Myth, mystery, or wives tale-- Melting GPs

[hairyboxnoogle]

Ok so ive heard a handfull of times on different forums that too much advance will "melt" your glowplugs. Ive also been told by several people that this is very unlikely or strictly impossible. Personally, i dont see how timing affects glowplugs, you should be able to advance the engine to the point it will barely run, or to the other extreme and it shouldnt matter one bit to the GPs. I do realize that at different timing you will have hotter / cooler combustion and CC temps, but how exactly are those supposed to get hot enough to take out GPs.... Anyway, fact or fiction people, sate my cuiriosity

 

['94IDITurbo7.3]

I have also heard that too much advance can melt the GPS. but i am with you i have no idea why.

 

[SparkandFire]

Too much advance will burn the tips off the glowplugs.

I had it happen on my '86.

When you get enough advance you can hear the engine "rattling" more. Some say it sounds more like a "powerstroke"

The sound you are hearing is coming from somewhere, it's basically preignition similar to what a gasser goes through. If the fuel is injected too soon into the cylinder the combustion event tries to push the cylinder back down the direction it was coming, basically reversing the engine. The only thing that keeps it from running in reverse is the momentum of the flywheel and the moving parts.

The flame front is hotter and therefore more corrosive to things like glowplugs...

 

[hairyboxnoogle]

Interesting.. still i would have thought that would require a rattle to the point of being terrified to drive it lol. Timed by ear i get a faint (possibly imaginary) increased rattle while the cold idle advance is on. Although theyre non working anyway, i may just pull em out and take a looksy, i was runnin more advance and fuel with the other pump and injectors due to their shottyness.

 

[Black dawg]

I dont think that it is just about heat, maybe more about cyl pressure. in my suburban advanced timing would eat the glowplugs all the way up to the seat. Never seen the glowplugs get eroded in my fords, but ive never ran much more than spec for timing.

also failure rate in both is higher running wmo.

 

[hairyboxnoogle]

Hmm another reason to check them out. I was running up to 50% wmo with the old pump and injectors as well. When i got the engine i checked the GPs all were dead so i grabbed the ones out of my buddies parts truck and ended up with 6or 7 good ones dont remember, but i threw them in. So at least i know what they looked like going in, none of em were malformed in any way, little soot on a couple but no pitting or anything major.
I wonder if the GP erosion has something to do with the material used in GPs. Or possibly just their vulnerable location.

 

[SparkandFire]

It has a lot to do with 'exposure time.' That being the amount of time the components are exposed to the combustion flame.

I could see that the pressure from combustion could cause acoustical damage to the glow plugs, but it stands to reason that the injector nozzles would be more prone to damage due to their small size.

An overly advanced engine will have a greater amount of time in which the hot combustion gas is exposed to the cylinder-side components.

http://www.google.com/url?sa=t&sour...K16_gr&usg=AFQjCNF9i_FwMbHCqPhmOi1seqUPkBUXgQ

 

[Black dawg]

It has a lot to do with 'exposure time.' That being the amount of time the components are exposed to the combustion flame.

I could see that the pressure from combustion could cause acoustical damage to the glow plugs, but it stands to reason that the injector nozzles would be more prone to damage due to their small size.

An overly advanced engine will have a greater amount of time in which the hot combustion gas is exposed to the cylinder-side components.

http://www.google.com/url?sa=t&sour...K16_gr&usg=AFQjCNF9i_FwMbHCqPhmOi1seqUPkBUXgQ

I have a set of injectors that the nozzle is badly eroded, came out of a cavitated 6.9 (saw the cyl walls out of the block). I always wondered if it was all caused by way advanced timing.

 

[Silver Burner]

I thought 6.9's pretty much couldn't cavitate out because of how thick the walls were? Was it running straight water its whole life??

 

[Black dawg]

I thought 6.9's pretty much couldn't cavitate out because of how thick the walls were? Was it running straight water its whole life??

dont really know anything about it, just saw it torn down.

 

[DragRag]

I just pulled my well worn 6.9 from my flat bed and pulled some parts from it. I nkew I had the timing way advance and wanted to see how long it took to burn up a set of glow plugs. All were done in about 4 months being over advance. Yes they were burned off, so it happens for sure. Those plugs were brand new 4 months ago.

 

[towtruckdave]

I am sorry for the crappy pic but here are some glow plugs that were out approx. 1 month before this pic was taken and were mint and working. I had them out when I installed a new IP. When Mel checked my timing, it was 20*btdc @ 1600rpm. Obviously way too much, but that 6.9 had really low compression and seemed to like the extra advance. In the pic, they are seriously eroded and non functional.

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[hairyboxnoogle]

Theoretically, any engine with high compression could be victim to cavitation, the 7.3 idi is just kinda known for it due to its very thin cylinder walls. The walls flex more increasing the rate of erosion. with the 6.9 you have thicker walls that flex less, and more metal to chew through so cavitation rate is very low. We had a loader cavitate on us, think it was the Cat 920, had around 10k hours on it tho too.