LF Alternator Swap?

On my LF120 I was not getting any reading on my amp guages; tach works o.k..* So, I pulled the alt. (motorola/prestolite) off; found broken wire to one of the diodes.* A new direct replacement, 300.00.* Local shop has Delco that is suppose to bolt right up; 75.00.* It's a one wire hookup; no tach connection.* Also, there was a wire going from the batt. term to a 'THING' (oil press. act. sw.) on the engine, then to the volt. reg. on the old alt..* My question is, 1) will the oil press. thing on the engine have to be powered up again in order to operate my boat?* 2) is there an after market way to feed my tachs off this one wire alt.?

* You should take it to an alternator shop. I found a 90 amp unit on e-bay and the local shop went through it and installed an a/c tap to run the tach., all for 55 bucks, I paid 46 for the unit plus 18 shipping.

Diodes come in a cheap kit at NAPA and are really EZ to swop.

I put the Delco on yesterday. The tension bracket didn't fit. But, I hung everything on loose just long enough to check out my guages. The amp was showing a reading as well as the oil pressure guage. Tach of course was dead. Can anyone explain the function of the thing in the picture mounted to the engine block (oil press. act. sw.). It has a batt. wire going to it, then a wire leaving it going to the volt. reg. on the orig. alt. When I connected the Delco I had to leave these wires disconnected. My oil press. guage was still working. So, what does this thing do? OBTW, the pic here IS the orig. alt..

OK, just left a LF site. Drawing there IDs the part as an 'oil pressure switch'. So, I'm guessing it is used to send an alarm to the buzzer if I have no oil pressure. Not sure how that works, the way it is wired (going thru the VR). But I'm hoping it is still safe to use the boat, as long as I keep an eye on my oil pressure guage (which I always do anyway).

dhiggins,* Did the low pressure alarm work before switching the alts?

Did a buzzer sound during start up until the pressure built up?

If you did not have this feature I assume it is safe to keep watching the gauge(good idea eitherway)

If you don't you can* probably add the alarm and use the switch you have.

Might want to test it with a temporary 12v test light and some wire.

I believe my lehman has an electric tach sender on the opposite side of the engine.

On the starboard side.* If goes with my VDO tachs.

JohnP

John, my alarm was working with the orig. alt. The alarm would sound when the key is first turned on; a few seconds after starting it stopped (guessing that was the oil press. sw.). The only other time the alarm sounded was when my water temp. got to high. A bad impeller and stopped up HX caused that one (I'll incl. pics). I'd don't recall if the low oil press. alarm went off yesterday (to concerned about loose belt, etc.). I'll check it out tonight to see if it still works.

dhiggins wrote:

John, my alarm was working with the orig. alt. The alarm would sound when the key is first turned on; a few seconds after starting it stopped (guessing that was the oil press. sw.). The only other time the alarm sounded was when my water temp. got to high. A bad impeller and stopped up HX caused that one (I'll incl. pics). I'd don't recall if the low oil press. alarm went off yesterday (to concerned about loose belt, etc.). I'll check it out tonight to see if it still works.

Just out of curiousity do you keep a spare belt on your engine, so you don't have to drain any coolant down to change it?

JohnP

Click to expand...

******** P.S.* Image is not my engine.

*


-- Edited by JohnP on Friday 18th of March 2011 04:17:37 PM

-- Edited by JohnP on Friday 18th of March 2011 04:23:04 PM

Since an alternator can attempt to make juice at tiny RPM, many are hooked up so the unit can not function during STARTING .

One way this is done is to use an oil pressure switch to allow the Voltage regulator only to "see" ground with oil pressure.

It also will remove the load should the engine be secured but the engine electrical power left on.

You can put an ac tach bolt package in that Delco alternator for about $3. I would imagine you are installing an SI series with a white two lead connector.

This is assuming that you are not using one of the (newer in years)*CS series which have a black rectangular plug in.* To the best of my knowledge they all had the tach lead built in.

Carl

FF wrote:
Since an alternator can attempt to make juice at tiny RPM, many are hooked up so the unit can not function during STARTING . One way this is done is to use an oil pressure switch to allow the Voltage regulator only to "see" ground with oil pressure. It also will remove the load should the engine be secured but the engine electrical power left on.

Click to expand...

********* FF,* I did not think of this but I bet that is the set up*dhiggins had. It makes sense!*I hope reconnects the pressure switch circuit.

********* JohnP

*


-- Edited by JohnP on Friday 25th of March 2011 06:44:11 AM

What FF said,

Here is a different way to say the same thing,

The 'oil pressure switch' near the alternator is open (not conducting) when the engine is not running. After the engine starts and develops oil pressure the switch closes and energizes the alternator field. This is to remove the alternator load from the engine during startup, and, like FF said to prevent the field from being energized when the engine is not running. Unlike in a car, the 'ignition switch' for a Ford Lehman does not power the alternator.

I have just replaced the alternator on my Ford Lehman.* G & H Auto Electric, Everett, WA supplied a Delco 105amp alternator with a three wire connector that has two wires for the field connection and a third wire to send a signal to the tach.

Larry H


-- Edited by Larry H on Saturday 26th of March 2011 01:48:54 AM