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Nagra III - with bits falling out. Recognise them?


SimonSays

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(Apologies for the shameless click bait title)

 

I've just acquired a 1963 Nagra III B. Long story short, it plays silently from a mechanical noise perspective. Accelerated fwd is also quiet. Rewind, however is making a fair amount of what sounds like spindle play/oscillation noise.

 

Today, having been cleaning and investigating (unit all ways up and down) it started making a more alarming bumping noise on rewind. When I went under the hood I noticed the pulley connected to the right/take-up spindle was bumping on each revolution. I disconnected that spring tensioning it to the motor plate and turned the tachymetric wheel by finger to try and track the bump down.

 

This crumbly brown/white stuff started falling from around the area of the tachymetric wheel... I've done a bit of macro photography with a loupe (pics attached). Any idea what this is? The bits are around 1-2mm down to more-or-less dust for rough scale.

 

My best guess is some sort of (very old) bushing. The teeth marks in bits of it might be the result of it sticking to the outside if the tachymetric wheel. Could the lack of this be the cause of the oscillation noise?

 

I'm hoping it's not something impossible to replace?!

 

Thanks for any assistance.

 

 

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It is the (ex-)rubber coating on the tacho disc, where the winding idler makes contact. I have one that had the same problem... You can buy belt sets for Nagra III, and in that set there are three belts: Two belts for the reels, and one that can be fitted on the tacho disc wheel. 

 

Here is an example:

 

https://www.ebay.com/itm/284563609320

 

If the reel belts are the grey neoprene type, I wouldn't replace them; they rarely fail.

 

It is not exactly easy to replace the belt/rubber coating; to do it you have to remove the motor and the motor chassis. The worst part is the removing of the motor from the capstan/tacho shaft. On the gearspace forum (reel-to-reel part) there is a description on how to change the bearing on a 4.2; you don't have to disassemble the motor, but it is described how to take out the screw holding the shaft. Be certain to pay attention to every single part; if you do that and you have some sense of mechanics, you can do it in an hour or two (or faster, but that is not advisable).

 

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Thanks, Dela. I’m certain that’s it (now it’s been pointed out!)…

 

That rewind o-ring looks to be ~65mm x 3mm from what I can see. It’s fairly easy to source modern nitrile o-rings of that spec so I’ve bought a few around that size to experiment with - as long as it grips the pulley and engages with the drive wheel i should be able to find something suitable. I couldn’t find your recommended Gearspace post but there are a couple of helpful YouTube videos so I’ll get busy and report back.

 

I do have the grey silicon drive belts so the o-ring should see me right.

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Or talk to Mike Harris (mikesfilmsound.com); he can help you with spares and/or do the actual repair.

 

As you write the belt size is not critical, but it will have to be completely smooth, or it will be very noisy when the Nagra is winding.

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To complete the thread, I can confirm that a 70mm (OD) 3mm nitrile o-ring fits the rewind pulley beautifully.

 

you could probably use something smaller (say, 65mm OD) but bigger would be too loose.

 

I would also say that the nitrile is probably too taught to be used as the main pulleys.

 

Thanks for the Mike Harris link, Dela. I doubt I’ll be leaving him unbothered for long :)

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