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Care & Feeding a DC Dart

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Old 11-09-2012, 03:42 PM
  #51
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Default RE: Care & Feeding a DC Dart

I kow I uploaded them with the reply but they didn't attach.  The site admin is aware of it.  The instructions are (1) very generic, and (2) very short.  If you want a copy, email me at  ama40916@comcast.net.  Steve_P.
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Old 11-09-2012, 07:54 PM
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Default RE: Care & Feeding a DC Dart

Well today's episode - The owner has an Allbon Dart that has shaft problems, and is going to see if Allbon piston will mate with the DC cylinder.

We may have this little bloke going yet.

The DC piston crown does look a bit ground down. Ray's suggestion of cherry bombing may hold water OR the factory hand in charge of grinding the parting off *** from the crown had an unfortunate accident. Either way it was never going to make for a happy runner.

More as it develops.

G
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Old 11-09-2012, 10:04 PM
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Default RE: Care & Feeding a DC Dart

Or the DC crankshaft in the Allbon?
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Old 11-10-2012, 12:56 AM
  #54
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ORIGINAL: fiery

Or the DC crankshaft in the Allbon?
That would be much better if it fitted nicely.

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Old 11-16-2012, 02:24 PM
  #55
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Default RE: Care & Feeding a DC Dart


Quote:
ORIGINAL: qazimoto


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ORIGINAL: Recycled Flyer


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ORIGINAL: qazimoto


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ORIGINAL: Recycled Flyer

Greg, if it is still hard to get going try the tip from Steve Rothwell - preheat the whole thing with a heat gun or hair dryer.

It just may help mate.

I can't really see how Chris. If the fits are marginal it will make starting even harder.

You usually heat the upper cylinder with a heat gun or cup of boiling water if the P/L fit is so tight that turning over is difficult.

Ray
If the whole engine (and I did say ''preheat the whole thing'' not just the upper cylinder) is brought up to a mild even heat I can see it making a difference over a stone cold one Ray.


Please explain!

Sure.

Heat is one of the essential ingredients for internal combustion and it is what we absolutely do not have in a cold stationary engine.

In a cold and primed moving engine (like a model diesel upon starting) we rely on the incredibly low flash point of ether and the quite high compression ratio for the 'flash' and futher a falsely high comp setting to reach this flash point just before TDC . As the engine warms we no longer need that high comp setting because the extra stored heat in the mass of the engine now supports a lower ratio and the now added heat would advance the ignition too far.

So, if the engine is suffering the abnormality of worn parts and the inevitable loss of compression this brings it will retard the ignition to sometimes an unusable starting point - and adding heat to the entire engine will reverse this process.

It is exactly the same starting principle with a real diesel and its glow plug, add a source of heat and it starts and remove it once run temps are achieved.
It is the same principle with methanol glow engines, they won't start without a secondary heat source.
And it really is the same with petrol engines and their spark plugs.

The difference here with model diesels is that the added source of heat ONLY comes from compression, so we aid that upon start up if compression is compromised.

It stands to reason that any engine should run best at 'run' temperatures so it should start best at that temp also, the problem with restarting a hot air cooled model engine is that not all parts are at run temps when you go to restart it due to incoming fuel cooling the piston more than the liner and shrinking the piston fit ( and here a model diesel with its leaner, drier fuel air ratio benefits by not cooling the internals anywhere near as much as a glow engine does). But remove the 'air cooled' bit with a heat gun and you are right back to correct run settings again.

So if the compression in a model diesel is compromised and retarding the ignition below the start threshold ,raise up it back up again with some added heat from the outside in.

Thanks.

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Old 11-16-2012, 02:53 PM
  #56
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Default RE: Care & Feeding a DC Dart


Quote:
ORIGINAL: Diesel Fan


Quote:
ORIGINAL: qazimoto


Quote:
ORIGINAL: Recycled Flyer


Quote:
ORIGINAL: qazimoto


Quote:
ORIGINAL: Recycled Flyer

Greg, if it is still hard to get going try the tip from Steve Rothwell - preheat the whole thing with a heat gun or hair dryer.

It just may help mate.

I can't really see how Chris. If the fits are marginal it will make starting even harder.

