STAEGER TENSIOMETER - RIFLEDRIVER!!

If one belt is "flapping about", be sure to check the lower pulley bearing of that side for play after you took the belt off, as I have seen them being bad on all F-cars that have this system. It seems the left ones (when viewed from the front of the engine) go more often than right. Unless the tensioner bearing is bad, it is unlikely that this difference in belt tension occurred for any other reason than that timing gear bearing going bad.

Do a search for "timing gear bearings" on this site for info on how to fix this. Not easy but very doable if you have the correct puller.

What mileage is on the car?

 

It may well be OK if there is no noticable play, but keep a close eye on it. Maybe the previous guy doing the belt change skipped the step of rotating the engine before final tightening of the belts.
If those bearings go bad they can be quite audible before they actually fail, in bad cases even from inside the car when running if you know what to listen for. If you have the engine together you might consider to start it before you have all the belt covers on; with a stethoscope or long rod to your ear you can then listen whether the bearings are silent or not.

Good luck with the tension measurement - that step is mostly for a final check to assess whether all is well. If your belt tensioners are good and you ran the procedure correctly no further adjustment should be needed. I have used a clipped on magnetic paperclip and a coil with an oscilloscope on 360s belts, to see the belt frequency when struck lightly. Never used this technique on the 456 though - but might be soon as I am in the process of changing them on mine. I just have to see if those values are obtainable. If not, I'll just trust my own judgement...

 

Pay close attention to the tension. The 456 / 550 / 575 models have a tendency to over tighten the belts if set by the spring loaded tensioner itself.

 

Good to know Dave, I will pay close attention to that. I assume that is one reason for the timing gear bearings to fail.

 

Jeremy- I believe the Staeger tensiometer is reading frequency so the 135 is Hertz (Hz) rather than strand strength in N or lb ft. When you whack the belt with a tool and measure tension, you are actually measuring the resonant frequency, which varies with tension.

That technique has been in use since before WW-II, when resonant frequency was used as a measure of stiffness in aircraft structures.

Taz
Terry Phillips

 

You're probably correct Terry, although I wonder since the Staeger seems to be of different construction than most current tensiometers. Maybe it is a different kind of animal and it measures a different value. I think the belts on the 360 were something like 140 Hz for the cambelts and 90-100 or so for the alternator so 135 Hertz does not sound odd to me.

 

If the previous mechanic was a j*ck*ss then he probably also did not replace the valve cover gaskets or O-rings. Mind you to fix the latter properly you will need to take the cams out. Maybe do this "while you're at it"?
There must be a way to convert that tensiometer that you have to the Staeger values - only question is how... ;-)

 

A number of years back I had to re-do a belt change on a 575 done by another. After 300 miles the covers and front of the engine were full of rubber dust. I can remember doing a good deal of research to understand what was happening and what the cause was. I took both Staegar readings as well as Hz measurements using various tensioning techniques and read the results both hot and cold over the course of a week plus, read, an expensive education! Since that time I have found the same on a number of occations with the late front engine 12's. Find a tension you are comfortable with and monitor the front covers for rubber dust or slap.

Taz,

Keep your brake thread updated, I find that very interesting. Brake technology moves so quickly these days it is hard to keep a finger on and your approach to this with both eye's wide open is quite refreshing. This is the one single area I feel Ferrari dropped the ball on this model, there is a lot to learn there. Thank you for that!

 

The formula for tension (N) in Newtons is N=belt mass(kg/m) x (length of span(m))² x (frequency)². Pretty worthless right now, but if we get the belt mass for the Dayton belts, we can measure the span and make a table of values.

Dave- The CCM brakes are nearly 20 year old technology and there had to be better stuff out there. My company made mirrors for high power laser applications out of pure carbon carbon (no coating, just polished CC) that were amazingly light and resistant to huge heat loads. Carbon ceramic and matrix technology has advanced a lot in those 20 years. The Mov'it rotors are carbon silicon carbide through-out. The CCM brakes are not. Hopefully we will see a longer life span. Not sure what the Gen 2 CCMs are like (fitted to the GTO), but hopefully better than Gen 1 and less expensive.

