worf928

Hey, I'm just funnin'
I think you would approve of the detail of the records I make.

UKKid35

I have used Theo's perspex tool, the Kempf tool and the Jaeger Sound file.

The perspex tool is not that easy to use, and the pattern doesn't seem to be available online anymore. However it was useful before I had access to a Kempf tool.

The Kempf tool is great, easy to use and excellent value.

But my favourite is the JagEng Sound File which is still available here. It is a clever and elegant solution, highly repeatable, and free to use. I recommend loading the file on to an MP3 player and using headphones. You will need a quiet garage though, its probably not possible to use roadside.

M. Requin

I used to make electric basses so this approach naturally appealed to me. As closely as I can measure it, the JagEng sound file shows the belt correctly tensioned at about 82Hz. It so happens that E2 - the bass E string - is 82.407Hz, which is pretty close. I used a little Boss hand-held bass tuner to set my tension (LED's show note and pitch) and to re-check it. I'll be getting a Kempf tool soon, and I'll let you know how close E2 really is. The only thing I need to do now is add a contact mike to get a clearer reading - UKKid35 is right, the amplitude is so low it's hard to hear except in very quiet surroundings!

F451

For the tone deaf like me the sound file is the kiss of death.

However, it had never occured to me to use an electronic tuner. Great idea. Was it always the intention of JagEng that you would use an electronic tuner?

I'll be sticking with the Kempf tool for now, but just curious.

blown 87

I knew you were kidding Dave, just not far off the mark.

Keeping records is a very good thing on these cars, just do not put a $ amount next to it.

worf928

Yeah. For our own selves as well as for those that might happen by the written figure and then come for us with axes...

VT928

For all my timing belt checks I use the Kempf tool. Actually I let Kempf use the tool and I admire his work. I am lucky enough to live close to Jay and his spacious garage. So I provide cheap labor for his projects and he lets me help him wrench on my car.

Paul

1980 Euro S Red/Blk Lea

H2

Like ROG, I used the 9021 to calibrate my Kempf tool and it's at the very top of the Kempf "window." I get the tension belt light when setting to the middle of the Kempf tool window although most cars may not be this sensitive. My feeling is that the Kempf tool "sets a bit loose" at the middle of the window for '85 and later 928s. However, the mid-window setting may be perfect for earlier cars?

Nevertheless, the Kempf tool is a breeze to use and entirely adequate for most uses.

Attached are fotos of the Kempf, the 9021 tool, and the rare Porsche P9131 T-belt tension checking/setting tool. As many of you know, the P9131 tool is no longer available and the very capable and similar Kempf tool has taken its place with more than a thousand or so sold. The other relatively well known tension measuring tool is the Porsche very sensitive 9201.

Directions for use of the P9131 are found in the 928 Workshop Manuals. It essentially works just like the Kempf tool and gives similar results. I find that the P9131 does not flex side to side like the Kempf tool but this is of no consequence to the cautious user. I think repeatibility of measurements of the P9131 are a bit easier but not enough to be concerned. Last time I checked, the Kempf tool was about $60 or so, a necessity in any 928 tool box.

The Porche 9201 tool is the $300-$650 tool (depending on where you buy and if used or new) and has a precise and very sensitive dial gauge built into it. While it's really the most accurate of all the tension tools (and more versitile), it's also the most difficult to use on the 928 t-belt. The problem with getting good measurements with the 9201 is the cramped working space and the really poor viewing angle of the dial. If you accidently twist the belt just a small bit to get a better view (easy to do), it changes the dial indicator reading quite a lot. That aside, in the hands of an experienced operator, this is the most accurate tool.

On the alternator belt, the 9201 is easy to get dead-on, and gives repeatable settings every time because of easy access. It's not so much the gauge but the operator's experience in finding the sweet spot and getting T-belt readings that are consistent. I spent 3 hours playing around with the 9201 before I felt comfortable that I had it pretty well figured out…and even then, I still make several repeatable measurements before I'm confident (that's a lot of turning the crank before each measurement). Your experience may be different but, for me, the Kempf Gauge was always at the upper end of the "window" as compared with the 9201 setting of 5.2 on my 32V 928s. I think there must be some belt tolerances in the 928 that allow for OK settings in the middle of the Kempf window on most 928s, although I've heard that the Kempf tool was originally made using the 16 valve car. With all the happy users out there, from middle to high end of the window must not make much difference or we'd all be hearing complaints about it on the forum. On the low end of the Kempf window, I feel that you will have too low a setting (at least too low for me)...but that's just my experience on 32V cars. BTW, I've checked the Kempf gauge against 3 different 9201 tools.

