alternator/water pump belt chewed up & slipping at high temperatures

[CHP2RA]

Superformance Cobra MK III Roadster SPO 2650, 7,000 miles, Roush 402R, Tremec TKO 500

Can anyone recommend an alternator belt manufacturer & size for this engine? Is a 36 degree angle belt what I should be using?

My engine has developed a crankshaft/alternator/water pump belt slipping/squealing/chewing problem. It only happens when it is hot outside: 100 f OAT, and the engine is hot: 100 - 110 c oil temp. More prevalent when I drive it hard, but will squeal at low RPMs when hot. The squealing can become almost continuous. Small bits of rubber on the underside of the hood, from the belt. I've owned this car just over a year. Other problems kept it off the road last summer, so this is the first I've driven it hard in the Texas heat.

The belt gets loose, I tighten the belt, the squealing/slipping goes away for a week or two, then returns. I tighten the belt some more, but the metal fan blades on the Delco alternator pulley (which I move outboard to tighten the belt) now dig a groove in the right front wheel well fiberglass when the engine torques to the right. My mechanic installs a shorter belt, and we repeat the squealing/chewing/tightening process, with the alternator fan blades eventually getting back to the fiberglass chewing position.

My mechanic verified that the Roush billet aluminum crankshaft and water pump pulleys are aligned with the steel Delco alternator pulley. The two Roush pulleys both have a dark deposit of belt rubber near the top of the groove. The Delco alternator pulley shows no belt rubber deposit. The two longer belts we removed showed wear/glazing on the sides near the top, consistent with the rubber deposits on the aluminum pulleys. The edges of the aluminum pulleys are blunt, while the edges of the steel alternator pulley are eased. All three pulleys are smooth.

The belt that was on the pulleys when I purchased it one year ago was:

Gates XL 7380 - 38 5/8" long, 13/32" wide, 36 degrees

The shorter belt we installed last month was:

Gates XL 7375 - 38 1/8" long, 13/32" wide, 36 degrees It was so short it was very difficult to install.

We just tried a wider belt - 15/32", 36 degrees, GATES 90385 - to effectively shorten the length, but that is chewing up even faster.

Any thoughts or advice is greatly appreciated. What belt do you use for your engine?

V/R,

Carroll Payne

[spdbrake]

It sounds like you have a water pump bearing or alternator bearing or an alignment issue. (I take it no power steering pump)
I'd check alignment of all three pulleys in relationship to each other using a metal straight edge or a yard stick. Also inspect the alternator if the nose appears tipped down or up. You may want to do these same checks again once a belt is installed.
If you don't mind sacrificing another belt, wait until it starts squealing and you're at a garage or home. Then cut the belt off and check the alternator and water pump for binding.

The tension should be 1/2" deflection of the belt when pushed with one finger in the center of the run from the water pump to the Alternator. Too tight and you smoke bearings.

Eliminate Belt Noise by Servicing the Entire Belt Drive System

[1985 CCX]

Fit the width of the belt to narrowest Pully.
I too chewed up belts till I did this.
My crank pulley was narrowest and stock Ford.
Once I did this, no issue.

Add pictures, helps us help you

[CHP2RA]

Hi SPDBRAKE, thanks for the reply. Interesting post on servicing the entire belt drive system. You are correct - no power steering. The alignment is good on all three pulleys. All three are co-planar, as well. When the belt was off yesterday, the water pump & alternator both spun without binding. So, it could be intermittent binding in either the water pump or the alternator. Because the squealing/slipping/chewing only happens at high temperatures, that may be the condition causing the pump or alternator to bind? The tension is as you described. After testing the wider belt yesterday, removed the belt, and the rubber build up appeared on the waterpump pulley, with none on the crankshaft or alternator pulley. An indicator the waterpump is intermittently binding when hot?

My past experience with non-performance waterpumps is when they go it is very loud and rough. This is an Weiand 8210 water pump - wonder if it would behave differently?

[CHP2RA]

Hi 1985 CCX. The alternator pulley is 1/32" more narrow than the other two pulleys. If I don't solve this puzzle before belt #3 get glazed, I may try a more narrow belt. 11/32"?

I would post photos if I knew how. Cannot find a 'how to post photos' link or thread.....

[spdbrake]

When you have the issue does your voltmeter droop somewhat at idle and or does the water temp start climbing compared to what your used to seeing?

If your sure of the Alt and water pump health you may consider going to a 6 rib (serpentine style belt) or a Gilmer cog type. Some folks are fond of the blower whine assoc with the Gilmer.
Mine uses the 6 rib and a March pulley bracket setup that moves the Alt higher even with the valve cover.
https://speedmaster79.com/pce4151004...mer-drive-kit/
Serpentine Pulleys - Pulleys - Ford Small Block 289, 302, 351 Windsor - Ford - March Performance

[CHP2RA]

Hi spdbrake, next time I run the Cobra I'll get it hot, and check engine temp and voltage output when it squeals. How did you know I'd replaced the amp meter with a volt meter?

[Bob Hess]

Have you tried belt dressing? It is available from belt suppliers like Gates, etc.
Another old time remedy it to rub a bar of soap on the belt as it is running, being careful not to get your fingers or other parts in the way of moving parts!!! By doing this you can eliminate the mechanical issues discussed earlier. You can also try to get a different style of belt from a professional belt supplier, not an auto parts place. Look under power transmission on the web or yellow pages. Maybe get a composite belt.

I had the same problem with my car but adjusting the belt a very small amount fixed the squealing.

[BAsque1]

I had a similar problem, when the car increased in temp the fans will go on hence the belts will squeal, the problem was the alternator pulley was too small in diameter. I change the pulley by increasing the diameter and problem was solved.
Lou

[CraftEngines]

We were having similar issues with some of our crate engines. We spoke with our bracket and pulley suppliers and they were thinking that these quick reving engines were reving faster than the belts could handle. We swapped to serp belts, but still standard rotation and the we have had no issues since.

[Jac Mac]

What is the diameter of the crankshaft pulley, we found with race cars that the larger stock crank pulleys..~6" to 7" dia.. induce a belt speed that is too high, reduce the crank pulley down to 5" or less.