Century JJ (non-turret) Lower Pad Roller Assembly Issues

[Ryan Gallagher]

The more overdue maintenance you attempt, the more you find that needs fixing. Century JJ Non-Turret model.

Short Version:

1. How is the lower pad roller assembly stop pin affixed to the main chassis? We have one that has some play in the stop-pin itself. The pin can also rotate slightly. I confirmed it does not appear bent by rotating it 90deg, but unsure if that is pressed in pin or threaded in?

2. Other than a new assembly, is there a way you can think of to work around an impression in the lower pad roller assembly mounting shaft left by what appears to be a sharp or overtightened set screw? When re-inserting the assembly and tightening the set screw it always wants to shift clockwise (away from the sprocket) as it homes in on the previous divot left by the set screw.

Scene:

After having cleaned and oiled the pad roller shafts/rollers in the mag heads with success, I moved onto the other pad rollers yesterday. Uppers were no problem. One of my lowers is seized in place it seems, and the other has the problems above. It is apparent this issue has been building over time. An unknown predecessor or tech replaced the factory adjustment hex screw with a longer flat-head one and a lock nut to get the reach they needed to the out of spec stop-pin. But it's too long and also contacts the chassis when open, causing the assembly to be in a mid-point and likely to snap closed on you. It is also not a screw you can adjust with a tool without removing the assembly to make your adjustment.

I did find an appropriate replacement for the too-long adjustment screw, but the wobbly pin becomes the next (original) problem.

Additionally, after cleaning and oiling, upon re-insertion I was fighting with it to get an adjustment that would avoid sprocket skips due to the optical reader tension, especially at splices etc. Obviously this is a pad roller adjustment issue. It seemed my adjustments (even with the longer screw) had little impact. Eventually after several attempts, I realized that the set screw has created a "home" impression in the shaft, and so with the assembly at it's minimum distance, once you tighten the set-screw, it jumps up into a home position that has too much gap between the sprocket face and roller. It's quite possible I created that issue but I sure didn't feel like I was using that kind of force, this set screw also has a cupped bottom, the one in our turret JJ is longer and has a flat face bottom.

Currently, if I back off the set screw slightly the assembly will still function, it will allow it to lower enough that I can at least get film running, but it seems very non-ideal and quite touchy, introduces some play in the pad roller position, never mind that I can't actually set a pad roller distance properly.

Photos. I have a couple short videos attempting to show the stop-pin play and assembly play but will have to upload to youtube later.

IMG_5623.jpg IMG_5629.jpg IMG_5627.jpg IMG_5628.jpg IMG_5622.jpg IMG_5624.jpg

My initial thoughts towards a "fix", what are yours?

0. Tighten the stop pin? (assuming this is not press-fit or some other aspect is worn out).

1.Replace set screw with one less likely to cut into the shaft?

2. Possibly disassemble the arm and re-clock the defect 180deg away from the set screw? This seems pretty tricky to take apart and might involve knocking out a pin in the knurled knob?

3. Seek a replacement Lower Pad Roller Assembly or just the damaged part. Not sure about the stop-pin though.

4. Maybe grind/sand down the defect with emory cloth in hopes of removing the "homing" behavior as you tighten the set screw. (But ideally would be machined out on a lathe with the shaft removed from the assembly, as any flat spot would introduce the same behavior).

5. Make it worse, file a point onto the set screw so at least it can lock in a new position one more time (at risk of it always wanting to lock there forever).

6. Decide if trying to remove the other seized assembly is worth it for cleaning/oiling, it is functioning and adjustable as is.

[Ryan Gallagher]

Update.

I decided to go with option 7 (not listed) because it involved modifying parts I could easily get replacements of.

I grinded a larger flat on the end of the set-screw with a dremel. This took out 95% of the "shifting" problem when securing it relative to it's old indentions in the mounting shaft.

Upon re-inserting and attempting to adjust pad-roller spacing, I was like, what... the stop pin doesn't even reach the screw now. Upon pulling on it a little it moved towards me. It's just a friction fit pin, of which ours has less friction and fit due to the hole being mis-shapen over the years. Well that answered the stop-pin question.

I think i'll look for thin shim to see if I can get a better fit on the pin, and if that works I might be good enough for the near term! Still would welcome input on a less bodged permanent fix on both fronts.

