Having used glow plug engines for over fifty years, I really should know the answer to this question!

[David Davis 2]

Most of my four-stroke engines audibly lose a few revs when I remove the glow igniter from the glow plug on start up, otherwise they run perfectly.

 

Does this mean that I have the low speed needle set too rich?

[J D 8]

Unless engine is very smoky, and some, Enya do like a rich low. I recon it is just because engine has not warmed up fully.  If reliable leave it as is.   John.

[Paul De Tourtoulon]

Yes, most 4 strokes and 2 strokes will drop a few RPM's, don't worry about it, throw it in the air where it belongs.

[Nigel R]

As noted above, glow motors often lose RPM at low speed without the driver. If the idle is reliable without it... well, who cares? Worry about nailing the full throttle tuning, and getting idle + transition reliability, everything else is not that important.

 

Just thinking aloud about factors affecting the ignition timing on our glow motors, there are a lot - heat of engine, heat of plug element, element wear, element composition, fuel/air mixture, how well the carb atomises the fuel... adding or removing a glow driver to the mix changes that balance by adding heat to the glow element + advancing the ignition point.

 

Worth noting that automotive diesel engines - which also rely on compression ignition - use direct injection at terrific pressure and can time the injection squirts to affect ignition timing. We have none of that control!

[Martin Harris - Moderator]

I use that as an initial indication that the idle mixture is too rich.  Unless massively rich you’ll probably get away with it but a properly designed carb will not give any obvious drop and should work reliably over its whole range if leaned correctly. 

[Nigel R]

I'd only somewhat agree Martin - I've several engines that I've tweaked and tweaked to get "perfect" transition and they've wound up in a slightly different needle setting to the "perfect" idle. It's a balance, as ever.

 

I'd add that carbs with an old or busted O ring are never going to be right, so there's that, too.

[Martin Harris - Moderator]

Absolutely - that’s why I qualified the design aspect.  Manufacturers don’t always get it right - I believe at least one had to replace a number of badly designed throttle barrels some years ago where the scroll was wrong and made them horrible to try to tune in  mid range. 

[Engine Doctor]

Very simply ,your engine looses a few revs as the glow plug cools slightly without the electrical current to heat the coil.  This efectively retards the timing slightly. As already said other factor all play a roll in the timing of a glow engines. If glow plugs are very old this slowing can be more noticeable. For the same reason you should never run a glow engine at full thtottle with the glow swithched on as this can cause pre ignition or knock and damage the engine resulting in extreme cases with a hole in the piston crown. Prop throwing is a prime example of over advanced ignition often caused by a weak mixture at full throttle. This knock will also shorten the plug life.  Modern designs have to a greater degree engineered out this  extreme knock. Assuming mixture is correct then its perfectly normal. If the coil in your engines glowplug looks white an crystally instead of silver then its getting past it. If engine still runs reliably apart from that then just fly it.

Us oldies will remember when fiddling with our cars that if the timing was set wrong we heard a tingling sound , a bit like the sound made when tapping the bottom of a cup with  a pencil . This only occured when engine is under load as  when accelerating , its called pinking. Also heard is a lower octane fuel than the engine was designed for was used. 

Edited April 11 by Engine Doctor

[Paul De Tourtoulon]

30 minutes ago, Engine Doctor said:

we heard a tingling sound

I was told it was 'pinking',

 

 Diesel Injectors, if my memory is right, were regulated as far as 230 bars on the 6 cylinder Volvo engines.

[Jim Hearnden 1]

Can be a sign that the plug is past its best, they go white & crystalline long before they fail. You'll need a jewellers loupe to check though.

Also sometimes worth playing with heat ranges as well.

[Cuban8]

Not something that I've given too much thought to, but the nature of the glow ignition system precludes any seperate ignition timing system that you will find on spark ignition systems. Usually highly critical, especially on high performance two stroke motor bike engines (still have my Mitutoyo dial gauge and spark plug adapter from back in the day) a mis-set engine would blow a piston crown very quickly. Points just open at 1.8mm BTDC IIRC on my Yamahas. Auto advance weights would take care of the advance from the basic static timing point.

How do our glow ignition (and I suppose compression ignition diesels) cope with the timing change requirements across the rev range? Presumably ignition has to advance as revs increase? With no mechanical or electronic advance - what's occuring?

