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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 05-03-2015, 11:29 PM   #11 (permalink)
dieselmike1
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Quote:
Originally Posted by Diaric View Post
IIRC Racer55 posted it a few times that the pulleys were different up to a certain point.
I did a search using different keywords Diaric, none of his posts were close enough to the top that I saw, and assuming that the FAQ sticky's would be correct. I just cant help but think of all who have seen that, members or non- members that may be running the wrong size pulley on their later model truck. Just glad its fixed now, seeing as we send all newbies to those FAQ's stickys at the top, and they see them as the 6.5 bible (so to speak).

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Last edited by dieselmike1; 05-03-2015 at 11:30 PM.
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Old 05-04-2015, 07:20 AM   #12 (permalink)
Rattler1
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Another thing to keep in mind is that the smaller pulley may not allow the belt to get the proper amount of tension from the tensioner.

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Old 05-04-2015, 08:14 AM   #13 (permalink)
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THe 96+ belt routing and tensioner is a flawed design from the start. Don't know what they were thinking. Most of the time the tensioner tends to flip over center and over tension the belt. I tried different length belts and had no success. A few washers under the AC compressor did the trick. Its held fine for like 2 years now. Before with a new belt it would take a few days to over center itself.

The -95 design is not a lot better but does not seem to be as bad. Getting the bigger alternator pulley on that did seem to help get the tensioner into what I assume is the normal range on its marks.
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Old 05-04-2015, 08:31 AM   #14 (permalink)
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Quote:
Originally Posted by Diaric View Post
IIRC Racer55 posted it a few times that the pulleys were different up to a certain point.
Quote:
Originally Posted by dieselmike1 View Post
I did a search using different keywords Diaric, none of his posts were close enough to the top that I saw, and assuming that the FAQ sticky's would be correct. I just cant help but think of all who have seen that, members or non- members that may be running the wrong size pulley on their later model truck. Just glad its fixed now, seeing as we send all newbies to those FAQ's stickys at the top, and they see them as the 6.5 bible (so to speak).
First of all, good catch Mike.

Did some digging for Racer55's posts. Here is what I found:

Quote:
Originally Posted by racer55 View Post
https://www.dieselplace.com/forum/5877034-post6.html

The research I found says that in 96 the alt pulley was standardized across the board?
So it's pre 96 that has the size difference to contend with.
Quote:
Originally Posted by racer55 View Post
Does it really seem that fast?
Does a scan tool agree with the tach?

There is an issue where if the wrong pulley is installed on the alternator the tach will read higher than actual.

The diesel pulley is bigger than the gasser pulley that is normally on replacement alternators.

This is supposed to be correct:
241250 6-Groove Pulley for Delco 10Si, 12Si, 15Si, 17Si, CS130, CS144 Series Alternators
And one more post on the subject:

Quote:
Originally Posted by Tracy View Post
The OD of the pulley for the outside lip/flange is 2 and 5/8 inches. The top of the grooves the belt acually rides on is 62mm or 2 and 7/16 inches. This is for the 92/93 mechanical engines, the newer engines changed thier belt drive systems a couple of times and maybe different than this. I'm certain of these figures since my alt. is still original with 190,000 miles (knock on wood). The typical small block chevy alt is 2 and 7/16 inches for the outside lip/flange OD. and is 2 and 1/4 inches (57mm) to the top of the grooves the belt rides on

Assuming a correct engine speed of 2200rpm the SB chevy alt. pulley would show 2400rpm and at correct engine speed of 3600rpm and the SB chevy alt pulley would show 3925 rpm.
What Racer55 said happened in 1996 and what Glagulator posted earlier in this thread about his 1996 & 1999 implies that 1996-2000 used the smaller pulley. The suspicion is the larger pulley is for the 1992-1995 trucks with the specs grabowski posted earlier in this thread.

So......anyone friendly with a GM dealer parts guy that can get part numbers and pulley dimension specs for model years 1992-2000? Then we will have the complete picture.

Absent having facts on GM's alternator pulley specs, the best way to confirm correct pulley size is to cross check Tach RPM with a scan tool.
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Old 05-04-2015, 09:05 AM   #15 (permalink)
90GMC62L
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I'll confirm that the '95 is still a 2-5/8" pulley. I have the original alternator on my truck and my RPMs match what I calculated with my tire size.
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Old 05-04-2015, 09:17 AM   #16 (permalink)
Freddyack
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Quote:
Originally Posted by 90GMC62L View Post
I'll confirm that the '95 is still a 2-5/8" pulley. I have the original alternator on my truck and my RPMs match what I calculated with my tire size.
Thanks!
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