Experience with Subaru at 358 Hours

[scsmith]

This is a fantastic thread and I have really been enjoying it.

I think I can add one tidbit to the conversation from my practical experience in ill-begotten youth.

I have run an engine for prolonged periods of time in MILD detonation. Namely a Volvo B-20 engine with CR=11.5. After about 1500 hrs, the engine was torn down, and all the rod bearings revealed some damage. The nature of the damage was that the bearing material was "wiped" away, indicating metal-to-metal contact over a very narrow band at TDC. This was indicative of very high pressure (enough to collapse the oil film) over a very short duration, i.e. during detonation.

Bear in mind, these old Volvos are tough engines with stiff cranks and large bearings. Of the dozens of them that I have looked inside over the years, I never saw a Volvo main or rod bearing that showed ANY wear at all, except this one.

I have also seen the same characteristic rod bearing wear on an old Triumph motor that was habitually driven hard on low-octane gas. Again, sustained periods of MILD detonation.

My point: The flaked or "popcorned" bearing damage that Ross found is NOT in my mind indicative of detonation.

[rv6ejguy]

Originally Posted by scsmith

This is a fantastic thread and I have really been enjoying it.

I think I can add one tidbit to the conversation from my practical experience in ill-begotten youth.

I have run an engine for prolonged periods of time in MILD detonation. Namely a Volvo B-20 engine with CR=11.5. After about 1500 hrs, the engine was torn down, and all the rod bearings revealed some damage. The nature of the damage was that the bearing material was "wiped" away, indicating metal-to-metal contact over a very narrow band at TDC. This was indicative of very high pressure (enough to collapse the oil film) over a very short duration, i.e. during detonation.

Bear in mind, these old Volvos are tough engines with stiff cranks and large bearings. Of the dozens of them that I have looked inside over the years, I never saw a Volvo main or rod bearing that showed ANY wear at all, except this one.

I have also seen the same characteristic rod bearing wear on an old Triumph motor that was habitually driven hard on low-octane gas. Again, sustained periods of MILD detonation.

My point: The flaked or "popcorned" bearing damage that Ross found is NOT in my mind indicative of detonation.

Yes, the old B series Volvo engine had very robust bottom ends and the same goes for many other types which you can rattle lightly almost continuously (Slant Six Dodge comes to mind). Nothing really breaks suddenly on these. Overloading and fatigue bearing failures look a lot different than mine, I've seen a bunch of these developing engines with very high specific outputs and we've had to find solutions. I have a great old bearing book with many color photos of various failure modes. They all show pretty much what I have on mine. Here is a god web based one from Mahle/ Clevite: http://catalog.mahleclevite.com/bearing/ I think section 19 shows the cavitation photos, you can see fatigue failures generally show larger areas of less severe damage as you'd expect from detonation/ overloading.

[rv6ejguy]

Ok, this has intrigued me enough, I had a talk with my electronics/ software guru here and he's interested to start a bit of testing and development for a way to instrument these things and do some actual measurements. Not sure how long it will take as it is a spare time project and we are busy now but... he loves new challenges and often does R&D at home after work.

We have some components in mind we have worked with before that could make this pretty easy- I hope.

[DanH]

Originally Posted by rv6ejguy

Ok, this has intrigued me enough, I had a talk with my electronics/ software guru here and he's interested to start a bit of testing and development for a way to instrument these things and do some actual measurements. Not sure how long it will take as it is a spare time project and we are busy now but... he loves new challenges and often does R&D at home after work. We have some components in mind we have worked with before that could make this pretty easy- I hope.

Or you could just use standard equipment and start next week

Examples:

http://www.atitelemetry.com/viewproduct-9043.htm

http://www.binsfeld.com/index.php/products/TT10K/

http://www.datatel-telemetry.de/en/D...ransmitter.pdf

.....and more.

Below is 1999....the stub in the prop center is an old WDC analog telemetry transmitter, the lowest of low tech, already obsolete as digital gear had reached the market. My buddy Ron is at the throttle and I'm recording data with a clipboard and pencil. That's an ancient 15mhz BK scope for signal and vibratory waveform (an Air Force castoff that arrived in a friend's scrapyard for free), and a true RMS Fluke for amplitude. Plenty of space on this propshaft thus a big 'ole Wheatstone bridge for torque.

