Throwing Drive Belts

Throwing Drive Belts

Author
Discussion

Jarcy

Original Poster:

1,559 posts

274 months

Sunday 9th November 2014
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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.

Green3R

400 posts

247 months

Sunday 9th November 2014
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Maybe alternator or aircon pump bearing?

XLRONYX

244 posts

166 months

Sunday 9th November 2014
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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

jdearden

1,746 posts

176 months

Monday 10th November 2014
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There is 2 positions it can go onto the air con pulley. There is on the 2.5. There is more groves than there is on the belt.

Adrian W

13,848 posts

227 months

Monday 10th November 2014
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Is this a recent fault, or has the car always done it?

Jarcy

Original Poster:

1,559 posts

274 months

Monday 10th November 2014
quotequote all
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.

Metalman

1,173 posts

217 months

Monday 10th November 2014
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Is there a chance your car has an underdrive pulley fitted and your fitting a standard belt?

2.5bluenob

1,620 posts

175 months

Monday 10th November 2014
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Metalman said:
Is there a chance your car has an underdrive pulley fitted and your fitting a standard belt?
I don't think the belt would fit Jason.

TuxMan

9,010 posts

237 months

Monday 10th November 2014
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I lost a belt last year , turned out the idle pulley was knackered !!! Jetstream supplied a replacement since then all fine .

Jarcy

Original Poster:

1,559 posts

274 months

Tuesday 11th November 2014
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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 frown

Jarcy

Original Poster:

1,559 posts

274 months

Friday 21st November 2014
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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 smile