Edited April 11 by Cuban8

[PatMc]

5 hours ago, David Davis 2 said:

Most of my four-stroke engines audibly lose a few revs when I remove the glow igniter from the glow plug on start up, otherwise they run perfectly.

 

Does this mean that I have the low speed needle set too rich?

David, I think that you posted this 10 days too late. 😉 

[Geoff S]

28 minutes ago, Cuban8 said:

Not something that I've given too much thought to, but the nature of the glow ignition system precludes any seperate ignition timing system that you will find on spark ignition systems. Usually highly critical, especially on high performance two stroke motor bike engines (still have my Mitutoyo dial gauge and spark plug adapter from back in the day) a mis-set engine would blow a piston crown very quickly. Points just open at 1.8mm BTDC IIRC on my Yamahas. Auto advance weights would take care of the advance from the basic static timing point.

How do our glow ignition (and I suppose compression ignition diesels) cope with the timing change requirements across the rev range? Presumably ignition has to advance as revs increase? With no mechanical or electronic advance - what's occuring?

 

I still have a 'pressure relieving' piston from my BSA BB34 Gold Star motorcycle (a 4 stroke, of course) which was caused by a worn out TT carburetor (I replaced it with a Monobloc).  I use it as as a soldering iron rest sometimes 🙂

[Martin Harris - Moderator]

2 hours ago, Cuban8 said:

Not something that I've given too much thought to, but the nature of the glow ignition system precludes any seperate ignition timing system that you will find on spark ignition systems. Usually highly critical, especially on high performance two stroke motor bike engines (still have my Mitutoyo dial gauge and spark plug adapter from back in the day) a mis-set engine would blow a piston crown very quickly. Points just open at 1.8mm BTDC IIRC on my Yamahas. Auto advance weights would take care of the advance from the basic static timing point.

How do our glow ignition (and I suppose compression ignition diesels) cope with the timing change requirements across the rev range? Presumably ignition has to advance as revs increase? With no mechanical or electronic advance - what's occuring?

Timing is self regulating by the amount of heating of the element.  As loading with increasing revs increases, the element (a catalyst) reacts with the methanol more readily, effectively advancing the point of ignition. 
 

If an engine such as the magneto equipped Zenoahs has no method of varying the timing, you have to compromise either to easy starting or maximum power.  Damage mostly occurs when timing is over advanced, causing detonation, which causes the damage to piston crowns etc.  Normal engine running is a controlled burn - not an explosion, which detonation is akin to. 

[Engine Doctor]

2 hours ago, Paul De Tourtoulon said:

I was told it was 'pinking',

 

 Diesel Injectors, if my memory is right, were regulated as far as 230 bars on the 6 cylinder Volvo engines.

Hi paul   . Yes pinking  thats what i said. Its nothing to do with injectors but compression and burn speed of the fuel being used in  the cylinder.

As for how our glow engine ignition works i can only give my  practical or  real world opinion as  I have no degree and im not into the theory side of things.

 If you run an engine where you can see inti the exhaust port , something like a cox 049 you can see the reflection of the glow plug. As you increase speed you can see the gp coil gets much brighter/ hotter . Connect a battery and it will glow almost white hot. Its the extra heat causing a quicker reaction with the fuel and platinum coil that advances the ignition process. The ignition ofmethanol is partly heat and partly due to a catalytic reaction with platinum and as we all learnt ar school heat speeds up these reactions.

Diesel engines or compression ignition  work similarly but with a much higher compression ratio typically 16:1 or higher.  The faster the engine  revs the hotter the cylinder gets so advancing the ignition point /timing. If our model diesels get too hot they over compress and will eventually stop. You may also have noticed if a vintage model when a diesel starts to over compress they eiund heavy and laboured. A  long shallow dive often cools it enough to run well again and even induce a occasional misfire or under compression as timing is retarded again.

 

[Geoff S]

I have a model on eBay at the moment and I browsed a bit and found glow plugs to be astronomically expensive (or out of stock?)

[Cuban8]

Interesting stuff. Not essential to know the ins and outs, but all part of the pleasure of the hobby. 

Wasn't aware that Zenoah sparkies had no advance and retard - rather like my lawn mower I guess - all a compromise to keep it simple.

[Engine Doctor]

4 minutes ago, Cuban8 said:

Interesting stuff. Not essential to know the ins and outs, but all part of the pleasure of the hobby. 

