The 1947 - Present Chevrolet & GMC Truck Message Board Network

Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > Info Center > FAQ Truck Tech > Engine and Drivetrain


Thread Tools Display Modes
Old 12-08-2008, 04:27 AM   #1
Registered User
Bruce88's Avatar
Join Date: Oct 2008
Location: Everett, WA
Posts: 326
V Belt pulley alignment 101

V belt pulley alignment

(General information about the tutorial)
The fallowing was used GM 350 crate engine, aftermarket high flow short style water pump, aftermarket harmonic balancer, aftermarket alternator 100 amp internal regulator, rebuilt power steering pump and all pulleys & mounting brackets from a 72 Chevy C10 350 engine. Measurements you view in the attached pictures are not exact, all shims where installed prior to the pictures, just trying to show where to take measurements from and I was holding both the camera and tape at the same time when taking the pictures.

There is no way this tutorial is going to show all possible pulley configurations or correct damaged pulleys and brackets. But you should be able to see how this technique can be used to check your pulley alignment and figure out how to fix it if needed. You should be able to get your pulleys within alignment of plus or minus 1/32 of an inch. Even from the factory pulley alignment can be off.

What is needed is a straight edge that is parallel to all the pulleys to measure from.

(Making a straight edge)
I went to a hardware store and picked up a peace of angled aluminum ĺ in x ĺ in x 1/16 in thick x 36 in long. Make sure it isnít bent, distorted, twisted or damaged in any manner you are making a straight edge.

Measure the distance between your water pump fan mounting bolts and the distance between water pump snout and the pulley thatís furthest a way form the pump. My measurements are 1-1/2 inch between mounting bolts and my Alternator to pump is aproximitly16 inches.

I added a few inches to the 16 in dimension and cut the straight edge material to approximately 19 inches long and laid out the 5/16 to 11/32 DIA holes a few inches from the end of the straight edge.

Ref pic # 1 I recommend to use a scrap peace of 2 x 4 wood to support the straight edge for cutting and drilling also start drilling the holes with smaller drill bits and work your way up to full size to prevent distorting the straight edge material. After Drilling make sure that any burs are removed so that the straight edge will sit flat on the mounting surface.

(Mounting the straight edge)
If you have your engine on an engine stand mount the straight edge on the fan spacer as shown in ref pic #2.

If you have the engine in the truck remove the fan and the fan shroud. You will also have to drill some additional mounting holes in the straight edge (making it shorter) to obtain clearance from the frame, cross member and hoses. This will require you to change the mounting position as you take the measurements. If you feel that there is not enough room between the radiator and the straight edge to take measurements remove the fan spacer and mount the straight edge to the front of the pulley with shorter bolts.

(Taking measurements)
Your drive belts should be loose enough that you can turn the water pump pulley by hand never turn this pulley using the straight edge it could bend the straight edge.

Turn the straight edge as shown in the ref picís #3, 4, 5, 6 & 7 taking measurements between straight edge and the drive belt edge keeping the tape measure square to the straight edge. If you have high performance pulleys (pulleys with deep groves) where the belt edge is not above the pulley, take the measurement at the belt edge run as close as possible to the particular pulley.

(What, where and how to shim)
Your measurements will probably be different than mine even if you use the same parts and pulley configuration. I prefer to use decimal numbers rather than fractions so all reference numbers below have been converted (top fraction # divided by the lower # then rounded to the third number past the decimal point). I also prefer to use a caliper or micrometer to measure my shim thickness not to say you canít use a tape measure and fractions its just easer math. If you need to make a taper shim that will be described below the taper is so small you will need a caliper or micrometer to measure it.

Start with the most aft belt, on this configuration itís the crankshaft, water pump and alternator pulleys (my ref numbers between the straight edge and belt edge are)
Crankshaft pulley -----4-3/8 = 4.375
Water pump pulley----4-3/16 = 4.188
Alternator pulley------4-5/16 = 4.313
Normally you will only have to shim behind one of the pulleys for the crankshaft or the water pump if required (subtract the smaller number from the larger and this is the shim thickness required). Recommend that you use manufactured shims for shimming the crankshaft or water pump pulleys if available, you can find them at JEGíS, Summit or performance shops. I will need a 0.187 thick shim = 3/16 thick shim behind the crankshaft pulley (ref pic # 10 manufactured 1/8 thick and 1/16 thick = 3/16 thick shim behind the crankshaft pulley).

