Carbon or diamond?

MikeT · Post by **MikeT** » 04 Aug 2008, 12:14

I thought I'd take a look at the injector under magnification to determine if they require cleaning and was amazed to see brilliant shiny points of reflected light dotted among a carpet of matt black carbon.

Are these diamond crystals? I can't imagine what else they could be.

How easy is it to DIY clean these injectors? I'm thinking of soaking them in a suitable solvent or buying an ultrasound cleaning bath from Maplins.

What are your thoughts?

Post by **CitroJim** » 04 Aug 2008, 12:25

Don't know about the diamond Mike. But I doubt it. More likely combustion products

Otherwise XUDs would suddently become exceedingly valuable if the somehow started creating diamonds from diesel!!!

Injectors can be taken apart and gently cleaned. The top of the body just unscrews from the lower and the injector can then be dismantled. Beware of the spring and the shim atop it. The shim sets the injection pressure and is unique to that injector.

Work in absolutely sterile conditions and treat the pintle with extreme care when cleaning it. Everything is calibrated and delicate.

Cheap ultrasonic cleaners are total rubbish in my experience. Use a soft cloth and a bit of solvent.

Be extra careful with No.3 Injector with the needle lift sensor on it.

After dismanting and cleaning, there is no guarantee the old calibration will remain valid. Professional diesel engineers use specialist equipment to check spray patterns and pressures after cleaning.

jgra1 · Post by **jgra1** » 04 Aug 2008, 12:25

not sure Mike.. but am keeping an eye on your posts as I am a few hours behind you

MikeT · Post by **MikeT** » 04 Aug 2008, 13:09

Jim, I doubt they are diamonds, I'm more thinking it's the crystals themselves that form diamonds. I assume the cylinder pressures and temperatures are sufficient but it's a far cry from producing anything of value otherwise I would have kept it secret

They are so brilliant in fact, they ruin the contrast to see where the carbon is, but under a lesser magnification I can see a small circle of carbon around the pintle and clumps/smudges lying around the that.

What solvent is best to dissolve this, bearing in mind it is well and truly cooked and glass-like?

Jgra1, I've been reading your recent posts and am interested about the oil leak you have. Is it similar to the one I'm trying to identify? See the Blogs & Galleries section for more info. You can blog your adventures there too if you like.

jgra1 · Post by **jgra1** » 04 Aug 2008, 14:22

hi Mike, have just read quite quickly through your entire post....

very good.. did not even know that section was there

Your car looks a carbon copy of mine underneath ! I will add pics to the blog detailed in my signiture, tonight...

Looking at the back of my engine before i jet-washed it, I really cannot see HG Oil leakage.... I am starting to hope the a more simple leak has been allowing oil around the block and down the back, for many years....

will keep you posted.. Should have head off tonight..

J

XantiaMan · Post by **XantiaMan** » 04 Aug 2008, 14:37

Yep, its a little known fact that the small, carbon crystaline deposits you see in your combustion chamber are a derivative of what we know as a diamond, also an allotrope of carbon to be more precise.

It's more apparant when vegetable oil is used for some reason. I would advise taking a sample of the deposits for examination to verify the quality, sounds like your engine is a bit of a gem...

MikeT · Post by **MikeT** » 04 Aug 2008, 14:55

What worries me is the cylinder temperature required to form these crystals - AFAIK, it requires 1200 degrees which, if that were the exhaust temperatures then my head may well be cracked

KP · Post by KP » 04 Aug 2008, 16:09

Engines can take a bit higher temp than that,

I've seen recorded temps near 1300 on coupe exhaust outlets before now, thats on the collector before the turbo as well so in cylinder and outlet port temps must be a bit higher...

XantiaMan · Post by **XantiaMan** » 04 Aug 2008, 16:35

MikeT wrote:What worries me is the cylinder temperature required to form these crystals - AFAIK, it requires 1200 degrees which, if that were the exhaust temperatures then my head may well be cracked

EGT's on petrols can easily exceed 900C, diesels quite a bit less though.

Post by **CitroJim** » 04 Aug 2008, 17:29

Diesel EGT is comparatively low. One reason why a Diesel Turbo cannot be used on a petrol engine. You risk melting it!!!