mark kibort

928 intl shipped me a special alternator on monday. should be here today.
never checked the alternator, but i did hook a voltmeter to the two terminals on the back and spun the alternator, and the meter didnt budge. (is that a possible check?) Im hoping this is it. Ill know in a few hours. otherwise, i have no idea what to look at next. those rocks in the alternator had to have done some damage, especially that copper winding piece. im sure it cant work with out a part of the winding or a connnection, but we will see.

MK

Alan

Mark,

No that is not a good check of anything - most alternators will not produce any output without an indirect battery feed connection to initiate. Also the 2 terminals on the back are not the power terminals you'd need - the big one is but the case would be the other (ground) terminal.

You can do a rudiimentary test in this manner with an appropriate exitation circuit (resistor/bulb to battery) - but you'd need to spin the alternator @ approx 700-1000 RPM - so certainly by hand will not do it - electric drill maybe...

This would only show it can produce some output - wether it meets its rated load whether it has damaged diodes on some phases would not be apparent from this... in the end its easier to take it to a shop that has propper load test equipment and oscilloscope to monitor output ripple.

Many shops will test for free - since by the time you take it in there are usually issues & they get rebuild businesss from this.

Alan

lorenolson888

Hi Mark,

Your car deserves a "Special Alternator"

Cool that you are able to be top 3 consistently... I am sure the car helps, but after going carting that one time I am sure it is multipled by your agressiveness and skill...

I would come in 20 out of 20 for fear of life limb and body damage to the holbert car!

Let me know if I can help out some time... I am home for a week with my new son... Alexander... his grandma is visiting so I can work on the car a bit...

Loren

Sab

My alternator had the same symptoms when it went out. Just replaced the whole thing with a rebuild from Dave and all was good.

lorenolson888

My belt was a little loose recently and was told by Dr bob that a max deflection by thumb pressure would be about 1 belt width! I never heard any slippage, but testing with a multimeter at the battery that my battery is charging more fully... it is subtle though... not a like a complete failure

I would assume by the pulley sizes that at idle the alternator spins at ~3K...

Auto zone tested my diode an regulator etc... if the winding brushes comm arm etc. were damaged by rocks I imagine that the output would be effected. It is a free test and the computer system contains the correct info and part# for 928s!!! It even has an accurate picture of the bosch style alternator!

Mark, hopfully your new alternator has no need for the cooling duct... which is a pain and a POS...

Any clue what kind it is (delco for GM?)

Loren

mark kibort

Thanks Alan. Guess i was missing a few MAJOR points there!
Well, if the new alternator doesnt cure the problem, its back to the drawing board. (or time to bolt in a big battery for the time trial this weekend)
Mk

mark kibort

Well, its top secret, but this is the 928 LIST, so i can tell.

Its a club sport lightweigh alternator. guaranteed to reduce lap times by .5 seconds . (how light can it be???? stock is 17lbs on an S4!)

anyway, i hope it bolts right in. i get nervous when i start using non stock S4 gear. Anderson also turned me on to the lightwight starter. it worked like a champ! So, im not too worried.

Mark

dr bob

Just make sure we are pressing with the correct thumb. Oh, and it's one belt --thickness--, just a tiny bit different from one belt width. Thumb pressure is too subjective to make into a 'rule' but it may be OK to use to detect gross misadjustments. The ribbed alternator belt runs much tighter than a comparable V-belt might.

Many moons ago when I was wrenching my way through school, a woman dropped off her Jaguar with overheating and electrical charging problems. Actually the car decided for her that it was going to stop. Her 'mechanic' had given her a significant estimate for replacing the alternator and the water pump. I gave her a ride to work, and later in the day discovered that the belts were way too loose. Put all new belts on it and suddenly it was cooling and charging correctly. A very low-cost solution. She told her friends, and I had years of Jaguar work after just that one episode. Too often it's the simple stuff. Too often, we go looking for the most ominous solutions to simple maintenance problems.

lorenolson888

Ah yes... my bad hehe one thickness... and it looks as though that had some effect!... My battery was charging in the proper direction... at 13V right now even after a couple of night drives...

Kiborts symptoms sound a little more extreme though can a battery run an entire race without some input from the alternator?

LO

mark kibort

A belt has to be pretty loose to create charging issues, even though the belt should be tighter than what is usually seen with V belts.

Yes, cars run fine with only a battery and no alternator, however, not for very long. you need 10amps or so, so a 50amp-hour battery will last about 2.5 hours of driving, thats because at somepoint the voltage will be too low to fire the spark or run the ecu. (on the 84 ljet, you dont need as much voltage as an S4 to run)
I also noticed the car was running leaner as the battery ran out in the race. the last two laps, it was full lean at WOT. so, i ran it only hard enough for the mixture to hunt. (i.e. half power)

MK

mark kibort

Yes, it was the alternator. those things that fell out of the alternator must have been important, like part of a winding, some solder connection point, etc!

anyway, installed the new alternator (by the way, the club sport alternator needs a nut on the top stud, as the alternator does not have a threaded hole there. other than that, the cover fits and the duct work from my old heating and A/C works great so i dont suck up any rocks or race rubber again.

as soon as it was bolted on, i turned on the power and turned the key. immediately, all the dash lights illuminated, including the voltage light. as soon as the car starts, they all go out. charging is much more robust, and resistance to fan load too. 13.8 to 13.9v

all fixed!

Thanks 928intl for the part and getting it to me right -on -time!

Mk

now, what do i do with the old one. can it be rebuilt? should it be rebuilt as a spare or is it just junk?

IcemanG17

MK
Right on......how much lighter is the club sport version?

mark kibort

13 lbs vs 16lbs. 3 lbs. should be worth .3hp.

RicerSchnitzzle

Congrats on the fix! Sounds like a few of us have the charging issue until we rev our engines. Does any one have a link to the fix? I think I remember mention of a light behind the dash gauges? When I pull up to a light to idle, with the electric fan on, my stereo cuts out. Rev up a tiny bit and everything gets brighter and works again. Was never a huge issue until I switched to the E-fan. Thanks!

SharkSkin

Fairly common problem with the early cars. Unlike most other cars, early 928s spin the alternator at only about 2x crank speed. I hear that Delco CS130 alternators work better, and I spent a lot of time trying to make the more powerful CS130D alternator work with no success because of the rotor speed. Carl at 928 Motorsports offers a high output alternator, but that's $$$. For now, I just try to manage my electrical consumption. It helped when I set my idle speed to the top of the spec.