Drive belt 'creep' on a SBC

Drive belt 'creep' on a SBC

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Discussion

Nabbott

Original Poster:

294 posts

135 months

Monday 10th November 2014
quotequote all
So just sanity checking my thoughts here.... amongst the myriad of problems I've had with the car - the alternator has been a major issue. I've now got a new 120 amp single wire alternator (and wire to the battery), bracket, and new belts and pulleys for the water pump, alternator and crank having binned the old gilmer belts.

I've taken the car out to day to test this (and a few other bits and pieces) and when I got home to inspect the new belts and saw that they are creeping 'back':



So given that the water pump and the crank are fixed reference points - this surely can only be a problem caused by alignment or tension of the alternator? Any thoughts?

Nabbott

Original Poster:

294 posts

135 months

Monday 10th November 2014
quotequote all
Jones Racing (specifically made for SBC).

Storer

5,024 posts

214 months

Monday 10th November 2014
quotequote all
Looks like the alternator pulley is not quite parallel with the crankshaft.

Probably needs 'minor fettling' but the back of the alternator needs to move slightly further away from the engine.


Paul


Nabbott

Original Poster:

294 posts

135 months

Monday 10th November 2014
quotequote all
Paul - so do you think that deflection on the alternator pulley will be enough to 'pull out' the water pump as the drive from the crank is also creeping.....?

Storer

5,024 posts

214 months

Monday 10th November 2014
quotequote all
If one pulley is not quite 'square' with the others it will pull the belt out of line on all them.


Paul



ezakimak

1,871 posts

235 months

Monday 10th November 2014
quotequote all
If the shaft of the alternator is not in plane with the crank then it's running surface for the belt will present itself to the belt as if it is cone shaped which will result in the belt running towards the smaller end of the cone.

anonymous-user

53 months

Monday 10th November 2014
quotequote all
Beats me why you'd want to drive an alternator, or any other FEAD device that doesn't absorb lots of power with a toothed belt? Fit a multirib polyV belt and it's job jobbed.....


Toothed belts will ALWAYS walk, unless they are tightly constrained on their pulleys, because unless the centre of pressure is perfectly in the middle, even in dynamic load conditions, the belt with shuffle along the pulley.

Nabbott

Original Poster:

294 posts

135 months

Tuesday 11th November 2014
quotequote all
Max_Torque said:
Beats me why you'd want to drive an alternator, or any other FEAD device that doesn't absorb lots of power with a toothed belt? Fit a multirib polyV belt and it's job jobbed.....


Toothed belts will ALWAYS walk, unless they are tightly constrained on their pulleys, because unless the centre of pressure is perfectly in the middle, even in dynamic load conditions, the belt with shuffle along the pulley.
Hindsight and all that! I was advised to go with this configuration by the guys who supplied the alternator and bracket, principally as it is lots stronger than the old Gilmer belts.... Having ponied up another $250 for the pulleys and belts I'd prefer NOT to scrap the lot for Poly V smile