Both of those thoughts crossed my mind as well.

 

I hade 375k on my e99 350 had replaced two injecters over that time and no glow plugs(but should have replace GP's as maintance)
A couple weeks ago had to have the heads pulled to replace bellowed GP's so replaced the cups as a preventative messure had soot and diesel smell in degas bottle after the work. I flushed system with cascade and am waiting to see if there is any other problem. Theres the catch 22 do you do the maintanace and hope its ok or do you leave it alone until there is a problem? Still stock inj and a super chip since 1999.

 

Could this be done?

 

Disasterous mod without a full machine shop and the heads off. Sooo not worth the effort.

 

Interesting thread Rich, glad you started it.

 

I might replace my gps this year

 

No, just torqued them down after listening to Dan preach about it for so long. The only reason I pulled them when I did is because the weather was nice and I had the time. I didn't want one to act up at an inopportune time.


But maybe I am just a punk kid. As for beating the crap out of it, I have had to pull the bed and weld it back together when the sheet metal started to tear and some pinch welds had broken loose.


Brass is also less corrosive and won't have a reaction due to dissimilar metals or get holes in it due to lack of coolant maintenance.

 

To me the most obvious candidate is thermal cycling. Brass has a temperature coefficient of expansion that is almost twice that of iron. I think the engineers used that to their advantage, causing the seal to get tighter with heat. This could explain why cups showing little sealant still did not leak; the sealant might really be more about filling voids and other small irregularities.

Picture how the cup goes in, constrained at the top and bottom by the iron head, but physically unsupported in the middle, where it is exposed to the hot coolant. I think that with every temperature cycle, that cup is "ballooning" out, which would account for the commonly-seen longitudinal cracks.

My theory is that the guys who start their trucks and drive them 100+ miles are the ones who get the high mileage out of their injector cups. The guys that drive 10 miles to work and back will have the premature failures, I think. More temperature cycles for a given amount of miles on the engine.

As far as EGTs, it doesn't seem to me that they would have much influence. The dominant thermal force on the cup is coming from the circulating coolant, and it is moving by pretty quickly. It would take a LOT of energy to get the temperature in that zone to rise much at all. EGTs down near the tip could certainly heat up that end of the cup a little more, but that is where the cup is constrained by the head, so I don't think it would result in stress cracking down there.

These are just my theories.

 

Thats good theory!

 

Mongo say science hurt brain. Mongo just want drive truck and no break cup.

Kel, you sure know how to sell a theory.

 

KelVarnson and I are whistling the same tune here.

Breaking it down, the initial question was: Is there something we can/should do (maintenance-wise) to extend the life of the cup?

akaFrankCastle poetically summarized the general concensus: "just want drive truck and no break cup."

 

I'm late to the party...

I'll add a little input though to support Kel's theory. My cup was cracked near the bottom. Also, the crack didn't extend into the area that was constrained by the head, it was in the middle that is open to coolant.


I also have a theory to bounce about why they used brass. It is a better thermal conductor than cast iron and steel. Injectors work really hard, and I'm sure they produce heat that needs to be transferred out. Brass was the ideal choice because it has adequate thermal conductivity while having ideal strength and expansion/contraction properties.

 

There was no turn when I torqued. Set the torque wrench to spec and turned..There was just the click letting me know the bolts were tight. All bolts were tight at the time. I have an aircraft maintenance back ground. Preventative maintenance was pounded into my head. At 20,000 feet there's no place to pull over when a problem arises. I adopted the same practices in my own vehicles. Maintenance, Maintenance, Maintenance is the key to longevity in engines and transmissions. Fluids and filter are cheap compared to repairs.

Jeff

 

They used brass because much like the copper washer on the end of the injector it easily conforms to the surrounding area it is being pressed into and is supposed to seal up without much aid like a copper washer.

One other thing I wonder is how thin some parts of the cups get when being formed. Like when you try to expand any metal it gets thinner and thinner till it cracks and like I mentioned brass is very prone to cracking. The heat cycles don't help. I would imagine if simply a thicker cup was used the cracking problem would be greatly reduced. That is if there is enough room to go thicker. I am curious as well if the replacement cups are thicker than say the E99's? Possibly the E99's were thinner than the rest and no one mentioned anything about it?

 

It's possible I guess, but from my understanding the only change was the compound. The E99 compound was more of a watery liquid, the junk on the rest is more like a paste.