My method is to initially (and quickly) set the belt tension with the Kempf gauge….then double-check it several times with the 9201 for any fine tuning if needed.

I don't think anyone would argue that the 9201 is difficult to use on the 928. The Kempf tool (or the Porsche 9131) is by far the easiest and adequate for the job. If I were having anyone else work on my car…I’d trust their use of the Kempf gauge much more than their use of the 9201…unless they were a highly skilled mechanic and used the 9201 regularly on 928s in their work. Even then, if they get in a hurry, they could get a wrong reading.

I think that every 928 owner should have a Kempf gauge in their tool box..and use it periodically.

I'm very skeptical of the "tone tuning" method that has been mentioned. Listening to a lot of rock music has to be a variable for some although country-western might not cause Tbelt calibration settings. Tbelts are probably more forgiving than we know, otherwise a lot more would be failing.

Harvey

M. Requin

Well, in terms of the physics involved, it (the plucked string method) is theoretically more accurate, in terms of data available to be evaluated, than any other mechanical method commercially available. To explain: tools which measure belt flexibility - the Porsche factory tool, the Kempf tool, aftermarket tools like the Cricket, all measure the force required to achieve a certain amount of elastic deformation to the timing belt. But consider: what are the units involved? In the case of all of these tools, the measurement is the radial displacement of a spring-loaded arm against a reference mark, and in the case of the factory tool, pretty much the same, just with a "prettier" measurement output - in other words, just a glorified, or specialized, torque wrench. On the other hand, it is very easy to measure an observed frequency of a plucked string extremely accurately, which in turn, as UKKid35 (?) noted, also means very repeatably - function of the tool used. So in terms of a lab exercise, if you want maximally accurate results, use the "plucked string" approach. The laws of physics describe the relationship of mass, length, and frequency of a vibrating string.

BUT! In my own shop, I'll use the Kempf tool. It's cheap, it's easy, it is pretty accurate by all reports (which is why I'm buying one), and it is repeatable. I'm into the string thing, as an instrument (musical) builder, and it's a nice exercise, and who knows, I might figure out a way to make it really easy. I'll also use it as a reference standard. But that don't mean I think it's practical!

Buy the Kempf tool,
Use the Kempf tool,
Be the Kempf tool!

FlyingDog

The kempf tool is far more reliable than the 85+ idiot light which comes on around 1 on the tension scale. IIRC the timing belt should be ~4.5-5.4.The belt is fiber-reinforced. As the belt ages and stretches, the ideal tone would change. The tone method would not be good to rely on for anything more than an emergency check.

M. Requin

That's exactly right! That's how it works, the tone changes as it ages and stretches, so you readjust the belt to produce the original tone. Just like the other tools. ALL of these methods are just indirect ways of measuring belt tension.

UKKid35

It is still available online but Theo's pages have moved:

http://jenniskens.livedsl.nl/Technical/TensionTool.htm

Bill Ball

I had the same experience except the variability was wide.

Gary Knox

I too have used both the 9021 Porsche tool and the Kempf tool. Earl Gillstrom and I have worked together on several engines for T belt changes or adjustments, using both tools. On the second engine, I painted the window section area of my tool in white, then using a pencil drew a fine line where the Kempf gauge was when the 9021 tool dial consistently showed 5.2 reading. The Kempf tool was just as consistent at that mark. (engine being turned over 2X - multiple times - with both of us taking independent readings several times after each 2X rotation). I later used a fine brush with black paint to paint the pencil line on the white background. I now have a very small "variance" when I adjust to that line. I'm very confident the final adjustment is between 5.1 and 5.3 were the 9021 tool to be used. NOTE: all my engines have been '87 or later, so I want to adjust to 5.2 reading on the 9021 tool.
I always borrow Earl's 9021 tool to do my alternator belt adjustments.

Gary Knox
West Chester, PA

H2

Gary,

I did essentially the same test on both my 928s, only I filed a small notch in the Kempf tool as my "5.2 marker". It was on the high side of the Kempf tool notch. I understand that this is pretty common with 32V engines. Was this your experience?

If I set belt tension to this mark, it's really close to 5.2 on the 9021. So much so that I don't always use the 9021 anymore just because it's a PITA to use and get consistent readings. Kempf tool does it nicely but I still set on the high side of the window. The middle of the window setting worked OK too but I got too frequent belt light warnings. Maybe it was just my cars?

Harvey