How tight is the jesus bolt? - RC Groups
Thread Tools
Dec 02, 2012, 03:03 PM
Registered User

How tight is the jesus bolt?

This is the FBL head for a VWinRC

The heli was sort of wobbling, so i tried checking the rotorhead. I noticed that that the control arm was rather hard to move. I confirmed this by disconnecting it from the swashplate and it does indeed take quite a bit to swivel.

As you can see in the pic, the jesus bolt just goes through the hole, it's not holding a clamp or anything.

The two control arms tho, are mounted on a clamp like part of the rotor head. However, if i do tighten then, they won't move.

Will this type of rotor head have any problems? If i don't tighten it, it means the single jesus bolt is the only thing holding the helicopter up. and if i do tighten, the arms won't move.
Sign up now
to remove ads between posts
Dec 02, 2012, 05:06 PM
the great Gassif´er
If the bearings freeze up when you tighten their bolts, most likely there are parts missing. Either shims or distance bushings.

I cannot see from here if there is one or two bearings in each arm.
If there are two bearings with a dam inbetween, there normally is a washer between the two bearing inner rings to prevent the inner rings to be squeezed together. If the bearings are in the same bore, or if there is only one bearing, than most likely the shim between bearing and rotorhub is missing. Tightening the bolt will in that case make the outer ring rub to the hub.

If that is all OK, check if maybe the bolt head is rubbing to the outer bearing side.

Because under normal conditions and with proper engineering, tightening a bolt should never lead to freezing up of the bearings.

Brgds, Bert
Dec 02, 2012, 08:21 PM
Registered User
It has two bearings, a brass shim inside between the two, and an aluminum shim on either side. The bearings are not in direct contact with each other, the rotor head nor the screw head.
Dec 02, 2012, 08:35 PM
Zippy Puffer
2Doggs's Avatar
It does sound like you need a thicker shim between the two bearings. I missed the shim out of one swash locker arm on my HK RJX head, and I can't tighten the pivot bolt as much as I'd like. On my Tarot head, however, I can tighten the pivot bolts all the way with no binding in the arms. The Tarot heads have separate clamping bolts, though, which I prefer.
Dec 02, 2012, 10:19 PM
Registered User
i would try to find a step washer to capture the inner race of the of the washout arm bearings
then you can torque it down
Dec 02, 2012, 10:32 PM
Registered User
Link to tarot head please? Maybe i should get that one.


It looks like the same thing, the control arms also look like they're used to clamp the rotor head.

The heli was rock solid on spin up, but starts wobbling in the air, google search suggested that it may be the jesus bolt being loose, implying that the jesus bolt in older flybarred heads also secures it to the shaft. Since the bolt on a flybarless isn't a clamp, i'm assuming that the job goes to the control arms.

I'm gonna take the head apart (again!) and experiment on a spare mainshaft. Hope i fix this soon, all this twisting is ruining my manicure
Last edited by Hajile; Dec 02, 2012 at 10:39 PM.
Dec 03, 2012, 03:17 AM
Registered User
450 shaft vibration (1 min 17 sec)

Is the swashplate vibrating too much? That's spinning at the lowest possible throttle. The disk on top looks solid, same with main shaft, swashplate is vibrating. It sort of disappears once i get up to speed but i wonder if this will also cause the heli to wobble.

Will i need to swap this, or will it be okay as long as i keep the headspeed up?
Dec 03, 2012, 03:58 AM
the great Gassif´er
Originally Posted by Hajile
It has two bearings, a brass shim inside between the two, and an aluminum shim on either side. The bearings are not in direct contact with each other, the rotor head nor the screw head.
Is one shim in direct contact with inner and outer race of one bearing? Or maybe in direct contact with both inner and outer races of both bearings?

Because something is either putting axial stress on the bearings or locking inner and outer race....

The shaking of your swash is not normal, and probably caused by these binding bearings: even if you do not tighten the bolts, it is very well possible that the forces at play when running, cause the bearings to bind.

