Starter Assembly - Bench Test results

[DWM76]

Hi all,

My starter is struggling to turn the flywheel. It's not bad with the spark plugs out but when they are in it's a struggle for sure.
Steps taken:
Multi-meter tested power supply (12.6v), tested solenoid when activated (12.5v), tested at positive to starter motor, solenoid activated (12.5v), tested with starter motor connected...drops to 5v.
Safe to say the starter is bad? I took it apart and cleaned it up. Bench tested after cleaning and it still has a big voltage drop even when it's not trying to turn the flywheel.

Thanks for your time and advice.

 

[boobie]

Take it to an auto-electric shop. They would have the proper equipment to check it out. Growler and ect.

 

[Faztbullet]

Throw that old field style starter away and install a newer magnetic style.....

 

[F_R]

If you are telling us you only have 5V at the starter, you either have a direct short in the starter (probably not), OR you have a serious voltage drop in the battery cables or a poor battery cable connection at the battery (most probable). OR a bad battery.

Remove and clean the battery cable connections. Don't just look at them or wiggle them, remove and clean them shiny bright. While you are there, take the battery and have it load tested. Inspect the cables for signs of internal breakage or corrosion.

 

[DWM76]

The power supply is good, new and load tested, the connections are shinny and new cables used for the tests.
All connections were tested at each point from power supply terminal to positive starter post. all over 12.4v. Testes were done with and without the solenoid.Voltage drops when the connection is grounded to complete the circuit and energizes the starter.
I'll take it to a shop for testing though. Thanks for the recommendation.
As far as the newer magnetic style goes do you happen to know a part number that would work to replace the old one?
It's a 68 Johnson 55hp (TRL-10R) the original part number is #382306

Thanks

 

[oldboat1]

Jump the starter directly from your vehicle -- pos. jumper cable to the post on the starter, neg. to the starter mounting bracket. If it cranks the motor that way, it's fair to assume the problem is elsewhere.

 

[Faztbullet]

Is it one of these Prestolite numbers???

PRESTOLITE

46-2118, 46-2196, 46-2438, 46-2447, 46-2502, 46-936, MGD4106, MGD4106A, MGD4110, MGD4115, POA4001, POA4002

 

[dingbat]

Don’t bother messing with it. You can buy a new after market starter for less than a rebuild

 

[DWM76]

It is a Prestolite MGD 4006 Z10

 

[F_R]

Do whatever you want. I might even own some stock in the starter factory. But you still haven't done proper tests.

Put your voltmeter negative (black) probe on the starter post (Not the cable). Put positive (red) probe on battery positive post (NOT the cable). Should show virtually zero. Same connections, attempt to start. In a perfect world, voltage would still be zero. But since the world isn't perfect, you will see some voltage. Around a volt or less might be ok, more is not. Significant voltage indicates a cable or connection problem.

Might be a language problem, but you keep referring to the "power supply". Is that a battery of proper capacity? Or something else? Check the voltage across the battery + and - posts while attempting to start. Should maintain around 11 volts or better.

 

[DWM76]

Thanks F_R.

Electrical is not my forte.

I used a couple different power sources but primarily I boosted off a vehicle, running, with a battery tender attached as well to ensure good power. The battery in the vehicle is new and load tested. The cables used are also new. I am very confident in the power supply. I am equally confident in the ground.
I used the above set up to boost the starter motor directly. Positive (red lead) to the Starter motor positive post and grounded the starter motor body to the power head.
My issue is the voltage drop when the starter motor is energized. It does spin, and the bendix activates to fully engage the flywheel, but the motor struggles to turn the flywheel adequately with spark plugs in. With plugs out it turns much better. (voltage drop is still the same though)
I have seen bench test videos that use a multi-meter to measure voltage before and after energizing the motor and the common theme is that the voltage drop should not exceed 1.5v when the motor is energized. I get a 6-7v drop. The voltage drop is the same when on the outboard and engaging the flywheel as it is on the bench not engaging anything. Insufficient voltage, I assume, equals insufficient torque/crank.

Likely not worth a rebuild as mentioned but I am having a hard time finding a replacement that will fit and is in spec.

Your advice is greatly appreciate. I am a total boat, outboard, and really anything mechanical rookie. I am learning a lot from taking on this rebuild myself which, I hope, best prepares me to safely enjoy my new toy.

 

[racerone]

The 68 is the first year of 3 cylinder production !----And the only year that had the small teeth on the flywheel and starter.

 

[oldboat1]

I used the above set up to boost the starter motor directly. Positive (red lead) to the Starter motor positive post and grounded the starter motor body to the power head.

Ground to the starter bracket.

 

[DWM76]

My understand of the general consensus here is that it is not likely an issue with the starter itself but rather there is some resistance in the current somewhere, at a ground or a terminal, or through a lead, causing a voltage drop, or that the battery does not provide enough cracking amps, and therefore insufficient voltage/amperage is getting to the starter for it to turn the flywheel at sufficient speed?

I will test your recommendations this weekend.

Thanks again for your help and expertise.

 

[jakedaawg]

If you're using jumper cables from a car to the starter your not getting accurate diagnosis. You need to take the battery out of the car and put it in the boat...no jumpers. Replace the cables if they are suspect. I find proper electrics, cables and such, to be the single most neglected part of the average boat...

 

[oldboat1]

....

 

[Tim Frank]

Had the same motor for close to 40 years. The starter was always a bit "iffy"....but adequate.

What numerous posters are pointing out is that the wiring needs to be solid and all connections clean and electrically sound.
Without that even a perfectly good starter motor may not (will not?) get the job done.
The inspection and remedial work on the wiring is essentially free.....just a bit of elbow grease and time; so it makes sense to start there.

Parts are available to rebuild the starter IF required, and it is not a difficult job.

 

[DWM76]

Right you are! I should have known better than to doubt the wisdom of the iBoats community. Starter is good. More progress on the rebuild. Slightly related follow up question: What kind of compression should I get on the pistons? I tested today, and they are all inside 10% of each other, but only 68-72psi. Is that bad? I read somewhere that the old motors had lower compression.

Thanks again,

 

[racerone]

Where are you reading this ???----A good one of those should read about 140 PSI on a good quality gauge !!