starter voltages on 90hp S/N OT087666 2000 yr model made in '99

[wn6ngp]

Lately when I first start up or if I'm out floating around and the motor gets cool when I go to start the starter goes.
uh.....uh.......uh......uh.......vroom start. So for about a 1/2 sec or so you think, oh,oh, we may have a low battery but then it hits vroom and it cranks fast.

I'm thinking that this is going to evolve to a real problem later so I did some testing on ear muffs. Unfortunately, on ear muffs I don't get the uh....uh......uh......it just goes straight to vroom.

I hooked up some meters and got the following data.

During start the battery voltage drops to 11.7 a 1 volt drop from no load. I tried 2 different batteries one a year old and the other 2 years old. They are labeled combo starting/troll motors. Got the same results.

At the starter I see 10.5 volts. I see a drop of .5 volts in the ground leg and .7 volts on the hot leg thru the solenoid.

Do those numbers seem about right? I was surprised at that much voltage drop in the cables.

Assuming those numbers are correct I am wondering why the starter gets off to a slow start sometimes. Could it be that brushes are worn down and/or commutator on armature js loaded up with graphite/grease and needs cleaning? The motor has about 300 hrs on it. No excessive cranking, but it is the old school 2cy so when cold it does take some fussing around to get started. Maybe carbon or oil build up around rings that makes compression higher at the beginning when cold?

 

[Texasmark]

10.7 is 0.7 more than I use for minimum starter voltage of 10v when troubleshooting. If your starter hesitates with that or more applied and it doesn't drop below during the hesitation, look at your starter.....maybe the Bendix (the mechanism on the starter shaft that connects to the teeth on the flywheel gear. Needs some cleaning up and lube....it may be hanging up on the way up to the flywheel teeth. Take your finger and see if it moves up the shaft from it's stopped position against the starter. If not you have your smoking gun. I assume that when you measured the voltage at the starter you measured the ⅜ stud, not the cable lug connected to it and the case of the starter, not the strap around it.......if not the problem could be a dirty ground or voltage input terminal. If all the previous are ok, then you might need some new brushes and/or the armature polished where the brushes rub. 1v drop in your cables is super......clean connections 11.7v across the battery terminals during starting is super.....low internal resistance.

Since you are running a voltmeter and checking with some "savvy" the starting current for that engine is like 150 amperes. You are dropping one volt across the battery innerds and 1 volt across the wiring so if your battery was fully charged to 12.7 when you started: 1v/150 amperes is o.0067 ohms........absolutely nothing!

 

[racerone]

Take starter apart.----Imspect brushes.---Should read infinity from commutator to shaft on a digital ohm meter.-----Costs no money to do that.----I install new brushes from local starter / alternator shop at $ 5.00 a set.

 

[wn6ngp]

Thanks for mentioning that starter current, 150A, wow. I didn't realize it was that high. Problem is that I haven't been able to make it fail at home, not even close. So those values are with things spinning properly. I have since redone the connections to the battery. At 150A its not going to take much of a mechanical mismatch on those terminals to cause problems so I'm hoping cleaning those up will take care of the problem. I had a stack of terminals squeezed down on the battery terminal before and that may have caused an intermittent additional resistance problem.

One of the problems with this Kenner boat is that the battery is mounted up under the casting deck and you almost have to stand on your head to check it out. So I've temporarily moved it so I can check those connections more easily when the problem re-occurs when I get to the lake. (maybe it won't reoccur),

Replacing brushes is probably a good idea too especially if they are so generic.

 

[Texasmark]

The number 150 came out of my service manual which covered the 3 and 4 cylinder 65 Jet thru the 125 inline engines. Didn't get it out of thin air. It's a real number course engine dynamics can change and change the load. It is a big number, larger than a lot of folks realize and with a 12v battery you don't have much room for error. Amazing how many folks out there with marginal systems get their rigs started and all.