toddalin

I've been fighting with a squealing alternator belt since???

I thought I could cure this by going to a wide cog belt and put on the Millerspeed Gilmer system. While I haven't thrown the belt, I noted an inordinate amount of flex in the system, and the belt goes all wobbly when the engine is revved and passes through a certain portion of the rpm band.

With the V-belt, I had always assumed this to be misalignment. But the cog belt lets/makes you get the alignment perfect (you center it on the cogs) and the visual is quite clear as you see the belt first walk forward then get wobbly against the front stop as the J-bars flex forward in an arc and the header-mounted alternator bracket stretches out like an accordion.

I've tried to overcome this flex through modification of the header bracket and the use of not one, but two J-bars that sandwich the alternator. While this greatly reduced the flex, it's still there to some extent, and certainly more than I would like.

There had to be a way to stabilize the alternator and keep it from flexing forward.

It occured to me that Delco put the rear mount on the Delcotrons to be used just for this problem. A similar problem was noted in the '84-'85 Vettes and GM added a rear brace for customers. In fact, C4s from '86-'91 use this rear pad as a mount to the rear #1 cylinder rear exhaust manifold bolt. So why shouldn't I do something similar?

I made an "L" bracket to go on the back of the alternator with a 5/16" hole for the alternator mount and a 3/8" hole for a spherical rod end. In my junk box I found a 3/16" steel "L" that was probably for a heavy gate or ??? I used a cut-off wheel, then bench grinder, then disk sander to form the bracket. The original piece of metal was actually formed as an "L" as is evidenced at the bend that has alternating strengtheners, rather than a piece of metal that was simply stamped into an "L" as the header brackets are. This should make a very strong bracket.

I ordered the March RA3.500 adjustable rod that extends from 5.5" - 6.75". This uses 3/8" spherical rod ends.

One end of the rod is connected to the bracket using an Allen bolt and I use a small spacer (~1/16") on the other side of the rod end so as to retain full movement of the heim. (If you put a heim next to a bolt head or solid piece of metal/washer, you limit its travel as it bumps into the obstruction.) The Allen bolts are stainless and I polished the heads spinning them against a file/sand paper/polishing compound in the drill press.

The header bolt is 3-1/2" long. The first 1" is taken up by the head threads and header flange. A 2" spacer takes up the next length and the heim joint takes the last 1/2" of the bolt. I can go with as short as a 3" bolt and 1-1/2" spacer depending of the geometry of the alternator bracket. I can't go less than 1-1/2" on the spacer or the heim joint will hit the header. The 2" spacer (actually 1.98") is being sent from March (free of charge) and should be here in a day or two.

Astrodokk

That's a nice design. Although my alternator is on the passenger side, I think mechron would be interested in your design since his is on the driver side and has a similar installation. I don't know if he ever had the flex problem though.
Wouldn't those adjustable bolt heads still allow left and right movement though, although fore and aft would be minimized by it? Or is it pretty well fixated in that configuration?

w1ctc

You should assemble kits and sell then.

toddalin

Side of the car doesn't matter, you have header bolts on both sides and if the alternator has the rear mount. Maybe this isn't even an issue with passenger-side mounted alternators. Instead of the belt being "snatched" from the alternator creating a torque, the belt is being "shoved" to the alternator releasing tension.

The spherical rod ends and adjustable length allow for misalignment which is inevitable seeing as how the alternator can be anywhere along the J-bar.

The problem is that the alternator flexes forward in an arc toward the centerline of the car. While it would be stronger to triangulate right off the #3 or rear #1 cylinder header bolt as is done on the '91, that would still allow the alternator to "sweep through the arc" moreso than if the restraint were further from the center point of this arc, such as 2" out.

But putting it 2" out puts a side load on the bolt and we'll see how much it flexes with the tube spacer installed. As I said, I can go 1/2" shorter on this bolt. I could also upgrade it to a grade 8 bolt (rather than stainless which are probably ~#5?), though I don't know how the grade of the bolt affects the side load properties.

toddalin

I've included new pics of the completed brace. It looks like I could align the bracket on the alternator a little better with the header bolt to get them in the same plane. It's kind of hard to tell how it will align when you first put it together because you have to bolt the bracket to the alternator before assembling the linkage. Now I have a point of reference and can just twist the bracket a hair clockwise to get it inline with the header bolt.

Anyway, it does firm up the alternator and reduces (but does not eliminate) its forward tweak when the engine is revved. The belt doesn't get as loose and wobbly as it did.

I guess that the next step (other than replacing the crumby header bracket, but nobody appears to make a decent one), is to try to "pre-load" the adjustable rod to increase its tension on the alternator.