I serviced my Perkins M50 (Volvo MD50) and did the timing and alternator belt oils and filters. Subsequently I cleaned out the bilge and engine bay also. No major impact i thought - just wipe around the wiring looms with a cloth and removing the rubber and dirt from between the wiring.

Subsequently the battery light has come on on the dash and the tacho ticking off zero regularly until I up the revs where it sits on normal level. If

i drop the revs it goes back to zero and ticks off there about 2 x a second.

The PO had had a lot of rubber chewed up from the alt belts he was using and noted how he used to use a lever to tension the alternator. His belts were x size and seemed to sit on the internal seat of the alt pulley not necessarily on the sides of the belt but they sat well on the engine pulleys that are of a different profile.

When the mechanic had a look at it he suggested that the belt was too small and that we try another. The new one sat better in the alt pulley and about 1.5 mm proud of the others.

When he tightened it he did it without a lever and just used a spanner i think to lever it out. Seemed too easy considering the PO had the boat for 5 years on a world circumnavigation and couldn?t crack the issue.

From memory but i cant be sure, when we started it post service there were no issues. surely I would have noticed it if the light was on but i cant be sure.

I have checked the batt and when running there is about 14.5v accross it.

I?m not at the boat atm but am wondering it the belt i slipping and that?s saying that there is an issue causing the batt light to come on or have i bumped a joint and have caused to to come on.

Any ideas?

SHea

Tacho might get its pulses from alternator in which case slipping belt could cause your symptoms. Otherwise while engines idling get someone to watch the tacho while you gently push the cables and plugs with a stick. Hopefully if it is a bad connection that might find it.

Trek said..
Tacho might get its pulses from alternator in which case slipping belt could cause your symptoms. Otherwise while engines idling get someone to watch the tacho while you gently push the cables and plugs with a stick. Hopefully if it is a bad connection that might find it.

Or better still, you watch the tacho and let your mate push wires, with out a stick

It is essential that all pulleys have to same profile for satisfactory performance.
If your alternator pulley is a different profile to the crank pulley therein lies your problem.