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Spring strength for lowering tone arm on Beogram 4002 / 4004

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ski4ever
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ski4ever posted on Sun, Jan 10 2021 5:20 PM

I have been working on restoring the tone arm lowering and rising mechanism on a BG 4002 that I bought used. After suspecting that I had used a too viscous and/or too much silicone grease in the damper, I cleaned everything again (second time) and applied a small amount of less viscous silicone oil (50 cSt which is similar to 10W motor oil in viscosity) instead of the heavier silicon grease I had use before (which I learned is 5000 cSt). I also checked that the inner valve in the piston works as intended. The damper seems to work very smoothly now and easily when the air valve in the back is opened.

I should say that the BG did not have much dirt when I cleaned it first after buying it a month or so ago. Also, there are clear signs of someone having worked on it before (some of them not good signs like solder iron having done slight damage to some wires).

When fully assembled and the main air valve on the damper is opened, all works as you would expect - compressing and extended the damper fully, but of course the arms lowers very quickly then. As I increase the damper effect by screwing in the valve screw, the arm lowering slows as intended. However, before I can get to the ~1s lowering time the spring is not able to operate the levers and the motion will stop at the point when the piston rod hits the vertical lever and experiences more resistance. The solenoid pushes the first arm that it is connected to all the way down rapidly and holds there, but the spring, which is responsible for pulling the piston out of the damper and lowering the arm, does not pull the sliding arm next to the solenoid all the way with it. The vertical lever connecting to the v-groove and the arm seems to have the right springiness and resistance - at least it is very close from what I can gage - and there is no sticking. A very slight push with my finger makes the spring, which is responsible for pulling the piston out of the damper and lowering the arm, contract fully and complete the movement. It mostly looks like the spring has weakened.

Has others experienced that problem?

Does anybody know what the specifications of that spring is and how to evaluate its elasticity (like a certain extension with a given weight other other method)?

Thanks,
Per 

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ski4ever
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ski4ever replied on Sun, Jan 10 2021 10:13 PM

I did a quick measurement of the spring - again, this is the one that is responsible for pulling the piston out of the damper and lowering the arm. The length (of the body without the end hooks) when removed and with no tension is 23 mm. When installed in the turntable and the arm is up it is stretched to 46 mm and the force is ~0.8 Newton (~80 grams). During the operation of lowering the arm it will stretch up to 4-5mm, so the force may then be up to ~0.95 Newton (~95 grams) as a maximum.

Has anybody tried to mease the force of this spring? If so, I would be very interested in knowing how much you measured. If this is normal, I guess will need to clean the vertical lever, which is a pain to do and I am getting a bit frustrated with the trial-and-error cleaning.

Thanks,
Per

Spassmaker
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Hi Per

Maybe you have not watched this?

https://beolover.blogspot.com/2015/08/beogram-4000-lubrication-of-seized-tonearm-linkage.html

Best regards

Christian

ski4ever
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Hi Christian,

Thank you for your comments. I am a big fan of Rudy's videos and have probably watched most of them by now, including this one. While I don't see any signs of the vertical linkage being tight or gummed up, I will indeed take it apart and clean that too. I bought a force gauge/meter on eBay and will try to measure some forces before and after. Used force gauges are pretty cheap online. If successful this will tell me if the cleaning improves the operation and by how much. It maybe even create some reference values that might be useful for others.

Thanks,
Per 

sonavor
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I think you are making it harder than it needs to be. I have never found the need to replace any of the springs for the lowering/raising. If there is a problem with it the usual culprit is dirt in the pivot Christian pointed out. The springs are designed for a normal clean condition so the simplest and easiest thing is to clean and lightly lubricate the pivot. 

The majority of problems with the mechanics of a Beogram 400x is that at some point in its life adjustments were made that were not correct and eventually something gets way out of alignment. I have had a few BG400x projects where I just had to reset the mechanical parts back to their centered positions and then start adjustments fresh from that point. 

-sonavor

ski4ever
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I got my little force gauge from eBay (and at a good price of $3 + shipping). That turned out to be quite helpful in getting a handle on the forces/drag that was causing my problem. As Sonavor opined, the spring are likely fine - thanks for that vote! All the horizontal parts had already been cleaned and lubricated, so before I started on the vertical lever, which actually felt like it was working well, I wanted to measure some of the forces in the horizontal part. I learned that there was a distinct point when the damper piston was being pulled out where the drag force went up significantly (~2x). I loosened screws holding the damper in place and by slightly moving the damper I could make the drag point go away. I secured it in place and the mechanism now works very smoothly. I guess this emphasizes that one needs to be carefull securing the damper such that the pull/push operation is straight along its axis. I have other things to restore, but for now I am off to listen to some records...

Thanks to all who read and especially to those giving their advice!

Per

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