Wasn't aware that Zenoah sparkies had no advance and retard - rather like my lawn mower I guess - all a compromise to keep it simple.

As you say a compromise hence the lower power than the electrnic ign models. The timing was also set at a compromise for srarting and best running. Very simple the mag models but you paid the price in weight and a heavy flywheel .

[Nigel R]

2 hours ago, Engine Doctor said:

Hi paul   . Yes pinking  thats what i said. Its nothing to do with injectors but compression and burn speed of the fuel being used in  the cylinder.

As for how our glow engine ignition works i can only give my  practical or  real world opinion as  I have no degree and im not into the theory side of things.

 If you run an engine where you can see inti the exhaust port , something like a cox 049 you can see the reflection of the glow plug. As you increase speed you can see the gp coil gets much brighter/ hotter . Connect a battery and it will glow almost white hot. Its the extra heat causing a quicker reaction with the fuel and platinum coil that advances the ignition process. The ignition ofmethanol is partly heat and partly due to a catalytic reaction with platinum and as we all learnt ar school heat speeds up these reactions.

Diesel engines or compression ignition  work similarly but with a much higher compression ratio typically 16:1 or higher.  The faster the engine  revs the hotter the cylinder gets so advancing the ignition point /timing. If our model diesels get too hot they over compress and will eventually stop. You may also have noticed if a vintage model when a diesel starts to over compress they eiund heavy and laboured. A  long shallow dive often cools it enough to run well again and even induce a occasional misfire or under compression as timing is retarded again.

 

 

Also worth adding;

 

at idle - with the engine running at a vacuum in the intake, there is comparatively little air/fuel charge to be compressed, with a low amount of compression comes a low amount of heating of the intake charge

at full throttle - the engine is running wide open, a much larger air/fuel charge enters the motor, thus more compression occurs, and with more compression comes a larger increase of charge temperature

 

the hotter mixture contributes to the advance of ignition

 

"Diesel engines or compression ignition"

 

Technically, glow engines are compression ignition - aided and abetted by the catalyst in the glow plug of course.

[Paul De Tourtoulon]

Pinking is pre-ignition too hot and or mix to lean on petrol engines.

[David Davis 2]

I asked the same question on "Glow Nation," on a well-known social media site. My post has been moved "lower in the feed" because it appears to incite violence! I promise you that I am not making this up!

 

Big Brother is indeed watching you.

 

 

"We moved one of your posts lower in Feed.

David John DavisGlow Nation

odnSeorspt7i6uhh10113ufh2gguig4m00c1a2iu671m5c646fgtg9t21c52  ·

Most of my four-stroke engines audibly lose a few revs when I remove the glow igniter from the glow plug on start up, otherwise they run perfectly.

Does this mean that I have the low speed needle set too rich?

After having used glow engines for over fifty years I really should know the answer to this question!

 

What happened

Our technology showed that this post looks like others that go against our Community Standards for Violence and incitement.

We don't allow people on Facebook to share content that leads to a genuine risk of physical harm, or a direct threat to public safety"

[GrumpyGnome]

Sadly, they do allow people to post absolute drivel and nonsense....

[Eric Robson]

3 hours ago, David Davis 2 said:

I asked the same question on "Glow Nation," on a well-known social media site. My post has been moved "lower in the feed" because it appears to incite violence! I promise you that I am not making this up!

 

Big Brother is indeed watching you.

 

 

"We moved one of your posts lower in Feed.

 

David John DavisGlow Nation

odnSeorspt7i6uhh10113ufh2gguig4m00c1a2iu671m5c646fgtg9t21c52  ·

Most of my four-stroke engines audibly lose a few revs when I remove the glow igniter from the glow plug on start up, otherwise they run perfectly.

Does this mean that I have the low speed needle set too rich?

After having used glow engines for over fifty years I really should know the answer to this question!

 

What happened

Our technology showed that this post looks like others that go against our Community Standards for Violence and incitement.

We don't allow people on Facebook to share content that leads to a genuine risk of physical harm, or a direct threat to public safety"

Best not mention shaping the nose with a razor plane or 6 policemen will turn up at your door.

[Chris Freeman 3]

A drop in revs could be mixture too rich, it can also be the fuel might not be good, more nitro needed or the plug not good or incorrect heat range.