Now for the Alternator pulley. On some Alternators you will not be able to move the a Alternator aft and this will require you to move both the crankshaft and water pump pulleys forward to match the Alternator. On this mount the Alternator can be moved aft with a washer or forward with shims between the block and the mount (ref picís # 8 & 10). If you do shim the Alternator aft make sure the bolt head clears the belt. Normally you will have to shim the Alternator forward if required. I needed to shim the Alternator forward, subtracting the ref number 4.188 water pump pulley from the alternator ref number 4.313 showing that I need a 0.125 shim = 1/8 shim between the block and Alternator mount. I found some 0.059 thick material in the shop and made two shims to use between the block and the mount (0.059 + 0.059 = 0.118 thick shim, close enough for me)

I Recommend that you do all the shimming required on the aft most belt pulleys before moving on to calculate the next belt forward because shimming the crankshaft or water pump pulleys may change how much shim is required for other pulleys.

Now, on to the power steering pump pulley alignment to the crankshaft pulley. The power steering pump can not be moved aft with shimming. Normally if shimming is required, it will be forward. I also have an additional problem with the power steering pump pulley. It will need to be moved forward and it is cocked not parallel to the crankshaft pulley so I will need to make a tapered shim. (Ref picís # 9 & 11 for where the shim will be installed, where the measurements will be taken and the math to calculate the shim).

Since my taper is from right to left, the first measurements (B) & (C) are taken between the straight edge and the edge of the pulley, (this is different measurements than above itís to the pulley edge not the belt edge) subtract the smaller # from the larger #, and it showed that I had a .125 taper. The DIA of the pulley is 6 inches divide the .125 taper by 6 and generate a taper scale (this is just the taper not the total shim thickness)

Now take the measurement (A) between the straight edge and the belt edge (this measurement is straight up from the pulley shaft) then take the measurement between the straight edge and the crankshaft pulley belt edge, subtract the smaller # from the larger #, and it showed that I had a total shim needed would be .156 (this is the total shim needed with out the taper).

Putting the taper calculations on the total shim required. First subtract the taper scale # from the center of the pulley DIA .062 from the total shim .156 = .094 The shim is 1 inch wide that will be used, so calculate the taper at 1 inch = .073 tapering to .052 add .094 to both of the numbers = .167 LH edge to .146 RH edge (this is the total shim thickness required with the taper). I found some aluminum material in the shop that is .0625 thick so I will be making a shim stack of 3 with one of the shims having the taper.

Yes, there are different ways to calculate the total taper shim requirements just trying to show the relationships between the pulley shaft and the shim required.

After installing the shims for the power steering pump it was required to elongate the aft mount hole a small amount so the bolt could be installed.

(Shim general information)
You should be able to find shim material around your shop, hardware store or from performance shops for manufactured shims.

Shims can be stacked to obtain the total thickness required.

When creating the shims make them to a size that will cover the brackets mounting area.

Tapered shims more than .030 inch taper over 1 inch you probably have a bent or damaged bracket and should not be used if it cant be straightened.

If the shim thickness is up around ľ inch or more you probably have the wrong bracket or pulley. Not to say you canít make a shim that will work you just have to be careful that everything clears and that your mounting bolts are long enough.

After shimming the primary mount you will need to look at the secondary/support mountings to see if they need shimming or modification.

After all shimming is complete and you have re-checked your alignment recommend pulling all the shims out and painting them to prevent corrosion.

(The end maybe)
If anyone sees where clarification or additional information is needed in this tutorial please feel free to contribute
Name:  strate-edage-1.jpg
Views: 13488
Size:  72.2 KB

Name:  strate-edage-2.jpg
Views: 12023
Size:  68.5 KB

Name:  Strate-edge-3.jpg
Views: 11537
Size:  94.0 KB
Bruce88 is offline  


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -4. The time now is 05:48 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 1997-2013