Unscrewing variator nut

[ktienation]

Hello guys, i just changed my j costa variator rollers in my ak550 for a bit heavier ones (but also recommended by the manufacturer for this scooter).

After a very short test drive (maybe 0,1 mile) and 2 accelerations the tightening nut holding the variatior to the crankshaft got completely loose despite the fact I applied the top recommended by the service manual force (90 nm) using a dynamo metric wrench.

It never happened to me before in any scooter I owned

Any idea what might be the cause? I am thinking about applying blue loctite but its not mentioned in the service manual so it should not happen without it…

[Ruffus]

@ktienation,
I could only think of:
-variator not ecactely in its sprocket teeth, caused by pinching its belt during mounting
-is there any washer missing under this variator nut
-variator nut worn out
Pls give a feedback.

[ktienation]

All elements mounted correctly,
Ak has a mechanism allowing to loosen the belt before tightening the nut.
The j costa has no teeth on its bell but it’s hold by 2 o rings before the nut (thin and thick).

I don’t know what I am doing wrong…

@ktienation,
I could only think of:
-variator not ecactely in its sprocket teeth, caused by pinching its belt during mounting
-is there any washer missing under this variator nut
-variator nut worn out
Pls give a feedback.

[ktienation]

Hmm I think I know now (I will test it tomorrow). I tighten the nut according to Kymco manual ~90 NM. But I found a YouTube wideo and than downloaded the j costa manual and it says not 90 but 160 NM for the j costa mount (same nut thought). It’s probably because the j costa bell doesn’t have the teeth on the bell which lock with the teeth in the crankshaft.

I hope it will solve the problem as 160 vs 90 looks like a really big difference.

[Ruffus]

Deems to be pretty high for me, pls reassure at your dealer with that 160nm.
Pls see att pic, don't know the axles diameter.

[ktienation]

Same for me, but the manual for this particular model of scooter posted in the j costa webpage and shipped together with the vario sama 160 NM so i  know what they are doping (the vario model is also dedicated for the AK550, i.e. The Tmax 530 uses a differemt model).

It seams to make sense as as the only thing that holds the vario in place is the torque from the nut (The vario and it’s belt does not have teeth that clamp with the sprocket teeth of the shaft it sits one - quite strange for me but that is how it is - both the vario and the bell has a plain hole for the shaft).

The bolt is like 20mm (it’s mounted directly to the crankshaft like in all other scooters). The nut uses 27 wrench.

[Ruffus]

Ah okay, with a 20mm bolt seems reasonable to me.
Uses thread/bolt/o-ring friction to sit and avoids demage in case of blocking.

[ktienation]

Problem solved. After applying 160 NM everything seems fine. I have only driven about 5-6 miles to test but it was only stop-wot-stop. The nut sits as it should. With the little heavier rollers I mounted (10%). Now the specs suit me more. Still I need to figure out how to make the clutch to engage faster (lower rpm), disengage later and be more 0-1 as the dry centrifugal clutches are. This wet multidisc has too much slip for me before fully locking.

[JJJoseph]

Any idea what might be the cause?

If the belt at the crankshaft end is at the bottom of its travel, the nut won't tighten properly.  The belt must be clear of the crankshaft in order for the nut to tighten.  In other words, the belt at the clutch end must be at the bottom of its travel for the variator nut to tighten properly.