rear wall, inserted the washer and carefully smeared Sika into the tiny gap round the outer edges... carefully cleaned the side walls of traces of Sika then let it dry for half hour.
Completed reassembly and fitted pump in place, started engine and..
No Leak..
Lasted me motoring the 90nm up to my berth in Fig da Foz.. and till the replacement seals arrived from the UK.
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Old 20-03-2021, 16:40   #11
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Re: S Bishop, re: Yanmar 3QM

Nice story, Boatie.

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Old 20-03-2021, 16:59   #12
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Re: S Bishop, re: Yanmar 3QM

Thanks,

I think I’ve just been trying to come up with a reason to re-power. I’ve never liked the size of the Yanmar. I bought it for $800 and had to build new companionway steps because of the size of the engine. It also has to sit further forward than the previous engine. It’s somewhat awkward entering and exiting the companionway with straight down steps off a platform. It’s a huge hunk of steel. I’ll take your advice and replace seals and hopefully get another season or so out of her.....I’d still like to hear what engine folks are replacing the old Atomic 4’s with.
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Old 20-03-2021, 17:15   #13
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Re: S Bishop, re: Yanmar 3QM

There's a Beta direct replacement.

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Old 20-03-2021, 17:30   #14
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Re: S Bishop, re: Yanmar 3QM

Quote:
Originally Posted by Sbishop View Post
Thanks,

I think I’ve just been trying to come up with a reason to re-power. I’ve never liked the size of the Yanmar. I bought it for $800 and had to build new companionway steps because of the size of the engine. It also has to sit further forward than the previous engine. It’s somewhat awkward entering and exiting the companionway with straight down steps off a platform. It’s a huge hunk of steel. I’ll take your advice and replace seals and hopefully get another season or so out of her.....I’d still like to hear what engine folks are replacing the old Atomic 4’s with.
The water pump will faster forever (almost) if you replace the impeller, seals, bearing and end plates as required. I have rebuilt a few water pumps over the years with the oldest being around 40 years old.

As for replacing the 3QM, I guess it depends on what you want from your engine. If you want a small and light engine, then the QM is not for you.

However if you want a dependable, run for days without stopping and long lasting engine, the QM has to be trumps. Unlike more recent (and previous) Yanmars which are (were) designed for the recreational boat market, the QM was always intended for workboats i.e. a commercial grade engine. It max rpm is lower than the others (2600/2800 compared to 3400/3600) and it is heavy in construction. It was made to last and be repairable (almost forever).

IMO, it is one of the best engines ever made by Yanmar but I grant you it isn't small or light. I'm told some clutch parts are hard to get but I haven't tried looking myself.
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Old 20-03-2021, 21:40   #15
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Re: S Bishop, re: Yanmar 3QM

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I have a C&C 39 with Yanmar 3QM series engine. Just forward of the impeller is a threaded hole that is weeping water when the engine is running. There is nothing in the hole. Is this a sign of problems to come or should there be a screw in this hole. I donít understand why itís threaded if itís meant for weeping.


It sound like the screw that secures the cam has corroded away. If this is the case then you might be about to experience an overheat when the cam moves within the housing and covers one of the pump ports.
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