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Glow Plug

From a book written by a well known English modeller... first printed

1978 and reprinted many times upto present date.

Basically he states... There are 2 main types of plug, the plain coil plug and the idle bar (or shielded) plug. The theory of using the latter plug is that at idling it protects the coil from impingement of fuel droplets and possibly assists in keeping the plug hot. Recommendation is... there are many types of plugs but start with the manufacturers recommended plug.

I have seen the same info. in other places as well as that book. The engine I was mentioning was over 15 years old and came with an idle bar plug as standard. The piston had a ridge formed on top of it and I guess that was to help in compressing the fuel charge and also possibly directing it around the cylinder head and not directly into the plug ??? The ridge was off-centre and on the inlet side of the piston.

Knowing what I do now I would have changed the plug for a much hotter version... however I only knew at that stage that the plug fitted had an idle bar and I was assured that they were very dificult to get now. I later found out that they are not difficult to get at all.

Fact was... it ran great in reasonably warm weather, as soon as the temp went down to around freezing it wouldn't start at all. I reckoned the fuel charge was cold enough, combined with the cold metal, to prevent the glow getting hot enough for ignition... effectively quenching the glow. Temperatute went up... engine back to normal. No amount of retuning would cause it to start in the cold. I spent 1 1/2 hours on it on one occasion.

My modern replacement engine has much better porting and an improved 'squish' area in the head.

Reg

Reply to
tux_powered
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That ridged piston is an old form of loop charging. It was an attempt to make the incoming charge take a longer path around the cylinder so that less of it would immediately exit the exhaust. Modern multi-port designs use something that was developed by Yamaha (IIRC) where the opposing transfer ports caused the incoming charges to collide, thus stopping their motion (relatively!) and the boost port attempted to flush the remaining burned fuel out. Many call this Schneurly (SP?) porting but the concept predates that by several years. I was working for a racing shop when the new Yamaha roadracing engines came out. It was a bizarre concept back then, but they won races!

The most likely reason that glow engines won't start at freezing temps is because the methanol just won't vaporize properly at those temps. Add to that the extra cooling of drawing it through a venturi and it may even freeze or ice up. Sure, then you get raw fuel drops on the glow plug but I think the battery would easily overcome that. No vapor, no fire.

Reply to
Paul McIntosh

I don't have any specifics, but one can probably do like the truckers and "winterize" the fuel with some percentage of pump gas?

Reply to
Steve Banks

That port design was developed a long time ago in the thirty's, not by Yamaha. The boost port is not required except for very high performance, it really only kicks in at high RPM. If you put very large props on your two strokes you may actually increase performance by blocking off the boost port. The control line guys do this on a regular basis, and OS recently did this on the LA series.

Reply to
Sport Pilot

Ah, that makes sense..another of life's little mysteries cleared up >:-)

Schneurl porting, I only recently came across a description of the basics, seems to be favourite and more efficient.

He,he, the only thing I didn't try was a flint and steel >:-) I think a bonfire was in the offing though until SWMBO suggested getting another engine.

Reg

Reply to
tux_powered

Never seen anything along those lines mentioned anywhere. A couple of ideas came up earlier in the thread.. a shot of WD 40 or a squirt of lighter fluid as a means to ease cold starting.

Reg

Reply to
tux_powered

I have known a prime of model diesel engine fuel to help on a very cold day with a recalcitrant glow engine.

I assume it's the volatility of the ether content.

On that basis one of the aerosol "cold start" products for automobile diesel engines, if they are still marketed, - I seem to remember these were ether with some form of propellant - a squirt into the venturi might do the job.

Malcolm

Reply to
Malcolm Fisher

No mixing - no "measuring" volume required!! When you arrive at your flying site and vehicle is still running: "Plug" the head of your models engine into the vehicles exhaust for a couple minutes. The engine then "thinks" it is summer and off you go!!

Reply to
Tony

If anyone is interested, I came across this web site from a club in NC

A really good source of info-

They have this link about all you ever wanted to know about glow plug ( types, brands, etc. ) very good point for reference.

http://209.15.36.61/rdrc/gloplugs.htm

-- valentr

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valentrd

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