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Is my engine broken? (Dual 504 belt drive)

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Is my engine broken? (Dual 504 belt drive)

Postby Scagerdude » 18 Oct 2017 16:38

Could somebody give me some advice?

I've been trying to get my Dual 504 belt drive up to the proper rpm (runs too slowly on both 33 & 45) and the pitch control doesn't seem to do a thing.

So far I've changed the belt and applied lubricant (polytetrafluorethylene) to both the platter socket and the motor.
However, it is still too slow. I've noticed also that the engine makes a soft noise and heats up, but only when the belt and platter are connected to the engine.

So, should I use a different lubricant, or throw out the engine?
Please advise :)
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Re: Is my engine broken? (Dual 504 belt drive)

Postby tcolegrove » 18 Oct 2017 17:19

Did it used to work at the proper speed? Is it a consistent speed or does it run fast and then slow down? Does the motor start up right away or does it take a while to get moving?
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Re: Is my engine broken? (Dual 504 belt drive)

Postby DualSpinsMyVinyl » 19 Oct 2017 04:48

In response to your non functioning speed/pitch control, I had the same problem on my 1249. They both use the same speed adjustment mechanism. Take a look at the the pulley on the motor. You will see that it is a segmented pulley with a conical insert in the center top of the pulley that is topped with a ball bearing. All of of this is mounted in a metal housing with a flat top. When you change the speed/pitch control, the housing with the flat top moves up or down applying pressure or reducing pressure on the ball bearing. This up or down movement causes the conical part of the center to move up or down into the brass fingers pushing the brass fingers of the pulley further apart making the speed faster or in the opposite direction to move closer together making the speed slower. What you need to do is see if this action takes place or if the center shaft with the cone on it is frozen in place. If so until you free the center conical shaft no speed change will happen. The service manual for the 504(in German) and the 1249(German and English) are in the library and both have instructions on how to service this mechanism.
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Re: Is my engine broken? (Dual 504 belt drive)

Postby Scagerdude » 19 Oct 2017 09:56

tcolegrove wrote:Did it used to work at the proper speed? Is it a consistent speed or does it run fast and then slow down? Does the motor start up right away or does it take a while to get moving?


It has run a bit slower since I got it, but it runs steadily and gets right up to speed.
However, I have no way of figuring out if it does run at normal speed when the belt is not attached.

@DualSpinsMyVinyl
That's really cool, I didn't know it worked like that! I will take a look at mechanism and service manual asap.
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Re: Is my engine broken? (Dual 504 belt drive)

Postby Solist » 19 Oct 2017 17:41

If the mechanism is not working and if you wont be able to fix it you can still use shims (I used some sort of hard foam) to raise or lower the mechanism manually. But then what you end up with is a TT that can play only 1 speed. If you can post a picture I bet we can figure something out.
"And those who were seen dancing were thought to be insane by those who could not hear the music." - Nietzsche
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Re: Is my engine broken? (Dual 504 belt drive)

Postby Scagerdude » 20 Oct 2017 10:26

I've discovered that the ball bearing of the central axis does not touch the metal housing of the pitch control (see photo) and that the metal housing hardly moves up or down when I try to adjust the pitch.

So my theory is now, that because of this the belt pulls on the axis without the support of the ball bearing and thus pulls the rotating part of the engine against the side, causing friction and slowing the speed.

I'll try disassembling the pitch control to have a look inside. worst-case scenario is I might have to bend the metal housing of the pitch control a little so that it at least applies support to the central axis, but that is only a final resort if I'd have to buy a whole new pitch control mechanism.
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Re: Is my engine broken? (Dual 504 belt drive)

Postby Scagerdude » 21 Oct 2017 12:26

I've managed to fix it. Turns out it was all due to the pitch control system.
The central cone (containing the ball bearing) that's supposed to push the fingers outwards the increase/decrease the axis radius was stuck and needed lubrication.
After changing this I was able to change pitch to the exact right hight.
Roxanne (The Police) sounds so much better when at right pitch :lol:

Thanks for the assist guys!
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Re: Is my engine broken? (Dual 504 belt drive)

Postby DualSpinsMyVinyl » 22 Oct 2017 02:05

Glad to hear that you were able to repair the pitch control. That was the exact same problem with my 1249. These older tables need lots of TLC.
DualSpinsMyVinyl, Dynaco-PAT4 Pre Amp, VTA ST-120 Valve Amp, Dual 1219,1249, Shure M97xE JICO SAS, V15 T III JICO VN35HE, M95HE, M75ED-T2, M71, Grace F8, Technics SL7-Ortofon TM14/Shibata stylus,Heil AMT-10b spkrs, Sansui QRX3500.
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