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Posted

You may recall, I asked people to contribute to this survey earlier this year.    I can now publish the results and have done so on the "Technical articles and Reviews Forum"

But apparently, that is restricted in some way - it was originally the private publishing site of Dave Sideways himself, and while I can put things there, there are still some restrictions.     I posted a Word document there but others couldn't read it, so  put the report in as a plain post, asking for comments - and others can't reply there!

SO!    Please go and have a read at http://sideways-technologies.co.uk/forums/index.php?/topic/7830-survey-on-crank-damper-pullies/&tab=comments#comment-103143

And post your comments here?

Thanks!

JOhn

 

Posted (edited)

That works John!

NB. Bestway is to right click on link and open in new tab, which won't close this thread, as you cant comment in the place the document opens, so saves jumping back through to get to this thread again.

Alan

Edited by oldtuckunder
Posted

Not yet, Steve!    Still have to develop the testing rig!

As my cousins will say, "Softly, softly, catchee Great Ape"

John

  • 1 year later...
Posted

Now the fruit of my research is available!

I'll be at the Triumph Weekend, Stratford-on-Avon racecourse, that historically is jointly held by the TSSC and the TRR, demonstrating my Crank Damper Test System.   

Look for me in the Outside Trade Area, or listen for the revving engine rig!

John

combined.jpg

Posted

Ooh, excellent John, now I have serious reason for attending ( rows of shiny static TRs are not my thing). Cant begin to imagine how you will explain it. Peter

  • 6 months later...
Posted

Hello John, Have finally found my way here,late as I was with your survey. What is the process of testing the dampers ? I presume (shouldn't do that) there is a flywheel and clutch/pressure plate attached and it is all spun up to x,xxx rpm? Regards,Michael.

Posted

I've published on the theory and procedure, in the Courier (Nos.472/3, October & November 2019) and, in print, in the TRR TRaction.  Rather than republish, please read those articles?

But, yes, a trigger wheel on the crank pulley, and a motion sensor, as used for distributor-less ignition, allows analyses of torsional vibration and damping.     This can be done at a range of revolution speeds, and can identify 'critical speeds'.

John

  • 1 month later...
Posted

Hello John,  It looks impressive  with a lot of  input put into it. I  hope it serves it's purpose well. I would send a damper but as I'm on the far side of our infected planet the cost would be astronomical. Regards,Michael.

Posted

With respect, michael, expensive but not astronomical!    A quick Google finds several shippers from the UK for such a parcel at less than £40.

And with modesty, AFAIK I am the only person in the world who can offer this test!

John

  • 2 years later...
Posted
On 2/7/2020 at 10:03 AM, JohnD said:

a trigger wheel on the crank pulley, and a motion sensor, as used for distributor-less ignition, allows analyses of torsional vibration and damping.     This can be done at a range of revolution speeds, and can identify 'critical speeds'.

Related to this subject, albeit for the 4-pot SC engine, I recently got hold of Autocar from Feb 1965 with an article by R. J. Bates of Standard Triumph about the evolution of the Le Mans Spitfire engine. It included this neat graph of damped and undamped torsional vibrations in the 1147cc crankshaft:

_20220803_132656.thumb.JPG.ec6fba5e30cf01b035422c27fb2703af.JPG

Posted (edited)

Thank you, Pete!  Even in this Internet age, to know someone with an extensive library can be an advantage!   I'd very much like to read that article in full - I'll be most grateful for a scan of it!

I think the graph shows why production Spitfires had no crank damper - few owners were going to rev it beyond 7K!   That resonance frequency is a factor of the crank length, and just like, say, a xylophone or Tubular Bells, the longer the deeper the tone and the lower the resonant frequency.   The straight six crank would resonate within the rev range.

John

Edited by JohnD
Posted

I keep meaning to scan it in John, but haven't got round to digging the scanner out (it's awkward to photograph as the pages don't lie flat). 

Crank vibration is not actually mentioned in the body of the article but there are lots of other interesting nuggets about problems and solutions that arose while testing the Le Mans engines. I shall get it scanned tomorrow or Friday.  

1 hour ago, JohnD said:

I think the graph shows why production Spitfires had no crank damper - few owners were going to rev it beyond 7K!   That resonance frequency is a factor of the crank length, and just like, say, a xylophone or Tubular Bells, the longer the deeper the tone and the lower the resonant frequency. 

Good point, I hadn't realised crank length was the important difference. Obvious now you mention it!

