S Bishop, re: Yanmar 3QM

[Sbishop]

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 don’t understand why it’s threaded if it’s meant for weeping.

[tkeithlu]

Welcome to the forum, Sbishop. I expect someone with knowledge of that engine will be along shortly.

[tkeithlu]

Actually, it woould help if you posted with the engine, something like "Yanmar 3QM weep hole" to attact those pesky Yanmar specialists.

[GordMay]

Greetings and belated welcome aboard the CF, Sbishop.

[boatman61]

If it is just behind the plate top centre..
Yes, there should be a screw in there.. its a bleed hole.

[jamhass]

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.

[Sbishop]

Actually, the threaded screw hole is on the bottom side and aft of the impeller. It’s not the scrub screw shown in the photo. I’m afraid you’re right in that it’s a sign that the water pump seal is leaking. I just don’t understand why it’s threaded with no screw in it. Im afraid if I put a screw in the hole I’m 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. What’s is everyone’s opinion on what engine for re-power.

[boatman61]

Originally Posted by Sbishop

Actually, the threaded screw hole is on the bottom side and aft of the impeller. It’s not the scrub screw shown in the photo. I’m afraid you’re right in that it’s a sign that the water pump seal is leaking. I just don’t understand why it’s threaded with no screw in it. Im afraid if I put a screw in the hole I’m 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. What’s is everyone’s 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.

[boatpoker]

Originally Posted by boatman61

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.

[boatman61]

Originally Posted by boatpoker

+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.

[JPA Cate]

Nice story, Boatie.

Ann

[Sbishop]

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.

[JPA Cate]

There's a Beta direct replacement.

Ann

[Wotname]

Originally Posted by Sbishop

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.

[skipperpete]

Originally Posted by Sbishop

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 don’t understand why it’s threaded if it’s 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.
Pete.