Brgds, Bert
Dec 03, 2012, 04:35 AM
Registered User
You may have a point, when i loosened the screws holding the control arms until they were just loosely hanging, the vibration lessened considerably. So it may be related to the control arms afterall. I'd never have called that.

Is it possible that i'd overtightened it and damaged the bearing or bent the shims? I thought you were to supposed to do that to tighten the clamp.

Since i don't have spare shims, i may have to buy new control arms.

Or is it better that i just get this?

EDIT: Read up on DFC, looks like it stresses the helicopter too much, so i'll skip that. Still interested in an alternate rotor head design tho.
Last edited by Hajile; Dec 03, 2012 at 06:16 AM.
Dec 03, 2012, 08:19 AM
Zippy Puffer
2Doggs's Avatar
In your video, the head is rotating very slowly. Some clone swashplates are a bit eccentric - you might try rotating the head by hand and see if you can feel any radial movement of the swash.

Your link to a Tarot head did indeed show an earlier style which lacked the separate clamping bolts - I did say they must do at least 10 FBL heads now!
Dec 04, 2012, 08:11 PM
Retired Old Guy
whitehedr's Avatar
I just assembled the 450 RJX head. It has a standoff that is 3.98mm in diameter and 2.74mm tall. The bolt head appears to capture the inner race of the bearing and so does the standoff. This allows the outer bearing race and the arm to rotate about the bolt when it is snugged up.

The picture you posted looks like the arms are to close to the head and possibly binding. The step washer is a good idea but make sure that the washer does NOT bridge between both races of the bearing. I am pretty sure you only want contact on the inner race. The bolt that secures the arms on the RJX head also does some clamping of the head to the main shaft which helps prevent wobble. The Jesus Bolt is also part of securing the head to the main shaft.

The arms on the RJX head flop around quite nicely.

Dec 04, 2012, 10:00 PM
Registered User
I just checked the control arms, and the inner bearing (it's called a race?) is actually bigger than the washer so there's not much chance of it clamping both inner and outer rings.

I've got ALZRC arms in the shopping cart. Hopefully that's all i need to get rid of the vibration.
Dec 05, 2012, 12:07 AM
Retired Old Guy
whitehedr's Avatar
The bearing we are talking about is commonly called a "roller bearing". It has three basic components. The outer race ( the outside ring ), the balls, and the inner race ( inside ring). The balls transfer the load between the two races and cut down on friction between the races.

In this particular function there are two roller bearings, one on the outside of the control arm and one on the inside of the control arm. The outer race of each bearing is held by the press fit into the control arm while the inner race is held by the bolt on the outer bearing and standoff on the inner bearing thus allowing the control arm to pivot freely about the bolt.

The step washer goes between the two bearings in the arm and transfers the load from bolt head to inner race of the outboard bearing to washer to inner race of the inboard bearing to the standoff and finally to the head. If the step washer is not there the load is not transferred efficiently or maybe not at all.

The bolt head, step washer, and standoff all must be sized so that they only contact the inner race of the bearing. If they touch both races of the bearing it will lock the races together and defeat the bearings purpose.

Remenber that these bearings are tiny and if you get carried away and tighten to much it is possible to distort the race and cause binding. Loctite is your friend. Snug up the bolt and let the Lottie do its job.

I hope this helps you figure out what is causing the tightness in your control arms. On the RJX head those arms rotate freely when snugged up.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question How tight should Heli blades be bolted oldboyiti Electric Heli Talk 2 May 15, 2010 02:13 PM
Discussion Belt CP Jesus Bolt size? surgicalCFe Mini Helis 4 Jan 09, 2008 05:32 PM
Discussion Jesus bolt? rudderbud2000 Mini Helis 9 Jan 19, 2007 11:04 PM
ECO 8: keep breaking Head bolt (jesus bolt) and Phx 45 start up problem? UAVProducts Electric Heli Talk 6 Jun 15, 2005 01:34 PM
Transient Head Bobble and How tight is good enough for head bolts .. Lost Horizon Electric Heli Talk 9 Jan 06, 2003 12:09 PM