My EGR cooler hoses finally gave up, world class engineering there, placing rubber bits in close proximity to hot bits! I figured I would replace the ceramic glow plugs with the metal ones. #3 came out first missing about 25 % of the tip, #4 & #2 were undamaged, and #1 was missing 50% of the tip. Sweet! Carbon build up on #3 leads me to think this was not a recent development. Lack of carbon on #1 is worrisome. I have access to a snap on borescope but the tip is about 9mm, too large for the glow plug hole. I would like to know the dimension of the injector tip to see if the borescope tip will fit through there. Thanks

I have not pulled my CRD injectors to check the tip size, but my old Perkins 354T had tips that were around 6mm to 7mm. My Wife's TDI tips are smaller. As injector technology advances they are getting smaller, not larger. I have no plans to pull my CRD injectors until I have to to have them rebuilt, but not being a gambler, I would willingly sucker bet that the CRD injector tips are closer in size to the TDI than the 6mm to 7mm on the old Perkins.
One thing you could do is order an injector copper sealing washer which will be slightly larger than the tip.

Looks like you better plan on pulling the cylinder head.

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2006 Pearl Green CRD
Magnaflow 2 1/2" Cat Back
KJ Extra Leg Room Brackets, Carter Lift Pump, V6 Airbox, ORM
Fuel cooler, Oil Separator, Progard 7
Gauges EGT Boost Trans Temp Oil Pres, Michelin LXT AT2 245 70 R16
7,000# Draw Tight hitch, PML EX Deep Trans Pan
Centrifuge, SunCoast, Transgo, RAM TCM, InMotion Stage 2
Wife's 99 TDI VW Beetle

The glowplug shaft (the portion of the glow plug that glows) is approximately 4.8 mm in diameter measured with a digital caliper this morning (Bosch ceramic) The end of the tip is tapered and much smaller