If CCMs are a $10K Corvette and Porsche option, you know there is a possibility of bringing in later versions for lower cost.

Right now, though, the Mov'its are not much less expensive than CCMs, just better quality and longer life.

Taz
Terry Phillips

 

Not the right place to discuss it but... I have watched the price of the Carbon components drop very fast over the last few years.

While not in the Vintage spirit, I am now looking at some of these to retrofit to the old race cars. My V8 Lotus 19 and the BBC CanAm cars use non vented rotors the size of a Pinto and the wheels used limit the size. The CSC design is starting to look like the answer to this problem with the next question being how to retain grease in the wheel bearings after a series of hard laps. As both cars have a significant history I also have to find a way to make this look 50 years old...

I will continue to watch your thread on that with great interest.

 

Dave- Mov'It will make custom rotors and pads for existing calipers, so it is definitely worth checking. There has been a bit of progress in wheel bearings, too. Somebody must make a more modern, sealed bearing in the appropriate sizes or one that could be adapted with little effort.

Taz
Terry Phillips

 

One gallon jug of my homebrew is guaranteed to age anything...lol

Though wheel bearing tech has improved for both metal and ceramic it is always sizing that can be the biggest problem.

Also a major improvement in lubrication tech also.

The brakes we used on the 917,935,956/962 panzers? Geeez, I see bigger on most street cars today. The only limiting factors for race cars are sanctioning rules for wheel diameters....for street there seems to be no limit except for how much wheel/tire combo I can stuff into the fender opening.

If I can get the brakes to live for 24hrs in a 917 using old tech there is absolutely no reason I can't stop a vintage race car using the newer tech of the same size.

With heat dissapation tech moving forward the right combo of rotor composition,hat material and coatings,hub coatings,drive pin material, and caliper construction(titanium pucs') and coatings, plus vastly improved wheel bearings and lubrication, I don't see any problem at this point.

Rotor and pad swapping using existing hats,hubs, and calipers is what I've dreamed of for many many years. Seeing the high rate of replacement for CC systems was for me out of the question due to economics, but this newer
CSC tech will in the very future produce competition and the price will start to come down to a level that is affordable.

 

Hey folks, just to clarify, there is a difference between the oscillating displacement, vibrational frequency of a flexible element ----- like a guitar string (or, in this case, a cam belt)........and the fundamental natural frequency of a rigid structural element, which relates to its elastic stiffness ---- like a bar of steel or a supporting structure (aircraft frame / car uni-body).

The "gauges" used for measuring belt tension (as a frequency) are detecting the oscillating vibrational frequency of the belt when it is "strummed", if you will. There are (2) basic types --- one is effectively a microphone / force transducer which picks up the induced acoustic disturbance and identifies its frequency of vibration (in Hertz). The second type is essentially a "tuning fork in reverse", which is used to absorb the belt vibration, transmit that energy to its own vibration, and convert it to an electrical signal analog which identifies the frequency (in Hertz).

Both types work equally well --- provided they are precision-made versions of their respective instruments.

The tension specification of [135 Hz] refers to the belt's "tone" when it is thwapped / strummed ---- and not to its stiffness (as a flexible element, it has next to none --- no matter how tight you tension it ). A string vibration of 135 Hz is actually quite low --- in acoustical / musical terms, you are still producing tones near the "bass" ranges .

By contrast, a structural element with a fundamental stiffness frequency of 135 Hz is actually very, very stiff. As an example, the typical frequency range for "space-junk" being strapped to a rocket for launch purposes is 60-110 Hz --- aircraft structures and car frames are generally less than that.

 

This type of instrument is neither. It is simply a static force vs. displacement / deflection gauge --- intended to make tension measurements when they are specified in terms of either tensile load or lateral load (whether it be in [lbs], [N], [daN], etc).

