Pacifica GT 800 knocking feeling while throwing

[ILiketothrowthings]

I bought a brand new Pacifica GT-800 in 2020 but it’s always given me a bit of a “knock” feeling or clunk when I’m throwing. I had previously tried adjusting the belt but after looking at it again it appears that the piece under the wheel head is kind of warped? Does anyone know if that can be adjusted? The belt seems to be straight. Maybe I’m missing something else? Please see the video below: 
https://imgur.com/a/Gwhy7NR

[Bill Kielb]

Just some ideas
It’s pretty hard to tell from your video other than the large cast pulley appears to wobble but the belt tracks pretty straight so for large pulleys - this may be acceptable. What’s more interesting is the visible vibration at high speed. If the camera is just set in place then watching the motor pulley there seems to be considerable vibration induced in the image at high speed.

This is really tough to diagnose from afar with a short video, but low speed assemblies like a wheel ought not to need much balancing and they are usually rigid enough not to require it and hence usually no visible vibration. So to that I would check:

Belt tension, it’s not too tight - follow the manufactures guide! Too loose is bad, but too tight is not necessarily better

Motor assembly and tensioning mounting bolts - they are all tight and nothing rocks in any direction if you wiggle it. This could be the motor pivot bolts or tensioner anchor bolts.

Everything should be flush, perpendicular …….. as in bolts. / nuts / motor orientation and are seated and appropriately tightened so nothing can wobble in and out of its correct plane or orientation. That’s not to say over tighten the belt tensioner to achieve that. The assembly has to be sturdy, rigid, in plane but the belt tension should be appropriate with a bit of deflection when you press in on the middle of it laterally. 

If you can ………. post a video of the motor assembly while cycling  through from low to high speed. it may reveal why the apparent vibration. Set the phone flat on the floor looking up, stationary and capture the motor and belt. You will not be able to hold the phone steady enough so it is important that it remain steady through the test. I could be totally wrong, but it is just a simple test.

Late add, finally turned the audio in the clip on and there is a high and low spot. How tight is the belt and for how long? Is the belt perfectly aligned with the grooves in both pulleys? In the video, it appears the trailing side of the belt tries to climb ever so slightly out of the large pulley during each wobble which would explain the vibration. The easy thing to say is that pulley wobbles too much and that may be true, but if everything is adjusted and in plane it may become much more acceptable.

on a positive note if I index the track of the top of your belt in the video, it’s stays fairly still in operation.

Edited November 18, 2022 by Bill Kielb

[neilestrick]

The wobble in the large pulley shouldn't affect anything. I've seen that in many wheels. If you're getting a rhythmic knock then it's most likely related to the belt, either a flat spot or a bump. Another possibility is that something in the belt system is loose and slipping. Check all set screws and such. If all else fails try a new belt.

[ILiketothrowthings]

9 hours ago, Bill Kielb said:

How tight is the belt and for how long? Is the belt perfectly aligned with the grooves in both pulleys?

Thanks Bill! So the belt is tight but does have a slight bit of give under pressure when I push against it with my hand. The Laguna video just says it needs to flex less than 1/2 inch which it does. I measured the belt at the motor and it’s 1/8th higher than the belt on the pulley. The motor pulley has grooves but the front pulley does not? I took another video of you could take a look with the sound on. 

https://imgur.com/a/gr6MOIi

[neilestrick]

The belt height difference shouldn't matter, nor should the  slight wobble in the large pulley. To me it sounds like the bearing. Is everything tight at the bearing?

[ILiketothrowthings]

Everything appears to be tight. I  tightened all of the other bolts for good measure as well. I did see that the motor mount bar appears to be bent. Not sure that would have any effect though?

https://imgur.com/a/JCFQlQQ

[ILiketothrowthings]

Maybe I’m just hyper sensitive to the sound of the wobble of the pulley and that’s what’s throwing me off. Next I’ll test throwing with headphones. 

[Bill Kielb]

16 hours ago, ILiketothrowthings said:

I measured the belt at the motor and it’s 1/8th higher than the belt on the pulley. The motor pulley has grooves but the front pulley does not? I took another video of you could take a look with the sound on. 

If you have room for best centerline alignment adjust the height of either pulley until the belt tracks smoothest in the large pulley without rubbing the side of the groove, this should minimize your vibration as much as practical. If it’s still not acceptable then large pulley replacement is next. If that still wobbles excessively then the shaft is the next culprit that could be bent. Usually not likely though. Below, minimize the “offset” condition in the center picture so the belt rubs least along the side groove of the big pulley. If the wheel is bent excessively the other two conditions will be present and you will likely need to replace the large pulley and or in limited cases it’s due to a bent shaft.

Of course definitely take the belt off and check for an excessive bend or flat spot for sure. Wheels are very slow spinning machines so everything should be rigid enough to not vibrate even when not balanced. Your first video showed a noticeable vibration in the motor pulley So I believe it vibrates excessively.

Edited November 19, 2022 by Bill Kielb

[ILiketothrowthings]

Thanks all, I’ll give that a shot!