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Old 06-17-2014, 11:33 AM   #1
old cool
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Question alternator misalignment

My GMC has an inline 250 six. The crank pulley has two grooves. The truck has no options. So, question one is: are double grooved pulleys standard even if truck comes without ac, ps, etc...?
Second question pertains to alignment of alternator pulley and crank pulley. The upper alternator bracket is flat and arc shaped. (I've seen upper brackets with "L" shaped bend) The bottom bracket connected to block only provides so much slide for alternator. Is bending, shimming, or modifying a bracket a good opition?
Lastly, my alternator belt is running off the outer pulley groove instead of the groove closest to block. I don't feel the upper or lower bracket are giving me much choice. I feel like I'd rather be running on inner side pulley even if just for appearance.
Anyway, back to most important point, is/are there simple solutions to aligning a belt, and an alternator that doesn't square up with block. I need some good advice before I ream out the bracket holes and use shims to align.
Thanks in advance for tips.
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Old 06-17-2014, 12:51 PM   #2
markeb01
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Re: alternator misalignment

Over the years I've come up with all sorts of spacers and modified brackets to get perfect belt alignment. They just need to be strong enough for the task. For years I used to eyeball the belt alignment which isn't very accurate. I found I could do much better by placing a 2-3 foot straightedge across the face of the lower pulley. It should contact the face of the alternator puller squarely, the only variance being the distance from the belt in the lower groove to the front edge of the pulley.

For example, some lower pulleys are cast or have thick flanges. Alternators not so much. If the lower pulley places the belt the same distance back from the front edge as the alternator puller, they should align perfectly. If the lower pulley is thicker, there will be a gap between the upper pulley and the straightedge, but the distance from the belt will be the same on both pulleys.

Having a hard straight surface to line up against, makes it much easier to avoid twist in the alternator mounting.
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Old 06-17-2014, 12:59 PM   #3
old cool
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Re: alternator misalignment

does using the inner or outer groove on the lower pulley make a difference? My eye would prefer using the groove closest to the block. But that will require some straightening and shims behind the bracket. Yet I'm still not certain my bracket will allow enough to slide of the alternator. I'm probably not making sense, but I'm sure you understand as you've done it.
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Old 07-03-2014, 02:52 PM   #4
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Smile Re: alternator misalignment

Mark. Thanks. Your response put me on the right track and problem was solved. To help others, I did use crank pulley as my straight-edge guide to assure all other pulleys were even. I did have to modify a sleeve-type spacer to better-anchor the alt from the bottom bracket; and added one washer to get alternator properly aligned. I also straightened both brackets to correct alt. angle(I did that first). Used a new performance NAPA belt, cleaned pulleys; no more cherp and everything looks square.
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Old 07-03-2014, 03:29 PM   #5
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Re: alternator misalignment

A lot of the I6 had double crank pulley's whether you needed them or not. most were single belt;crank, w/p and alt. if for some reason(application) a 62 amp delcotron alt was required then you usually had a double belt alt. the extra pulley on the crank was more than likely for p/s even though most never had p/s
the reason that you have a double pulley alt is the previous one was nfg and here was this one with a d/pulley lying around and seemed to fit
ron
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Old 07-03-2014, 06:23 PM   #6
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Re: alternator misalignment

Thanks Ron. I was wondering why I had a double pulley crank. That takes care of another curiosity.
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