Whipple Belt Chirping Explained and Corrected


eg1985

GT Owner
Jan 7, 2007
82
Fresno, CA
Recently I have been asked quite a bit about what the issue is with some of the Whipple S/C'd cars and the belt "chirping" and how was it that we were able to eliminate it. I will start by saying that it was not until we recently completed a Whipple install on a GTX1 and did some different things in relation to the drive and pulleys to accommodate the GTX1 hatch that I fully understood the dynamics at play and through a collective effort we worked out a solution.

To date, I have personally performed this procedure on close to a dozen GT's with a 100% success rate. Now, some of the cars we have seen that do not exhibit the belt "chirp" do have correctly adjusted sliding idlers, proper belt sizes for the S/C pulley used and all that we can attribute this to is that there must be some minor production variances within the cars that we have inspected. I would like to thank the guys at Whipple for all of their help and input as we worked this out.

For years, I was under the belief that the "chirping" sound was coming from the Whipple sliding idler pulley (bearings) or the belts themselves; I saw how some people either moved the sliding idler out all the way or just removed it all together in an effort to reduce or eliminate the noise and many times it worked but at the expense of belt slip at high RPM and boost levels. In the past, I have even changed many belts and idler pulleys in a effort to stop "chirping" only to have it typically return a short time later. The thing that did not make sense as we discussed this with the R&D dept. at Whipple was the fact that those same idlers were being used in many of their marine kits where belt speeds are often much higher than what we are dealing with on the FGT kit and those RPM's are being sustained for prolonged periods of time without any bearing failures. What we discovered on the problem cars as we looked closely into the issue was a slight misalignment between the S/C pulley and the 8-rib grooved idler at the front of the RH head; this alignment issue is further compounded by the fact that the belt is routed tightly through the two smooth idlers between these two pulleys (as it should be and needs to be); with this loop, it does not allow for the belt to run fore and aft; thereby creating a strong "bind" I'll call it, as the belt transitions from the sliding idler to the S/C pulley. We confirmed this in my shop with the help of a Gates Laser Alignment tool which proved to be an invaluable asset during this process. What this revealed was a mis-alignment of about .090-.100. With a .100 spacer between the S/C hub and pulley along with longer pulley bolts, we were able to achieve as a near perfect alignment as we were able to measure. We went one step further and carefully machined the pulley on the lathe at each end with a slight reveal to allow the belt to relax slightly on the shoulder; we did this to further quiet those belts that were cut with slight imperfections at the edges (a belt with anything more than a slight imperfection should be replaced). After inspecting many belts, I would add that those belts from Gates have been much nicer and given us virtually no trouble than the early supplied Bando brand belts; I would recommend changing over to the Gates belts if you have an older kit with the Bando belt.

Before you start the procedure, verify there is no issue with the supercharger itself and check the oil level in the front sight. We just performed this procedure on a car in the shop and I documented the procedure in an effort to provide some answers hopefully clear up some misconceptions.

Here are a couple examples of where the sliding idler was to start with on this car. This example is really not that bad but the belt wrap could be improved.
idlerstart.jpg


idlerstart2.jpg



At this point, loosen the S/C pulley bolts with a 5mm allen wrench.
pulleywrench.jpg



I've been asked what we use to tighten and adjust the sliding idler and here's one of our specially made "J-Tools"-nothing more than an extra long 3/8" allen wrench that has been shortened on the bent end and has a strategically placed bend to clear the rear glass. Works like a charm!
idlerwrench.jpg



With the sliding idler loosened and slid all way out, you can release tension on the belt and remove it from the S/C pulley.
idlerout.jpg



NOTE-Every effort should be made to closely inspect the belt too because a belt that exhibits edge damage like the example below will most likely continue to make noise even if the geometry issue is corrected. I recommend physically removing the belt and inspecting it closely, although, we have studied the belts as they run at idle under bright lights and by starting and stopping the engine at different points in an effort to look at every inch of the belt; it is more work to remove the belt; however, it may reveal minor defects that would not otherwise be detected with the belt still installed on the engine.
wornbelt.jpg



Here is a good example illustrating the forces at work, note how the forward facing edges of the grooves and shoulder clearly show a wear pattern in the anodized finish.
wornpulley.jpg



Now, notice how the rear facing edges do not exhibit the same wear pattern.
unwornpulley.jpg



A side-by-side example showing the pulley modification.
pulleys.jpg



The required parts include a .100 spacer, 4-16mm long bolts, and the specially machined pulley.
kit.jpg



Install the new pulley, placing the .100 spacer behind the pulley, using the 4 new 16mm long bolts. Tighten the bolts by hand with the 5mm allen wrench (you will do a final tighten once the belt is reinstalled).
newpulleysc.jpg



An additional step to insure complete alignment is to slide the idler up close to the S/C pulley and compare the distance between the front and rear edges of the S/C pulley to the smooth sliding idler. With the sliding idler up close to the S/C pulley, snug down the 3/8" bolt retaining the sliding idler and use a feeler gauge to measure the front and rear edge dimension; we typically like to get it around .004 or less. If this dimension is greater, it will be necessary to slightly loosen the set bolt on the collar around the drive snout and gently move the idler plate forward or rearward to achieve alignment. NOTE-This step is generally not required and extra care must taken so as not to damage the idler plate or the drive.
feelergauge.jpg



Next, reinstall or replace the belt, being careful to route and also adjust the 6-rib and O/P belt correctly (if they were removed).
With the tension released on the S/C belt, slide the idler up close to the S/C pulley as pictured and tighten the bolt. Check the clearance between the idler and the S/C pulley giving the maximum amount of belt wrap without "crashing" the two pulleys together.
wrenchidler.jpg



Here's a look at the sliding idler when properly adjusted.
adjidler.jpg



Lastly, do a final tightening of the 4 S/C pulley bolts with the 5mm allen wrench, then recheck all of the belts and fasteners once again and review everything prior to starting the engine. When the engine starts the "chirping" should finally be gone.
 

cobra498

GT Owner
Jul 14, 2010
310
Central Ca;ifornia
Great job explaining the technical side of belt chirp Evan, you are the only one I want working on my GT!
 

eg1985

GT Owner
Jan 7, 2007
82
Fresno, CA
Thanks Bruce!
 

