Measuring belt tension in frequency Hz. The new and accurate DIY way?

[bebbetufs]

I just came across this article on how Ducati has begun to specify belt tension in Hz
Also take a look at this professional frequency based tension meeter.
The Hz can be easily measured by "plucking" the belt and recording the sound with a cheap microphone and a shareware computer program like GoldwWave.

It would be nice to somehow adapt this to the 944. It could end the "belt fear" and discussions once and for all.

The challenge is to convert the specified tension into hertz.
One way would be to measure a properly tensioned belt new and used belt.

It would probably be more accurate to calculate the frequency. One would need to know:
1. The belt density
2. The length of the vibrating section
3. The required tension

Here is a link to the manual of a professional tension meeter.
It includes instructions on how to determine belt density to calculate frequency. A little bit too complicated for me, but perhaps someone can make sense of it.

Another possible problem is that the plastic cover might interfere with the belt, stopping it from vibrating freely enough to take a proper measurement.

Any thoughts on this?

Example of a belt measurement in GoldWave linked from the first site.

[Techno Duck]

Originally Posted by bebbetufs

It could end the "belt fear" and discussions once and for all.

Any thoughts on this?

I really do not understand the fear timing belts on these cars. Practically every single engine on the road today is of an interference design. The only difference is these cars have much longer service intervals between retension and replacements or use a timing chain which will probably last longer than the chassis of the car. Tensioning the timing belt is not rocket science. All that one needs to do is follow the retension and replacement intervals. For those who do not have the tools, time or skill to do belt jobs themselves, yes..it sucks having to pay someone to do it for you every 35-40k miles, but if you cant hack it, then find another car to own. I dont buy the 'its a Porsche, deal with it' line many people say. Its a car and if you cant handle the maintenance intervals on it, find something else to drive.

Warning; i am going to start ranting here. I respect anyone willing to do the belt job themselves, but if you honestly cant hack the extra money to pick up one of the 2 tensioning tools available maybe you should have bought a car with a serpentine belt. The 9201 or Bruce Arnn's 920x at practically 1/4 the price of a used 9201 would eliminate many of the 'oh jeez how do i know the tension is right by twisting, pushing, measuring deflection, how do i use this $10 Kriket tool' questions.

My thoughts on this new method, more trouble than its worth. The 920x from Bruce Arnn is pretty much fool proof with his directions. I have personally tested the factory 9201 vs the beta test version of the 920x and can tell you you will actually get FAR more consistent results with the 920x and with that said, the 920x will tension the belt correctly when rechecked with the 9201. The 9201 is in my opinion difficult to use with cars that still run the belt covers and i usually can not get consistent results with it. The 920x works fine and even allows real time adjustment.. no needing to spin the crank over by hand to check tension again with the 9201. This tool last i checked was about $150. If the home mechanics who can do the belts themselves cant afford this one tool that will save you having to cringe every time you start your engine for fear of your belt snapping, again, maybe you should buy another car. Whats $150 to 40k miles of not having to worry about your belt snapping?

Under all the *****ing above, what i am trying to get at is the timing belt thing on these cars is so blown out of proportion on the forums. Anyone who reads the horror stories of a broken timing belt should be asking themselves these questions.

How many miles were the belt and how old was it?
How many miles were on the waterpump?
How many miles were on the rollers?
How bad were the oil leaks from the front of the engine?
Was the tension checked at 1k, 15k, 30k intervals? (or whatever schedule you follow.. i personally retension at 1k, 15k and replace at 30k)
Who did the work and what tool did they use to check tension?

I bet asking any of these questions will be answered with a 'Well..' . Sure, freak things to occur on properly maintained cars (944 or not) sometimes. But this belt fear is unfounded i think.

[bebbetufs]

I do partially agree with you that $150 is not a lot for the tool, but the fact remains that many people would rather spend the money on performance upgrades or a resealed steering rack, and so these questions continue to surface. I for one will easily admit to being a cheapskate when it comes to buying specialty tools. That does not mean I should sell my car and by a Daicia Sandero. I frequently end up spending more time fabricating stuff then it would take to earn the money to buy it, but I enjoy it. To me finding alternative solutions are part of the fun, if they are cheap and easy all the better.
I still hope this will interest someone to have a crack at it. Who knows, we might be able to build a frequency library and eventually learn to predict belt failure by frequency

[SolReaver]

Well first to answer the question. Yes, you CAN adjust tension by sound. I do it all the time when I tune my guitar. Yes, the 944 belts have a distinctive tone when they are properly tensioned and the proper tool to interpret this sound is located on either side of ones head...they are called ears. Even better than those neat acoustic sensors are these things for working on cars...called HANDS. At the side of each hand is an opposable digit called a THUMB. ( not going to fast for ya am I?)

YES the whole tension thing is over rated. Adjust it to just below whine when cold and there ya have it. re tension at 1K, check (inspect everything, not just the belts) at 15K and replace at 30K or 3 years whichever comes first. Replace rollers after two belt changes or when the go bad. Replace seals when they leak. Replace Water pumps at 60K to 90K, depending on your budget and how lucky you feel. Are we done here?

[speedracing944]

If I had the proper sound recording equipment I would be able to get your required Hz range for properly tensioned belts. I am doing somebody's belts next Saturday with my P9201.

I think anybody interested in the 944 series cars and willing to work on the car should just purchase a P9201 or a Arnn Works P920X.

Recover the cost of the tool when you sell the car.

Speedy

[fmartenies]

Porsche is not the only vehicle where owners fret over the timing belts...find any older vehicle with a dedicated following and you will find the same concerns, superstitions, etc. on their forums. Its not rocket science, the belt needs to be tight enough to stay on and run the accessories without being too tight to prematurely wear or stress the accessories. Find that range through educated trial and error and check periodically to make sure it is in spec. Over time you will get better at it where you know its right by feel and more comfortable where you don't check it outside of the regular schedule. The tool just gets you there faster, and IMO possibly gives you a false sense of security depending on how much credit you give it.

You guys act like you are 14 years old and the timing belt is a hot girl. Your engine won't shatter on impact unless you are so far out of spec range that you probably should just not work on this car anymore.

[speedracing944]

Originally Posted by fmartenies

... Find that range through educated trial and error and check periodically to make sure it is in spec.

Trial. A tryout or experiment to test quality, value, or usefulness.

Error. An act that through ignorance, deficiency, or accident departs from or fails to achieve what should be done.

I don't think people have an issue with the trial but might have an issue with error and the results it causes.

Our Porsches are not rocket ships but most people want to avoid trashed valves and the proceeding head rebuild which comes from under tensioning. They also want to avoid premature wear on bearings and components due to over tightening.

Speedy

[fmartenies]

Errors are qualitative, not pass fail. Your error could be that the RESULTS you are looking for are less ideal than the week prior's check. Error doesn't necessarily mean you made piston and valve babies.

My two cents is that everyone wants security in a tool, etc. Think of all the variables involved. Belt age, quality, materials. Heat. Driving Style. Wear and tear on the sprockets, etc. Barometric pressure and altitude (don't laugh, thats a major variabel in carb tuning.)

If you focus on one variable, belt tension, and are putting all your faith in a tool that sounds like it can give differing results by user, you are asking for trouble. Making the method more important than the results. Now the veterans I am sure are somewhere in the middle, using the tool to augment the results they are observing. But the number of people who come in with limited mechanical knowledge and are over their heads (until they get in and learn) far outnumber the veterans out there.

[speedracing944]

We can take the definition of error "departs from or fails to achieve what should be done" and apply it to belt tensioning. There is a proper tension range which has been established by Porsche to ensure longevity and reliability. Too loose of tension will result in skipped teeth and resulting valve damage. Too tight will result in excessive and accelerated wear on bearings and components. Porsche determined the proper range that they would sign off on for new engine building and dealership maintenance.

I would argue that errors can also be quantitative as in it is a quantitative error when under tensioned belts cause skipped teeth and damaged valves. That surely is quantitative.

I can get very repeatable results using my P9201 within +/- 0.1 on the gauge. I take 5 readings each time I check to ensure I get a good sample set. Anytime I do somebody's belts I have the owner over my shoulder to observe the results and am always willing to let them check tension themselves.

The results are #1. The method is the way to ensure you get the desired results without "errors".

