New scooter - new concern By sjrainsford (Read 1,394 times)

[sjrainsford]

Hi all!

So this is my first proper post here apart from my pictures I've put up. I have a brand new 125cc scooter based on the ZNEN ZN125T. It's quite common in 50, 125 and 150cc formats.

It has now done about 600 miles, but since I've had it i've noticed that I get vibration under my arse when I hit about 50mph. So long as I'm below this speed it runs smooth.
I've checked the wheel balancing and that was way out, so thought I'd solved it. But after a nice ride out today it seems to be exactly the same.
The bike seems to happily go over 50mph, but that vibration naturally makes me feel uneasy, especially as this is my first scoot.

Any suggestions?
Thanks all in advance.
By the way tyre pressures are correct too.

[sjrainsford]

No ideas? Ive taken it back under warranty, but they say there's nothing wrong. But then, being an engineer I struggle to trust a lot of places.
Plus to me, vibration means something wrong.

[Alleyoop]

Have you tried balancing the tires they have balancing beads that you can pour into the tire and balance the tire out at speeds. They do not work if going slow but in your case they just might do the trick since it happens at high speed which is where they work.
Alleyoop

[sjrainsford]

Thanks for the reply Alleyoop. I've balanced my wheels with tyres on with a static balancer, and they balance out fine.
The quoted top speed for my scoot is 55mph, so maybe I'm just getting too close to the top speed. However it gets to 50mph quite well and otherwise seems happy to sit at that speed on level roads. In fact it feels as though it's got more left in it.
I'm beginning to wonder if It's got a dodgy tyre on it. Will investigate further when I have time and let you all know my findings.

[sjrainsford]

Well, I took the scoot out again yesterday on a particularly hilly 50mile round trip. I purposefully gave it some beans on the straight sections and it pulls up to 50mph no problem, but as mentioned as I approach this speed the vibration starts and continues as the scoot pulls through 50mph up to around 55.

However. One stretch was downhill so I was able to get to 50 and back off the throttle. The vibration then stopped. So, it's not the fact that I'm going 50 that's the problem, it must be something else. It's quite a fast vibration, but obviously not wheel related now.
So I can only guess engine or drive? Belt perhaps?

I just didn't expect this on a brand new bike. I've now clocked up 800 mile and it hasn't changed. Oh and another thing, it seems worse after riding for 30 minutes or so, such as when the engine and drivetrain is well and truly warmed through.

[frmrwiseguy]

Wondering if the crank throws are out of spec.
This will cause the vibration described.
I see max OE is .004, I find this excessive.
You should be under .002and ideally under .001on the truing stand then have Crank pin tack welded so it stays in place.
Unfortunately you have to remove the engine and split the cases to get the crank out and inspected.
Went thru a bunch of these with Old Sachs Sled motors, rev em and they went out of balance, we just trued and tacked them.
Hope this isn't your problem, not a easy fix

[Bashan]

Aug 28, 2013 5:42:40 GMT -6 sjrainsford said:

However. One stretch was downhill so I was able to get to 50 and back off the throttle. The vibration then stopped. So, it's not the fact that I'm going 50 that's the problem it must be something else.

Yes, it's going 50 under throttle that causes it. An engine under throttle is a different animal then a coasting engine. A bike, and indeed your car, have harmonics. That means the complex vibration patterns generated by all the moving parts sometimes reinforce each other and sometimes cancel each other out. The former causes vibration and buzzing, the latter smooth sailing. When you apply throttle all those explosions change the harmonics. If you've ever read a motorcycle road test, one measure of smoothness is the amount of mirror vibration. If your vibration is a buzzing, I'd check all the bolts around the engine, including the motor mount. If they're secure I'd say it's normal and live with it.

[sjrainsford]

Thanks for the replies. It does feel like harmonics I must admit, and so far am happy to live with it. The dealer I bought it off aren't very helpful and said there's nothing wrong with it. Like you say though, perhaps there isn't anything wrong with it!

[shop242]

Could be an out-of round tire.. Had that to happen b4.. Balancing wont fix that

[mike6736]

Yes some of the tires they put on them are hard and out of round. I changed them out on my IB 300 and what a difference

Magoo

[jct842]

A decent set of pirelli's might make a whole lot of difference but unfortunately the only way to know for sure is to buy them. I put them on my zen right after i bought it and night and day difference.

[sjrainsford]

You're all right, those tyres are a bit crappy. Fortunately 10" tyres don't seem to be too expensive, but I'd want white walls again.

I have 3.5x10 at the moment, would I have to use the same or can I use better newer style ones? I'm guessing they're radial now.

[kz1000st]

Nope. It's time to replace the belt. It's stretched. I had the same thing on the Bashan at 2,400. Once I opened it up you could see where the belt was rubbing the inside of the variator case cover. To prove it take off the side cover over the variator and ride it. Near top speed the belt is highest at the variator and any slack in the belt causes it to hit the cover. Installed new belt, problem gone.

[sjrainsford]

Thanks for your comment KZ. The belt was looking like my number 1 choice for where the vibration was coming from. It sort of feels like its that sort of area if that makes sense.
Probably due to it being a cheapo belt. Any tips for belts? We cant seem to get Gates belts here in the uk, even though they sell automobile belts here. Perhaps there are chinese brands that are ok?

[kz1000st]

How about Bando, the Japanese company? Even if it's not an aramid belt it will still be better than a Chinese rubber/nylon one.

Check Ebay UK for one.

www.ebay.co.uk/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0.X743-20+30+Bando+scooter+belt&_nkw=743-20+30+Bando+scooter+belt&_sacat=0&_from=R40