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lindenengineering
10-09-2013, 04:34 AM
Guys I saw this post on the iatn network for techs.
Thought it was worthy of a share, here it is ad verbatum :-

Hey guys, I hope this isn't a tip that I think is awesome
but everybody already knows!

This week I had to compression test a Smart ForTwo diesel
but couldn't remove the glow plugs. They would unscrew to
the end of the threads, but carbon buildup on the long tip
prevented me from being able to remove them. No amount of
prying, pulling, or even my mini slide hammer would remove
them.

I actually came across this trick from a guy on some Smart
Car forum when I gave up and Googled the problem. I screwed
each glow plug back in (in order to ground them again) and
then used a jumper wire to power them up for over 3 minutes
straight. This "burns" the carbon off and they came out so
easily I couldn't believe it!

Hopefully this saves somebody some time and frustration!
Chris Dekker
I am going to try this the first opportunity I get.
Cheers Dennis

Altered Sprinter
10-09-2013, 04:54 AM
Or build a heat box to enclose the plugs,spray with deep creep DE-TOX leave overnight for the penetrate to do it's job, and the heating process will dissolve the carbonation on the thread simply put it will come out,lefty lossy, righty tighty,back and forth, and no stripped threads will result.
Cheers Richard

Aqua Puttana
10-09-2013, 01:15 PM
... I screwed each glow
plug back in (in order to ground them again) and
then used a jumper wire to power them up for over 3 minutes
straight. This "burns" the carbon off and they came out so
easily I couldn't believe it!

...

Cheers Dennis
Nice solution. I'm always impressed with simple solutions.

Just a reminder that the NCV3 glow plugs are not rated for 12 volts. I would try putting the 3 glow plugs per side in series with the 12 volts. Edit: :bash: Won't work because the one side of the GP is ground. An alternative would be to use 2 each spare GP in series with a stuck GP. Using the 3 GP's in series as voltage dividers wouldn't impress full voltage on the individual GP, but would probably still provide enough heat. In fact it may even be less stressful on the GP elements.

Any comment as to whether the GP's would be worth reusing after a 3 minute long burn off? I'd be inclined to think that they would be toast after that.

vic

Edit: After further reflection, the control winding should help to limit current during a 3 minute burn.

54948

autostaretx
10-09-2013, 04:58 PM
An alternative would be to use 2 each spare GP in series with a stuck GP. Using the 3 GP's in series as voltage dividers wouldn't impress full voltage on the individual GP, but would probably still provide enough heat.
Although i haven't tried it with GPs, my usual "current limiting" load for stuff like this is a headlamp.
(i'm old school... i'd dig in my basement to find a sealed beam unit)
The Sprinter's H7 lamps are 55watts... at 12v that's 55/12= 4.6 amps, and 12/4.6= 2.6 ohms
Assuming a 1 ohm glow plug, the 12v gets distributed as 4.6 v across the plug. (see below)
If the GP is lower resistance (0.6 ohms, for example), then it's only 4.6a * 0.6 ohm = 2.76 v across the plug.
(it'll actually be less in both of the above cases, since i didn't factor in the plug's resistance in the current calcs)(now i have, see below)

If you've got a dual-beam lamp, you can put the filaments in parallel to double the current flow.
(which would double the voltage drop across the GP).

--dick
factoring in the plug's resistance, assuming a single-filament H7 lamp:
1 ohm GP: total in-line resistance 2.6 plus 1 ohm = 3.6 ohm. At 12v, that's 12/3.6= 3.3 amps, thus 3.3v across the GP
0.6 ohm GP: total res: 3.2 ohm, at 12v that's 12/3.2= 3.75 amps, 0.6 * 3.75= 2.25 volts across the GP.
Note that 3 to 4 amps through the plug is far less than their normal operating range (8 to 25, according to Vic's manual page). That's why i'd double the current with two filaments in parallel.

IF you have disconnected your battery's negative terminal, you can run *two* GPs "in series", even when they're screwed into the cylinder head. Just feed the positive into one plug, and connect the negative to the "positive" lead of the second plug. The engine metal will serve as "the wire" tying the two plugs in series.
If you have a 6v motorcycle battery at hand, that battery plus two plugs would seem to be the best answer for "3 v across each", although the actual current would be controlled/limited by the two plugs' rising-when-hot internal resistances.

Aqua Puttana
10-09-2013, 05:49 PM
...the best answer for "3 v across each", although the actual current would be controlled/limited by the two plugs' rising-when-hot internal resistances.
The GP's are rated 4.4 volts per JDCaples.

As to the original repeated glow plug failure question...

The NCV3 glow plugs are rated at around 5 ... 4.4 volts (thanks Jon). ... FWIW. vic

http://sprinter-source.com/forum/showthread.php?p=201003#post201003

Of course there are many ways to step down voltage. I think that using 3 glow plugs in series provides an easy equal step down for each GP while using the available vehicle battery. Good point about removing the battery ground to get 2 each GP in series.

I am ass-u-me'ing that the newer design 4.4 volt glow plugs have a control winding similar to the T1N full voltage type.

vic

Altered Sprinter
10-09-2013, 11:33 PM
Australian GP TIN IN A CAN 4-IN-LINE 5 IN-LINE ARE BOTH RATED 11.5V The tips can be cleaned and restored to OEM operating condition if you wanted to be bothered doing so:thinking:
January 2005 production all GP plugs are original factory installed,number three had a 30 second time delay before going off, but it now is operating 100%,ignition on GP dash light turns off in-less than one second,start engine one second, glow plug light stays off.
I don't think any one has done this ever:idunno: but they can be restored if not fried.
Cheers Richard
PS I meant to add, we cleaned spark plugs of carbon residue, why not a glow plug! the principle is the same for pre ignition of heating fuel based stocks for a quick start.

shortshort
10-10-2013, 03:55 AM
Perhaps because there is no economy in cleaning plugs, glow or otherwise.

Altered Sprinter
10-10-2013, 04:33 AM
Perhaps because there is no economy in cleaning plugs, glow or otherwise. True but it was fun,fooled WIS..OH >> and we FRANCHISE:bash: change perfectly good GP relays as well.
Thar's a method in my madness:bounce: