Friday, 20 May 2011

Glow Plugs

Jobs you haven't done before, especially when the internet is full of forebodings of woe, seem a bit daunting. When it all goes well and may even appear to have been some use, I wonder what all the fuss was about.

Starting isn't one of Tortoise's BMC's fortes at the best of times. One thing I wanted to check was the glow plugs, so I hoiked them out one at a time and had a look. They all glow nicely when powered up (albeit taking a while to get to red hot), so there doesn't seem to be any rush to buy new ones quite yet.

Three out of four, though did seem to be pretty much bunged up with carbon - I cleaned out the holes with a 4mm, then 4.2mm drill bit, which seemed to do the trick. Tony Brooks et al suggest 11/64", approx 4.35mm, so I should be OK. I did worry about losing the drill bit inside the engine block, though.

Afterwards the engine started OK, but it often does, so at least I hadn't made it worse. The electrics leave something to be desired though - the voltage at the starter battery (itself an old domestic one of unknown history) when the glow plugs are running is less than 12v, and there's a 0.7v volt drop to the glow plugs. A new starter battery (anyone used a smaller 40Ah car battery as a starter - any reason why not?), and/or thicker wires for the glow plugs (or even better a local relay connected to the starter volts into the solenoid) would improve things no end.

No pictures, although I really should have taken some.

In other news, it's Towel Day on Wednesday, and just in case you were wondering, wikipedia have a lengthy article on the meaning of life, so we need wonder no more.

I'll have a wander around Rickmansworth festival on Saturday; it beats working.


Halfie said...

You say that the voltage at the battery when the glow plugs are glowing is less than 12V, and that there's about 0.7V dropped across the cable to the plugs. If you were to lessen the voltage drop to the plugs by some means the plugs would draw more current (and get hotter quicker - good) but would mean even less voltage would be available at the starter motor for turning the engine. Just a thought.

Simon said...

better the current goes into warming the glow plugs than the wiring...

TBH the poor battery just serves to highlight other weak points in the system; it would be good to remove them all.

Neil Corbett said...

I think amp hrs are not important for starter batteries. What you need to know are the cold cranking amps CCA and I think for a 1.5 diesel to cope in cold weather you might need 700cca or more. I think mine is 900.

Good work with the glow plugs. I ought to drill out mine. Did you have anything to hold the drill bit or just your fingers?


Simon said...

ah, useful, car batteries seem to be about 300CCA, although that's on far too little research. I'm sure I used a car battery for a while a few years back, though. ;-)

Drill bit was just held in the hand, although since the 4.2mm bit is supposed to live with my tap & die kit, I realised the tap handle would have done fairly well as a handle. Having said that access was a problem, for removal as well as reaming out; I ended up removing most of the fuel injection pipes, just to get the things out...