Referring to the graph above, I wonder how much amplitude is significant; is there a rule-of-thumb threshold for torsional damping? Before fitting overdrive I used to spend a fair amount of motorway time around 4500rpm or above. Which is close to that peak of 0.4 degrees. But my crank isn't broken yet so maybe 0.4 degrees is trivial :wacko:

Another question - I presume the resonant frequencies are characteristics of the crankshaft only, but is the amplitude also a function of reciprocating mass? I'm wondering how well that graph represents all small-bearing crankshafts or if it's specific to the engine under test. 

Posted (edited)

I can't compare that graph with my results directly,  Pete, as they graph amplitude against RPM.    Mine use amplitude, in different units, "decibels", rather than degrees, against frequency and I run a test at various engine speeds.   This allows a more detailed analysis.

Certainly, the higher the revs the more likely is a resonant frequency to become significant, and potentially damaging.   I may have shown  this graph before:

 

image.png.fed18d2f457d23074e82f09ab38497d1.png

 

This compares eight different dampers.   The "Chrome" damper was a rebuilt one, kindly lent by a friend, as my 'control'.    It shows four other used dampers closely matched the control damper, but three, 1,   3 and 6, did not, and allowed much more vibration (recall - The decibel is a logarithmic scale!) at critical frequencies.

But this was on a six cylinder engine, as I am concerned that while Triumph thought a damper necessary, they chose the cheapest and simplest type that had rubber little different from tyre rubber as the compliant component.   After fifty years, I wouldn't trust a tyre, let alone one I had run that close to engine!   This fear is confirmed by the above results,  and the survey, which found that 10% of owners had seen a failed crank damper.

Triumph did not consider a damper was needed on the four cylinder, as the significantly resonant frequencies were in a rev range never used, except in a racing engine!   I could do a similar study of such engines, with a cooperative owner, as I am developing 'bolt-on' sensors that I can use on an engine that is still in a car.

John

Edited by JohnD
Posted

That graph that Pete posted may partly explain why I suffered a broken crank on my “fierce” 1300 Herald engine many years ago. That saw the far side of 7k fairly frequently, albeit for very short bursts only. Not sure sure how much over 7k as that was the end of the tacho…. 

The previous official cause was a dodgy fillet radius blend on no.1 BE journal, but as it broke through the web from #1 BE to the front main and the front of the crank isn’t carrying much torque load, there had to be something else in the mix….

Posted

Nick,

I haven't but if you wanted to apply Holzer Analysis to the Spitfire crank, you're welcome to a copy of my dissertation, in which I described the process.

Holzer was, is, an enormously protracted, iterative calculation  so that it fell out of favour, but today once you have set up your spreadsheet, it's fun to enter different engine speeds and see where the torque is greatest!

John

Posted
9 hours ago, JohnD said:

I may have shown  this graph before:

That's the first time I've seen it John, thanks for sharing. Think I get it, you've measured different vibration frequency vibrations at particular rpm, yes? So the different peaks are different modes(?) of oscillation, if that's the right word. 

9 hours ago, JohnD said:

Triumph did not consider a damper was needed on the four cylinder, as the significantly resonant frequencies were in a rev range never used, except in a racing engine!

This is it, I was thinking about racing applications. I wonder if any Spitfire racers ever use(d) dampers. Might pose that question on the 'Racing the Triumph Spitfire' facebook group. 

Posted
3 hours ago, Nick Jones said:

That graph that Pete posted may partly explain why I suffered a broken crank on my “fierce” 1300 Herald engine many years ago. That saw the far side of 7k fairly frequently, albeit for very short bursts only. Not sure sure how much over 7k as that was the end of the tacho….

Interesting, you wouldn't have to be far over 7k to climb up that resonant peak.

Incidentally the fillet radii are also mentioned in the Autocar article, which I've now added as a separate thread. See near end of 2nd page (bottom right of 1st image):

 

  • 1 year later...
Posted (edited)

And now for something completely different - NOT!

No photo description available.

This is a crank pulley damper from a Mk6 Ford Transit, probably with a Duratorq engine, 3 months and 3000 miles after being fitted.   The picture was recently posted on the FB forum.

     Gosh, if only a small proportion of original Triumph crank dampers, all at least 50 years old, have failed, why am I bothering offering to test them for owners?   But I suspect that this wasn't a 'Ford' part but a cheap bit of crap!   Allegedly marketed  by "Kamoka" Auto Parts, so be warned.

John

Edited by JohnD

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