Maybe the hive has a solution.

I have a Raby 2300 with 7000 redline. Anytime I rev above 5000 the monster throws the alternator belt off. I've tried a few different types of belts, with no success.

It limits me to driving short distances in the daylight hours only.

I'm thinking the original design never intended to spin the alternator that fast.

Any solutions out there?

when I raced a -4
it was common to have belt problems with any over rev
the shock... of rpm change would throw the belt

we used to take a zip lock bag...
put a new belt into it with lightweight oils.
WD40 or something similar

it would slightly penetrate the rubber after an day or 2 in the bag

wipe the belt down and install

this causes the belt to slip but not throw off when under too much load
our cause was different than yours, but it helped a lot on the track

might be worth a try

you may want to loosen the tension also... to facilitate the slip rather than come off action.


brant

Worth a try.

I had not thought of that. I was thinking I would have to find a larger pulley, but I like this idea.

Thanks!

^^^ Clever

if it doesn't help... at least your only out the price of a new belt

also... the belts with the cog-notches on the outside belt face will hold better (not original style)

I think it was the gates brand that had these... can't completely remember
but those belts worked much better for us

brant

I zipped my racer to 6-7k without issues.

However, I used to have a problem: turned out I had the alternator pulley flipped around so it wasn't perfectly aligned. So maybe check belt alignment?

GA

I had a similar problem on a VW GTI I road raced years ago and a hot rod boat engine that would see north of 7000 RPMS...I ended up turning up some rings on my lathe and welding them onto the pulleys to make the VEE much deeper. Worked like a champ.

The correct solution is a larger alternator pulley or smaller crank pulley or both...but that's easier said than done on a type 4

Most the of the belts sold not are NOT the correct width. Correct width is 9.5 x 965 NOT the 10 x 965. Click to open picture of size on belt

I will add one thing on the alignment (you may have already checked). I was chasing the same problem a couple of years ago on my race car. I found the back hole on my mounting bracket to be very worn and egg shaped, the alternator was always canted inward. I welded a washer centered up on the hole and have not had a problem since. I regularly change gears in the 65-6,800 range.

had much better results using belts with cog-notches and correct width on the track cars

all great info!

I'll spend some time following up on all the ideas presented so far.

The belt I was using is 965 x 10. Interesting....

Check that first...the alignment is critical...my bracket was cracked ...once I fixed that no more problem...

You are correct that OE design was never intended to support those sort of RPM's.

When accessory drive systems start throwing belts (V-belts, sperpentine, whatever) you're going to find two likely causes.

1) Static Pulley misalignments that put side loads on the belt, making it inclined to jump.

2) Dynamic pulley alignment issues. The system is going into resonance at some critical speed. When the system goes into resonance, it is shaking in on (or more) of the X, Y, or Z planes. The only solution to resonace is to move the resonant frequency. Doing this is not as easy as it looks and usually requires a few accelerometers to be placed on the components to understand the frequency of the resonance and its modes (what motions are occuring).

The 914 alternator brackes are a terrible design but work well under the stock operating parameters (i.e. only short excursions to about 5500 rpm).

Click to view attachment

The U-bracket that attaches to the fan shroud is very weak and is going to be inclined to resonate fore/aft. As it does so, the pulley alignment will be affected.

The alternator adjustment braket is even worse and provides very little if any additional fore/aft support. It is long, thin, and operating in single shear.

Bottom line, it's archaic . . . but works in stock configuration.

If I were trying to improve it, I would likely move toward some sort of billet U channel arrangment that would have far more fore/aft stiffness than this little steel U-bracket.

As noted by others try, the proper belt size, and make sure your pulleys are properly aligned (statically). After that, you're going to be looking at design modifications to improve dynamic robustness.

Anybody got specifics on the 9.5 belt with exterior notches ?


.

Translation from Engineer-ese to normal human language.

"If you are going to run those kinds of RPMs, you need a stronger mounting bracket."

Maybe someone here can make a billet aluminum bracket that is stronger than the stock one?

Thank you!

I'm using belts with the notches on the inside, have never seen a replacement belt with notches on the outside?

I imagine the somewhat flimsy upper arm/mount adds to the problem. Prone to cracks and breaks too.

Interesting.... I take my mostly stock engine over 5K rpm fairly regularly without any issues.

Have you tried pinging Jake Raby to see if he has any thoughts? He has contact information in his member profile and he has been active on this board recently. @jake raby

I pulled the whole assembly apart after I was able to visually see the mis-alignment.
Removed the bottom mounting bracket (flimsy). See picture in one of above posts. It was bent and the hole opposite the square hole was wobbled out.
I bent the piece straight, then welded up the hole and re-drilled it straight. Then I made a steel plate to act as a "washer/stiffener" between the bolt heads and the bracket. That plate runs from bend to bend inside the bracket. It is not so thick as to make the bolt heads hit the alternator body.
Put it all back together.
Drove it pretty hard and the belt has stayed on.

Take a few mins to ensure that the pulleys line up. My belt has been popping off at about 5500 and when I checked the lower bracket was tilting the alternator. A little tweak of the two lower "ears" and seems to make all the difference in the wold.

The twist is GONE. NOTE the 2 pulley planes are parallel to each other.
The "V" groove is camera perspective

Click to view attachment

Another victory, thanks for sharing