Tensioner Pulley problem L59 swap

[90gmcsierraL59]

I misdiagnosed what I thought was an imminent 33 year old AC compressor failure on the 90 GMC that just got the L59 4L60E swap a little over 3000 miles ago. I was hearing a groaning noise at idle that only happened when the AC compressor was engaged. Cut the AC off and all was quiet. I bought a reman AC Delco OEM compressor and dropped the truck off to have it changed. My good friend who owns the shop called me and said the tensioner pulley on the newly installed Dirty Dingo AC bracket was very close to failure as the noise was still there after he swapped in the new compressor. A close inspection detected slop in the pulley with the bolt tight indicating a bad bearing. He put a new tensioner pulley on and all is well.( I am most certainly not blaming Dirty Dingo or calling them out as the bracket and assembly is a work of art) It says right on thier website that they use Gates pulleys exclusively and any company can get a bad pulley or bearing from a supplier due to a defect. That being said to the best of my knowledge that's the 1st failure I can ever remember having of a Gates part. I don't feel a bit bad about changing the original compressor either as it is 33 years old with over 250K on it. I am thankful it didn't fail at speed and tear up a bunch of other stuff.

 

[Komet]

I had a bad tensioner pulley bearing on my L98. I didn't want a replacement because they weren't shaped the same, so I pressed out the bearing with my m18 shop press system:

You must be registered for see images attach

Found a replacement bearing on ebay for like $7, pressed it back in, works great.

 

[GoToGuy]

Unfortunately you fell into a common trap. With belts and pulleys.

 

[90gmcsierraL59]

The conundrum continues. We had a couple days in the 70s last week and I used the AC. Groaning noise at idle was back. Inspection with it running revealed the belt flopping up and down at the tensioner at idle. Turn off AC and the groaning noise and flopping stops. More thorough inspection revealed belt stretched and the distance between the idler pulley and adjacent tensioner pulley is considerably less than the two inches specified by Dirty Dingo in the installation instructions. The belt in question is a Gates K061120 which has a usable length of 112.37 inches or 2845 MM. It has stretched what looks to be roughly 1/2 inch in 8500 miles. So I went to O' Reilly's and bought a K061120 and a K06115. The K06115 has an effective length of 111.29 inches or 2827 MM or .070 inches shorter. I figured the K06115 would be a tight fit but would stretch to the correct spacing in short order. After 1.5 hours of cussing and straining including idler pulley removal in hopes I could press it diwn enough to get the belt on and restart the attach bolt no joy. The K06115 is about 1/8 inch too short to go on. I took a tie down strap and tied the tensioner down so I could use both hands and still no joy. Put the new K061120 on and it went on. It yielded about 1 3/4 of an inch of distance between the tensioner and idler pulley as installed and there is no groaning noise or flopping at idle with the AC on. After the 61 mile ride to work I checked it and noted no visible stretch and the AC is quiet. By the way I checked all the pulleys and all are good. No slop no noises. Even further research revealed Gates has a high performance line of belts called Gates RPM. Lo and behold they make a K061119 RPM with an effective length of 111.93 inches or 2843 MM for the low low price of ....$144.99, which ironically is likely exactly the one I need. I have to ponder that some. It only takes a couple minutes and $40 to put on another regular K061120....

 

[90gmcsierraL59]

I did more research and figured out the idler pulley by the alternator crosses to a Dayco 89006 which has an OD of 90 MM or 3.54 inches, a width of 30MM or 1.18 inches and a bearing ID of 17MM or .66 inches.
I downloaded the Dayco pulley guide PDF and found that a Dayco 89055 is 100 MM OD or 3.9 inches with all the other dimensions being identical to the 89006. It is in stock at my local Advance Auto Parts for $34.99. I am going to give that a try and see if I can get the K061120 on with that pulley.

You must be registered for see images attach

 

[90gmcsierraL59]

A valiant effort was made but the 100 MM Dayco pulley even with a swapped bearing had slop in it brand new out of the box. Damn shame too as it gave me the 2 inch dimension specified in the Dirty Dingo instructions. So we put the 90 MM Chevrolet pulley back on. I will be contacting Dirty Dingo to see if the might have a solution. I can live with it as is and carry a spare belt. I was hoping for better though.

 

[90gmcsierraL59]

I spent about two hours of my life that I will never get back talking and texting with Dirty Dingo today. I explained the issues to the tech guy and he said the shorter belt K061115 will fit if the K061120 won't. ( it doesn't) He also said tensioner pulleys are a non-replaceable item that I needed to order a new tensioner. I pressed him further and he said that though it is a Gates tensioner that he could not provide a Gates part number for the tensioner assembly or the pulley. I texted my friend who replaced the defective tensioner pulley way back when this debacle began with a tensioner pulley off of a 94 Jeep Wrangler with a 2.5 liter engine (Gates 38042). I told the tech guy what the part number was in case someone else is having the same issues as me. Back to square 1 living with it. That being said it is certainly usable as is. I was just hoping for better.
A random search of the internet for LS swap ac brackets yielded this one:

You must be registered for see images attach

It looks like I can simply remove the ridged idler above the tensioner and try a shorter belt. It will only take a few minutes to give it a try...