Engine Vibration - bottom end? (Wuyang WY125-24B)

Hi - just joined and hoping to get some pointers.

My Wuyang WY125-24B (Honda Innova clone) is not behaving itself...

In the last couple of weeks I've noticed some excessive vibration through the seat and foot rests. Here's some detail I hope might help:

- it happens when I'm on a 'balanced' throttle and when off the throttle - very noticeable when I first roll off the throttle
- not at all evident when accelerating
- appears to be rev related, fairly high up the rev range but do not have a counter so can't be more specific. Get it in 3rd gear at about 32-35mph and 4th gear at 40-45 mph, also when revving in neutral as revs start to fall
- engine is not showing any other signs of ill health: no increase in oil usage, no change in power output (still underpowered ;o)

Last weekend, I thought I'd best just tick off the usual culprits to ensure it wasn't anything simple, so changed the spark plug (old one was fine), adjusted plug gap and checked and adjusted valve clearances. The oil was fairly recently changed so I left that, but just checked the level again. After that the engine started a bit more brightly (though it was starting fine before) and it idled a bit better, but nothing I wouldn't expect from a brand new NGK and valve clearance adjustment.

I warmed her up for a few minutes and then revved it a bit on the centre stand - still got the vibrations and it made the bike creep backwards. Bit of a surprise, but it could be normal?

Used it Monday and Tuesday but now together with the vibration, there's a new noise that accompanies it. I'm calling it a fluttering flappy sound. It's not popping from the exhaust - it's more mechanical.

I've tried holding onto every bit of the bike I can find while revving the engine in the hope it's a loose bolt, but it's still there and sounds like it's in the engine, though it's not easy to locate as it's a low pitch.

So, where should I concentrate my diagnosis? Could this be a bottom end issue? If it was valves/rings then I'd expect increased oil consumption, a smokey exhaust and/or a loss of power.

I had a Honda C90 before and kept the Haynes manual. The closest symptom in the engine troubleshooting section points to:
- Excessive run-out of crankshaft
- Worn crankshaft bearings (rumble)
- Worn connecting rod or big end (knock)

I don't think it's a knocking or rumbling sound.

Any ideas?

Cheers,

Matt

A little update...

On Sunday I went for my weekly bike lesson and mentioned the problem to my instructor. He reckoned the most likely reason would be loose bolts where the engine mounts to the frame.

So when I checked all the engine mount bolts - they were all fine. I went round tightening up anything I thought might allow a vibration to occur and even some that couldn't rightly be the cause of the problem.

I fired it up, let it idle until warm and tried revving it to see if I could notice any difference or spot something loose. I noticed the foot pegs and gear selector vibrating, so tightened them both up and didn't find anything else.

Then, I went for a ride...

My usual journey is just ten minutes, covering about 2.5 miles across town. I just kinda pootled around with it behaving just as before though the fluttering flappy sound appeared to have gone. I kept going and after about 15-20 mins the vibrations had at first reduced and then gone completely!

So, I presume this is somehow related to the engine being cold?!?

I'm a bit at a loss as to where to dig further, but I did figure that if it can go away after an extra few minutes of use then it can't be that serious (?), so I've been riding it to and from work again this week, but no sign of it going away on my usual journey length.

It's definitely happens when traveling at a steady speed and when coming off the throttle to slow down and also when changing gear, so could it somehow be gearbox related?

I'm keen to fix it myself, but just don't know where to look and I don't want to strip the engine down unless there's good reason to suspect I'll find something when I get in there.

Any thoughts will be very well appreciated!

Cheers,

Matt

Matt,

My first reaction to your problem was a broken engine mount. I had a Jialing that exhibited those exact same problems. Also had a lot of extra buzz in the handlebar. It all made sense when I took off the tanks and noticed one of the the cheap metal plates of the valve cover engine mount was cleanly snapped. For your bike though, you'll need to take off some plastics to get at them all.

If it goes away under acceleration, it may be worth checking the rear suspension linkage and back wheel alignment.

Another place to check is your exhaust pipe fittings. Make sure all joints and hangers are tight and not broken (which can happen from over tightening on some systems). Heck, while you're at it... probably worth going over every screw nut and bolt!

Also, does it have a clutch or clutchless transmission?

CC

Hi Carl,

Thanks for the tips.

Wheel alignment is an interesting idea, though it's odd that the vibration went away on my 'long' ride on Sunday. It'd be nice to repeat that sort of ride to confirm it wasn't some sort of fluke and is somehow related to 'prolonged' use. I'll have a go this weekend.

I checked the bolts on the springs were tight, but what about where the swingarm connects? Again, funny that it went away after a longer run though.

It's a semi-auto gearbox like a Honda Cub, so not clutchless, but no manual clutch lever. It's not far different from Forchetto's Zongshen that I see he's shared the manual for on here.

A clutch issue was becoming my favourite source of the problem. I wondered if it's possible that it's not getting the oil it needs until it's had some use, but I have no idea if that's really likely.

Thanks again! If anything else springs to mind, let me know.

Cheers,

Matt

OK, I think the longer run on Sunday when the vibrations disappeared might have been a red herring as I went for a long way home this evening and despite going a bit further than Sunday, it was as bad as ever.

It's not conclusive but I couldn't repeat it, so maybe that rules some stuff back in.

I might be getting the Swarfega out a few times this bank holiday weekend!