Blow it, it won’t shift

Canal Boat - - Back Cabin: -

QI de­cided to check the glow­plugs in our BMC 1.5. Two were okay, one glowed only half­way up, and the other one snapped off and left the glow­ing end stuck in the cylin­der head. I can just get a pair of long nosed pli­ers on it, but can­not budge it. My only thought is to spray some oven cleaner around it and try turn­ing the en­gine over and see if the com­pres­sion will move it. Do you have any other sug­ges­tions?

MARK BROWN, via email

ATONY REPLIES: Oven cleaner might work, but as the cleaner will have to pen­e­trate sev­eral mm of baked hard car­bon, I rather doubt it. To do the job with 100% like­li­hood of suc­cess you should take the cylin­der head off and that in­jec­tor out, so you can blow and shake any swarf out of the pre-com­bus­tion cham­ber. If you will set­tle for a 98% chance of suc­cess, leave the head on and re­move the in­jec­tor plus the ‘in­verted top hat’ heat shield from below the in­jec­tor (a new cop­per washer should be re­fit­ted un­der the heat shield upon re­assem­bly). If a 95% chance of suc­cess is okay, sim­ply re­move the in­jec­tor (re­place the atom­i­sa­tion washer). If you will set­tle for a 90% like­li­hood of to­tal suc­cess, leave the in­jec­tor in. (The risk is that the end of the bro­ken tip might em­bed it­self in the pis­ton, or get stuck un­der a valve – nei­ther has hap­pened to me yet.)

Get a drill bit no more than 0.5mm larger than the glow­plug tip (I think it’s 7/64in) in a hand or low power bat­tery drill, grease the tip of the bit and drill the tip out for a few mo­ments. Wipe the grease and swarf off the tip of the drill and re-grease. Drill again for a few mo­ments and re­peat un­til you feel the drill break through into the pre-com­bus­tion cham­ber. Use the same drill to drill the car­bon from all of the other glow­plug holes. Pro­tect your eyes and spin the en­gine on the starter to blow any swarf and loose car­bon out of the holes.

Coat the tip and thread of all the plugs with cop­per grease be­fore re­fit­ting. To avoid this prob­lem again I would sug­gest that you re­peat at three-yearly in­ter­vals.

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