Leaky injectors

[Jet A]

I recently rebuilt my injectors, using the same stock nozzles. Two of the injectors have started leaking. they are leaking from around where they screw into the head. and maybe a little bit at the middle threads on the body. I have lapped and lapped and lapped these. they are smooth and flat, and torqued to spec. they run for a bit, then start leaking. what am i doing wrong. i believe i am using 2000 grit w/ cutting oil. probably spend maybe 5-10 min on each surface, rotating the part as i do a circular motion. WHY are these stupid things leaking. i have done this several times. Is it possible i am not torquing enough? seems like the spec was 75 ft/lbs. what else would cause these to leak?

originally the cups that go in the middle of the injector, they had a little bit of a ring worn into the are where it hits the top of the nozzle. i have complety gotten rid of this through lapping.

Lapping was done on a 3/8 milspec ground glass plate. its flat!

[AdAm84]

Are you sure the nozzle retainig nut isn't cracked. I have seem this happen from over torqueing. Though that doesn't usually happen on that style of injectors. Did you lap the mating surface on the nozzle? That could cause issues if they are old nozzles and were not lapped.
Also, as a tip, we lap injectors using a figure 8 pattern. I don't know whya figure 8, but the boss taught me that way and he's been building the stuff for 25 years :shock: so i don't question it.  :lol:

[Jet A]

I lapped 4 surfaces nozzle top bolt sides of the thing ma jig and the surface on the upper body.

The nozzles work for a bit, then start leaking. no cracks in the nut

[AdAm84]

thing a ma jig = intermediate plate :wink:

i don't know what to say then. hopefully some others will post some ideas. sorry :?

[theman53]

I thought the injector torque was the same for the injector torque to the head. Which was around 51ft/lbs. and if that is it maybe the thread between the two injectors is sprung and leaking.....Just a theory and I am not sure on the torque setting.

[Jet A]

the threads dont seal, it is the lapped surfaces that do the sealing correct?

Since it is bubling out of the head threads, i am guessing that the prechamber or atleast the injector area is full of diesel, no?

[jtanguay]

the threads dont seal, it is the lapped surfaces that do the sealing correct?

Since it is bubling out of the head threads, i am guessing that the prechamber or atleast the injector area is full of diesel, no?

the pressure from the cylinder should be pushing it out

[Smokey Eddy]

Did you not replace the heat shields? :|

those little disks that are often stuck in the injector boss. (i had a hell of a time threading meaty wood scews into them and using a slide hammer to hammer them out. which still didn't work i ended up setting up an elaborate, not really, lever system which involved me smashing a steel bar with a sledge hammer and that fired the heat shields out.)

[burnt_servo]

the other thing that comes to mind ,  did you measure the pop presure after you lapped each  injector ?  
each surface you lapped will change the pop presure , and if you don't measure and make each injector the same , who knows when  they are firing in a running engine.

[blkboostedtruck]

it also says using same nozzels!
did you replace with new nozzels or use your old one's over again?
did you poptest?
Duane

[Jet A]

If you didn't replace the nozzles, then you had absolutely no business opening up the injectors in the first place :!: [/color]

Torque spec fro the injector halves is 52 ft lbs as is the torque spec for installing the injectors into the head.  

Sometimes in the process of installing injectors or if the return lines are leaking, fuel will get spilled into the threads where the injector screws in.  After the engine is started, the fuel will boil off looking like a leak at the threads in the head.  If it is just residual, it will usually burn off after a couple of heat cycles.  If it is still bubbling out after a couple of times of getting the engine up to temp, then it is leaking from the top of the nozzle.

USE NEW HEAT SHIELDS EACH TIME YOU TORQUE DOWN THE INJECTORS.

Andrew

Actually, i could have opened them up to see what made them tick....like i do everything else i get my hands on.  :twisted:
I did replace the nozzles, till i found out they were cheap chinese knock offs, so i pulled them and replaced them with the stock nozzles for testing the engine till the BFI get here.

I have a whole slew of new heatshields for exactly this reason.

Seems like any of the lapped surfaces not sealing would cause it to leak at these spots. IMO it would be hard to diagnose where the actual leak is occuring.

all injectors are pop tested plus or minus 75psi.

Also, pulled all of the injectors lastnight, and went over them with some polishing paper. (something like 4000 grit i believe) and finished up each surfrace baby smooth. cleaned them up and torqued to 75ftlbs (give or take a little bit on each injector for pop pressure) but none less than 65.

Got them in last night and none leak so far.

[Vincent Waldon]

I'm a big fan of spray brake drum cleaner and compressed air to help find afuel (or oil) leaks... you can get your injectors bone dry very quickly and then leaks are much easier to track down.