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October 18, 2018, 17:35:31 PM

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Author Topic: DLE engine  (Read 484 times)

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Offline THE BLACKBIRD

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DLE engine
« on: September 26, 2018, 11:18:49 AM »
I have a DLE 55 in a 50cc Revolver, i was at home setting the engine this morning last time out it died on me, had it running when all of a sudden the prop flew off, all four bolts had sheared off, the prop was not loose when i started it
Wooden 23 x 8 prop, big alloy spinner, all went sailing through the open door into the hanger, luckily no more damage
What could have caused it to happen

Tony 
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Offline PDR

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Re: DLE engine
« Reply #1 on: September 26, 2018, 11:50:04 AM »
Assuming it's nothing obvious like a beig-end failure or snapped rod, the usual cause is detonation (aka "pinking") due to over-lean mixture, excessive compression ratio or low-RON fuel.

PDR
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Offline itsme

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Re: DLE engine
« Reply #2 on: September 26, 2018, 13:22:37 PM »
Any slight looseness in the bolts can cause them to shear. May not be noticeable when flicking, but I have seen them snap like that.


Offline alangorham

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Re: DLE engine
« Reply #3 on: September 26, 2018, 13:26:53 PM »
Your own thread on the same problem from 3 years ago had some good ideas on it:

http://www.rcmf.co.uk/4um/ic-engines-rc/dle-55-side-exhaust/

Offline wunwinglow

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Re: DLE engine
« Reply #4 on: September 26, 2018, 13:54:33 PM »
I have heard of a few instances of DLE prop bolts failing, there's a suspicion that the originals are made from inferior material; replace them with good quality HTS bolts.


Offline ludwig

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Re: DLE engine
« Reply #5 on: September 26, 2018, 18:25:12 PM »
My DLE 30 once  backfired when starting and all four bolts sheared off.

Offline THE BLACKBIRD

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Re: DLE engine
« Reply #6 on: October 13, 2018, 09:34:22 AM »
Ok iv got my DLE55 running sweet now, but iv had problems with the wrap around exhaust coming loose, so this time i drilled the bolts holding it, tightened it all up good, when running it on the ground setting up the engine it stayed tight, goodho i thought cracked ir
Went flying with it this morning ans after one flight it was loose again  :'( how can this be, the bolts are still wired with the piano wire through them, so they have not moved

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Offline Charlie C

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Re: DLE engine
« Reply #7 on: October 13, 2018, 16:48:44 PM »
Don't know if this is of any help to you, but it has always worked for me and all the other guys using DLE's, DLA's and other assorted engines.

Take the silencer off. Throw the gasket in the bin. Very carefully, abrade the silencer mounting face with 400 wet and dry.
Very carefully, only enough key that surface.

Mix up some 1/2 hour epoxy and apply carefully to engine mounting face.

Fit silencer and lock the bolts using thread lock as well. Personally i wire lock them, but, as long as they are locked and tight.

Leave over night then go fly :af

BTW.

If you are using a wooden prop, i tighten up the four cap heads, using a plain washer onto the prop and a spring locking washer between the plain washer and bolt head.

I always start the motor, run it for a couple of minutes, shut down, re-check the four bolts then ckeck them again after a few flights. Wooden prop hubs compress, not just on tightening but in running, especially with vibration.

I also try to balance the prop properly as well.

Just my 2p's worth.

Charlie C






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Offline THE BLACKBIRD

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Re: DLE engine
« Reply #8 on: October 13, 2018, 17:05:07 PM »
Thanks Charlie, i always do just as you say with the props, and iv tried it without the gasket but using metal epoxy, came loose straight away, been on it this afternoon and the bolts both turned in half a turn, iv taken the large spinner off and will try it again tomorrow, but i think the problem is the silencer, it is a wrap around i bought from America and i dont think the metal is very good, it should be though for a 150
Iv tried four different props im on a Menz 22x10 at the moment, been running 23x8
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Offline Charlie C

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Re: DLE engine
« Reply #9 on: October 13, 2018, 17:13:06 PM »
I am running acouple of 55's at present, one on a Xoar 23 x 8 and one on a Menz 23 x 8 with no issues, though the Menz was well out of balance.

