beta 300 vibrating

[werst]

Hi.
Im having excessive vibrations on 2015 beta 300. It started couple weeks ago and i cant find the source(i didnt notice vibrations earlier but now my hands are getting numb and its really bad through pegs also . Ive retorqued engine bolts(released all of them together and then retighten), new pipe o rings and rubber mounts. all bolts are tightened by hand feel. Couple months ago i checked my swingarm bearings and overall condition, all seemed good and i put it back together. Is it possible that i overtightened swingarm and now something has given in or has worn out? any ideas what can be the cause of the vibrations or what should i recheck?

[Dirt ninja]

Any odd noises? How's the plug ?

[werst]

There was an engine knock on deceleration and 1/8 of throttle for quite a while that i tried to solve with jetting. Turned out to be leaking stator side main seal. https://ibb.co/bFy64vT this is the plug after driving about 30 mins throughout all throttle range and before changing seal. Old plug was burned from one side also. Dont have picture for my current plug but it looks ok now. I didnt feel any crankshaft play when i tried to move flywheel. Piston should be done 30-40 hours ago. I think i did see some uneven wear when i looked through exhaust port, ill try to make a picture of it. Can it be crank that causes too much vibrations or is it possible that too small piston has been putten in and now that it has more wear its rocking inside of cylinder? 185hours on bike

[Dirt ninja]

Looks like it was pretty lean. Are you comfortable taking the motor apart and inspecting it yourself? I would check the piston for wear and such. Check the bottom end for free play. It won't take long to check and just buy the gaskets needed to check.

[74ossaguy]

does the bike shift and clutch well? Im guessing it does so no loose clutch assembly or busted gears or such in the drive train.

How does it feel while at idle and just revving the motor while standing still? Pull in the clutch lever while revving at stand still. Do you see, feel anything causing vibration?
You said the exhaust pipe was tightly fastened. Spin the rear wheel while on a stand, should roll freely, detect anything inside the main shaft that seems wrong?

You can pull off the magneto cover and try to pull/ push on the crank end to check for bearing play.

That all leaves the crank main bearing and the piston. If the piston is vibrating badly & crank, you should be able to feel it, sense it, while revving the motor in neutral gear.

If its none of that then your hands are going south -you might be old like me!

[werst]

Cant find anything loose or moving the way it shouldnt. I will try to get gaskets and take cylinder off this weekend and see if i find anything wrong there

[werst]

Ok so i took the cylinder off. First thing that caught my attention was that cylinder head connection bracket bolts were quite difficult to unscrew. Later when reinstalling the holes didnt align very well so i had to use a little force. Piston itself looked good but there was a little wear on exhaust side skirt(about 1 cm in height) c size prox piston. Cylinder looked good aswell. Felt no excessive play in crank. There was slight rocking from side to side between piston and con rod, didnt seem to be any play up and down tho. Pin and bearing looked to be ok aswell, only slight marks on pin.(could this be the reason i still hear a slight knock on decel and 1/8 throttle?). It had a. 5 or. 6mm base gasket that i changed to .3mm as that was readily available and should be as default. Gonna measure the squish this week. Anyway i took it for a ride and at some point i think the vibration got better. But what still bothers me is a slight knock on decel, 1/8 throttle positions and a little rev hang after wot. As if it still gets some air leak. Also changed my needle to necj from n2zj. Its now really crisp and sharp after that wreched 1/8 or so. 168mj, 38pj around 15 degree celsius at sea level. https://ibb.co/RhrwMs5. This is the plug after riding 1 hour. Looks to be really lean and timing is off? Ground wire was burned all the way till threads

[aj_mariner]

There was a lot of threads on the decel knocking. Some mistake the engine knock (which sounds like the engine is fucking itself) with “pipe bang” (which is an overly rich indicator). In my case, I found the knock happening the most when clutching in after high revs, like when you go over a log. I though it was misfiring, or thought something was wrong with the piston.
The best thing I’ve found is to change the BPR7ES plug for a BR7ES, which was an accident at first. It broadens your jetting window allowing more forgiveness. It’s just a stab, but figure BPR7ES gets too hot and can’t cool down fast enough...needs more fuel to help.
If you don’t like changing plugs, then you need to maintain richer low to mid jetting.

MY 2017 Race came stock with a 0.5mm base gasket. If I had gone any smaller, the top of the piston at TDC would be above the top of the cylinder. This is not recommended. You always want the piston at TDC to be either perfectly flush with the top or slightly below, as per engine repair manual.

Rev hang means you need more fuel

[wwguy]

There was a lot of threads on the decel knocking. Some mistake the engine knock (which sounds like the engine is fucking itself) with “pipe bang” (which is an overly rich indicator).

The primary cause of pipe-bang is unburned fuel being trapped in the cylinder due to the engine running while the throttle is closed, which restricts airflow through the combustion path. When the residual fuel eventually ignites it results in temporary increase in RPM for a single combustion cycle... thus the "bang". Too-rich jetting will certainly exacerbate the effects of pipe-bang. but isn't the root cause.

More info here and here, if interested.

[aj_mariner]

I must respectfully agree with you. I still don’t see how our observations differ. Is “unburned fuel” more PC than “overly rich”