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HomeAircraftHelicopterHIROBOHirobo SDX › SDX Fan hub loosened on O.S. shaft
05-12-2011 01:57 AM  7 years agoPost 1
TJ Present

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Oakland, NJ USA

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After a perfect flight yesterday, I probably flooded the engine during refueling. When I went to start the engine with my Sullivan Dynatron starter, it seemed to back the fan hub off the shaft. Either that, or it had started to loosen up. The top nut that secures the hub also had backed off. I had used only blue Locktight.

Thinking of using red on the hub and the nut but wondering if when it comes time to remove (using a heat gun) I'll warp the plastic fan.

Any thoughts from anyone who has been down this road?

Tom DiBella
The ox is slow but the earth is patient.

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05-12-2011 02:28 AM  7 years agoPost 2
fung_jeff

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Vancouver, BC, Canada

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Upgrade to an aluminum fan(aftermarket such as Lynx) and use red loctite?

Jeffrey Fung...15 Years old - FLEET: Evo 50, Raptor 30, Trex 500, SDX's, X-Spec, Logo 10/400

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05-12-2011 02:53 AM  7 years agoPost 3
Leif

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USA

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No need to go to a metal fan. The stock one is just fine.

I find that the main reason for the hub loosening from the crankshaft is either:
1. You had a hydro-lock from a flooded engine and your starter is so powerful that it just unscrewed the hub rather than stalling.
2. Maybe you didn't use loctite on the shaft/hub threads, but rather used it just on the nut?
3. You may not have tightened down the hub enough before threading down the nut.

When installing the hub onto the engine I first thread some M3 bolts most of the way into the clutch holes in the hub, then use a screwdriver shaft between these bolts to get leverage on the hub as I'm tightening it down. I use the 'toothbrush shaft in the crankshaft' technique to lock the engine with the backplate removed and I typically use a VERY SMALL amount of blue loctite on the crankshaft when installing the hub. I use additional blue loctite on the nut.

Green loctite is a better alternative if you're looking for something a bit stronger. Red is too strong and you'll have a devil of a time removing the hub later if you use it.

The other trick is to make sure you don't try to force start a hydro-locked engine. Just remove the glow plug and then blow out the fuel with the starter.

Leif

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05-12-2011 02:57 AM  7 years agoPost 4
gouki

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philippines

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i used red loctite after it happened to me. i can remove it no problem when needed, but it's a little tougher. i got scared my frames couldv'e warped when the hub loosened and pushed the engine down so i use red loctite just to be sure

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05-12-2011 07:05 AM  7 years agoPost 5
TMoore

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Cookeville, TN

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No loctite is needed on fan hubs ever. If you don't tighten them properly they will come loose.

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05-12-2011 02:30 PM  7 years agoPost 6
TJ Present

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Oakland, NJ USA

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Leif

Thank you for your detailed explanation. I'll go with that and needless to say, avoiding a flooded start would have been preferable. Still not sure, thought I pinched off the line when I refueled but why else would the engine flood?

In any event. Seems like you feel that green locktight (which I have as well as blue and red) is probably not needed.

T. Moore- do you have anything to add regarding the correct way to install the fan hub?

I did not know until now that there is an after-market fan for the SDX. I have not had any cooling problems, so it seems like the stock one is fine. I do not run the extended shroud that Hirobo offers as an option.

Thanks to all. BTW I have the O.S. crankshaft lock and pull the back-plate, lock the engine when installing the fan hub.
I did use a small amount of blue locktight on the crankshaft as well as the retaining nut.

Tom DiBella
The ox is slow but the earth is patient.

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05-12-2011 02:41 PM  7 years agoPost 7
TMoore

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Cookeville, TN

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T. Moore- do you have anything to add regarding the correct way to install the fan hub?
It's pretty straight forward actually, get a crank lock tool get a tool so you can snug the fan hub down, tighten the nut enough so the nut doesn't come off and use a dial indicator to check the clutch runout after the fan hub is locked in place.

I NEVER use loctite on engine nuts, EVER because it isn't necessary. If you tighten the nut properly the hub doesn't come off. If you don't assemble and tighten the nut correctly you could weld the nut to the crank and the hub would still come loose.

TM

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05-12-2011 03:07 PM  7 years agoPost 8
TJ Present

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Oakland, NJ USA

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T. Moore

I use the O.S. crankshaft locking tool to lock the shaft, so no problem there.

You're saying no locktite needed at all.

How tight does the hub need to be on the shaft so the nut will not come loose? Is that the important part in terms of the nut or shaft coming loose?

BTW- I have a dial indicator and do check the run-out with the clutch installed. Not sure how tight is tight, if I follow what you are saying.

Sorry to belabor the point but I don't want to fall into the "only the dumb questions don't get asked" trap.

Tom DiBella
The ox is slow but the earth is patient.

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05-12-2011 03:45 PM  7 years agoPost 9
TMoore

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Cookeville, TN

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Tom,

Once the fan hub is snugged up and tight on the washer then you can torque the nut. How tight is a relative term but I typically lay the engine over on a workbench, hold it down and using a 3/8" ratchet and my hand snugged up near the head will tighten the nut about as tight as I can get it with the crank lock in place. Once the nut bottoms out, probably another 1/4 turn or a little more. You can feel when the nut is just about done up. By choking up on the ratchet you limit the amount of torque that you can get on the nut but still apply enough. On a 1/4-28 thread a quarter turn is only going to compress the assy .008" of an inch so if just snug the nut up and go a tiny bit more and then depend on loctite to hold it....it won't. Loctite without torque is useless.

TM

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05-12-2011 05:34 PM  7 years agoPost 10
gonkulator

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Sutter, ca., usa

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I use a locknut (metal type not nylock) and have never
had a problem coming loose.

Is this fun or what :)......

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05-12-2011 05:45 PM  7 years agoPost 11
TJ Present

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Oakland, NJ USA

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Thanks T Moore, for the specifics.

Hi Gonk!

Tom DiBella
The ox is slow but the earth is patient.

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05-12-2011 05:52 PM  7 years agoPost 12
gonkulator

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Sutter, ca., usa

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Hi TJ how's it going? Are you tearing up that
SDX? Great machine, my daily fliers. How's the weather
on the other side of the world
gonk

Is this fun or what :)......

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05-13-2011 02:40 AM  7 years agoPost 13
TJ Present

rrNovice

Oakland, NJ USA

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SDX is great. We're having an old-fashioned spring with great cool weather.

Tom DiBella
The ox is slow but the earth is patient.

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