Try epoxy instead of metal epoxy.

I remember a few years ago, i had a 55 with a wrap around  silencer in a Bearcat. I got a bracket alloy welded to it that i attached to the firewall for some extra support (i do the same currently with an Evo 80).

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Online The Saint. (Owen)

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Re: DLE engine
« Reply #10 on: October 13, 2018, 17:46:11 PM »
I use blue gasket sealant, works a treat.  :af
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Re: DLE engine
« Reply #11 on: October 13, 2018, 17:56:27 PM »
Easy fix, replace with a Zenoah😃😃
Never had an exhaust come loose or a hub bolt shear.

Offline kinverflyer

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Re: DLE engine
« Reply #12 on: October 14, 2018, 07:50:11 AM »
Heat will be the cause of the exhaust bolts coming loose, ensure the engine is well ventilated, the outlet vents are more important than the inlet, should be as a rule of thumb 3 times the area of the inlet.

With regard to the prop bolts shearing 99% certain it will be loose prop. Wooden prop hubs compress when tightened, however they must no be over tightened. Keep checking the tightness until they settle down.

Offline PDR

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Re: DLE engine
« Reply #13 on: October 14, 2018, 10:54:27 AM »
Ok iv got my DLE55 running sweet now, but iv had problems with the wrap around exhaust coming loose, so this time i drilled the bolts holding it, tightened it all up good, when running it on the ground setting up the engine it stayed tight, goodho i thought cracked ir
Went flying with it this morning ans after one flight it was loose again  :'( how can this be, the bolts are still wired with the piano wire through them, so they have not moved

whits end

Dear Whit - if the silencer is coming loose but you are absolutely certain the bolts aren't moving then none of this gluing/sealing malarky will do anything as far as I can see, and something else is going on. As Hercules Parrot said tr Dr Watson - if you have eliminated all the impossible then whatever remains must be an excuse for another book...

Looking at it analytically - there are two strong candidates:

1. If the holes in the cylinder are blind then the bolts are bottoming in the holes rather than clamping the silencer. This may be disguised if the bolts are very close to clamping as they bottom in the holes. As soon as there's a bit of vibration and heat the lack of real clamping becomes apparent an it gets loose.

2. The attachment flange of the silencer is soft, and the bolt heads (or even the cylinder material on the back) are sinking into it under vibration.

Personally I think (2) is unlikely because you'd see signs of it in wear/chafe marks on the silencer which would stand out like a gliderist at a social event. So my guess would be (1). First check would be to remover the silencer and screw the bolts back into the cylinder - when they bottom in the holes is there a gap between the underside of the bolt-heads and the cylinder? Is it similar to the thickness of the flange on the silencer? That would be a strong clue. If the answer is "yes" then fit some spacers under the bolt-heads - something like a few washers (or a plain washer and a spring/star washer) and try that. If for some reason that's not practicable (eg no room for washers) then you'll have to shorten the bolts. This should be done very carefully with a cutting disk in a dremel or similar to try to be absolutely certain that the threads are undamaged - the bolt goes into a cast allow cylinder and if there's even a hint of thread damage it will soon wreck the threads in the holes. A better solution might be to make a copper gasket to space the silencer off the cylinder - just cut off a short a bit of copper central heating pipe, slit it then anneal it (heat to cherry red and quench in water) so you can bend it into a flat sheet. Then drill holes, cut to shape etc and anneal it again before clamping it in place so it snugs against the surfaces. The gasket will be work-hardened by vibration in about a minute the first time you run the engine, so after each of the first couple of runs you should re-tighten the bolts, but after that it should be OK.

