Yanmar 3GM30 Belt changing

[mikedefieslife]

Going to attempt the water pump belt tomorrow whilst in a bit of a lively anchorage, since it's the only thing I can think of as to why my engine is now overheating.

I knew I shouldn't have posted in that overheating thread yesterday. haha.

Anyway, is there a trick to changing the belts? I've got a service manual, but oddly the belts aren't mentioned in all 300 pages of the thing.

[Vasco]

Changing is pretty straight forward. But there is adjustment there if you want to tighten it. It's a small belt, not a lot of tension on it.

[mikedefieslife]

One part of it is only about 4mm thick, the other part closer to 8mm so I'm guess it's on it last legs.

It looks like the alternator belt has to come off first. On other engines I've seen, the alternator can slide to assist in changing the belt. I can't see any such mechanism for the alt belt on this engine.

Reason for changing the belt is cooling.

If I hook up a line from my water supply in place of the pump, I get a nice flow of water from the exhaust and a cool engine.

If I hook up the pump and either fill the strainer manually or open the seacock, I get nothing coming out of the exhaust, though the engine does take on a little water.

Now if I sick one end of the pump in a bucket and turn it by hand, then I get water coming out of the other end.

All that to me adds up to the belt not spinning the pump sufficiently. What do you think?

[sailorchic34]

If your engine is getting too hot it could be a loose belt. But also check that the discharge elbow and the brass 90 that connects to it is not partly clogged. Very common after 300-500 hours. A bicycle spoke makes a fair tool to clean out the crude in the elbow and the first half of the discharge elbow.

On replacing belts, Yes you pull the alternator belt off first. 12mm wrench for the raw water pump bolts and 12 and 13mm on the alternator adjusters/bolts

[Captsteve53]

When did you last change your raw water pump rubber impeller(should be checked every season) and for me i just replace it every season regardless of condition and sleep easy knowing i have good water flow, in side the pump there's a cam as well but that normally lasts years,

I have seen rubber impellers that look !00% but in fact the rubber has lost it's resilience or slipping on it's bronze bushing (hard to inspect) so for $20/30 bucks a year the peace of mind is worth it!!

Cheers Steve

[Captsteve53]

Just saw your last comment,you need to check the water pick up hose is not partially blocked(dont know if you have a strainer /filter or not) also check that sea cock/thru hull valve is working and that you haven't picked up a "bag fish" in the hull fitting or even just barnacle growth,

Cheers Steve

[mikedefieslife]

Hi all,

Thanks for the tips.

Just to let you know, it was the belt.

Take a look a look at this!





This should have been an easy spot, save for the fact that from that front access hatch I have you can't barely even see the belt at all.

Anyway, all good now, and I changed the alternator belt at the same time.

Just in case anyone else is doing this on a 3GM30. It's 14mm for the top alternator bolt, and 12mm on the nut behind it. It likes to spin as you turn the bolt so you will need both wrenches.

The bolt that allows the alternator to swivel is 13mm and is accessed from the rear. There no nut on this at the other end (at least in my case).

All water pump bracket nuts are 13mm. 7mm for the small bolts that hold the back of the impeller cover on.

[01kiwijohn]

Should be able to see the pump pulley turning when the engine is running. DO Not over tension that belt or you will destroy the bearings.
There is a slide adjustment on the alternator, take another look.

[EmeraldCoastSailor]

It is very important not to over tighten belt as it will kill your new water pump bearings.

[mikedefieslife]

Yes. The manual tells of the correct deflection.

My method is to loosen the belt just enough so that the engine doesn't spin the pump. Then tighten it up just to the point that it does. With a new belt it can feel relative tight, but shouldn't be a problem.

Something to keep an eye on as when the belt stretches, as the belt will need tensioning from time to time.