[John Eickhof]

you should stop at this point, last fall I repaired a lower jj pad unit for a well known film society that was having problems with it like yours, there is considerable care in design. Finally they shipped it to me and I replaced some missing internal parts ie the detent balls one missing and one worn, also one spring and resurfaced to main rind and the ball sockets, i replaced the stop screw and loick nut with correct ones, sent it back and it has been performing properly since then. I would not suggest that you take it further apart unless you have had experience with them. on the lower pad to lace the film century designed it to be rotated halfway between 35 and 70 then rotated back to set the rollere, and NOT opened by flipping the assy open like the upper as usually the lens holder interferes so it would not open enough for easy threading of 35mm. once it is set up roperly, you will never need to flip the assy open, just rotate the format knob to mid position.I can usually repair and return in less than 7 days once it is received at a modest cost, please pm if interested.I forgot tho mention, the stop screw is designed to properly set the clearance of the pads at two thickness of film, once set both the 35 and 70 pad rollers will be at proper distance without opening the arm.

[Ryan Gallagher]

you should stop at this point, last fall I repaired a lower jj pad unit for a well known film society that was having problems with it like yours, there is considerable care in design. Finally they shipped it to me and I replaced some missing internal parts ie the detent balls one missing and one worn, also one spring and resurfaced to main rind and the ball sockets, i replaced the stop screw and loick nut with correct ones, sent it back and it has been performing properly since then. I would not suggest that you take it further apart unless you have had experience with them. on the lower pad to lace the film century designed it to be rotated halfway between 35 and 70 then rotated back to set the rollere, and NOT opened by flipping the assy open like the upper as usually the lens holder interferes so it would not open enough for easy threading of 35mm. once it is set up roperly, you will never need to flip the assy open, just rotate the format knob to mid position.I can usually repair and return in less than 7 days once it is received at a modest cost, please pm if interested.I forgot tho mention, the stop screw is designed to properly set the clearance of the pads at two thickness of film, once set both the 35 and 70 pad rollers will be at proper distance without opening the arm.

Thanks John. Yeah I figured getting inside the assembly arm was not something for the faint of heart. I've got her back to a state where we can get through the remainder of our season (I think, it ran a full reel splice heavy trailer reel without issue). Pad adjustment essentially works again, although I still had to use the longer screw cause of non-perfect pin location, though stop-pin is more solid now than it was. I chopped a few threads off the long screw so it opens more completely without contacting the housing, but the tip about just rotating between formats for threading is a good one! Cheers.

Outside of reconditioning the lower assembly shaft, it seems my stop-pin hole that requires shimming to eliminate play is the main problem. I suppose you could operate without a stop pin using the format threading trick, assuming your set screw could reliably lock the assembly position for pad roller spacing.

Perhaps you can clarify the process in the manual. When setting lower pad roller spacing, would you start from a minimum clearance with the set-screw locked and increase the gap using the adjustment screw? Or would you not engage the set screw until you have set the 2-film gap via the adjustment screw. Seems like one way relies on the detent for precision, the other way relies on the stop-pin and adjustment screw.

[John Eickhof]

ok, first, part id 18 on the parts list is the PN-25 pin (is this the pin you refer to?) anyway, it is factory fixed to stop the arm from opening too far and not for adjusting the pad roller clearance, thus it is not necessary to try and adjust. All adjustment is made using part 12 or SC-2287 it is a 6-32 fillister head screw with lock nut that sets pad distance against the projector frame casting boss, this is adjusted down (or threaded outward) until proper clearance is set then lock it down with the nut. Some early jjs had an additional allen screw to lock against the threads. Normally, the mounting stud of the arm part 14, BU-27 is machined with a surface where the locking screw engages it, there is no indent like the 35mm only heads have, thus to set it up install assy, with arm in closed position, and push down against sprocket in 70mm mode if it contacts sprocket, then tighten mounting setscrew from front of projector under lens holder, then adjust stop screw until a tight 2 thicknesses of 70 is present, tighten locknut, the flip to 35mm and double check clearance, it should work just fine. If it is too much distance, adjust stop screw to get pad closer. If there is slop in the 35/70 knob and rollers then it will need to be worked on. otherwise thats about it. very late model jjs had an eccentric pad roller shaft that was adjustable separately if the 35 or 70 rollers did not both line up.

