Metco idler broke. Pics inside

[Tob]

If you could rule out any sort of installer error for a moment and consider the dynamic loads applied via the factory tensioner are not linear I could absolutely see a condition of a peak force or load exceeding that of the design threshold. There is quite a bit of offset/cantilever where the force vector is directed relative to the bolt/standoff location. I'm still digging to see if I can find how powerful any of those spikes may be in systems with similar designs. Witness 500Matt's comment that "Kent at Evo Performance says he has seen it 3 times. Each time the car has been road raced on a track."

Something is happening under extreme conditions that doesn't sit well with this specific bracket. But there are so many other unknowns or variables that I agree with you. More data/analysis is needed. Or a design change. Note - I didn't get above 200lbs with respect to Von Mises. I'm going to go back now and try 300+ and see how it looks.

If I had this version of that idler and I pushed the car at the appropriate venues I'd definitely be taking a closer look at the areas shown.

 

[Robert M]

Over the past 10 years we have sold thousands of Metco idlers and this is the first and only failure I've seen.
Rick, Christy and Aaron at metco are the BEST and stand behind their product.

No need to reinvent the wheel over 1 failure. Call them, get it replaced and enjoy the car!

Glad your happy!

Jay

Jay - That has been where my questions and comments have been aimed.............How many failures have there been with this design?? I have not heard of any except this one, and I'm sure there are plenty of them out there from the multiple design changes, in many different configurations both belts and pulley's, balancers etc.




R

 

[BROK3N-SVT]

The 84" Blue will be a perfect fit for this application.

I'm going to see how this one fits when it gets here on Monday and then I will get ahold of you if I'm not happy with it. 84" is what I want with a 2.4 and the idler then?

 

[Van@RevanRacing]

I'm going to see how this one fits when it gets here on Monday and then I will get ahold of you if I'm not happy with it. 84" is what I want with a 2.4 and the idler then?

Yes sir. 84" with that set up.

 

[Tob]

I ran some more SimulationXpress Von Mises numbers. I know this isn't ideal and welcome commentary from trained eyes. I started at 300lbf and went up in 100lbf increments.

300lbf was at 19,831psi
400lbf was at 26,441psi
500lbf was at 33,051psi
600lbf was at 39,662psi

Note at 600 I'm barely above a factor of safety of 1 so I went to 605lbf...

605 was at 39,992psi

If you compare the numbers, it looks as though each 100lbf increment added ~7,000psi.

Unless I'm off, at 300 lbs of tension (a new belt for example) you could be seeing a 600 pound force, as pointed out earlier. The Von Mises shows that at 605lbf you've exceeded the Yield Strength of 6061-T6. Again, Xpress is fairly basic and I'm far from being well versed in this realm. Serpent, I'll try Solidworks Professional simulation and see if I get anywhere.

 

[Robert M]

When I received my car back from the Shelby Mod Shop there was an idler in the box with my take-off parts. A KB 2.8 was installed, what idler was changed and what was it changed to? Apparently there is an idler that needs to be changed with the 2.8 KB install...........but I'm not sure which one it was...........or why it needed to be changed? The car only had 8 original miles on it so it was not that I had a bad idler.



R

 

[BROK3N-SVT]

It is probably one of the stock idlers and swapped out with a bigger one. It's just to compensate for the smaller SC pulley and stock belt. This is the same concept, but just adding an extra idler to the system to take up the slack.

 

[Robert M]

It is probably one of the stock idlers and swapped out with a bigger one. It's just to compensate for the smaller SC pulley and stock belt. This is the same concept, but just adding an extra idler to the system to take up the slack.

I forgot about that, they also sent back my original length belt with the take-off parts.


R

 

[Tob]

Another consideration (in addition to any shock loading, etc) beyond fatigue is the effect of elevated temperatures on the 6061-T6 aluminum. I spent some time going through the ASM Metals Handbook (if you are into really dry technical reading, have at it) and found some interesting data. When temps hit 300+ degrees the yield strength of this alloy nosedives...

I found mention on a PracticalMachinist forum that "another reference (CINDAS-Purdue Structural Alloys Handbook 1996), for 1/2-hour exposure at 400 degF, the strength is reduced about 25%." I'll take a closer look at my own engine with an IR gun to see hot it gets in that area on well warmed engine.

 

[Robert M]

Below is linked the Metco site info. on the importance of serpentine belt tension in the S/C application(s)............

http://www.metcomotorsports.com/proper_supercharger_belt_tensioning.asp



R

 

[Thump_rrr]

View attachment 18691I still can;t remember which brand my guy recommended, but here's a pic.

That is the Thump_RRR Racing PM-2005-GT500 billet tensioner.
This is the same tensioner supplied to Ford for the Cobrajet program minus the Ford Racing logo.

We have done extensive testing on tensioners, idlers and brackets.

The greatest amount of force is being exerted when you lift off the throttle during a shift.
That is the moment when belts, tensioners, and idlers snap.

We sent 2 tensioners to Ford for a couple of engine test mules a few years ago before being asked to provide the tensioners for the Cobrajet program.
Neither tensioner failed.

 

[Tob]

Thanks for chiming in. I'd have to dig to find it but a member here was talking about trying to use one of the new Gates Blue belts as he and a few CJ owners have been snapping blower belts. I had never heard of it. Is that anything you can elaborate on? In addition, does the spring in your tensioner impart more pressure than the stock one does or is the spring rate the same as stock?



On Edit, found it...

I know myself and several of the cobra jet racers in renegade are breaking belts pretty regular. Anytime I rattle the tires hard or spin it usually pops one. I will be glad to put one these new belts to the test.

I think what is happening the tensioner "thump R'', goes to bouncing back and forth hard and snaps the belt. Myself and the 3 JLP cars have had this problem.. we also run the big KB blower unlike other cobra jets. If this one breaks it will be like ripping a 100 dollar bill in half, lol

From here.

 

[HooperWest]

Just buy the VMP idler that replaces the stock one

+1

…and a THUMP tensioner.

Metco: No thanks.

 

[HooperWest]

The idea is to spread the load imparted from under the head of the bolt when torqued properly. That washer, regardless of type, doesn't have the necessary surface area. I'm not correlating or attributing this to the failure seen here, just making mention of it from the perspective of a properly designed fastening system (bolt, washer, torque figure, surface area, etc).

It can't be a general purpose washer - that would a big fail. Something along the lines of this style washer would have been far more appropriate with the design they created...

The washer I see in the OP's photos is akin to the chair seen here...

Lmao!

 

[Robert M]

+1

…and a THUMP tensioner.

Metco: No thanks.

I went to the Thump site and they do have some nice pieces. Which Thump idler serves the same purpose of belt wrap around the S/C pulley? I didn't see one with the bracket that would bolt in this area like we see with the Metco shown previously and would serve that purpose.



R

 

[Tob]

I see various tensioners, idler pulleys, grooved pulleys, blower pulleys, and accessories, but I don't see an idler pulley and bracket on Thump's site that fits in the same location as the Metco piece on these pages.

I'd still like to know if the Thump RRR tensioner for GT500 applications uses a spring in it that matches the stock spring in terms of rate. Peter?