1987 1500 12si bearing question, need advice.

[olllie]

Ok.. the front bearing on my Alternator is done. I think I have a 12si 94 amp (stamped 94) unit in my truck but I'm not sure which front bearing I need.

The only kit I can find.., it looks correct but includes a capacitor looking part that my alt. does not have. The Diode setup and other parts look right though.

http://www.summitracing.com/int/parts/pwm-912/overview/

Do you guys think its worth rebuilding a 12si (if that's what i have), or should I just spend $140 and buy one with more output? My 87 also has the odd V belt/ 5 rib serp setup. Will my ribbed alt. pulley bolt onto any shaft?

Are there any bolt in better alternators I could go with? cs144?

thanks for any advice on any part of this post

[rfmaster]

Originally Posted by olllie

Ok.. the front bearing on my Alternator is done. I think I have a 12si 94 amp (stamped 94) unit in my truck but I'm not sure which front bearing I need.

The only kit I can find.., it looks correct but includes a capacitor looking part that my alt. does not have. The Diode setup and other parts look right though.

http://www.summitracing.com/int/parts/pwm-912/overview/

Do you guys think its worth rebuilding a 12si (if that's what i have), or should I just spend $140 and buy one with more output? My 87 also has the odd V belt/ 5 rib serp setup. Will my ribbed alt. pulley bolt onto any shaft?

Are there any bolt in better alternators I could go with? cs144?

thanks for any advice on any part of this post

CS144 will not bolt in - it has a larger body diameter than 10/12 SI. If you want to upgrade to CS series the best bolt in alternator with V belt pulley is REMY #91310 Rated Output 105 Amps found in late 80's GM cars
http://www.rockauto.com/catalog/moreinfo.php?pk=474329

Finally you'll need an adapter harness between CS and SI plug.

Most of the connectors for the CS alternators are four wire but will only use two of them and the wiring is the same as the SI.


You need to purchase a conversion adapter that is just 2 short wires and 2 connectors (Napa, O'Reliley + zone) . One is a CS connector to plug into the alternator, the other is a female connector to accept the SI plug from your original harness. There are two different types of conversion adapters. One is a non-resistor and the other has some resistance built-in it. The "L" wire that energizes the alternator needs some resistance (35 ohms or more) in it otherwise it will cause the alternator to fail. If you have a warning light in the dash then that bulb serves as the needed resistance and you should use the non-resistor adapter. If you don't have that bulb or have less than 35 ohms resistance in the "L" wire then you will need the adapter with resistance built in. If the "L" wire has more than 350 ohms then there is a problem with "L" circuit and it will need to be fixed.

Non-resistor adapters:
- AC Delco: 8077
- Haywire: 2110
- Painless Wiring: 30707

Resistor adapters:
- AC Delco: 8078

//RF

[olllie]

Thanks RF!!

Can I ask.. will my 5 rib pulley fit on any 12si style alternator? also If i buy a new one and stick with a 12si case style, what alternator do you recommend? power master, tuff stuff?

[rfmaster]

GM OE 5 rib pulley should fit 10/12 SI alternator, however you may need to play with a spacer between fan and pulley body. The shaft length is the same on all 10/12 SI units. You'll need impact wrench to get the nut off - I use shop rug to keep pulley from spinning. This way there is less of a chance of damage.

A side note: most CS144 units used wedge style locking nut which requires a whack on a pulley for it release. This style locking system is common on CS144 and some CS130 alternators.

IMHO there is little difference in internals between name brands. Most, if not all get their internal parts from WAI for stock or near stock applications. For 12SI alternator the output current limiting factor is a diode trio heat dissipation capability limited by the airflow and alternator case dissipation. For your 12SI application look for 94 amp, at 9:00 orientation (AC-DELCO # 321-269, Lester #7294-9). You can always re-clock 10/12SI alternator by removing 4 bolts and twisting half's (without separating them!) to achieve desired connector orientation. Autozone gold line alternators have life time warranty and with online discounts can be a cost effective alternative to 'name brands'.

10/12SI alternators are perhaps the easiest ones to rebuild. A complete service parts kit should be under $30 (WAI). The only tough thing to do is to remove pulley and replacing bearings. There are couple video's on youtube that show the whole process.

//RF