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TT 54 propeller thread is anticlockwise to unscrew!

Starter motor just unscrews the prop!

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Jim Burton 107/09/2011 14:38:19
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Given the direction of rotation, I would have thought it sensible to have a 'anti-clockwise to tighten' prop shaft thread arrangement. But no, those boffins at Thunder Tiger disagree. Consequently, almost every other time I apply the starter motor, it unscrews the prop - locknut and all.
 
How can this be stopped? More torque (how much is safe) on the prop nut?
 
I've removed the spinner and have mounted an APC 10x5 directly onto the backplate with the TT-supplied centering-slightly-convex black metal washer, followed by the securing nut and the TT locknut. Plenty of spanner to the point where I fear for the integrity of the APC plastic, then the locknut similarly tightened whilst holding the first nut steady. Apply starter and whoah! off it comes again!
 
Little help here?
Lee Smalley07/09/2011 14:59:40
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10x5 on a 54 four stroke !!!!!!
 
Lee Smalley07/09/2011 15:01:06
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i have a 130 tt and this is not the cae with mine, is it the old design silver one not the black anodised version
Martin Harris07/09/2011 15:13:21
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The boffins at every other manufacturer agree with TT's I'm afraid. It's a case of whether you'd prefer to loosen the prop when starting or when it's in the air! The normal torque reaction will tend to tighten the prop when it is being driven by the engine.
 
What is probably happening is that the engine is attempting to kick back when reaching compression, jarring the nut undone. The first thing is to get that nut tight - and I've yet to meet a modeller who has stripped the threads on a decent quality crankshaft by leaning on a normal spanner. Don't try using the sort of thing you find on some plug spanners - just use a standard spanner of the correct size and lean on it until your eyes bulge. Then do the same with the lock nut...the APC should withstand the pressure easily.
 
If you still get kickbacks then you need to reduce that tendency - the first thing I'd try would be a larger prop - the 10 x 5 seems rather small to me (I'd be looking at a 12 x 6 or 11 x 7 as a starting point) - which will provide some more inertia. You might also try reducing the glow if you're using a power panel to retard the ignition point slightly.
 

 
 

Edited By Martin Harris on 07/09/2011 15:22:53

Frank Skilbeck07/09/2011 15:20:23
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Check that that it's not hydraulically locking either, make sure you can turn it over by hand without the glow clip connected.
Jim Burton 107/09/2011 15:30:37
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Thanks Guys,
 
First off - my bad - it's the recommended 11x5 not a ten inch as stated above.
 
Lee, it's the 9803 black anodised job.
 
 

Martin, thanks for the info - I'm using the TT recommended 11x5 break-in prop, but I have only managed two tanks of fuel thus far. I've got a 11x6 on another plane - I could give that a go. I'm just using a 1.25 clip-on battery glowplug energiser and leaving it on whilst using rich running in mixture. I'm looking to lean that off on tank three to maybe 2 turns on the needle valve then pull the energiser off and start on the slow mix adjustment.
 
While you're online could you clarify this:- the breaking-in instructions say "during tank three lean off the mixture for optimum revs". What are 'optimum revs' in this context ( I have a tacho).
 
Biggles' Elder Brother - Moderator07/09/2011 16:21:03
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OK, prop throwing like this is a bit of a hobby with 4strokes. As Martin says its propably misfiring. This can happen for lots of reasons but having the mixture very much too rich is one of them. It could be that you're setting very rich for running in - but actually its a bit too risch now that its had a couple of tanks you should be able to back off a little and you might get fewer misfires and so hang on to your prop a bit longer!
 
Optiium revs - its a bit like with your 2 strokes. As you wind the needle in the WOT revs will increase. This will have a maximum point from which if you continue to wind in the revs actually go down - at that point its too lean. I would say that optium revs was about 2-300rpm below the maximum speed on the rish side of things. So, screww in the needle, find the max revs point using your tacho, then screw out the needle just a little until the revs drop by 2-300 rpm or so.
 
BEB
Lee Smalley07/09/2011 16:26:47
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yeah same as my 130 and mine only kicked prop nut off when either too rich or too lean and pre ignition started, yours sounds too rich, i know your only running it in but do the engine a favour and get rid of that horrible flexible spinner eventually
Martin Harris07/09/2011 16:51:01
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Just a quick word of warning - your test set up looks a little awkward if that's where you're running the engine although the camera may have foreshortened things. Please make sure that you can access everything easily and without having to reach over any part of the running engine. Bob Moore's thread may make useful reading...

Edited By Martin Harris on 07/09/2011 16:54:34

Jim Burton 107/09/2011 18:03:18
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Thanks BEB, I don't know what 'WOT revs' means...but anyway, I'm assuming these adjustments are made with the throttle fully open, then lean until revs go down, then back to max revs, then enrich to lose 2-300rpm.
 
Lee - no worries, red plastic spinner is in the bin
 
Martin - thanks for your concern - the test rig is only sitting on the edge of the sink coz I brought it in from the rain When I fire it up it's in the garden, screwed down to a cast iron chair. I'm super-cautious of not only the prop but the whole rig taking off - you must have seen that lucky bloke on YouTube with a test mount held on to a table top with a couple of G-clamps...you can guess the rest :-0
Tim Mackey07/09/2011 18:11:11
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WOT = Wide Open Throttle
Jim Burton 107/09/2011 18:48:38
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Obliged for info.
Jim Burton 107/09/2011 18:56:36
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I'm sort of surprised that no-one suggested LocTite Blue as a screw thread (non-permanent) fixative to counter this nut unscrewing effect caused by application of the starter on a new and/or incorrect mix setting engine. Is there a reason for this e.g. LTB doesn't work or maybe can't be shifted when it's prop change time?
Lee Smalley07/09/2011 20:08:17
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yeah its a pain to remove when on field
Martin Harris07/09/2011 20:09:16
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I don't see why you couldn't try it but it's really designed for anti-vibration with small amplitude movements and I doubt it would make very much difference. The prop should stay on if everything's tight.
 