Actually there is one more possibility, but I think it's very unlikely - it's possible that the threads in the cylinder are badly formed with too big a core diameter. it's possible (but very unlikely) that there is just enough engagement in the threads for the bolts to appear to snug-up, but under load that can "jump back" a thread or two, so the bolts are coming loose without rotating. But I really doubt this.

0.009 supplied,

PDR

PS - Googling "DLE55 muffler" does return a lot of hits about silencers continually coming loose despite every effort with threadlocks, glues, patent gradmother's locking lotions, preying to Mecca or attemping "wingardem silence-osa!" with (and without) a thorough swish&flick of a powerful wand. I also note that when supplied new they come with a flat-washer + spring-washer combination for the silencer bolts. Amongst other things, that combination will space the bolts back about 30 thou, which could be enough if the bolts are bottoming in the holes.
« Last Edit: October 14, 2018, 10:58:34 AM by PDR »
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Offline PDR

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Re: DLE engine
« Reply #14 on: October 14, 2018, 11:01:54 AM »
Heat will be the cause of the exhaust bolts coming loose,

Can't see how. If the bolts are tight when the engine is cold then as it warms up the alloy of the flanges will expand far more that the steel of the bolts - it should make them tighter, not looser. Even if the silencer flange is steel the alloy of the cylinder should draw the bolts in rather than loosening them.

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Offline THE BLACKBIRD

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Re: DLE engine
« Reply #15 on: October 14, 2018, 11:52:29 AM »
It is No, 2 Pete the metal on the silencer is being removed, and it dose stand out, now,
So now im hunting for some copper pipe, not easy to come by in Cyprus, but im sure i have some somewhere  :-\
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Offline British Victory

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Re: DLE engine
« Reply #16 on: October 14, 2018, 12:54:59 PM »
PDR, it ain't necessarily so, the screwed holes in the crankcase expand more radially than the set screws, vibration does the rest also the hole actually deforms slightly, so the cross section is similar to a longitudinal section of an egg, the larger size is on the hotter side as there is a temperature gradient, albeit a small one.
The tapping size for the screws is pretty important, a midge's dick too big and the screws will never hold, how much faith do you have in chinese engineering that they get that right?
I had a similar problem with a saito, the answer is to get some full size exhaust system jointing paste and try to get that down the holes, it expands on heating (bit like tooth filling material) and cures it for a time; as you had to buy a wacking great tube you can do it many times for the same price. It isn't a permanent solution, which is to drill out the screw holes accurately and re-tap them the next size up not do-able with a saito exhaust though( I have heard from a mate whose mate had this saito problem that a helicoil sorted it for once and for all but I can't vouch for that).
I'm quite surprised OS didn't go the throughbolt route as per their 2 stroke glow engines.
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Offline PDR

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Re: DLE engine
« Reply #17 on: October 14, 2018, 13:15:09 PM »
It is No, 2 Pete the metal on the silencer is being removed, and it dose stand out, now,

Which side - against the bolt head or against the cylinder? If it's the bolts eroding their way into the flange then I would just get a bit of steel (at least 16swg/30 thou thick) and make the biggest spreader plates you can fit. Drill the clearance hole for the bolt and then saw/file the plates to try to cover the whole surface of the flange to spread the load and stop them digging trenches. Then just clean-up the surfaces of the flanges a bit, but just get rid of any burrs or trumpetting (ie don't bother filing down to a flat surface again). You just want a surface on which the spreader plate can sit flat and parallel to the seat. I would then fit the bolts with either spring washers or (preferably) a proper serrated washer like a DIN6798A (or J if it's all you can get).

PDR
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Offline THE BLACKBIRD

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Re: DLE engine
« Reply #18 on: October 14, 2018, 17:10:58 PM »
Its on the engine side, i was wondering if i got some high heat gasket rubber, that i can get here, would that do the job, we use to use rubber gaskets on back boilers in the old coal fires years ago, still looking for some copper tube, its in there somewhere lol
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