[Brad Miller]

on the lower pad to lace the film century designed it to be rotated halfway between 35 and 70 then rotated back to set the rollere, and NOT opened by flipping the assy open like the upper as usually the lens holder interferes so it would not open enough for easy threading of 35mm.

John, the upper pad roller on the Century JJ head does not flip open. It ONLY rotates. Only the lower pad roller flips open. Also when the bottom pad roller is flipped open, it does not interfere with the lens holder in any way (turret or single lens mount). Also rotating the lower pad roller halfway makes threading noticeably more difficult and if that was the way it was designed to be operated, then there was no need to have the flip open part of the design. It could have been an exact clone of the upper pad roller just like the penthouse pad roller, but it isn't. Opening and closing the lower pad roller arm during threading does not cause any harm to the machine. In fact I have never seen anyone ever thread the lower constant feed sprocket by twisting the lower pad roller.

[Ryan Gallagher]

John, the upper pad roller on the Century JJ head does not flip open. It ONLY rotates. Only the lower pad roller flips open. Also when the bottom pad roller is flipped open, it does not interfere with the lens holder in any way (turret or single lens mount). Also rotating the lower pad roller halfway makes threading noticeably more difficult and if that was the way it was designed to be operated, then there was no need to have the flip open part of the design. It could have been an exact clone of the upper pad roller just like the penthouse pad roller, but it isn't. Opening and closing the lower pad roller arm during threading does not cause any harm to the machine. In fact I have never seen anyone ever thread the lower constant feed sprocket by twisting the lower pad roller.

Brad, To be honest, I did look at it and the format flip method on the lower assembly seemed to leave far less space to work than opening the assembly as intended. But in the case of a wobbly stop-pin, maybe there is something to consider in John's thoughts.

John, For the sake of clarity, I believe the stop pin (mine that was wobbly) is PN-0742 in the parts list of the Main/Major Assemblies:

I was originally following the manual for the re-insertion (with format set to 70mm etc), but that is where I ran off the rails, because to get my adjustment screw (SC-2287) to contact the pin (PN-0742) left me with the pad rollers with far too much clearance still, and backing off the adjustment screw did not permit the assembly to get any closer until I solved that set screw causing the assembly to clock out of the minimum setting.

JJ-MainMajorAssemblies.png

And my lower pad roller assembly part that has deeper than desired set screw impression is perhaps referred to as the "14. Bushing BU-0027" and it's corresponding pin PN-0025 pin.

JJ-LowerPadRollerAssembly.png

I did arrive at a place where things essentially "work" as intended, with the only hack being a longer than usual adjustment screw to contact the stop-pin that doesn't sit true in it's hole anymore.

I also caught a tiny nick on my pad roller that was aggravating my sprocket skip problems. Will probably look to order one now but it buffed out and is not causing that issue at the moment.

[Ryan Gallagher]

And for my understanding conceptually. A correctly adjusted pad roller should essentially not spin, or spin very little only when contacting aberrations and splices in the film?

Most of ours spin to some degree, but are easily stopped with a light touch of a finger. They all need minor adjustments to the 2-film spacing?

[John Eickhof]

no, that sounds normal, the loop action will vibrate the film enough to spin the pads...as long as there is no hard contact to the film pushing it down on the sprocket.slight rotation is a sign of nice free turning pads...keep them cleaned and if metal a drop of oil every six months or so in the hole in the center of eac pad

[Ryan Gallagher]

Thanks re some spinning being normal. These pad rollers lack a hole, removing to clean and put a swipe of oil on the shafts was what started me down this path. ;-)

[John Eickhof]

if they are either delrin or nylon, (white or black plastic) they do not require lubrication, only to be removed and cleaned inside and the shafts periodically. If you lube plastic it will gather dust and dirt and soon gald or freeze up, only silicone or a light drop of synthetic lube can be used, but dry is best. Only metal pads need oiling "(either aluminum or steel.

[Ryan Gallagher]

Noted John. The shafts and axels definitely warranted the cleaning. The tiny bit of oil was probably superfluous and I’ll be removing it next time I clean them.

Had our first screening last night since futzing with them, went great, no sprockets skipped with my “issue” one either.