You usually heat the upper cylinder with a heat gun or cup of boiling water if the P/L fit is so tight that turning over is difficult.

Ray
If the whole engine (and I did say ''preheat the whole thing'' not just the upper cylinder) is brought up to a mild even heat I can see it making a difference over a stone cold one Ray.


Please explain!

Sure.

Heat is one of the essential ingredients for internal combustion and it is what we absolutely do not have in a cold stationary engine.

In a cold and primed moving engine (like a model diesel upon starting) we rely on the incredibly low flash point of ether and the quite high compression ratio for the 'flash' and futher a falsely high comp setting to reach this flash point just before TDC . As the engine warms we no longer need that high comp setting because the extra stored heat in the mass of the engine now supports a lower ratio and the now added heat would advance the ignition too far.

So, if the engine is suffering the abnormality of worn parts and the inevitable loss of compression this brings it will retard the ignition to sometimes an unusable starting point - and adding heat to the entire engine will reverse this process.

It is exactly the same starting principle with a real diesel and its glow plug, add a source of heat and it starts and remove it once run temps are achieved.
It is the same principle with methanol glow engines, they won't start without a secondary heat source.
And it really is the same with petrol engines and their spark plugs.

The difference here with model diesels is that the added source of heat ONLY comes from compression, so we aid that upon start up if compression is compromised.

It stands to reason that any engine should run best at 'run' temperatures so it should start best at that temp also, the problem with restarting a hot air cooled model engine is that not all parts are at run temps when you go to restart it due to incoming fuel cooling the piston more than the liner and shrinking the piston fit ( and here a model diesel with its leaner, drier fuel air ratio benefits by not cooling the internals anywhere near as much as a glow engine does). But remove the 'air cooled' bit with a heat gun and you are right back to correct run settings again.

So if the compression in a model diesel is compromised and retarding the ignition below the start threshold ,raise up it back up again with some added heat from the outside in.

Thanks.


Could you explain a bit more please because I'm confused?

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Old 11-17-2012, 02:46 PM
  #57
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Default RE: Care & Feeding a DC Dart

Received said DC from the owner, now has the Albon P&C installed.

Fits seem ok - see above.

Will mount it on the test board and attempt to fire it up, probably later today and report findings. Till then????

G
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Old 11-17-2012, 05:23 PM
  #58
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Default RE: Care & Feeding a DC Dart

Quote:
ORIGINAL: greggles47

Will mount it on the test board and attempt to fire it up, probably later today and report findings. Till then????

G
Well I guess we'll just wait here in anticipation and theorize about why or why not gently heating a clapped out piston/liner could possibly help starting.

Otherwise I've just dug out the fuselage of my DC Dart powered Ebenizer.

It could do with a good clean. I think I might pull the Dart out, clean it up and take a pic of it running, and then stick it on ebay.




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Old 11-17-2012, 06:27 PM
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Default RE: Care & Feeding a DC Dart


Quote:
ORIGINAL: qazimoto

Quote:
ORIGINAL: greggles47

Will mount it on the test board and attempt to fire it up, probably later today and report findings. Till then????

G
Well I guess we'll just wait here in anticipation and theorize about why or why not gently heating a clapped out piston/liner could possibly help starting.

Otherwise I've just dug out the fuselage of my DC Dart powered Ebenizer.

It could do with a good clean. I think I might pull the Dart out, clean it up and take a pic of it running, and then stick it on ebay.

Apparently there was a guy used to fly Aerobatics.
He used a diesel.
To save having to warm up the engine as you would with all our other diesels he ran a fixed comp head and would go out to the flying line with leads attached to a glow plug that was also fitted to the head.
I'd presume a really high nitro cold one with maybe 2 volts supplied to it.
Once he'd given his ready signal, only then would he disconnect the leads from the pre heater and proceed to start the engine!

