Alternator Woes...Pully Diameter? - ZR-1 Net Registry Forums

KJL · 09-04-2014

I have had intermittent issues with the alternator. I discovered the pully on the existing unit is quite large and it is very difficult to install and replace the serpentine belt. I had to use pliers to walk the belt off of the pulley. I purchased a new 140 amp Powermaster (I have heard good things about these) unit from Summit. The pulley on the new unit is smaller. It will probably still work but need to do a test fit. Should I swap pulleys? I am concern that the new unit will not behave properly if I use a larger size pulley.

Nothing is easy...

Any thoughts?

-=Jeff=- · 09-04-2014

what sizes are the pulleys? I have seen 3 different sizes

KJL · 09-04-2014

Powermaster web site recommends a driven to drive pulley ratio of 3:1. The crank pulley outside to outside is approx. 7.125" and the stock pulley is 2.875", this yields about a 2.5 ratio. The new pulley measures in at approx 2.125" which yields 3.35 ratio. Powermaster says you can't overdrive an alternator but you can underdrive. They recommend staying above 2400 rotor rpm at idle speed. If I idle at 900 rpm that will put me at 2250 rotor speed. I may test fit the existing pulley to see if there is enough tension in the belt. Plus I am not 100% sure if the alternator that is in the car is the stock unit. Anyone know what the stock pulley diameter should be?

Please note these dimensions are to the outside lip. They are approx the same and for calulating ratios, it shouldn't matter.

WVZR-1 · 09-04-2014

Pulleys are measured at the belt top notch of the V and not the OD of the pulley.

Here's a post I did quite some time ago with the CS144 choices and then one for what is considered to be correct for the LT5 from the GM service charts for the correct alternator. There's also a reference to the rear spacing to fan which I mentioned in your CF post need to be compatible. If you've questions and you've got a "new" PM alternator call PM.

The application chart says you have the correct part. There's sources out there that have incorrect LT5 applications. That I believe happened to "always code 390"

http://www.zr1.net/forum/showpost.ph...27&postcount=2

That is where I would think you would also measure for over/under ratios. I do believe it would make a difference in the numbers. The height of the retaining ridge I would think could be different. I have never checked.

KJL · 09-04-2014

As long as I measure to the same place on each pulley, the ratio will be the same. Yes, there may be some small differences in ridge height but measuring the crank pulley in the car correctly is not an easy task so I will settle for an approx value which should be very close.

I will see if I can get a depth measurement of the retaining ridge for the crank. (Both are 1/16")

I checked out the pulleys and the biggest one shown is 2.44" in diameter. That would yield a ratio of 2.86. That would be perfect. The one on my existing alt. is 2.6". Something tells me this is not a stock unit. I will look and see if I can track down this pulley locally. It is the one by itself in the second post. #241250

KJL · 09-05-2014

The Powermaster Alternator did not work out. Aside from the pulley being to small, the electrical connection was in the wrong place. I returned to Summit. I have never had this much difficulty buying an alternator. Kinda funny. Shame on Powermaster....like they care.

PhillipsLT5 · 09-05-2014

Find someone local to re build yours

KJL · 09-06-2014

I am sure there is somebody out there I could trust but sometimes I have to laugh when a read posting where people assume there is a good mechanist, welder, mechanic, engine builder....etc just down the street. Here in Atlanta, the city of transients, we are awash with unqualified people who land in these positions because they have failed at everything else they have tried...possibly through no fault of their own. The really good ones, the people who consider it their career, not just some fall back position, don't need to advertise in most cases, don't have web sites or email addresses and are very hard to find especially for people like me who do everything themselves 99.9% of the time. Heck, I don't even know where I would bring my car if I needed a simple mechanic around here.

Anyway... I did have my old unit checked at Advance Auto Parts after a thorough cleaning of the single wire contact area, they brought me back to watch the test and the unit appears to be OK. I suspect my problem may have been a bad wire connection. I sanded and cleaned all the contact points. Hopefully this fixed the problem. I did learn a lot and plan on tracking down a spare and ordering the correct pulley separately from the post from WVZR-1 above.

