Adding a second tension pulley - ATI D1SC
08-06-2017, 12:15 PM
#1
Adding a second tension pulley - ATI D1SC I just installed a second idler pulley on my Procharger D1 SC – 2005 version on my 1998 Z28 Camaro.
I installed the DM Engineering standoff for the second idler pulley with a Procharger 2.5 idler pulley. The ATI crank drive pulley is 7.65 with 4.38 drive pulley on the D1 head unit.
This is thread is to show how easy it is to install the DM Performance standoff. But also to show what I found when Bob as Brute Speed sent me a new idler shaft for the j bracket tensioner pulley.
Pics explaining the installation for the standoff, and the comparison of the old and new idler shaft are in this link.
I don’t know when Procharger changed the design of the idler shaft.The newer design might only apply for those of us who still have the old version. My D1 kit was mfg around early 2005 just after ATI added the eight rib pulley to their kit for the f body.
This is what I discovered.
Hope this helps others who might want to install the new part if changing a belt, a worn out idler pulley, or if adding a second idler pulley. I would definitely change out the old with the new – it is not that expensive (less than $25) from Brute Speed.
The end of original idler shaft that protrudes in the adjusting slot did not sit flush with the j bracket. In addition steel washers to hold the idler shaft in place were not thick enough. The largest thin washer would concave as the bolt is tightened down.
Why? Because there is a gap between the edge of the idler shaft, the thickness of the j bracket, and the flat washer (see pics in link). As a result the idler shaft can shift from side the side in the j bracket and/or shift fore and aft in the j bracket as the idler shaft pulley is pushed downward to tighten the belt.
Unfortunately the engineers at ATI did not address this issue with the new version. The idler shaft should to be longer so its end sits flush with the edge of the j bracket. It also needs to be thicker so it will not rock back and forth in the slot.
What they did change is the circumference of the shoulder on the idler shaft. The original idler shaft version has a very small shoulder on the pulley side of the shaft which also contributes to misalignment. The new version is much larger so it is less likely to shift as it is tightened to the j bracket (more surface area).
The 2.5 idler pulley has some offset (similar to the offset on our wheels on f bodies). Because of the offset the outer side of the pulley farthest from the j bracket has the most load on the bearings.
The new version of the idler shaft places the pulley on the shaft so the bearings in the pulley are on the outer most side of the pulley compared to the old version that is opposite.
When you install the idler pulley on the new version of the idler shaft the pulley is flipped inside to outside on the shaft. See pics.
IMO this design change should help to prolong bearing life as well belt wear on the outer edge of the bearing and the idler pulley. See pic of my original pulley and how it wore down because of improper alignment of the idler shaft and design of the idler shaft.
IMO the new design also reduces the tendency of the belt to walk to the outer edge of the pulley as it wears in.
Now for the adjustment for the idler pulley. Perhaps there are additional instructions explaining how to adjust the tightness of the idler pulley. If so they are not in my 2005 instruction manual.
What I found is this.
The largest flat washer on the idler shaft bolt is not thick enough. So replace the largest flat washer with a thicker washer. The thinner washer will concave into the idler shaft slot as it is tightened during final adjustment. A thicker washer will not. See pics.
Next and very important when tightening the idler shaft bolt. Do this before turning down the jack screw.
First tighten the bolt into the idler shaft enough so that the pulley and idler shaft is perfectly aligned on both sides of the j bracket. Tighten enough so the idler shaft does not shift in the slot but not so tight that the jack screw can’t force the idler pulley downward into the slot. The reason this step is important is because of loose tolerances between the idler shaft and the slot in the j bracket as explained earlier.
Because the shoulder of the idler shaft that rides on the pulley side of the j bracket is much larger than the original version, it’s much easier to get perfect alignment fore and aft as the jack screw is turned downward to tighten the belt.
I didn’t tighten the bolt on my first adjustment enough. As a result the pulley cocked in the slot causing the pulley to grind in the jack bracket – see pics. Thankfully I didn’t ruin an $80 idler pulley. There is a pic in the link showing the wear on the pulley due to misalignment of the idler shaft.
Now about the installation. Installing the DM Performance standoff. Do this first.
When removing the head unit from j bracket remove the largest bolt first holding the head unit on the j bracket. Do not remove the other 4 bolts yet.
Replace the bolt you removed with a 3/8 X 16 X 2 inch bolt with the hex head cut off. We'll call it an alignment stud. Screw it back into the head unit. Now remove the other bolts (4).
Doing so will make it much easier to remove the other bolts while at the same time holding the head unit in place so it doesn’t drop on you when you remove the remaining four bolts. This bolt will also make it easier when you install the head unit, so leave the bolt in when you reinstall the head unit. It’s simply amazing how much easier it is to remove and reinstall the head unit if you install this guide bolt.
The guide bolt also makes it easier to install the belt because it allows you to swing the head unit up and down to fit the belt into place on the head unit drive pully. My pulley is a 4.38.
