Starter Problem, after pop sound

B

Bergy

Member
While my 29 roadster was on blocks, awaiting some wheel parts, I decided to do a compression test on the engine. While turning the engine over without any plugs, while testing the 3rd cylinder, there was a "pop" sound and no more starter. I now have nothing when I try to engage the starter.

I've checked voltage throughout. I have 6+ volts at starter, at terminal box, on both sides of coil, and at points. I've read all posts about starter issues and haven't come across my circumstances. What are the likely culprits and where do I start in trying to narrow down the problem? Any thoughts and wisdom are greatly appreciated.

A bit of additional info. I'm replacing front motor mount & radiator, so my wiring harness to lights and horn are not in place (loose wires laying about). I do have a cut off switch between battery and starter, but have 6+ volt power across it. I also have a fuse on top of the starter, which is ok (6v across it). Since I don't have wheels on car right now, I can't rock the car (saw that was a solution if starter had locked up). Also I do not have a hand crank.

The "pop" sound was kind of like something grounded out, but I can't seem to find any wires burnt off. The engine cranked fine while testing first two cylinders, and prior.

Thanks in advance for any help or guidance you can provide.
 
Unbolt the starter if it does not want to come out and is jammed whack it with a block of wood and large hammer to pop it loose from the flywheel ring gear.
 
Disconnect the battery before messing with the starter. You could also try turning the rear brake drums with car in gear.
Paul in CT
 
Starter has been removed with no problem. Bendix spring is intact and looks ok. The two bolts that hold the bendix spring ends are not in a line as shown in the manual, they are offset by about a bolt head (don't know if this is normal or indication of a problem).

Any other thoughts on what to look for next? Thanks again in advance.
 
P.S., any way to do a quick test to confirm this open coil/cirucuit in the starter? Any detailed guidance on testing would be appreciated.

I currently have the Starter on the bench. Have checked the brushes to confirm they're ok - they're about 7/16" long.

I haven't done any of the bench tests mentioned in the manual yet as the manual advises to take the bendix off before bench testing (spinning). I didn't want to dismantle the bendix yet as it seems to be ok (except the misaligned bolts I mentioned earlier). Thus I'm hoping for other possible causes/tests/etc before I dismantle bendix.
 
If you have a voltmeter, you should be able to spin it by hand and see voltage between the little button "nub" on top and the case of the starter. This assumes you have removed the starter switch. That switch is also suspect.
 
Clamp the starter motor firmly in a vise . You can put cardboard in way of the vise jaws if you want to save the paint . Remove the starter switch it is held on by the 4 small screws there should also be an insulating pad under the switch . Connect a pair of jump leads by clipping the positive ierminal to the starter body anywhere where you can clip onto like the outer end bearing cap . Touch the negative terminal {crocodile clip) onto the exposed round copper terminal and the motor should spin , if it does the switch itself is faulty . It doesnt matter which way round you connect up the jump leads the motor will still spin the same way anyway .

John in nice weather evening Suffolk County England
 
P.S. John, I've performed your test, with results below.

Spun motor by hand with volt meter connected between case and copper button (with switch removed). I got a small reading .1-.4 while on the ampere scale. I got no reading on the voltage scale.

I then hooked up auto jumper cables from my battery to starter case and touched the other on the copper button. Nothing, no spark, nothing. I double checked my battery voltage to confirm it was ok - it was 4.6v (obviously needs a charge). Also confirmed 4.6v at the end of the battery cables.

Do these results imply that the starter is shot. As I understand the tests the starter should have spun with the battery cable test, if starter was good (ie, the problem would have then been isolated to the switch), Correct?

Any other checks or steps to confirm the problem(s), before I go purchase a new starter?
 
You should have had more than a volt by turning the starter by hand, and when you connected your battery in the manner described by John, it should have spun.

Time to disassemble the starter.
 
With a reading of only 4.6 your battery is fully discharged or shot. Put it on a 6 amp battery charger for 8 hours and try the starter test again.
 
Tested again with fully charged battery - nothing. Dismantled starter and didn't find anything obvious. Tested the magnets in the casing, nothing when voltage added. Time to take it to the starter shop for the experts to fix or give a death certificate.

Thanks to all for your ideas, guidance, and wisdom. I really appreciate your help.
 
Have you remove the starter switch and put the battery cable right on the copper button? When you say nothing, do you mean no sparks at all? If you use jumper cables, be sure they are very heavy wire.
 
Tom, yes switch was removed. One cable on casing, one cable on copper button - nothing, no spark, no spin when assembled, no magnetic field when disassembled, dead as a door nail.
 
With the band off you say the brushes are good, so I assume they have strong springs and all 4 make good contact with the commutator? Also, the armature spins freely?
 
Tom, yes, yes & yes. The key clue here was the "pop" sound before failure. It sounded like a wire or component failed.

We've narrowed the culprit to something inside the starter. Since we don't have any power to the magnets inside the casing, there seems to be an open circuit in those components.
 
It could be a short at the insulated brush holders There is four insulator washers that are installed under the rivets on the brush end plate that hold the brush holders. check the brush holders for continuity between the brush holder and end plate. the carbon brushes are insulated and shouldn't have continuity between the holder and end plate.
 
Last edited:
Sorry for late final diagnosis - things were in storage for the winter.
The problem ended up being a blown coil inside the starter.
Thanks for all the guidance.
 
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