Throwing Drive Belts
Discussion
Does anyone have any suggestions for a likely cause of repeatedly throwing my drive belt (alternator/aircon)? I'm getting sick of calling the AA. Lasts about 30 miles then shreds. Both times today, the belt has managed to move one tooth away from the engine side, and then shred on the edge of either the top pulley or the crankshaft pulley. I understand that the crankshaft pulley can wear as it contains rubber.
Each time I fit a new belt, it looks to be running straight and true, but of course I can't see what happens or causes it to pop off. I wonder if one of the pulleys has a wobble? We've tried adjusting the washer spacing on the idler pulley too, but that didn't help.
I've tried many different lengths and makes of belt, from 6pk1700 to 6pk1708. The latest to shred was the correct Gates part 6pk1708. Any help or suggestions greatly appreciated. Thanks.
Each time I fit a new belt, it looks to be running straight and true, but of course I can't see what happens or causes it to pop off. I wonder if one of the pulleys has a wobble? We've tried adjusting the washer spacing on the idler pulley too, but that didn't help.
I've tried many different lengths and makes of belt, from 6pk1700 to 6pk1708. The latest to shred was the correct Gates part 6pk1708. Any help or suggestions greatly appreciated. Thanks.
On US engines, it's the idler pulley. It is not properly aligned with the rest of the pulleys. I don't mean an in/out misalignment, I mean that its rotation axis does not form a right angle with the front of the engine.
On US engines, the idler pulley bolts to a big (heavy!) welded steel bracket that locates the air-con compressor. After all my tricks with shims failed, I removed that bracket, held it in a big vice, and beat on it with a big hammer until the pulley hole made a right angle with the bracket.
I must have got lucky with the measuring and beating because I've had zero belt problems since then.
Jeff
On US engines, the idler pulley bolts to a big (heavy!) welded steel bracket that locates the air-con compressor. After all my tricks with shims failed, I removed that bracket, held it in a big vice, and beat on it with a big hammer until the pulley hole made a right angle with the bracket.
I must have got lucky with the measuring and beating because I've had zero belt problems since then.
Jeff
Thanks for all the suggestions. It has to be one of the pulleys at fault, and suspicion still rests with the idler pulley. Interesting what you say about the bracket not being perpendicular. That might explain it.
Adrian - The car did it once last year just after a new belt was fitted, as the old one was slipping causing the power steering to whine on full lock. The AA replaced it with a 'belt from a Fiesta', which ran fine for a year, except that too was slipping so was changed recently setting off these recent episodes of failures.
I think the aircon pump has 8 teeth, so yes we're careful to select the appropriate position for the belt on that pulley.
Another idea is to try a 5pk belt, but I really want to identify and fix the problem properly.
Pulley bearings may be a problem, but the car's only done 29k miles.
Adrian - The car did it once last year just after a new belt was fitted, as the old one was slipping causing the power steering to whine on full lock. The AA replaced it with a 'belt from a Fiesta', which ran fine for a year, except that too was slipping so was changed recently setting off these recent episodes of failures.
I think the aircon pump has 8 teeth, so yes we're careful to select the appropriate position for the belt on that pulley.
Another idea is to try a 5pk belt, but I really want to identify and fix the problem properly.
Pulley bearings may be a problem, but the car's only done 29k miles.
OK, after another good prod around, I'm convinced that it's the idler pulley. We've packed it out with an extra washer to get the belt to run central on it, but as a result it's well out of alignment with the alternator pulley. And upon looking with the naked eye, I reckon Jeff is right - the rotational axis of the pulley isn't at right angles. So maybe it's off with the aircon compressor bracket and a little application with a persuader to get it straight. Doesn't look like an easy job
Update. We found that the angle of the aircon compressor bracket was ok, but the idler pulley bolt was not a snug fit in the bracket allowing it to sit at a slight angle. Maybe the hole in the bracket has opened up with wear. By packing the bolt with larger penny washers instead of the pre-existing washers and spacer, we found that the pulley could now sit flush and perpendicular to the bracket. We also changed the pulley for good measure. The result is the drive belt is now able to sit closer to the engine case and run true. The belt is on the second tooth on the aircon pulley, which is closer to the engine case than another Noble I compared it with (3rd tooth along). A few runs out and all is good.
I have had a catalogue of misfortunes with my car over the summer. Rear clam ripped off, front turbo gasket failure, rear manifold failure, ECU failure, countless attempts to get my aircon working, and a holiday missed through drive belt failures. I don't want to tempt fate, but at last I hope I've cracked them all and got my car fully working. Just in time for winter!
I still think it's an awesome car though
I have had a catalogue of misfortunes with my car over the summer. Rear clam ripped off, front turbo gasket failure, rear manifold failure, ECU failure, countless attempts to get my aircon working, and a holiday missed through drive belt failures. I don't want to tempt fate, but at last I hope I've cracked them all and got my car fully working. Just in time for winter!
I still think it's an awesome car though
Gassing Station | Noble | Top of Page | What's New | My Stuff