-=Jeff=- · 09-06-2014

Hmm, I would get a reman one from a local parts place and pay the core to keep yours.. I got the one in my car from O'Reilly auto.. I will finish rebuilding mine this winter. I am thinking of polishing the case first

09-04-2014	#1
KJL Join Date: Mar 2013 Location: Roswell, GA Posts: 234	Alternator Woes...Pully Diameter? I have had intermittent issues with the alternator. I discovered the pully on the existing unit is quite large and it is very difficult to install and replace the serpentine belt. I had to use pliers to walk the belt off of the pulley. I purchased a new 140 amp Powermaster (I have heard good things about these) unit from Summit. The pulley on the new unit is smaller. It will probably still work but need to do a test fit. Should I swap pulleys? I am concern that the new unit will not behave properly if I use a larger size pulley. Nothing is easy... Any thoughts? __________________ 1995 ZR1 #159 Ported,Corsa,4.10 Rear, Dual Disc RAM Clutch, Alum Flywheel, Haibeck Chip, ZFDoc Plates, Relocated Battery 400 rwhp 1992 ZR1 #280 Ported, Locked Secondary's, Flowmaster Exhaust, Haibeck Chip, 375rwhp 1996 Collectors LT4 (Stock) 1972 Convertible 434 Small Block 572 rwhp

09-04-2014	#3
KJL Join Date: Mar 2013 Location: Roswell, GA Posts: 234	Re: Alternator Woes...Pully Diameter? Powermaster web site recommends a driven to drive pulley ratio of 3:1. The crank pulley outside to outside is approx. 7.125" and the stock pulley is 2.875", this yields about a 2.5 ratio. The new pulley measures in at approx 2.125" which yields 3.35 ratio. Powermaster says you can't overdrive an alternator but you can underdrive. They recommend staying above 2400 rotor rpm at idle speed. If I idle at 900 rpm that will put me at 2250 rotor speed. I may test fit the existing pulley to see if there is enough tension in the belt. Plus I am not 100% sure if the alternator that is in the car is the stock unit. Anyone know what the stock pulley diameter should be? Please note these dimensions are to the outside lip. They are approx the same and for calulating ratios, it shouldn't matter. __________________ 1995 ZR1 #159 Ported,Corsa,4.10 Rear, Dual Disc RAM Clutch, Alum Flywheel, Haibeck Chip, ZFDoc Plates, Relocated Battery 400 rwhp 1992 ZR1 #280 Ported, Locked Secondary's, Flowmaster Exhaust, Haibeck Chip, 375rwhp 1996 Collectors LT4 (Stock) 1972 Convertible 434 Small Block 572 rwhp

09-04-2014	#4
WVZR-1 Join Date: Oct 2004 Posts: 1,890	Re: Alternator Woes...Pully Diameter? Pulleys are measured at the belt top notch of the V and not the OD of the pulley. Here's a post I did quite some time ago with the CS144 choices and then one for what is considered to be correct for the LT5 from the GM service charts for the correct alternator. There's also a reference to the rear spacing to fan which I mentioned in your CF post need to be compatible. If you've questions and you've got a "new" PM alternator call PM. The application chart says you have the correct part. There's sources out there that have incorrect LT5 applications. That I believe happened to "always code 390" http://www.zr1.net/forum/showpost.ph...27&postcount=2 That is where I would think you would also measure for over/under ratios. I do believe it would make a difference in the numbers. The height of the retaining ridge I would think could be different. I have never checked. Last edited by WVZR-1; 09-04-2014 at 05:26 PM.