Remove the j bracket then remove the lower standoff. Measure the remaining stud length. It must be at least 1 inch long but less than 1 ¼ inches. See pics.
Screw on the DM Performance standoff and tighten it.
Install the second idler pulley on to the DM Performance standoff. I used an ATI 2 ½ pulley which is the same pulley and size as the ATI tensioner pulley.
Install the washer on the standoff which is included with the DM Performance standoff.
Install the j bracket. Install and tighten all three bolts for the j bracket.
Slide the idler shaft to the top of the slot in the j bracket making sure to tighten as explained earlier.
Install the belt between the upper and lower pulley leaving enough length for the head unit drive pulley.
Install the head unit using the guide bolt to hold it in place. Shift the head unit up or down to place the loop of the belt unto the head unit drive pulley.
Next guide the belt unto the ATI crank drive pulley. I used a Gates K080427 Micro Groove Green Belt. My crank drive pulley is 7.65 inches. The head unit drive pulley is 4.38 inches.
The belt is tight when placing on the crank pulley but not so tight that you have to use a tool to guide it on. Install the remaining three head unit bolts along with the largest bolt after removing the guide bolt. Move the head unit up or down making it easier to get the belt onto the crank drive pulley. After the belt is installed on both pulley install the remaining three bolts attaching the head unit to the j bracket.
Next we will tighten the belt. Turn down the jack screw into the j bracket slot making sure as you turn it down that the upper tensioner pulley does not shift or clock in the slot so it rubs against the j bracket. If it is tight enough it will not shift.
After adjusting belt tension with my pulley combination, I still have about 5/8 inch of clearance between the upper tensioner pulley and the standoff pulley. There is still plenty of clearance left if the belt stretches and we have to adjust again. A two inch pulley provides even more clearance. I plan to make a 2 inch pulley. A 2 inch pulley allows us to install the 5th bolt attaching the head unit to the j bracket. A 2 1/2 inch pulley covers the hole for the 5th bolt so it can not be installed.
See pics for belt wrap.
Thanks to ChevyChad for the idea in the first place and also to DM Performance for mfg the standoff.
https://ls1tech.com/forums/forced-in...p-fbody-3.html
Lastly. I think it might be possible to drill out a hole on the j bracket so a fifth bolt can be used to clamp the head unit to the j bracket. If there is room to screw in the bolt, this bolt will be exactly 180 degrees opposite the single large bolt at the tip of the j bracket. Will post again if this will work.
See pic below.
https://www.flickr.com/photos/18359304@N07/35894968130/
I installed the DM Engineering standoff for the second idler pulley with a Procharger 2.5 idler pulley. The ATI crank drive pulley is 7.65 with 4.38 drive pulley on the D1 head unit.
This is thread is to show how easy it is to install the DM Performance standoff. But also to show what I found when Bob as Brute Speed sent me a new idler shaft for the j bracket tensioner pulley.
Pics explaining the installation for the standoff, and the comparison of the old and new idler shaft are in this link.
I don’t know when Procharger changed the design of the idler shaft.The newer design might only apply for those of us who still have the old version. My D1 kit was mfg around early 2005 just after ATI added the eight rib pulley to their kit for the f body.
This is what I discovered.
Hope this helps others who might want to install the new part if changing a belt, a worn out idler pulley, or if adding a second idler pulley. I would definitely change out the old with the new – it is not that expensive (less than $25) from Brute Speed.
The end of original idler shaft that protrudes in the adjusting slot did not sit flush with the j bracket. In addition steel washers to hold the idler shaft in place were not thick enough. The largest thin washer would concave as the bolt is tightened down.
Why? Because there is a gap between the edge of the idler shaft, the thickness of the j bracket, and the flat washer (see pics in link). As a result the idler shaft can shift from side the side in the j bracket and/or shift fore and aft in the j bracket as the idler shaft pulley is pushed downward to tighten the belt.
Unfortunately the engineers at ATI did not address this issue with the new version. The idler shaft should to be longer so its end sits flush with the edge of the j bracket. It also needs to be thicker so it will not rock back and forth in the slot.
What they did change is the circumference of the shoulder on the idler shaft. The original idler shaft version has a very small shoulder on the pulley side of the shaft which also contributes to misalignment. The new version is much larger so it is less likely to shift as it is tightened to the j bracket (more surface area).
The 2.5 idler pulley has some offset (similar to the offset on our wheels on f bodies). Because of the offset the outer side of the pulley farthest from the j bracket has the most load on the bearings.
The new version of the idler shaft places the pulley on the shaft so the bearings in the pulley are on the outer most side of the pulley compared to the old version that is opposite.
When you install the idler pulley on the new version of the idler shaft the pulley is flipped inside to outside on the shaft. See pics.
IMO this design change should help to prolong bearing life as well belt wear on the outer edge of the bearing and the idler pulley. See pic of my original pulley and how it wore down because of improper alignment of the idler shaft and design of the idler shaft.