As a rule, the method of establishing belt tension according to, and by measuring, its "frequency" is far more precise than the load / deflection method.

 

David- I did not remember which gauge the Staeger was, a frequency measurer or a displacement vs force (N, lb, etc) measurer, just what is used now. The frequency measurer has obviously moved to the forefront because it is more precise. Finding a conversion table was difficult, because it differed for every application depending on belt and span. Since those are fixed for each Ferrari application, it probably would be possible to build a conversion table over the small range of acceptable values.

Affirmative on the difference between tension and stiffness, only the basic physics of a resonant frequency for both applications apply. If you look at something like an Atlas III pressure stabilized/stiffened launch vehicle, you can pat the side of it with your hand and watch ripples run the entire length of the launch vehicle and return. More like a dirigible than a zeppelin and definitely different from belt tension.

Taz
Terry Phillips

 

Cheers Terry ---

For sure, the skins, shells, and fairings of launch vehicles are indeed "balloon-like" But, I am referring to the stiffness of the "stuff" we mount inside / on top of them

Generating tables would be a good approach, as the proper mathematical expressions for converting beam deflection type parameters to stiffness frequencies are solved through a series of differential equations to include all the higher order effects. However, unique tables would have to be generated for each belt material / construction / geometry being used ---- and, although I am retired, I still don't have that amount of free time --- so, I ain't gonna do it -- LOL

All the "back-of-the-envelope" conversion formulae are merely first order approximations. So, I don't recommend using them if accuracy is of high importance. For the tension of a cam belt on a 456, I don't have any idea what amount of margin is allowable, so I would defer to someone else's judgment on that.

I do think it's prudent to use a frequency spec when it's been provided and available --- and to use a frequency measurement instrument, though ---- rather than to attempt an approximation of another sort or conversion to another type of measurement.

....just my $0.020 (0.013 GBP)..........that was supposed to be funny....

 

David- I was in the UK being paid in dollars when the GPB hit $2.48 in the early 80s. Much better now.

Taz
Terry Phillips

 

Terry, I look at the Staeger tensiometer picture in WSM, it has a dial, it is not measuring in N or ft ?.
Sark

 

Sark ---

I suspect it measures deflection [likely in arbitrary scalar units] corresponding with a pre-loaded, spring detent in the gauge to apply a fixed load (lateral) --- the same scheme used by the old-school "cricket" gauges from Gates.

 

Doh !!!

Jeremy ----

Please excuse my digressions ....back to some (hopefully) helpful info for your situation I would try contacting the belt manufacturer (Gates, DayCo, TRW, whomever) ---- I guarantee they have the computed equivalent specs for measuring the belt tension with other methods and using the gauges you have at your disposal.

However, you may have to sweet-talk one of the Engineers into giving you the data, because both the belt manufacturers and the auto makers are really pushing the frequency spec / measurement these days (even the belts on my daily-driver Mitsubishi truck are specified in frequencies) to become the new standard for belt tensioning. The downside to that is it takes the job away from the scope of many of the small shops / DIY'ers, but the upside is that it is a much, much more accurate method to set the tension --- so, belt life increases, and failure rates decrease

 

Do you know anything about the "natural frequency" of a car frame and its relationship to the mathematical proper wheel rate when trying to find out a good starting place for spring selection and the relationship of the wheel rate to the spring rate of the tires? It is a new topic for me I'm trying to get my head wrapped around.

 

The Staeger was a deflection gauge. I was fortunate many years ago when I ordered the checking standard for the Staeger gauge.... opened the box to find a whole new gauge and standard. I obtained my frequency measurer in a cash deal stuck over lunch in the Ferrari caffiteria when I was there for 360 training.

Part of the work we did after finding the rubber fluff in the engine bay was to start a log attempting to identify a ferquency conversion to the deflection readings given by the Staeger. In this case repeatability is difficult and the process will take many examples tested many times before I am comfortable with the results being conclusive. There are just too many variables involved for it to be obvious but we have a good start at this point.