: 99 STS Cylinder head different than 97 STS Cylinder head (alternator bolt holes)

05-19-10, 12:33 AM
Hi Everyone,

Thanks to the immense amount of info on the forums, I'm almost done replacing a bad left head (stuck valve) on my 99 STS with 226,000 miles.

But, just now I discovered that my alternator won't bolt into the head I bought (sold as "1993 - 1999 Northstar left head")... because it seems to be missing the two bolt holes facing the radiator. :alchi:

I looked in the GM FSM and it looks like the pre-1998 redesign cars had the air-cooled alternator that only bolts to the front (drive pulley) side of the engine, while the 1998 and later models have bolts both on the drive pulley plane and the radiator plane.

Anyone think I can get by without those two alternator bolts facing the radiator? I'll have to firmly attach the ground cable to the alternator with a nut and bolt (already melted my small "Jump Start Negative" when I cranked without the main ground attached).

Thanks for your expertise!!! Have a great evening!

05-19-10, 11:20 AM
I'm going to compare the two heads and see if I can drill and tap the two missing alternator bolt holes, after careful measurements, of course.

The pre-98 alternators are lower output, but has anyone used them on a 98+? Thanks for any input!

05-19-10, 11:38 AM
And I think you can do it - you will need 97+ heads though, they have the meat there to drill out.... 96 and prior do not.

Mark C
05-19-10, 12:22 PM
The gross separation of heads are 93 to 95, 96 thru 99. 93-95 heads have small slots on the intake gasket flange to support the older EGR design and there are some different bolt patterns for the older intake, can't use those at all with 96 and up cars. 96 thur 99 should be mostly the same with possibly some accessory mount issues. The 96 and 97 used the CS-130 style alternators that have a rear mounting bracket that attaches the alternator to the head with 2 bolts into the head, the 98 and 99 use the LR-630 liquid cooled alternator (the 99 anyways) which has a totally different mounting configuration.

05-20-10, 03:36 AM
Thank you for the detailed info 97EldoCoupe and Mark C! I will update this as soon as I figure it out - though hopefully no one else makes my mistake!

97EldoCoupe, I should've read your year-by-year stickied motor guide before starting the repair!