Derry

GT Owner
Mark II Lifetime
Apr 5, 2006
345
buffalo, NY
Wow excellent post! Thanks. My chirp is only at idle as far as I can determine, is that something you have seen? It started 2500 miles after the whipple was put on.
 

eg1985

GT Owner
Jan 7, 2007
82
Fresno, CA
Yes actually, the majority of the instances I have seen and corrected typically manifest themselves at idle to lower RPM's
 

Derry

GT Owner
Mark II Lifetime
Apr 5, 2006
345
buffalo, NY
ok, thank you.
 

Shelby#18

GTX1 Owner/Moderator
Mark IV Lifetime
Le Mans 2010 Supporter
Dec 15, 2006
1,623
Nev./So. Cal./Minn.
Excellent post. I've had the same problem with my Whipple car.
 

RALPHIE

GT Owner
Mar 1, 2007
7,278
Perhaps this post should be repeated in the FAQ section, in order to be found easily in the future.
 

zrchris

GT Owner
Aug 12, 2009
116
Brentwood TN
I think it should be added for general reference that the "correct" position of the idler depends on your pulley size and belt length and should be set relative to the stock tensioner range of motion. Some say shoot for the middle of that range, certainly not good to bottom it out either way.

eg1985 - are you selling the spacer or is that a Whipple item? Do you believe this problem is the same on both the 3.4 and 4.0? Clearly Whipple needs to revise their components if this is true across the board.
 

2112

Blue/white 06'
Mark II Lifetime
eg1985 - are you selling the spacer or is that a Whipple item? Do you believe this problem is the same on both the 3.4 and 4.0? Clearly Whipple needs to revise their components if this is true across the board.

+1
 

Fubar

Totally ****** Up
Mark II Lifetime
Le Mans 2010 Supporter
Aug 2, 2006
3,979
Dallas, TX
Tremendous problem identification and solution explanation! Thank you for taking the time.
 

MoTeC Magic

Spectator
Aug 21, 2009
99
Dallas, TX
Good write up, thanks for sharing

Another contributing factor I have found is the idler pulley bolt flexing from too much tension in the belt. The idler pulley bolt is in single shear and can flex if too much force is placed onto the pulley. When the bolt would flex slightly it would "pitch" the idler pulley into a different plane (angle) than the SC drive pulley is on. This angle in the idler pulley would steer the belt a different direction, then requiring the drive pulley to bring it back into its proper placement creating the chirp in the process as the rubber is "scooted" back over. This explained to me why backing off the idler, effectively releasing tension and therefore the bolt flex, helped to eliminate the chirp.

Cheers
 

eg1985

GT Owner
Jan 7, 2007
82
Fresno, CA
I think it should be added for general reference that the "correct" position of the idler depends on your pulley size and belt length and should be set relative to the stock tensioner range of motion. Some say shoot for the middle of that range, certainly not good to bottom it out either way.

eg1985 - are you selling the spacer or is that a Whipple item? Do you believe this problem is the same on both the 3.4 and 4.0? Clearly Whipple needs to revise their components if this is true across the board.

With the correct length belt installed you will want the sliding idler adjusted up relatively close to the S/C pulley just as I have illustrated. This will give you maximum belt wrap. When properly adjusted, the tensioner will be nearly fully loaded, meaning there is very little in the way of off-tension motion. Think in terms of the forces at play on the belt; it will not tend to shrink in length from it's static adjustment but rather it will grow as RPM's and associated forces increase; in this way the tensioner will compensate for this just as intended.

I do have the spacers and can sell you one or Whipple can too. I have performed this on the 3.3/4 & 4.0 kits as well all with complete success. As I noted; however, we have seen some cars that were properly adjusted and do not exhibit the "chirp" so I tend to take it on a case-by-case basis at this point. I do believe the current kits shipping from Whipple have these changes implemented as a result of our collaboration over the last few months.
 

eg1985

GT Owner
Jan 7, 2007
82
Fresno, CA
Good write up, thanks for sharing

Another contributing factor I have found is the idler pulley bolt flexing from too much tension in the belt. The idler pulley bolt is in single shear and can flex if too much force is placed onto the pulley. When the bolt would flex slightly it would "pitch" the idler pulley into a different plane (angle) than the SC drive pulley is on. This angle in the idler pulley would steer the belt a different direction, then requiring the drive pulley to bring it back into its proper placement creating the chirp in the process as the rubber is "scooted" back over. This explained to me why backing off the idler, effectively releasing tension and therefore the bolt flex, helped to eliminate the chirp.

Cheers

That is an interesting point; we have closely studied the idler bolt during our many dyno pulls and I have not noted any flex in either the bolt or the front plate; not saying it couldn't happen, I just have not personally identified an issue there. We have seen several idlers that were not parallel with the S/C pulley which obviously contribute to the problem and that is why I always check and adjust (if needed) that clearance in the front plate; it is crucial that the idler be in perfect alignment. :thumbsup
 

Slow Poke

GT Owner
Jul 13, 2009
32
Bay Area
I had a very bad belt chirp. Evan Guyett fixed the problem perfectly. Smooth running and no noise.