Rotor arm failure - how? why?
Jon M
Last night, returning home from work, the engine cut out suddenly, and
without warning, while queueing for a roundabout. It was running
perfectly 'til then.
It then refused to start. Not even a splutter. After much messing
around to no avail, I got a tow home.
Just found the problem - replaced the rotor arm; perfect running now
restored.
Does anyone know how/why rotor arms fail? I've examined the old one
very carefully - no signs of tracking or hairline fractures, but if I
refit it - dead engine.
Could the new, aftermarket coil I recently fitted be placing too much
strain on it, due to higher voltage?
Car's a 1979 Viva, 1256cc, with AC Delco dizzy. (Some had Bosch ISTR)
Regards, Jon.
'79 Viva, '75 Ventora, '63 Cresta.
---
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Chris Wilson
museum.freeserve.uk.co says...
> Just thought I'd share this, anyone have any ideas?
>
> Last night, returning home from work, the engine cut out suddenly, and
> without warning, while queueing for a roundabout. It was running
> perfectly 'til then.
>
> It then refused to start. Not even a splutter. After much messing
> around to no avail, I got a tow home.
>
> Just found the problem - replaced the rotor arm; perfect running now
> restored.
>
> Does anyone know how/why rotor arms fail? I've examined the old one
> very carefully - no signs of tracking or hairline fractures, but if I
> refit it - dead engine.
>
> Could the new, aftermarket coil I recently fitted be placing too much
> strain on it, due to higher voltage?
>
> Car's a 1979 Viva, 1256cc, with AC Delco dizzy. (Some had Bosch ISTR)
Could be the extra HT.I recall back in the days when the OHV Vauxhall
engine was current,we used to stock a few Delco rotor arms,maybe their
construction / material was a bit marginal.Some aftermarket caps and
rotors seem very iffy.An aftermarket cap on a V12 Jag engine can fail
within miles.An original Lucas sometimes lasts as much as a year <VBG>
--
Best Regards,
Chris Wilson
http://www.f3.u-net.com
mailto:ch...@f3.u-net.com
Jon M
>Could be the extra HT.I recall back in the days when the OHV Vauxhall
>engine was current,we used to stock a few Delco rotor arms,maybe their
>construction / material was a bit marginal.Some aftermarket caps and
>rotors seem very iffy.An aftermarket cap on a V12 Jag engine can fail
>within miles.An original Lucas sometimes lasts as much as a year <VBG>
Think I'll try to find an original spec. coil, just in case. The
aftermarket coil makes starting so much easier, so I guess there's a
few more volts floating around...
New rotor's genuine Delco, as was the failed one, but I've now got 2
aftermarket spares in the glovebox - don't want to get caught out
again, for the sake of a couple of quid.
BTW - Lucas cap for Ventora/Cresta six doesn't fit. Every time I get
one, I have to attack it with a file to get it to sit properly on the
dizzy. Can't find any other makes to try, though...
If you're wondering why I didn't just bin the old rotor; but felt I
had to post here about it, I'm just naturally curious - I like to know
'how' and 'why' for everything - always taking things apart <g>
Cheers, Jon.
Andrew W. MacFadyen
What engineers call "a classic brittle failure", laying aside that the
Delco rotor arm is/was never a great bit of engineering -- pretty
minimalist and always slack fit on the spindle. The Bakelite the arm was
made from has a "low fracture toughness", in non engineering terms it is
brittle and has had minute cracks since manufacture (engineers call these
Griffith flaws) subject to stress (centrifugal force) and vibration these
crack grow slowly until they reach a critical size then grow literally at
the speed of sound.
All materials have these Griffith flaws some like good quality mild steel
are very resistant to crack growth others like aluminium alloys and
welded joints in steel structures are susceptible to crack growth --
essentially this the mechanism which cause the Comet disasters and the war
time Liberty and T2 Tanker ship to suddenly break in half without any
warning. The Comet was fatigue followed by a sudden brittle failure and
and Liberty ships were almost instant brittle failure from weld cracks
accelerated by cold North Atlanic winters.
Andy M
Chris Wilson
am...@post.almac.co.uk says...
>
> What engineers call "a classic brittle failure", laying aside that the
> Delco rotor arm is/was never a great bit of engineering -- pretty
> minimalist and always slack fit on the spindle. The Bakelite the arm was
<snip short thesis>
Wow... :-) Well,he *did* ask <VBG>
Jon M
>In article <3703A149...@post.almac.co.uk>,
>am...@post.almac.co.uk says...
>>
>> What engineers call "a classic brittle failure", laying aside that the
>> Delco rotor arm is/was never a great bit of engineering -- pretty
>> minimalist and always slack fit on the spindle. The Bakelite the arm was
>
>
><snip short thesis>
>
>
>Wow... :-) Well,he *did* ask <VBG>
I did, indeed.
Andrew, Chris, thankyou, sirs. I bow to your wisdom.
Probably, then, the old arm now has an /internal/ crack running from
the hole where that springy thing is rivetted on, down to the spindle.
Hence total deadness with no external signs of failure.
I also suspect that the Bosch dizzys the Viva Club has in stock are
more reliable - counterbalanced arm, and more modern material...
Maybe if I lurk around here long enough, I just might learn something
about proper Engineering (not this software/electronics stuff I do...)
and maybe stop posting stupid questions. Give me a year or twenty <G>
Anyone else would just stick a new arm on, bin the old one and not
give it a second thought. Not I!
Just off to look up 'Griffith flaws' - think I've got a book
somewhere... Fascinating.
I'll email each of you a virtual pint if you like ;-)
Thanks again, regards Jon.
Andrew W. MacFadyen
Andy M
Andrew W. MacFadyen
and was working on jet engine design in the UK before Whittle he later went on to
design the Rolls Royce Avon engine.
Andy M
Jon M
Jon M
Paul Giverin
<am...@post.almac.co.uk> writes
working gas turbine. Griffith was trying to use an axial flow compressor
in his engine as opposed to the centrifugal compressor in Whittle`s WU
engine.
Griffith had the benefit of official funding and backing for his project
at RAE Farnborough while Whittle had to borrow money from his friends
and suffered a breakdown as a result of the workload.
Sir Frank was streets ahead of Griffith and was the first to overcome
the problem of burning vast amounts of fuel in a small combustion
chamber. As a serving RAF officer, Whittle could not benefit financially
form his work. When he had perfected his engine, he had the project
taken from him and given to ROVER (note the feeble attempt to get back
on a motoring topic). Rover couldn't handle it and gave the project to
RR in exchange for a Tank contract.
--
Paul Giverin
Big Frank Whittle fan.
Jon M
Had a good search around; found this fascinating site, which does
mention A. A. Griffith on one page:
'The Jet Genesis' http://www.soton.ac.uk/~genesis/Index.htm
There is a tiny motoring connection; on there are two aircraft using
*piston engines* driving compressors, a 1910 Romanian 'Coanda'
and a Caproni, which also used an afterburner! Fascinating stuff.
I also found something about Griffith flaws in dolomites; did Triumph
use dodgy rotor arms, too? ;-)
Jon (generally curious about everything!)