Need advice on a jerky 7750 (28.800)

[Rolexman]

I received a Navy with the 7750 (28.800) movement. Chrono second hand ran smooth. Gave it a service, chrono second hand runs jerky

So I changed the clutch, chronograph wheel and oscillating pinion to ETA, just to be sure...... still jerky

Running seconds are smooth BTW so the train gear is okay.

So now I think it perhaps has something to do with friction wheel. What to you guys think?

Thanks!

[Bike Mike]

Check to make sure both the jewels are not varnished up... Try hitting them with a little One Dip and sharpened Pith Wood.

[Rolexman]

Check to make sure both the jewels are not varnished up... Try hitting them with a little One Dip and sharpened Pith Wood.

Thanks Mike. All jewels, plates and posts are clean as a whistle. I'm running out of options. Think I will try cleaning the nylon bushing of the friction wheel an bending the spring a bit... see what that does

[Bike Mike]

Let us know what you find out...Only other thing I can think of is the nylon bushing is okay, is the tilting pinions engagement...but it sounds like you may have tried that already.

[Rolexman]

Well, it wás the friction spring! It was not providing enough upwards tension (rotor side). Therefor the oscillating pinion teeth weren't engaging properly and the movement was jerky. You were right on the money Mike.

Hopefully this post will provide some helpfull information in future searches

@ Bike Mike thanks for your contribution. Nice to know I can always count on your usefull insights!

[Bike Mike]

Anytime! Glad you narrowed it down and got her fixed.

I have learned to look for "spring back" on the 60sec. Chono Wheel after running across a couple movements where the jewel setting on the Automatic Winding Bridge was tweeked. It was out of place just enough to allow for no up/down movement on the chrono wheel, causing either complete lock up with the chrono's active or the sweep second hand not to run smooth. One more thing for you to look for!