My $0.03

Speedy

[Roman944]

I think that with internet and such, for many people it will be fairly easy to find someone in the area that's local and can help you out "hands on" when time comes to do any kind of maintenance on these cars

with that said, I think that if you have questions or doubts, why not hop on here and see if there is someone local who can lend you a hand, or show you how to do something right, and then watch you do the same thing yourself, or tell you what to do and guide you through the process

I'm not a mechanic by any means, this is the first time I have ever taken apart the engine, hell, my dad did MOST of the "taking apart" for me (he used to drive a box truck in the motherland and they did a lot of fixes out of what was available etc)

now when time comes, when I put everything back together, I'll follow my own advice and try to get someone local to show me how to do the belts properly

I mean, these cars (like my early 944) are 27 years old, and 924's are even older, I'm sure you can find at least one person in the area or within a 2 hour drive - who'd me MORE then willing to share their experience etc on helping someone new with wrenching on these cars

there's my .02$ for what it's worth

[Rasta Monsta]

Originally Posted by solreaver

adjust it to just below whine when cold and there ya have it. Re tension at 1k, check (inspect everything, not just the belts) at 15k and replace at 30k or 3 years whichever comes first. Replace rollers after two belt changes or when the go bad. Replace seals when they leak. Replace water pumps at 60k to 90k, depending on your budget and how lucky you feel. Are we done here?

+10

:d

[fmartenies]

Knew I would stir up a hornets nest...

All I am saying is, relying on a measurement (that reading through forums we can't even all objectively and definitively agree upon) without understanding what you are doing is not a very good idea. The precision attained through some of these tools is well below the margin of error due to all the other factors. Most people posting on 944 forums, other than the select few that are good mechanics in addition to knowing the vehicle, are looking for the black and white answer. A tool and an exact measurement should only be part of a recommendation for a gray area.

If 9201 were the exact answer, how come Porsche used the 90 degree twist method for the early cars? And how come they are only available because some guy in Germany started selling them out of his house? I'm just saying, a belt is not the mystery some people make it out to be. And given the price of the tools and the target market I am inclined to say there is a lot of incentive to keep that myth alive.

[bebbetufs]

A tool and an exact measurement should only be part of a recommendation for a gray area.

I mean, these cars (like my early 944) are 27 years old, and 924's are even older, I'm sure you can find at least one person in the area or within a 2 hour drive - who'd me MORE then willing to share their experience etc on helping someone new with wrenching on these cars

I see now that a new method might only increase the confusion.
I admit to believing that a black and white answer could be found - at least a safe range to aim for.
I thought the point of the tool was for Porsche to ensure that any mechanic working on their cars, most who probably look at their job as "just a job", actually do it properly and get within that safe range. But if a tool is not enough how can I safely gain the experience needed to succeed? If it only wasn't a 10 hour round trip to the nearest experienced Porsche mechanic! Thankfully I can rely on the superb resource that this forum is. Some of us are more dependent on your help then you might think. I just want to thank the forum for all your help so far, and please keep it coming!

[Roman944]

Originally Posted by bebbetufs

I have to say I'm a little bit jealous. Over here there is nobody with that kind of knowledge in my area. That's why I have to rely extensively on the superb resource that this forum is. I am also a member of the national P club, which is great, but the local branch is not too active. So I just want to thank the forum for all your help so far, and please keep it coming!

there is a couple people who know 944's around here, 1 that I have actually met and he's a very cool dude, and every time I have had a question - he was always there to answer

sometimes just throwing out there "hey, I'm from *, is there anyone around that knows these things?" really works

unless you are in some other country then USA, that might make it tougher

but between Pelican, Rennlist, 944online, and other 944-specific places, I think you should be able to find someone around

and yeah, huge thumbs up to all you guys for all your help! and ofcourse the hosts!

[bebbetufs]

Sorry for editing my post while you were answering. I didn't like the tone of it I found it too negative, and ended up changing it completely. Please excuse my bad manners!

unless you are in some other country then USA, that might make it tougher

Confirmed

[Roman944]

ah yes, remember to be politically correct

[smokin_944]

Am I missreading the chart or is that 11K on the chart? 11025Hz?

[bebbetufs]

I don't know why it says that. This is a quote from the website.

As you can see at the bottom of the screenshot, Goldwave displays the length of the selection as 0.171 of a second. Multiplying the reciprocal of this number by the total number of cycles (waves) in the selection will provide the frequency in Hz. We have 25 cycles displayed in the example above. This belt measures 146.2 Hz (1/0.171*25=146.2) that is too tight and should be slackened before the engine is run.

[mikepellegrini]

It's not rocket science, it's just s stretchy rubber composite belt. My kid and I do ours by feel and it's worked great for us with four cars through maybe 8-10 belt jobs (or tensionings) in the last 4 years.

My favorite "belt tensioning without the tool" thread at Clark's Garage: Clark's Garage Message Board :: View topic - Belt tensioning without the tool

[mattdavis11]

Just reiterating what Techno Duck, and mikepellegrini posted, it's not rocket science, it's a rubber belt. I don't know about you guys, but I was born with an index finger and thumb on my dominate hand. They are damn fine tools to have when tensioning a belt.