Erratic Yanmar 3YM20 Rev Counter

[NPMR]

I have an intermittent problem with the rev counter on a 3-season old Yanmar 3YM20.

The problem is that the pointer will occasionally jump, to show maximum deflection (revs) and cannot be restored to 'correct' operation until the engine is switched off and restarted, when it seems to operate properly. Obviously, the engine revs are NOT jumping around!

We also have an issue with batteries not charging very well.

As I believe the rev counter works off the alternator ........ ???

Anyone got any ideas? Yanmar don't have anything useful to say on the matter, it seems.

 

[rob2]

I think you could be on the right track as all the above rely on the alternator wiring. It must be wirth checking all the external wiring for dodgy connections, but the second step would have to be taking the alternator to an auto electrician for checking/rebuild. It's a lot cheaper to find your local man (not one of the garages they service) than to fund a replacement from Yanmar!

Rob.

 

[William_H]

I don't know if you have an amp meter in tthe alternator output or battery charge circuit. Well worth having. This would tell you if alternator is dicky. Bad wiring or more likely bad brush contact on the slip rings will cause intermittent charge and of course tacho no good. good luck olewill

 

[charles_reed]

I have an intermittent problem with the rev counter on a 3-season old Yanmar 3YM20.

The problem is that the pointer will occasionally jump, to show maximum deflection (revs) and cannot be restored to 'correct' operation until the engine is switched off and restarted, when it seems to operate properly. Obviously, the engine revs are NOT jumping around!

We also have an issue with batteries not charging very well.

As I believe the rev counter works off the alternator ........ ???

Anyone got any ideas? Yanmar don't have anything useful to say on the matter, it seems.

Same problem, same engine. Fortunately the Hitachi alternator melted and the 90 amp €69 replacement, has cured the problem.
I wouldn't spend too much time or energy on trying to correct the problem - the recent Hitachi alternators appear to lack cooling capacity and if asked to deliver full charge for more than an hour literally melt.
My replacement was from the auto-electric wholesaler in Agrinio - bigger field-windings than the Hitachi and an external fan made fitting it a trifle difficult.

 

[BabaYaga]

I have an intermittent problem with the rev counter on a 3-season old Yanmar 3YM20.

The problem is that the pointer will occasionally jump, to show maximum deflection (revs) and cannot be restored to 'correct' operation until the engine is switched off and restarted, when it seems to operate properly. Obviously, the engine revs are NOT jumping around!

I have had exactly the same problem on a 20 hp Beta (Iskra alternator). After giving a good douse of contact spray into the multi pole plug and socket in the engine harness the problem has not come back.