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Author Topic: Century belt tension tricks? Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-26-2005 09:16 PM                        I almost lost a show (actually, two shows) today due to a slipping belt between the soundhead (R5) and picture head (S200? R200? it's an odd cross between a late-model "C" head and an early-model SA, and has a straight gate). It took a couple of chewed Dolby loops before I figured out what was happening. I managed to increase the tension by removing the belt and adjusting the position of the idler roller, but now the machine is somewhat harder to turn over by hand than it was before. My major concern during the first show was that the motor might overheat, but it didn't seem to get any warmer than usual. Is there some sort of trick to setting the belt tension? Are there dire consequences to having the tension set slightly too high? I didn't have much time for trial and error, as I had a difficult time removing and re-installing the belt and I had a sold-out house with less than half an hour until showtime. Most of my experience with Centurys has been with the direct-drive (MSA) models or C heads that are gear-driven by SH-1000 (or similar) soundheads, and I've never had to deal with belt tension between the picture head and soundhead. My initial reaction is that it is touchier than the Simplex 5-star belt tension. It is probably worth noting that this particular machine doesn't get much use and hasn't been run for a couple of months. I did run it for 30-60 seconds without film at the beginning of the day and it ran fine; the belt-slipping issue only seemed to occur with film in the machine. Might this have been related to the cause of the belt tension being too loose?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 12-26-2005 10:13 PM                     Not knowing the R series of heads but the Century "standard drive" with the "L" series of gearbelts are notably more forgiving of belt tension than 5-stars. There is normally a pretty good wrap on both the soundhead and projector head pulley on the Century projector. The larger "L" type gear belt also is less likely to jump as compared to the 5-Star which uses the "XL" type of belt (speaking of those prior to the round tooth variety). I suspect that you have other issues working against you there...like the machine has binding in it somwhere causing the belt to flex. Steve  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-27-2005 03:32 AM                     I think Steve is on the right track here. The belt idler should be adjusted for just zero belt deflection in the belt between soundhead and projector. Excessive tension here can cause premature bearing failure. Also...to see if its the machine thats binding slip the belt off the lower pulley on the soundhead. Check to see if the projector head can be turned over easily by turning the main drive shaft pulley or shutter dhaft knob by hand..... the head should turn over quite freely. Compare that one to the other head assuming this is a two machine booth. While the belt is off also check the belt tensioner roller. Last week while performing booth maintainance I discovered that a belt tensioner roller on a customers machine had seized up, this was on an SA/R-3 standard drive and was causing the exact same problem as yours. Turns out the roller itself had a flat spot worn into it, the belt was loose because of it and causing the film to jump the teeth on the sprockets at startup. I replaced that old style phenolic roller with the updated ball bearing version.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-27-2005 06:22 AM                        Thanks! I'll ask the theatre manager to get the technician in to take a look at it. The theatre in question is a nonprofit that doesn't run much film, and I was hoping that they wouldn't need to have a service call, though that sounds like the best course of action at this point.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-27-2005 10:44 AM                        The belt sprocket located on the soundhead shaft (bottom sprocket) is only held in place with 2 small set screws and no flats. Breaking Dolby loops means to me that sprocket is not tight and is slowly slipping. There is no reason to overtighten that belt, as stated by others, it almost cannot slip. Just remove 95% of the lost motion. (Rock the motor flywheel back and forth 1/4 turn.) Louis  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-28-2005 09:17 PM                        For whatever it's worth (not much, probably), I made it through six perfect shows with the quick-fix. Hopefully it will get fixed properly and I won't need to find out if it will last through a seventh next month. The projector head itself is a "200B"--does anyone know what this actually is? It has a 4" lens holder, a C-type straight gate, and takes flat aperture plates like the SA.  |  IP: Logged Robert Throop Master Film Handler Posts: 412 From: Vernon, NY USA Registered: Jun 99 posted 12-28-2005 09:39 PM                     Is this an RCA 200? They were rebadged Century model C's. Bob  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-29-2005 11:47 AM                        Ir is almost certainly a "BX-200." made at the end of Brenkert production to fulfill contract obligations. (They had enough soundheads, amps, and speakers.) Louis  |  IP: Logged

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