maybe starter issues...maybe not

[speedo]

I am close to "bringing to life" a 2.7 RS spec carbed engine in my SWB R clone. When I trigger the solenoid, I get the "click" and the starter barely provides a 90 turn of the crank. Seems like what you would expect with a dead battery, so I charge a new battery and get the same response. Hmmm, bad starter, so I pull the starter and put a different.08 starter in...same thing. I pull that starter out and bench test them both...they both work perfectly on the bench. I realize that on the bench, they are not under "load", but nonetheless, they work at least in the "bench environment. I decide to put one of them back into the car and bring a battery back to the starter, and jumper the starter with the + going to the positive pole and - going to a stud on the engines valve cover...same thing, a click and hardly turns the crank at all. So I know it isn't a short in the + cable coming from the battery up in the smugglers box.
I did a continuity check on that cable and it was good. I have not checked the two studs where the trannie and battery are grounded to the car...as there may be either paint or POR 15 preventing a good ground to the car on the stud. However, when I jumpered to the solenoid + and valve cover stud -, essentially eliminating the ground straps from the equation, I got the same result?
I took the three .08 starters to a local shop this morning for him to test. He was surprised when I told him that they all spun up easily on my bench, but didn't perform while in the car. I guess it is possible to have three anemic, but operational starters...but one would think that at least ONE of them would work.
Yes the engine turns by hand. And the compression on the Mahle P and Cs is only 8.5, so it is not like I am trying to start a 14-1 race engine with a .08 starter.
Am I wrong using the valve cover stud as my ground when trying to "jumper" the starter directly with a battery?
I love sorting electrical gremlins

[speedo]

Nobody going to weigh in

[304065]

How is the contact between the trans ground stud below the right rear seat and the strap?

[speedo]

John that looks ok...decent metal contact. When I jumper the battery positive directly to the starter though, and run the battery ground to the engine, that trannie ground shouldn't matter ...right? The engine is the ground. When I do that, I get the solenoid to trigger, and I get the same "marginal" grunt from the starter...a small effort and maybe 90 degree crankshaft turn. Basically nothing.

Thanks for responding.

Lars

[davep]

You need someone to help troubleshoot, and use a voltmeter across the starter when it is turning. A very low voltage will indicate poor electrical connections.
The starter pulls a few hundred amps when starting, and this requires exceptional wiring and a good battery. Can the battery be load tested to ensure that it can deliver starting amps?
A continuity test on a harmess is almost worthless on the starter circuit. I have had many circumstances where I can measure a voltage under no-load conditions, but as soon as a load is placed on the circuit, the voltage falls almost to zero. With a long piece of wire going to a battery post you can measure a voltage difference between the negative post and the starter housing (local ground) or the postive post and the starter stud where the starter cable attaches. This way you can determine which circuit, positive or ground, is causing the greatest voltage drop. Then you can work on that circuit to solve the problem.
This is sort of an innovative use of the voltmeter, using it only on one side, but it works very well for finding losses in the wiring. Every foot of wiring will cause some loss when under load, and if you have body sheetmetal, ground studs and the like along the way, it can add up quickly. Battery post clamps also go bad.

[Scooter 911]

Been thinking about this since I read your post earlier today. When you ran the negative to the stud on the valve cover, did you leave the ground cable attached to the transmission ground? If so, maybe the additional ground to the stud was not actually doing anything, but the transmission ground was still acting as the ground source. If this is the case, then maybe your ground source is the culprit. I would get under there and wire brush the transmission ground, then try it again.

[Flieger]

I would think that the current would ground to the path of least resistance/best conductivity. If he had a good ground to the engine, it should not matter that there was another, weak ground attached to the circuit as well.

[Scooter 911]

I would think that the current would ground to the path of least resistance/best conductivity. If he had a good ground to the engine, it should not matter that there was another, weak ground attached to the circuit as well.

True. I am thinking that the engine ground was faulty in some way and that the starter was still relying on the transmission ground for some reason. Just grasping at straws here.

[911quest]

You need to check how much voltage you have on the main lug of the starter. You said you have the battery in the smugglers box..correct? How are your connections I presume you made them yourself. Checking continuity is a good idea but is not as reliable as a voltage check. You can have continuity thru two strands of wire and still wont be able to flow the amps needed to turn the car over.

[edmayo]

A couple thoughts come to mind; some jumper cables are so small a wire as to be worthless. Is that a possibility with yours? Remove all the spark plugs and try again, that removes all load from engine. Could there be a bind between your starter gear and the flywheel teeth, what flywheel are you using. Could you possibly have one of the VERY early flywheels with the wrong tooth count for your starter. I use a induction ammeter that I can just place over the battery cable to starter, it will give you a reasonably close measure of amps. I think I got it from Mac tools. (of course that was a hundred years ago) Although the valve cover stud should work why not go to one of the lower engine to trans bolts. Surely you aren't in gear with the hand brake on!!! I know dumb question, it's like when I ask a customer with a non-start if they have gas, they think they do until you find out the sender is stuck!!