I've also experienced that WD-40 type lubricants will fire if you flick an engine you've just bathed in heat.
There's no doubt heat helps a recalcitrant engine fire Ray regardless of its mechanical condition, though a well fitted engine will be much more liable to burst into song if it's had some heat soaked into it.
Of course you can go too far!
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Old 11-17-2012, 07:20 PM
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Default RE: Care & Feeding a DC Dart

I've often had CRC 5-56 fire in a diesel that's just been cleaned, reassembled, and given a quick squirt of 5-56 as lube then flicked over with a prop on to distribute it, without any heating required at all. If it occurs at all it's usually within a few seconds of applying the CRC 5-56 (directly into the open exhaust) and I imagine that the hydrocarbon propellant gas helps create a 'fireable' mixture. On a couple of occasions I've had one run-as opposed to just fire-for a second or two on the CRC. CRC 5-56 and WD 40 are fairly similar products..............

ChrisM
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Old 11-17-2012, 07:37 PM
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Default RE: Care & Feeding a DC Dart

I have had WD 40 fire off got a good finger whack martin
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Old 11-17-2012, 07:47 PM
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Default RE: Care & Feeding a DC Dart


I had a new Nova Rossi .21 glow give a burst on the bench about a week ago, on glow fuel without the plug being connected to the power source, after a bump from the electric starter.

Some of the Norvel 15 glows occasionally do the same when flicked, especially with tight Rossi liners.

My experience has been that many engines with very tight p/l fits do need to be heated with boiling water from a thermos flask to get the initial run going.

Once they've had a few runs they gradually become possible to hand start. But this is a issue of fits and expanding the liner top just a little more than the piston via the application of external heat.

Yes, a warmed up diesel with fits good enough that it will start and run at the same compression setting, will start better hot than cold.

However we've been talking about a well worn DC Dart that wouldn't start at all!



Ray
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Old 11-17-2012, 09:47 PM
  #63
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Default RE: Care & Feeding a DC Dart

As a parallel try looking at the old Hot Bulb engines,  they were crudely made two strokes that had low compression ratios and ran on kerosene quite well and needed heat added to start.

And they were the precursors to compression ignition engines.
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Old 11-18-2012, 12:03 AM
  #64
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Quote:
ORIGINAL: Diesel Fan

As a parallel try looking at the old Hot Bulb engines, they were crudely made two strokes that had low compression ratios and ran on kerosene quite well and needed heat added to start.

And they were the precursors to compression ignition engines.

Chris,

what you're suggesting violates the 2nd law of Thermodynamics: That: heat flows spontaneously from a hot to a cold body.

Given similar rates of heat expansion between the liner and piston, if you heat from the engine outside the liner will

always be expanding away from the piston, lessening compression seal. Normally the combustion space heats the lot much more equally.

Ray
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Old 11-18-2012, 12:54 AM
  #65
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Default RE: Care & Feeding a DC Dart

And what happens (following the 2nd law of Thermodynamics) when the heat is removed ?
Will the "isolated system spontaneously evolve towards thermal equilibrium again?"

Does not the liner rapidly contract firstly because it has the greater surface area?

There simply has to be a point of greater benefit where the fits are optimal and the added heat can be of use.

The worn Dart suffers a lack of compression, right? And what use at all is the compression if not to give a heat rise?
So it follows that a lack of comp equates to a lack of heat rise and this is the major reason why it will not start.

These after all are heat exchange engines - no heat, no exchange.


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Old 11-18-2012, 01:17 AM
  #66
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Default RE: Care & Feeding a DC Dart

My brain hurts.
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Old 11-18-2012, 01:46 AM
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Default RE: Care & Feeding a DC Dart

Steve, Ray is right in a s much as the outside exposed surface will expand firstly  - but it will also cool firstly leaving the central mass (the most stable) to cool off the last.

What seems to be the difference in thinking here is the want to relieve a tight liner by a few flicks of a heat gun or using a dip in hot water vs heat soaking the entire engine to proper run temperatures.
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Old 11-18-2012, 02:10 AM
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Default RE: Care & Feeding a DC Dart

Chris, leaving aside fundamental issues of thermodynamics, don't you usually find that an engine with marginal compression becomes, once heat-soaked, an engine with virtually no compression at all?
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Old 11-18-2012, 03:43 AM
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Default RE: Care & Feeding a DC Dart

Diesel Fan said"The worn Dart suffers a lack of compression, right? And what use at all is the compression if not to give a heat rise?
So it follows that a lack of comp equates to a lack of heat rise and this is the major reason why it will not start."

Chris,

The poor little Dart Did not have serious lack of static compression. The problem as previously shown was a pair of cracks around the piston.

