perkins 4108 injectors. Broken collars and bent studs !!

[pcatterall]

Feeling rather pleased that my rebuilt engine was working fine and just making the odd final adjustments.
I thought one of the injectors was not sealed so tested the tightness of the securing nuts......crack!...…. the cast securing collar broke!

I had just posted advice on this as on the 4108 the head nuts are close to the collars which have to be correctly positioned to clear them
so I was fairly confident that the collars were not fouled by the nuts.

On examination I discovered that the adjacent injector had the same problem!

On checking with a spare collar to see that it was seating correctly I found that the collar would not fit over the studs. removal of the studs showed that 2 of them were bent.
They could not have been bent when I fitted the injectors so I don't understand what has happened.
I will get a new set of studs and check the seating of the injectors before tightening them down.
These are the same studs and injectors that were removed,(just new washers) I am at a loss to understand what has happened and wonder if there are any ideas or suggestions.

Out of interest I note that the dished side of the collar is fitted upward on my injectors, I wondered what benefit the dish then had? if fitted dish down then the dish could possibly help accommodate being 'off parallel' when it bears down on the top of the nozzle. They are all fitted like this ( as is a 'spare set' ) so I don't intend to change them round ! but will be interested if any one can explain the purpose of the dish.

 

[PaulRainbow]

They should be fitted with the dish uppermost, as yours are.

 

[pcatterall]

Thanks Paul.
I just wondered why the dish at all, it looks like a 'thing o purpose' and I wondered what !! (was the purpose).

I have replaced the studs and the injectors, I checked as I progressed to see if I could understand what had happened.
The torque setting was quite low and I wonder if when I gave the nuts a final 'check' ( without using the torque bar) I was just too heavy handed.
Looking at the collar in situ I can see that excessive tightening could well put a 'snapping load' on it. The downward force would then be transferred sideways and possibly bend the stud(s).
Thats my current theory. So one step forward and 3 back today !!

 

[PaulRainbow]

Thanks Paul.
I just wondered why the dish at all, it looks like a 'thing o purpose' and I wondered what !! (was the purpose).

I have replaced the studs and the injectors, I checked as I progressed to see if I could understand what had happened.
The torque setting was quite low and I wonder if when I gave the nuts a final 'check' ( without using the torque bar) I was just too heavy handed.
Looking at the collar in situ I can see that excessive tightening could well put a 'snapping load' on it. The downward force would then be transferred sideways and possibly bend the stud(s).
Thats my current theory. So one step forward and 3 back today !!

I think over tightening will break them Peter. Not sure why the dished surface is there, but if you fit them the other way up the injectors won't tighten.

 

[AndrewB]

When I did mine, I found surprising difficulty re-seating the injectors correctly. They wanted to go in at an angle, and then I can well believe you'd get the above result if you did them up tight. Don't know how to explain that they are correct, except that they should do up smoothly and you should have no sense that one side is harder than the other to tighten.

It may be easier to replace them in when the head is off, but care needed not to damage the tips when the head is refitted.

 

[pcatterall]

I realise ( now) that the 'collars' are quite 'fragile'. They look very solid but in use are being stressed over the injectors nozzle. I am surprised that I have not heard about this possibility before or perhaps I am exceptionally heavy handed!

 

[pcatterall]

When I did mine, I found surprising difficulty re-seating the injectors correctly. They wanted to go in at an angle, and then I can well believe you'd get the above result if you did them up tight. Don't know how to explain that they are correct, except that they should do up smoothly and you should have no sense that one side is harder than the other to tighten.

Yes you are right! It underlines the importance of being/making sure that the threads are clean and the nuts turning smoothly so you know that the torque is being applied correctly. Lesson learned!

 

[penberth3]

...The torque setting was quite low and I wonder if when I gave the nuts a final 'check' ( without using the torque bar) I was just too heavy handed.
Looking at the collar in situ I can see that excessive tightening could well put a 'snapping load' on it. The downward force would then be transferred sideways and possibly bend the stud(s)...

I might be stating the obvious here, but don't just heave on one end of a bar or torque wrench. Support the "business end" with your other hand, that will help to avoid any bending or twisting