Rectifier, stator, amp guage and timing

cp4000 · Sep 23, 2010

Hi guys,
I finally tank tested my newly purchased 1976, 70HP. It ran good with pee-hole mod installed. Problem is...only the temp guage worked and I am fairly sure the other guages are wired correctly....The Tach and Amp guage had no response. The Tach guage may be bad but I doubt if both are. I put a meter on the battery before running the motor and during...Both readings were 12.6v. The Amp guage stays at zero, on or off. I don't think the motor is charging the battery. Rectifier? Stator? Would this affect the RPM guage? The other question may be a long shot but...the service manual says timing is 17 BTDC at 5500?? How do you check at WOT?? I can rev it I guess when I get my tach to work but...is there a way to rev in nuetral?? I checked the control box pretty good and do not see a way to rev the engine in nuetral?? Any help much appreciated

Ratboy14 · Sep 23, 2010

Re: Rectifier, stator, amp guage and timing

cp4000 said:
Hi guys,
I finally tank tested my newly purchased 1976, 70HP. It ran good with pee-hole mod installed. Problem is...only the temp guage worked and I am fairly sure the other guages are wired correctly....The Tach and Amp guage had no response. The Tach guage may be bad but I doubt if both are. I put a meter on the battery before running the motor and during...Both readings were 12.6v. The Amp guage stays at zero, on or off. I don't think the motor is charging the battery. Rectifier? Stator? Would this affect the RPM guage? The other question may be a long shot but...the service manual says timing is 17 BTDC at 5500?? How do you check at WOT?? I can rev it I guess when I get my tach to work but...is there a way to rev in nuetral?? I checked the control box pretty good and do not see a way to rev the engine in nuetral?? Any help much appreciated

Well I'm not sure about the main problem but for revving in neutral with my control box I have to pull it out to the left so try that with yours

cp4000 · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

I may have heard that the motor will not charge the battery unless its is running at 2000 rpm or higher? Is that true? That would make sense why it wasn't charging...I just had it idleing.

F_R · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

Do not rev it to 5500 in neutral unless you want to scatter the parts all over the landscape. The correct way to do it is with a test prop. That makes it a dealer job. The other way is on a boat, in gear and hanging over a snarling flywheel at 40 MPH. Rather foolish, I think. I know another way, but I don't publicize it.

Back to the original question, check the rectifier. It is probably shot. That will make it not charge, and the tach won't work. Also the ammeter won't show a charge. Speaking of the ammeter, the motor did not come with one, so somebody has added it. Perhaps it has a wiring fault. That also will keep all the other stuff from working. So...check BOTH the rectifier and ammeter wiring. If the ammeter wiring has a fault, that will blow the new rectifier that you are about to install.

It does NOT have to be running at 2000 rpm to charge. However, the charge rate will be a couple of amps higher at that rpm.

bktheking · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

PM it to me, I'm interested in your recluse activies on high rpm testing F_R

wilde1j · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

If the ammeter is wired correctly, it would indicate something, regardless of whether charging is occurring or not. It would read negative if there's no charging. I would say little chance it's wired right.

cp4000 · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

Well the guage says AMPS and it goes from +15 to -15 but I am starting to think it is just a voltage guage. It has four posts, one 12v switched, one ground, one lights, and signal line which goes to the power pack? (connection block on motor) I dont think an amp guage can be wired like this? My guess is that it is a volt guage just says amps on display? sound more logical? The fact that my rpm guage and amp guage didnt register could be that the rectifier is bad? Will try to do more testing tonight...

Daviet · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

An amp guage will not work as a volt meter, wired differently. Why don't you replace the amp guage with a volt meter, a lot easier to wire, all you need is a switched 12 volt source and a ground.

F_R · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

An amp meter has to have a wire coming from the rectifier, all the way forward to the meter, and another all the way back to the battery cable connection on the starter solenoid. The motor harness is not pre-wired for it. In addition, the existing connection between the rectifier and solenoid is eliminated.

All that extra wire and vulnerability is why a voltmeter is the preferred way to go.

Niether is ever wired to the power pack

cp4000 · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

I would like to keep the Amp guage if I can so....I do have one heavy guage wire coming from the rectifier (not the power pack) all the way to the guage. Not quite sure where I would connect the other wire going to the starter solenoid? The back of the guage has 4 connectors, they are labeled L, I, G, S. I have the rectifier going to the S, G going to ground, I going to 12v switched, and L going to the lights. I understand an amp guage needs to be in the current loop, so where / how would I complete the loop to the back of the guage.

F_R · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

I certainly don't understand the marking on the gauge. An ordinary ammeter has only two posts, Bat (Battery) and Gen (Generator). Add two more for the illumination, if applicable.

So, if you have the illumination ones figured out, the remaining two have to be Bat and Gen.

The rectifier output wire goes to the Gen side. The Bat side goes back to the starter solenoid--same big post that the battery cable connects to.

If you have any accessories that you want to register on the gauge, they connect to the Gen terminal.

cp4000 · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

Thats why I wondered if it was some kind of guage that read volts but maybe translated it to amps? It has the same connectors on the back of it as the temp guage does? It is wired the way I got it, just new wire. If it was that type of guage, a bad rectifier would probably cause that not to work? It sounds like more trouble than its worth, I'll probably go with a volt meter and install new rectifier which is hopefully why the tach doesnt work either. (Temp works good) Thanks for all your help and if anybody can figure that amp guage out, Im all ears.

wilde1j · Sep 24, 2010

Re: Rectifier, stator, amp guage and timing

An ammeter and voltmeter are completely different. One cannot be wired as the other.

F_R · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

wilde1j said:
An ammeter and voltmeter are completely different. One cannot be wired as the other.

Well, it COULD, if somebody went to all the trouble. You could measure the volts across a shunt resistor and interpret it as amps. That is actually what an amp meter does internally. Seems unlikely that is what we have here, but who knows??? Strange things go on when we aren't looking.

wilde1j · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

Agree ... they're both galvanometers, but you would have to calibrate and add a new scale to use an ammeter as a voltmeter. I should have said "practically" completely different. But I guess you could use a dump truck as a school bus too, they're both vehicles.

F_R · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

Yep, that's right. Just completely impractical. Hm.m.m.m, come to think of it some of the school busses I rode kind of resembled dump trucks, painted yellow. One would do 1 MPH going uphill in grandma gear, but Katy bar the door when going down the other side. The driver got clocked doing about 80.

wilde1j · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

Boy, did I ever go to boring schools!

cp4000 · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

Ok, I think I finally figured out whats going on

One wire goes from rectifier striaght to amp guage. I took careful records when I pulled all the wiring out and noticed I had the other lead going directly to the pos post of the battery. I made the mistake of just hooking that up to 12v switched (access) instead of back to battery which goes directly to starter solenoid / battery conn. The wire that goes directly from starter soleniod switch to rectifier was disconnected like F_R said it would be. So I will be running another wire from amp guage to starter solenoid instead of battery. Still gonna need a rectifier though, I probably fried it. Lesson learned! Thanks F_R and everybody else who contributed, you guys are great!

wilde1j · Sep 25, 2010

Re: Rectifier, stator, amp guage and timing

Your wiring for the ammeter should look something like this (the starter feed is functionally the same as the B+):

The important element is that all loads (except the starter itself) come off the ammeter, not directly from the B+.

Rectifier, stator, amp guage and timing

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