If you have a competent assistant you could get them to connect the glow while the engine is being spun over which would lessen the tendency for it to kick back until thing's adjusted correctly.

Edited By Martin Harris on 07/09/2011 20:10:43

Biggles' Elder Brother - Moderator07/09/2011 20:54:54
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If as Martin says you get the prop on nice and tight with a proper "splined" lock nut, then eliminate the backfiring, you'll find its fine. I think nearly everyone has this problem with their first 4 stroke - once you know about it you just adjust the mixture and bingo everything is great. No need for LTB.
 
BEB
Jim Burton 108/09/2011 14:41:22
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Martin and BEB, thanks for that: 'everything tight' is certainly what I'm aiming at - I've had my fill of standing in front of this brute and being attacked by a free-flight prop
 
I've gone with Martin's colourful descriptor of 'eye bulging' pressure with a standard well fitting short spanner, but it could still go tighter, I can definitely feel that.
Your best helpful descriptions are, of course, necessarily subjective and experience-based. What I'd really like is a torque-wrench setting figure, so I could whack a 12mm socket on the nut and give it the beans.
 
Finally, I'm not quite sure what BEB means by a 'splined' locknut - do I need to get one? I'm just using the standard TT arrangement of nut with 'tighter-by-pressure' stick-out 'forks' upon which the locking nut squeezes. You'd think it would stay put - but no!

I'll certainly remember my first 4 stroke.
Biggles' Elder Brother - Moderator08/09/2011 15:31:07
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Those "forks" are what I mean by a splined nut! They give the lock nut better purchase by compressing.
 
I've never used a torque wrench on a prop so I can't really give you a figure. But I think Martin is saying don't use a short spanner - you won't get enough torque. Just use a standard 12mm spanner. TBH I usually use two when putting the lock nut on; one to hold the prop nut and the other to tighten the lock nut. One could be an adjustable as long as its a good quality one that fits well on the nut.
 
Once you stop it backfiring it wont throw props - honest!
 
As I said before a lot of folks have this problem with their first 4 stroke. Once you have the knack you'll wonder why you ever had the problem!
 
BEB

Edited By Biggles' Elder Brother - Moderator on 08/09/2011 15:31:58

Jim Burton 108/09/2011 17:31:29
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Appreciate your time and encouraging words.
 
Best to all.
Peter Beeney08/09/2011 18:47:28
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I must admit I find this thread interesting, to say the least; probably because once again things described are not quite as I’ve generally found them. I certainly wouldn’t profess to be any sort of expert on engines, but I have spent virtually all my life using and also running-in 2 and 4 strokes, for myself and other people and I can’t say that I’ve ever really experienced these problem that other people seem to have.

Lee seems not to like those plastic spinners and yet again I’ve always used them with impunity. They are cheap, simple and in my experience very reliable; whereas some of the others can be difficult to fit, and will not fit the starter cone easily; they can also get thrown off into the bargain. I couldn’t agree more about tightening the prop nut though, the very first little piece of instruction that any beginner gets. I’ve personally had very few cases of props being starter thrown indeed; but I’ve seen a few of other peoples coming adrift, usually 2 strokes. I really can honestly say that I’ve never seen this to be an issue with four strokes.

I don’t understand the ‘backfiring’ situation either, what’s that all about? One trick that I’ve understood that can be used to stop a prop being thrown is to fit a thin card washer between the prop and the prop driver, I’m told this works well but I’ve never personally needed to try this.

When running in I tend to not to fiddle with the mixture too much, after all, you can’t easily adjust the mixture on any other engines and they seem to manage ok. What you can do though, is to increase the oil content a snifter for the first few runs, so you can buy a 100 ml bottle of caster oil from Boots and put up to a quarter of this in each of the first four full tanks. Whatever oil you use subsequently.

The exploded picture is interesting, the locknut assembly at 1 particularly so. I don’t know if this is the official assembly instructions, but I would certainly reverse that locknut. The large nut should be the the one holding the prop on, in front of the convex metal washer, with it’s tapered recess facing the front, and as Martin and BEB have said, really winched up tight. Then BEB’s ‘splined’ and (my description) ‘clinch’ nut screwed on, with it’s taper into the large nut; also tightened with a capital T! I do stress this would be my method and by no means how others might see fit to do it and it’s certainly not necessarily correct. My theory is that if the prop tries to ‘undo’ the main nut and the clinch nut is trying to standstill the main nut will tighten the ‘splines’ even tighter onto the thread and ‘clinch’ it ever tighter. So that either of the nuts cannot be undone. Hope all this makes sense to someone…

I would very surprised indeed if it was not possible to prevent the starter spinning the prop off. If it can be loosened this easily then that might lead to rather more serious problems, as in the following paragraph perhaps.

I’ve always thought that the locknut was an effort to stop the prop being thrown when the engine ‘detonates’ and stops dead; the prop can keep going for some considerable time, and distance, definitely taking the main nut with it, if there is no locknut; and occasionally the locknut as well, that’s why you never ever stand in front of a running engine, whatever the circumstances. This can be violent too, I’ve seen an engine smashed when this has happened. There is a very good explanation for this, but a touch lengthy. If I say this only happens at maximum volumetric efficiency that’s a good start, but in this context it only means at full throttle.

I don’t think this happens very often, but when it does it’s quite impressive. The instant silence of the exhaust and the strange noise that the prop makes spinning through the air is a bit different!

PB

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