BMC 1.5 Injector 'top hat' heat shields

[Guy J]

Heat shields

On removing my injectors I discovered cylinder 1 injector was without a ‘top hat’ heat shield, just the lip in the hole and nothing beneath, neither was there a  heat shield stuck on the top of the injector, as in photo 1.

Cylinders 2, 3 and 4 have the lip and then a washer, seated in the hole, as seen in photo 2. This is definitely a washer as we rotated one by 90 degrees.  Cylinder 1 piston head had significant scoring, which could have been caused by the washer disintegrating and falling into the combustion chamber.

I bought one heat shield to try in cylinder 1, with all correct washers in place and the ‘top hat’ shield is too big to go down beneath the lip, so the injector is not inserted far enough, as shown in photo 3

The outer diameter of the ‘top hat’ heat shield is 17.4mm, and the diameter of the hole bored beneath the lip is 14.5, therefore there is no way the shield will fit in the hole. The diameter of the injector nozzle is 13.8mm.  When the top hat shield is fitted over the injector nozzle, there is about 1.5 mm of play.  The new injectors are exactly the same dimensions as the old ones, the engine is standard, as far as I’m aware, probably 1980s, and was running, seemingly very well, without heat shields but with these washers balanced in place for quite a few years.

What should I do?

Guy

[Tony Brooks]

I have been conversing with Guy on this - I now suspect Perkins injectors. @Tracy D'arth do you have the relevant nozzle lengths - or anyone else. Thanks

[Tracy D'arth]

I don't have the nozzle lengths to hand but I know that the Perkins ones will push the bottoms off the heat shields even though the extra length is not a lot.

A decent diesel shop will know if you phone them. If they say the injectors are the same they are wrong, wallies, and phone someone else.

[Tony Brooks]

2 minutes ago, Tracy D'arth said:

I don't have the nozzle lengths to hand but I know that the Perkins ones will push the bottoms off the heat shields even though the extra length is not a lot.

A decent diesel shop will know if you phone them. If they say the injectors are the same they are wrong, wallies, and phone someone else.

 

Thanks, that is basically what I told the OP. It looks as if he has got hold of overhauled injectors, but if it is Ebay, goodness knows what they are.

[Tracy D'arth]

2 minutes ago, Tracy D'arth said:

I don't have the nozzle lengths to hand but I know that the Perkins ones will push the bottoms off the heat shields even though the extra length is not a lot.

A decent diesel shop will know if you phone them. If they say the injectors are the same they are wrong, wallies, and phone someone else.

If the heat shield is a larger diameter its the wrong one.  But are you sure that the sleeve of the old heat shield has been removed from the hole?  Has it lost just the flat bottom end, that is what usually happens.

You have to have a top hat shield in as otherwise the steel corrugated fire washer has nowhere to sit!

[Tony Brooks]

22 minutes ago, Tracy D'arth said:

If the heat shield is a larger diameter its the wrong one.  But are you sure that the sleeve of the old heat shield has been removed from the hole?  Has it lost just the flat bottom end, that is what usually happens.

You have to have a top hat shield in as otherwise the steel corrugated fire washer has nowhere to sit!

 

Emailed him that possibility 5 minutes ago and asked for a photo of the hole with no heat shield in place. He said he had washers down the hole but no more info, he also said it started and ran OK so I doubt the heat shields were totally missing.

[Tony Brooks]

Update. I have been sent a photo, and it very much looks as if Tracy is correct in that the old, but broken, heat shield is still in place.

[Tracy D'arth]

I thought that was a possibility.

A big thread cutting tap is what I use to pull the old top hats out.

[Tony Brooks]

4 minutes ago, Tracy D'arth said:

I thought that was a possibility.

A big thread cutting tap is what I use to pull the old top hats out.

 

Funny you should say that, we had one brazed to a slide hammer.

[Tony Brooks]

To add to the above: sometimes the act of getting the tap to bite into the heat shield was enough to twist it free.

[Guy J]

Thanks very much Tony and Tracy.  Really useful. 

 

You were right! The old heat shields are firmly wedged inside.  One is completely missing its bottom, that's one of the photos I sent yesterday.  I think a tap, as you suggest, will be the best (probably the only) way of removing them.  Another has a bottom which is coming away from the rest of the shield, and uncannily resembles a washer!

 

Regarding the length of the injectors, it's identical, including the nozzle, to the old ones, but I wonder if you could clear something up?

 

We have been trying to figure out why the bottoms of these injectors have become detached, and assume it was through the lack of a copper washer at the bottom of the shield, and also overtightening of the injectors, which I see should only be 12 lb ft.

 

But we would be grateful if you could confirm the following.  When the atomiser washer and the copper sealimg washer are in place with the heat shield over the injector, the copper sealing washer at the base of the heat shield (if it were a hat it would be just above the brim) is still just moveable.  Is this correct?  I am assuming that when the securing bolts are tightened to 12 lb ft, it is slightly compressed and forms a seal, but the top of the top hat is not over stressed by being forced onto the injector (and thus detaching from the rest of the shield).

Am I correct?

 

[Tracy D'arth]

OK,  with NOTHING in the injector hole.  First in is a thin copper washer onto the land in the bottom of the bore.

Then the top hat goes in onto the washer.

Then the steel corrugated fire washer into the bottom of the top hat.

Then the thicker copper washer onto the top flange of the top hat.

Then the injector goes in.

10 minutes ago, Tracy D'arth said:

OK,  with NOTHING in the injector hole.  First in is a thin copper washer onto the land in the bottom of the bore.

Then the top hat goes in onto the washer.

Then the steel corrugated fire washer into the bottom of the top hat.

Then the thicker copper washer onto the top flange of the top hat.

Then the injector goes in.

Section 51D of the manual is the fuel system, fig 1 is the injector assembly and fitting.

If you have not got the manual I can send it to your email address, its too big to go on here.

10 minutes ago, Tracy D'arth said:

OK,  with NOTHING in the injector hole.  First in is a thin copper washer onto the land in the bottom of the bore.

Then the top hat goes in onto the washer.

Then the steel corrugated fire washer into the bottom of the top hat.

Then the thicker copper washer onto the top flange of the top hat.

Then the injector goes in.

Section 51D of the manual is the fuel system, fig 1 is the injector assembly and fitting.

If you have not got the manual I can send it to your email address, its too big to go on here.

Be certain that your injectors are BMC with the tiny tiny side spray hole offset from the needle, Perkins ones WILL push the bottoms out of the top hats.

10 minutes ago, Tracy D'arth said:

OK,  with NOTHING in the injector hole.  First in is a thin copper washer onto the land in the bottom of the bore.

Then the top hat goes in onto the washer.

Then the steel corrugated fire washer into the bottom of the top hat.

Then the thicker copper washer onto the top flange of the top hat.

Then the injector goes in.

Section 51D of the manual is the fuel system, fig 1 is the injector assembly and fitting.

If you have not got the manual I can send it to your email address, its too big to go on here.

Be certain that your injectors are BMC with the tiny tiny side spray hole offset from the needle, Perkins ones WILL push the bottoms out of the top hats.

Its the length of the bottom thin end of the injector that is longer on the Perkins not the overall length of the injector stem. It matters not how tight you screw the injectors in over 12 ft/lbs, if they are wrong parts, the damage will be done as soon as you tighten them down.

Edited March 3 by Tracy D'arth

[Tony Brooks]

Wot Tracy said ^^^^