TT Vibration with new drive belt

[thejeebiejar]

Hi all, I posted a question on this matter a while back and thought I had solved my problem but it's back !!!

So, the drive belt I have for my recently acquired TT was loose and loose enough that it was audible during playback. I bought a new belt and it seems to be a perfect fit - sits on the platter hub with minimal stretching and fits around the motor shaft without lateral movement.

Problem is after a minute or so of playback strong vibrations start, causing the stylus to skate all over the record ! After lifting the tonearm the TT continues to shake. I should mention it is suspended on springs. I have oiled the spindle and the bottom of the motor shaft but no joy !

I managed to play one side of an old test record and assumed the problem was fixed. I put on a 180g vinyl and vibration starts again ! So if the slight extra weight is causing this what is the problem ?

Is the motor failing and unable to produce the required torque ?

Any suggestions would be much appreciated

[Gary362]

Hi Jeebiejar,

I did not pick up what TT you have. You might want to check the Platter - Thrust bearing and the motor bearings for proper lubrication. The Thrust Bearing is the Assy. that the Platter rides on. Be sure to wash the Bearing and Races with Isopropyl Alcohol, to remove all the old grease which can get "clumpy". Don't use paint or lacquer thinners because some bearing have plastic guides! If it has been running without sufficient lube, for an extended period, the bearing (individual balls)could have developed flat spots and are "skidding" along instead of rolling. You might need a new bearing in that case. Repack the bearing cup with Phono-lube grease which is light bodied synthetic such as GC Electronics makes. It is stable at a large range of temperatures. Synthetic Automotive Wheel Bearing Grease will work for heavy platters (like with Dual T.Ts) and you don't have a manual with the recommended lube spec. I have used Lithium grease but it dries out faster than a real W.B. grease. Note don't get this on any other surface that the belt may ride on. That could ruin a perfectly good belt. Gary

[Alec124c41]

It is the top bearing of the motor that needs oil the most. A drop on a thin screwdriver will usually reach under a pulley or drive spindle, to the shaft of the motor.

Cheers,
Alec

[thejeebiejar]

Thanks for the replies guys. I should have mentioned the make and model : it's a CEC BA 300 from the 70's I think. Not much info out there, I don't think the company was around for long !

Alec, I have oiled the drive shaft from the top side of the TT. I put a few drops as close to the bottom as I could. There was an obvious improvement after this, the motor was much quieter at least until the vibration kicks in !

I've attached a photo of the workings of the turntable, taken when I first got it, hope it's clear enough. My question is how do I tackle this motor and gain access to the lower bearing ?

I'm thinking the grey plate, held by the two bolts ? Just want to be sure

Cheers

[duficity]

if you take the belt off, does the motor still vibrate? Does the platter spin freely without the belt on?

[thejeebiejar]

The platter spins freely with the old stretched belt and when the belt is disconnected from the shaft with no vibration. The motor can't handle the tension of the new belt for some reason. I've measured it correctly and it fits well.

Thanks

[pivot]

How do you know this is the right sized belt? Really sounds like you have a belt that is too tight.

[thejeebiejar]

Hi Pivot,

from what I've read it should fit around the platter hub with minimal stretching, which it does. I measured the circumference of the hub to be 659 mm and I found a belt with an overall length of 660 mm. I think the distance required to fit around the motor shaft provides the correct tension.

Does that sound about right or should I have allowed for the distance between the hub and the drive shaft ?

Thanks

[pivot]

By "hub" do you mean the part of the platter the belt runs on? I'd call that "sub-platter".

If I read you right, snug on the sub-platter with minimal stretching, does sound to me like you could end up a belt too short.

You have the orignal, yes? How does the size of the old belt compare to the new? I would think the streched out old belt should no more than about 5% longer.

[thejeebiejar]

Yeah the part the belt runs on.

There is a noticeable size difference between the two but the old belt is nowhere near snug on the sub-platter and when fed through the speed selector lever it hangs considerably with no tension. So when I start the TT the platter takes maybe 10 seconds to get up to speed. I think the previous owner replaced the original at some stage.

Is there a rule for calculating belt size ? I just measured the diameter of the sub-platter, used pi*D to get the circumference. I read that this should be the belts overall length. The user manual for this TT is hopeless and has no spec details for things like this.

Cheers

[pivot]

A rough idea might come from tying a string snugly along the belt path including the motor pulley. Subtract about 3 to 5% for the strech of the elastic belt.

Not foolproof but should get you in the ballpark.

[Gary362]

LP Gear (on-line) Shows that they sell a replacment belt for your model T.T.
Of course they don't say the size up front. You can have the correct length belt with a different width causing them to slip/grab differently.
The link to LP Gear is: http://www.lpgear.com/product/CECBA300.html

The fact that you said it started vibration about One Minute after starting to play a record might be significant.

I repaired a Fisher T.T. with a similar vibration. Once it warmed up enough to start the vibration, taking off the belt and "carefully spinning" the T.T.
by hand, with the Stylus on the Record, the Vibration showed up. This took the Motor and the Belt out of the equation. Just a T/S thought...Gary

[duficity]

Your belt is way too tight. It should just lightly ride on both the platter and motor pulley, just enough not to slip too much. It will, and is supposed to, slip on start up a bit, until it get traction. If you just got one the size of the sub platter it is way too small and putting way too much load on the motor shaft. Get one about 10mm smaller than the old one, at most.

[thejeebiejar]

Great thanks for the link. I must have missed that since I was checking sites here in the UK. I might just have to get that ordered.

As you pointed out above Gary, it might be a good idea to clean and lube the bottom bearing ? I'd still like to give that a shot to get this TT running nice. Any tips on how to go about it ?

From the pic above - I'm guessing removing the grey plate with the two bolts next to the brown, green and red wires ?

Thanks