TREX 700 Starter Shaft

[Si Goodchild]

Is it just me that thinks the TREX 700 start shaft is a bad design? The other day I went to start it and the starter cup just spun on the shaft. Of course I tried tightening up the grub screws but couldn't align then with the dimples on the shaft so had to give up. (you can easily align the grub screws with the dimples in terms of the angle but not the length of the shaft)

So today I swapped out the whole start shaft for a new one, removing the engine and making double-sure that the grub screws aligned with the dimples. That was a pain in the A to do. First attempt to start - the cup spun on the shaft again.

I genuinely think that the dimples on the start shaft need to be bigger as the grub screws have no real chance of making a strong engagement. The Raptor 50 start shaft is much meatier and a far better design for getting a solid join. I'm tempted to take the Dremmel to the shaft and make a better flat for the grub screws but the shaft is pretty thin and I'd hate to weaken it further.

Do any of you guys have any experience in this area to share? And what's the best way to assemble the start shaft: engine out, or take the clutch stack out the top of the heli by parting the frames slightly?

Cheers,

Si G

[rapidgaz]

I have done both to remove mine, but if you dontneed engine out for any reason then the top method is ok by taking some screws out on 1 side. Never had a prob with starter shaft in 15 months of having mine.


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[mark Taylor]

Daniel jetschin was helping his mate at Weston to start his 700 today
His was slipping

I think you'll find it's not the cup spinning on the starter shaft,
But the start shaft not gripping the clutches one way bearing.

I had the same problem for years with my 700
Tried a few different clutches/start shafts , made no difference

You using a dynatron by any chance ??

I oiled my one way with tri-flow which cured it, but after a short while it would start to slip again

I gave up in the end and learned to live with it

Cheers

[Si Goodchild]

I think you'll find it's not the cup spinning on the starter shaft,
But the start shaft not gripping the clutches one way bearing.

Yeah I did wonder about that, but the cup gets really hot, suggesting that's where it's slipping.

[rapidgaz]

Yeah I did wonder about that, but the cup gets really hot, suggesting that's where it's slipping.

If the grubs are in there should be some scoring on the shaft.


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[sacko]

..bit of a bump

Bought a new starter shaft this week for the 700, and noticed that the dimples are a lot shallower than the original ones I pulled out.

I fitted it anyway, and guess what happend!

Ended up drilling them out slightly with a 3mm bit.

[Si Goodchild]

Crikey, that's going back a bit. As I remember the cup was spinning on the shaft and I put this down to "shallow dimples" for the grub screws. I opened them up a bit with a Dremmel mini grinder and have not had a recurrence.

[LipolyGone]

Maybe the dimples need to be made a flat instead with a file fairly simple job with the ade of a vice.

[Si Goodchild]

Maybe the dimples need to be made a flat instead with a file fairly simple job with the ade of a vice.

Absolutely.

[sacko]

Mines working a treat now after enlarging the dimples with drill.

Would be better with a bolt through it, or make the top of the shaft a hex shape.

[LipolyGone]

Problem with bolting through is the strength of it Paul you would loose alot of torque strength off the shaft & it would probably break. A hex shape would work but broaching out the socket would be time consuming.

[Steve]

Old thread alert!

I've had some issues recently with the starter shaft slipping in the one way bearing, so I got a new bearing, fitted it into the existing clutch and tried it today - still slipping.

What next? New starter shaft maybe?

Also, how much play do you expect through the shaft when it's mounted in the plastic carrier on the bearings? Should it be reasonable well held or wobbly as a kid's jelly bowl?

Starter shaft and bearing assembly have never been changed since new, over 4 years ago.

[Si Goodchild]

Steve,

Are you sure that's where the slipping is coming from? if so, suggest you lube the one-way bearing. Drop the main gear out and lube the bearing with your finger.

[Si Goodchild]

Problem with bolting through is the strength of it Paul you would loose alot of torque strength off the shaft & it would probably break. A hex shape would work but broaching out the socket would be time consuming.

Agree. Just deepen the dimples with a mini grinder. The heli is still flying great.

[Steve]

Steve,

Are you sure that's where the slipping is coming from? if so, suggest you lube the one-way bearing. Drop the main gear out and lube the bearing with your finger.

Yes, I'm sure. Definitely no starter cup spinning on the shaft - the starter shaft is one of the old ones with deep dimples, so no problem getting the grub screws to lock in nicely. Like I said, one way bearing is brand new - first use today, and I oiled it when I put it in a few days ago.