IMO the new design also reduces the tendency of the belt to walk to the outer edge of the pulley as it wears in.
Now for the adjustment for the idler pulley. Perhaps there are additional instructions explaining how to adjust the tightness of the idler pulley. If so they are not in my 2005 instruction manual.
What I found is this.
The largest flat washer on the idler shaft bolt is not thick enough. So replace the largest flat washer with a thicker washer. The thinner washer will concave into the idler shaft slot as it is tightened during final adjustment. A thicker washer will not. See pics.
Next and very important when tightening the idler shaft bolt. Do this before turning down the jack screw.
First tighten the bolt into the idler shaft enough so that the pulley and idler shaft is perfectly aligned on both sides of the j bracket. Tighten enough so the idler shaft does not shift in the slot but not so tight that the jack screw can’t force the idler pulley downward into the slot. The reason this step is important is because of loose tolerances between the idler shaft and the slot in the j bracket as explained earlier.
Because the shoulder of the idler shaft that rides on the pulley side of the j bracket is much larger than the original version, it’s much easier to get perfect alignment fore and aft as the jack screw is turned downward to tighten the belt.
I didn’t tighten the bolt on my first adjustment enough. As a result the pulley cocked in the slot causing the pulley to grind in the jack bracket – see pics. Thankfully I didn’t ruin an $80 idler pulley. There is a pic in the link showing the wear on the pulley due to misalignment of the idler shaft.
Now about the installation. Installing the DM Performance standoff. Do this first.
When removing the head unit from j bracket remove the largest bolt first holding the head unit on the j bracket. Do not remove the other 4 bolts yet.
Replace the bolt you removed with a 3/8 X 16 X 2 inch bolt with the hex head cut off. We'll call it an alignment stud. Screw it back into the head unit. Now remove the other bolts (4).
Doing so will make it much easier to remove the other bolts while at the same time holding the head unit in place so it doesn’t drop on you when you remove the remaining four bolts. This bolt will also make it easier when you install the head unit, so leave the bolt in when you reinstall the head unit. It’s simply amazing how much easier it is to remove and reinstall the head unit if you install this guide bolt.
The guide bolt also makes it easier to install the belt because it allows you to swing the head unit up and down to fit the belt into place on the head unit drive pully. My pulley is a 4.38.
Remove the j bracket then remove the lower standoff. Measure the remaining stud length. It must be at least 1 inch long but less than 1 ¼ inches. See pics.
Screw on the DM Performance standoff and tighten it.
Install the second idler pulley on to the DM Performance standoff. I used an ATI 2 ½ pulley which is the same pulley and size as the ATI tensioner pulley.
Install the washer on the standoff which is included with the DM Performance standoff.
Install the j bracket. Install and tighten all three bolts for the j bracket.
Slide the idler shaft to the top of the slot in the j bracket making sure to tighten as explained earlier.
Install the belt between the upper and lower pulley leaving enough length for the head unit drive pulley.
Install the head unit using the guide bolt to hold it in place. Shift the head unit up or down to place the loop of the belt unto the head unit drive pulley.
Next guide the belt unto the ATI crank drive pulley. I used a Gates K080427 Micro Groove Green Belt. My crank drive pulley is 7.65 inches. The head unit drive pulley is 4.38 inches.
The belt is tight when placing on the crank pulley but not so tight that you have to use a tool to guide it on. Install the remaining three head unit bolts along with the largest bolt after removing the guide bolt. Move the head unit up or down making it easier to get the belt onto the crank drive pulley. After the belt is installed on both pulley install the remaining three bolts attaching the head unit to the j bracket.
Next we will tighten the belt. Turn down the jack screw into the j bracket slot making sure as you turn it down that the upper tensioner pulley does not shift or clock in the slot so it rubs against the j bracket. If it is tight enough it will not shift.
After adjusting belt tension with my pulley combination, I still have about 5/8 inch of clearance between the upper tensioner pulley and the standoff pulley. There is still plenty of clearance left if the belt stretches and we have to adjust again. A two inch pulley provides even more clearance. I plan to make a 2 inch pulley. A 2 inch pulley allows us to install the 5th bolt attaching the head unit to the j bracket. A 2 1/2 inch pulley covers the hole for the 5th bolt so it can not be installed.
See pics for belt wrap.
Thanks to ChevyChad for the idea in the first place and also to DM Performance for mfg the standoff.
https://ls1tech.com/forums/forced-in...p-fbody-3.html
Lastly. I think it might be possible to drill out a hole on the j bracket so a fifth bolt can be used to clamp the head unit to the j bracket. If there is room to screw in the bolt, this bolt will be exactly 180 degrees opposite the single large bolt at the tip of the j bracket. Will post again if this will work.
See pic below.
https://www.flickr.com/photos/18359304@N07/35894968130/
Last edited by dlandsvZ28; 12-27-2019 at 08:07 AM. Reason: edit content
08-06-2017, 10:23 PM
#3