Point is, you don't need to invent the wheel (or have a NASA budget) to know exactly what sort of vibratory torque(s) are present in your system, and at what RPM. The only unknown is finding a good physical arrangement for the strain gauges.

[rmeyers]

Fascinating thread. So fascinating that I signed up just to comment. Been visiting this forum occasionally for some time while trying to get the energy to finish my 6A.

I have a question for Dan. In setting up for a Holzer analysis, how does one determine the correct length for the 'equivalent length' shaft?

I have 'Mechanical Vibrations' by Hartog, an earlier version than yours apparently, since I do not have the 4 cylinder diesel generator example. It does have a 6 cyl diesel marine engine directly driving a prop shaft and prop.

In this example, it seems that he uses the cylinder spacing for the equivalent shaft length. Does this imply that we are placing our equivalent mass at the place where the actual center of gravity would be for the real crankshaft piece? That would seem to make sense, but you know how that goes....

[Mike S]

Originally Posted by rmeyers

Fascinating thread. So fascinating that I signed up just to comment. Been visiting this forum occasionally for some time----

Randy, to VAF

Good to have you aboard.

[DanH]

Originally Posted by rmeyers

I have a question for Dan. In setting up for a Holzer analysis, how does one determine the correct length for the 'equivalent length' shaft?

Sounds like you're attempting a detailed model incorporating each crankthrow as an individual inertia/stiffness pair. I have a reference at home (BICERA) which would be helpful, but here's a path you'll like...

The classic reference work is "Practical Solution of Torsional Vibration Problems" by W. Ker Wilson. Later editions are a multiple (5 or 6?) volume work and cover every detail you can imagine. Out of print, so you look for it in a university library. I have borrowed the 1956 edition from the University of Alabama on inter-library loan. They even have it at Auburn and Georgia Tech

Go here, click "Find in a library", enter your zip code:

http://catalog.hathitrust.org/Record/009911016

That said, hey, this is the internet. The copyright has apparently expired on the original 1935 edition, see below, start at page 79. You can download single page PDF's:

http://hdl.handle.net/2027/uc1.$b530640

Second edition Vol 2:

http://hdl.handle.net/2027/uc1.b4335883

While poking around in a Google search for Ker Wilson I ran across this...nice discussion in Sec 2, and it references both Wilson and the BICERA book:

http://www.engdyn.com/images/uploads..._-_tdf&clh.pdf

[rv6ejguy]

Originally Posted by DanH

Or you could just use standard equipment and start next week

Examples:

http://www.atitelemetry.com/viewproduct-9043.htm

http://www.binsfeld.com/index.php/products/TT10K/

http://www.datatel-telemetry.de/en/D...ransmitter.pdf

.....and more.

Below is 1999....the stub in the prop center is an old WDC analog telemetry transmitter, the lowest of low tech, already obsolete as digital gear had reached the market. My buddy Ron is at the throttle and I'm recording data with a clipboard and pencil. That's an ancient 15mhz BK scope for signal and vibratory waveform (an Air Force castoff that arrived in a friend's scrapyard for free), and a true RMS Fluke for amplitude. Plenty of space on this propshaft thus a big 'ole Wheatstone bridge for torque.

Point is, you don't need to invent the wheel (or have a NASA budget) to know exactly what sort of vibratory torque(s) are present in your system, and at what RPM. The only unknown is finding a good physical arrangement for the strain gauges.

We like building stuff... You learn more by building it than buying it and maybe have some commercial applications down the road. Often we can apply some lessons learned in developing new products.

[scsmith]

Unless you have a prop extension?
I can't imagine a place on my engine-propeller combination where I could put a strain gage.

Maybe somewhere inside the gearbox? I would think they would package it pretty tight so there is no bare shaft exposed anywhere.

[DanH]

Originally Posted by scsmith

I can't imagine a place on my engine-propeller combination where I could put a strain gage.

Physical space for the strain gauges is a classic problem.

In the case of the drive system above, I knew I was going to strain gauge it when I designed it. The usual choice for a prop extension is a machined aluminum spool. The steel tube with flanges was much harder to fabricate, but it worked nice.



Something like the Egg Gen3 would be difficult to strain gauge, which is why some of us snorted when Jan claimed to have done it.

The Marcotte gearbox Ross is using should be easy. It has an inner bore in the right place for a pre-made Wheatstone (red):