09-04-2014	#5
KJL Join Date: Mar 2013 Location: Roswell, GA Posts: 234	Re: Alternator Woes...Pully Diameter? As long as I measure to the same place on each pulley, the ratio will be the same. Yes, there may be some small differences in ridge height but measuring the crank pulley in the car correctly is not an easy task so I will settle for an approx value which should be very close. I will see if I can get a depth measurement of the retaining ridge for the crank. (Both are 1/16") I checked out the pulleys and the biggest one shown is 2.44" in diameter. That would yield a ratio of 2.86. That would be perfect. The one on my existing alt. is 2.6". Something tells me this is not a stock unit. I will look and see if I can track down this pulley locally. It is the one by itself in the second post. #241250 __________________ 1995 ZR1 #159 Ported,Corsa,4.10 Rear, Dual Disc RAM Clutch, Alum Flywheel, Haibeck Chip, ZFDoc Plates, Relocated Battery 400 rwhp 1992 ZR1 #280 Ported, Locked Secondary's, Flowmaster Exhaust, Haibeck Chip, 375rwhp 1996 Collectors LT4 (Stock) 1972 Convertible 434 Small Block 572 rwhp Last edited by KJL; 09-04-2014 at 08:08 PM.

09-05-2014	#6
KJL Join Date: Mar 2013 Location: Roswell, GA Posts: 234	Re: Alternator Woes...Pully Diameter? The Powermaster Alternator did not work out. Aside from the pulley being to small, the electrical connection was in the wrong place. I returned to Summit. I have never had this much difficulty buying an alternator. Kinda funny. Shame on Powermaster....like they care. __________________ 1995 ZR1 #159 Ported,Corsa,4.10 Rear, Dual Disc RAM Clutch, Alum Flywheel, Haibeck Chip, ZFDoc Plates, Relocated Battery 400 rwhp 1992 ZR1 #280 Ported, Locked Secondary's, Flowmaster Exhaust, Haibeck Chip, 375rwhp 1996 Collectors LT4 (Stock) 1972 Convertible 434 Small Block 572 rwhp

09-04-2014	#2
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,169	Re: Alternator Woes...Pully Diameter? what sizes are the pulleys? I have seen 3 different sizes __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Flowmaster Cats - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

09-05-2014	#7
PhillipsLT5 Join Date: Aug 2005 Location: Scottsdale, AZ Posts: 2,452	Re: Alternator Woes...Pully Diameter? Find someone local to re build yours

09-06-2014	#8
KJL Join Date: Mar 2013 Location: Roswell, GA Posts: 234	Re: Alternator Woes...Pully Diameter? I am sure there is somebody out there I could trust but sometimes I have to laugh when a read posting where people assume there is a good mechanist, welder, mechanic, engine builder....etc just down the street. Here in Atlanta, the city of transients, we are awash with unqualified people who land in these positions because they have failed at everything else they have tried...possibly through no fault of their own. The really good ones, the people who consider it their career, not just some fall back position, don't need to advertise in most cases, don't have web sites or email addresses and are very hard to find especially for people like me who do everything themselves 99.9% of the time. Heck, I don't even know where I would bring my car if I needed a simple mechanic around here. Anyway... I did have my old unit checked at Advance Auto Parts after a thorough cleaning of the single wire contact area, they brought me back to watch the test and the unit appears to be OK. I suspect my problem may have been a bad wire connection. I sanded and cleaned all the contact points. Hopefully this fixed the problem. I did learn a lot and plan on tracking down a spare and ordering the correct pulley separately from the post from WVZR-1 above. __________________ 1995 ZR1 #159 Ported,Corsa,4.10 Rear, Dual Disc RAM Clutch, Alum Flywheel, Haibeck Chip, ZFDoc Plates, Relocated Battery 400 rwhp 1992 ZR1 #280 Ported, Locked Secondary's, Flowmaster Exhaust, Haibeck Chip, 375rwhp 1996 Collectors LT4 (Stock) 1972 Convertible 434 Small Block 572 rwhp Last edited by KJL; 09-06-2014 at 11:30 AM.