These cracks may well have been caused by Mr Piston making frequent contact with Mrs Contrapiston. The primary cause of this contact would be the bevelled piston crown, meaning that to get a running setting, the piston would make the unwanted contact.

All the applied heat in the world wouldn't help the thing to run, unless that heat was applied locally and actually welded the cracks closed.

As for heating worn engines to get them running, I'll leave that to smarter blokes than me. But it does seem to be counter intuitive. The scenario I see is an ill fitting P&C being heated up and thus becoming even less well fitting.

I'm sorry but I don't get it.

Greg
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Old 11-18-2012, 06:45 AM
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Default RE: Care & Feeding a DC Dart

OK GUYS Just my thoughts glow or diesel lets look at an ABC liner with a slight taper near top really tight pinch at top when cold when hot it expands thus pinch lessens diameter has increased ever so slightly. It follows that with a clapped piston for any reason worn, cracked, the compression is now less, for our diesels this is the end of the line for starting. With a steel liner think the same happens, before the piston
expands. the liner expands before piston regardless of material it is made of martin

one of you had stated the piston may have cracked due to hitting the contra that is most likely
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Old 11-18-2012, 02:35 PM
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Default RE: Care & Feeding a DC Dart

Is the radial tank shown a genuine DC accessory?
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Old 11-18-2012, 02:50 PM
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Default RE: Care & Feeding a DC Dart


Quote:
ORIGINAL: steve111

Chris, leaving aside fundamental issues of thermodynamics, don't you usually find that an engine with marginal compression becomes, once heat-soaked, an engine with virtually no compression at all?
Hey Steve,
yes of course a heat soaked engine is easier to turn over regardless of its condition but the point that I am labouring to make is that the only reason compression exists is to provide heat at the correct angle of rotation.

The less heat gained from compression the more that you will need from some other source, how else does 3:1 compression ratio kerosene fueled (note - no ether) poorly made non injected two stroke diesel run? Answer, it uses an auxillary source like a heat bulb.

Let me sign off with one last poser for all, imagine if you will heating up the entire engine so that the combustion chamber is at say 200ºC, would you then need less of a compression ratio to get it started?

And yes, I have tried this but admittably only the once but it seemed to work and be of benefit.

Thanks.

And Greg, yes Iwas running on the assumption that the engine had poor comp but Ithink that this thread has evolved way beyond that specific engine.




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Old 11-18-2012, 03:13 PM
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Default RE: Care & Feeding a DC Dart


Quote:
ORIGINAL: fiery

Is the radial tank shown a genuine DC accessory?
Yes-unquestionably. However it is a 'cuckoo' in the sense that the radial tank mount was originally developed for the DC Bantam, not the Dart-but since the Bantam uses the Dart crankcase the radial tank also fits the Dart. It only appeared in the early 60's-(possibly as early as 1960) with the development of the 'Bantam de-Luxe' variant-you will not find any mention of a radial tank mount in any 1950s DC adverts or literature, though radial backplate flange mounts for the Dart were produced back then. The final iteration was the same tank mount resized for the DC Wasp/Frog Venom backplate (which is larger diameter than the Dart/Bantam. Otherwise near identical in appearance however. The mount was designed with an identical bolt spacing to the Cox Babe Bee/Golden Bee/QZ/Black Widow/Venom/Texaco reed valve range so DC engines could be used in lieu of the Cox imports.

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Old 11-18-2012, 03:58 PM
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Hey Steve,
yes of course a heat soaked engine is easier to turn over regardless of its condition

Chris, that is not what I was saying at all, as you must surely be aware. What I said was, "Don't you usually find that an engine with marginal compression becomes, once heat-soaked, an engine with virtually no compression at all?" Which is quite a different thing.
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Old 11-18-2012, 04:33 PM
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Quote:
ORIGINAL: steve111


Quote:
ORIGINAL: Recycled Flyer


Hey Steve,
yes of course a heat soaked engine is easier to turn over regardless of its condition

Chris, that is not what I was saying at all, as you must surely be aware. What I said was, "Don't you usually find that an engine with marginal compression becomes, once heat-soaked, an engine with virtually no compression at all?" Which is quite a different thing.
No, how would it keep running if it had virtually no comp?



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