By May 16, 2008 Read More →

Fan Belts Keep Jumping Off

My question is, I have an RV with a 454 chevy engine and it keeps throwing the fan belts.

Engine was rebuilt about 4 years ago, I have had 4 diff. mechanics look at the problem. Pulleys are in alignment, correct belts, everything has been checked, but I still have the problem. Any Ideas.




Howdy Jay,

I KNOW you have already checked these items but I feel pretty strongly that something simple is being over looked here. It usually IS the simple things that cause the problem, but mechanics….mine included, tend to overlook the obvious and go straight for the complex issues.


I would inspect the following, all of which you can do yourself


  • With the engine running at idle stand perpendicular to the belts and watch the belts run along the pulleys….are they straight or wobbly?
  • With the engine at FAST idle (2500RPM) are the belts tight, or do they flop around because they are loose or out of alignment
  • Is there an accessory pulley that is hard to turn ( can you turn the p/s pump, a/c clutch, water pump, alternator etc. etc. pulley by hand)
  • Watch the bottom harmonic balancer pulley, does it wobble around? Sometimes when they are bad they will float forward of the engine causing the belts to be out of alignment. Look at the back of the harmonic balancer to see if the rubber is coming apart or has already come apart and is missing.
  • Is there a belt tensioner? Or better yes, WAS there a belt tensioner pulley that might be missing…or was not re-installed after the re-build? You can buy a universal tensioner and try to add it to the block somewhere if you see one of the belt flopping around too much.
  • Are you using the right kind of belt? They make an industrial application fan belt (we use them on our wreckers) that do not stretch like a normal fan belt. A 454 has a lot of torque and heat, a standard vehicle belt might not be what you should be using. Ask your auto parts guy to give you a the same belts but in industrial application.
  • If you have a serpentine belt, count the number of grooves in the pulley then the number of grooves in the belt……they should be the same or the belt will never fit the pulley properly.

Here is more info from Gates belts


Austin Davis

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Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

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