Yanmar 2qm20 not starting troubleshooting

[Dalestr]

With that voltage, you are not measuring properly or the charge circuit is not connected as even while engine off you should have full battery voltage at the alternator output post. In most cases, the heavy alternator wire connects directly to the battery (+) through the battery switch.
You might also look for a proper ground wire from alternator (~10 AWG) to the engine block unless this depends on the alternator mounting for that (poor practice). The fact that the loose belt was squealing in the video though, says that the alternator was acting as expected, providing a load to the engine (trying to charge a low battery) and it can't do that unless things were correct electrically... Yes, you should see 13.6-14.2V for the system voltage when the alternator is charging, dependent on battery state and to some extent engine speed. Alternator load is greatest for the first minutes after starting.
Thanks for the great post on your shaft seal swap!

[thesauvage]

Thank you for your advice.
I've measured the alternator like shown in this video:

https://youtu.be/4XJT91-kP2A

Shouldn't there be always at least a 13.5V output from the alternator, no matter how it is wired? (Measured at the alternators housing & the 'Positive' port).

I've found this replacement alternator on ebay:

https://www.ebay.fr/itm/Lichtmaschin...1-3913606ce710

The seller says it is compatible with my 2qm20 and it has also the 70A of my current (dead) one. What do you guys think?

Maybe I should make the shaft seal change an independent post, to save the resource for other people as a reference.

Good News: France allows for sailing from May 11th again whohooo!

[Cheechako]

Originally Posted by thesauvage

Thank you for your advice.
I've measured the alternator like shown in this video:

https://youtu.be/4XJT91-kP2A

Shouldn't there be always at least a 13.5V output from the alternator, no matter how it is wired? (Measured at the alternators housing & the 'Positive' port).

I've found this replacement alternator on ebay:

https://www.ebay.fr/itm/Lichtmaschin...1-3913606ce710

The seller says it is compatible with my 2qm20 and it has also the 70A of my current (dead) one. What do you guys think?

Maybe I should make the shaft seal change an independent post, to save the resource for other people as a reference.

Good News: France allows for sailing from May 11th again whohooo!

Just make sure the mounting feet and spacing and location are correct for the Yanmar. I was not aware that Perkins and Yanmar had the same setup.

[Dalestr]

Hi thesauvage. You are probably beyond this point now but here's my response.
---the utube video shows that he sees battery voltage at the alternator and so should you. It must be directly connected (through the battery switch) to the battery. Only when the alternator is spinning fast and the alternator has initialized (triggered into charging mode) will you see charging voltage. Some alternators require a small current (via 3W LAMP) to initialize. That lamp glows when the alternator is not charging.

Make doubly sure of all your connections, including the ground path. Adding a separate grounding wire can't hurt as that carries 50A. Never run an alternator without full wiring or disconnect the load while charging.
For the proposed replacement alternator, I would ask for dimensional drawings and electrical schematics (wiring diagram at least). You want it to be compatible, electrically, with what you had and also the Yanmar warning circuit ("no-charge" lamp and horn). Also, do you need a signal to drive a tachometer? Do the mounting lugs have correct bolt size and spacing including the "clock" position, the angular orientation of the tensioning lug?
Look at Yanmar alternator schematics for further details. "L" is for the charge lamp circuit.
Let us know how you made out.

[OloteleMtn]

The tach sender on the 2QM20 is on the bell housing of the transmission, above the rear of the starter. Mine has a 30 amp (new) alternator; higher amp alternators tend to take off horsepower, so unless you have a larger battery bank and higher electrical loads, you may want to go with a lower amp rating.

[Wotname]

Just to add to the general knowledge of the 2QM20 tacho arrangements.

Early models came with a mechanically driven tacho which was driven by gears off the camshaft timing gear.

On later models the tacho was an option and driven by a sender as described by OloteleMtn (post #80).

If this option was not fitted, some owners fitted an alternator sensed tacho however this needed the alternator to be changed or at least modified to provide the "W" terminal required by a alternator sensed tacho.

Thus there are four possible scenarios with the QM series engines.
1. No tacho
2. Tacho magnetically driven by the flywheel ring gear
3. Tacho mechanically driven by a cable
4. Tacho alternator sensed off the W terminal.

[sfnz]

the bog standard 2QM20 30 amp internally regulated altenator has 3 connections, 1 positive, 1 negative and one WL or warning light, the warning light is used to "excite" the altenator into working . A very quick way of seeing if the altenator is any good is to take all wires and the drive belt off, take a wire from the pos terminal to a battery, take another wire from the neg terminal to the same battery get your battery drill out and pop a socket to drive the altenator on it, give it a whirl and it should spin freely, next take a wire from the positive battery to the warning light terminal, give it another whirl, if the drill loads up then the altenator is doing something, if not then it aint, the negative terminal is NOT electricaly connected to the altenator case
Another "to watch for" on the QM series is corrosion on the rocker oil feed line as it passes below the exhaust riser at the back of the engine, oh and while you're at it, make sure the crankcase breather tube is not blocked as if it is you'll do a surprisingly quick oil change, don't be alarmed by the uneven note of the starter motor either as these 4 stroke diesels have a one up one down crankshaft and not both pistons rising and falling together as is the norm in 4 strokes

[Wotname]

Originally Posted by sfnz

.......... don't be alarmed by the uneven note of the starter motor either as these 4 stroke diesels have a one up one down crankshaft and not both pistons rising and falling together as is the norm in 4 strokes

Perhaps off topic but I am very curious to know what twin cylinder four stroke engines have both pistons rising and falling together. I sort of remember an old Honda twin motorcycle did but I haven't see it in any twin cylinder marine diesels. Perhaps I need to get out more .
????

[OloteleMtn]

I would be surprised if any 2 cylinders did that; Harley engines are opposed V twins, and they vibrate quite a lot....if they rose and fell together they would bounce you off your seat (seas)

[jimbunyard]

Pretty sure Harleys (and I assume the various V-twin knockoffs) run split-fork con rods on a single crank journal; i.e the pistons do rise at (almost) the same time but alternate power strokes.

But, even with various counter-measures, they vibrate much more than their in-line sewing-machine cousins...

[Tiri57]

I hawe same proplem . Has anybody injector pump dokuments how to chance inside parts?

[OloteleMtn]

https://www.lsm-diesel.dk/2012/yanma...qm20-3qm30.pdf
parts manual with detail

[thesauvage]

Originally Posted by Tiri57

I hawe same proplem . Has anybody injector pump dokuments how to chance inside parts?

Did you make sure it actually IS THE INJECTOR PUMP, that prevents your engine from starting?

[thesauvage]

The Alternator I've ordered did fit the mounts without any modification. Charge warning lamp is off. Works great so far, have tested about 3h when motoring.

[jimbunyard]

Service manual with a very detailed injection pump section here.

http://www.hunter37.com/Yanmar_3qm30.pdf