Intermittent no crank/start + flaky tach - 78 115

[77_starcraft]

Having issues with intermittent no crank start. started last season so I inspected all the connections and replaced a few ring terminals. still having issues.

-batteries are in good shape
-terminal tight and corrosion free
-seems to do it only when motor is cold
-dash voltmeter reads 12.2V and does not dip when key turned (no big current flow to starter)
-solenoid clicks but Bendix does not raise gear up to flywheel.

these conditions seem similar to low voltage/dead bat, but then the motor will crank and fire as normal.

Tachometer issues - don't know if related?
I installed a tach 2 years ago and it has worked fine until this weekend.
I get no reading (0 RPM) until about 1200 rpm then the need jumps and all is good until about 3500, then back to zero.

Grounding issues? GND connection on block? (looked good, I choose not to replace ring terminal after inspection).

Next time it fails (only time to try to diagnose) what to do?

probe voltage on solenoid (all 3 terms; starter, bat cable, from key) while cranking.
move starter gear a few degrees? brushes?

 

[rndn]

Re: Intermittent no crank/start + flaky tach - 78 115

Just because the connection looks good does not mean it is good. Take off the wires and clean them so they shine before putting them back. All connections from the battery to the starter including grounds.

 

[tashasdaddy]

Re: Intermittent no crank/start + flaky tach - 78 115

check your battery cables, they get knicked and deteriorate from the inside.

 

[77_starcraft]

Re: Intermittent no crank/start + flaky tach - 78 115

I disassembled & cleaned all the terminals, washers, nuts and posts on all the starting circuit connections. I hope that will resolve this issue

I guess it is also possible that the solenoid coil circuit (little terminals) could be getting a weak voltage/low current and not fully engaging the starter too.

Good new is that the head work, cooling system, latch/lift linkage, carbs and fuel plumbing I did don't have any problems.

Thanks to all the people here that helped me get through those issues.

 

[emdsapmgr]

Re: Intermittent no crank/start + flaky tach - 78 115

An erratic tach likely the sign of a bad rectifier. That device charges the battery and also counts pulses to drive the tach. If your tach is erratic and you continue to run it, you could soon have battery problems. Do you have a voltmeter on the boat?

 

[77_starcraft]

Re: Intermittent no crank/start + flaky tach - 78 115

Do you have a voltmeter on the boat?

Yes, I put one on the dash several years ago. last outing it didn't read much over 12.5v when at high RPMs. My 78 model has a 7 amp non-regulated generator (i think) and I have seen 14-15 volts at WOT, IF the batteries are near fully charged. (7 amps isn't going to raise a discharged batt voltage much)

An erratic tach likely the sign of a bad rectifier. That device charges the battery and also counts pulses to drive the tach. If your tach is erratic and you continue to run it, you could soon have battery problems.

what type of problems? lets say one or more recitifer diodes are open, battery won't charge? can it damage something else?

Guess it's time to bust out the manuals and test the charge curcuit.

Thanks

 

[ezeke]

Re: Intermittent no crank/start + flaky tach - 78 115

When the rectifier goes bad, wires can fuse within it and allow the battery voltage to reach the ignition system. This can then damage any component of the ignition sytem. The rectifier is there to provide charging for the battery and a signal for the tach. It is not necessary for the operation of the engine and can/should be removed until you test it or replace it.

BTW, it is good practice to disconnect the battery when working around the ignition system. Any voltage reaching a powerpack' kill wire can instantly severely damage it. Most preliminary testing of the ignition can be done with an ohmmeter.

 

[77_starcraft]

Re: Intermittent no crank/start + flaky tach - 78 115

OK, don't want possible high current DC to the stator.

I removed and tested the rectifier. All diodes are open. I ordered a new one and hope to have it installed & tested by our next fish/ski/camp trip.

thanks!!

 

[77_starcraft]

Re: Intermittent no crank/start + flaky tach - 78 115

Finally found a pattern for the no crank/start. if the boat is moored overnight it will not start. the solenoid won't close to pass high current to the starter when its cold. once its warm its OK.

The flaky tack was the tach wire pinched in the control housing. made it look like the stator was shorted. rectifier was OK. my tester was bad so I wasted $ on a new rectifier. all fixed.

hopefully someone can use this info in the future to fix the same problem.