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Author Topic: Main Drive gears wearing out too fast Michael Rourke Expert Film Handler Posts: 159 From: San Luis Obispo, Central Coast of CA Registered: Feb 2002 posted 03-29-2005 12:58 PM                     I went and changed all my main drives on my Century's and less than 1 year later I have had 3 break. I chalked it up to the rebuilt intermittents being too hard on the main drive, but I've looked at all of them and they are all ready to be changed again. These are the Lavezzi gears, at first I didn't know because they came in a bag, but the last two I ordered came in little sealed Lavezzi boxes. Has anyone had similar problems? I know Lavezzi as a good source of parts, but I ordered some main drives from Wolk this time and I'll let you know how those hold up.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-29-2005 01:03 PM                     Did you replace the steel one at the same time as it may be the one cutting up the fiber one  |  IP: Logged Michael Rourke Expert Film Handler Posts: 159 From: San Luis Obispo, Central Coast of CA Registered: Feb 2002 posted 03-29-2005 01:10 PM                     No I didn't replace the steel ones, could they be responsible for all 7 of the main drives wearing out too fast? I don't think that is why, because I changed just a main drive gear on a projector about 6 years ago and that got chewed up by a crappy Strong rebuilt intermittent, who knows how long it would have lasted. I am thinking that the gear itself is weaker to begin with now.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-29-2005 01:25 PM                     When you inserted teh new intermitent and rotated it to the stop position was it snug often the stops need to be set to match the machine depending on its history otherwise it will be to tight and wear the machine  |  IP: Logged Michael Rourke Expert Film Handler Posts: 159 From: San Luis Obispo, Central Coast of CA Registered: Feb 2002 posted 03-29-2005 02:02 PM                     I used the standard dime spacer to set the stop for the rebuilds, if anything they were more sloppy than tight.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-29-2005 04:42 PM                     I do not agree with others that steel and fibre gears must be changed as a set but I do feel that one must evaluate the steel gear each time. If you really look close on the steel gear on the main drive (GR-4 on standard, GR-182 on direct) you will see some ridges on a worn gear. These ridges act like a serrated steak knife and will naw away at a fibre gear and dramatically shorten its life. I've seen it many times. The surface (contact points) of the gear should be smooth and look like they were just taken off the hobber. If there is anything more than some glazing on the contact surface, out it goes. If there is ANY question, change the steel gear. What have you got to loose? A few more bucks? To prove it to yourself, at least change out one of the steel gears and see how long that gear set lasts compared to the rest. Watch out for out of round gears...we have come across them from all manufacturers. It got pretty bad from one of them but that was a few years ago. You can't check just the OD either you have to see if the gear is starting to bind anywhere in the gear too. Check all of your gears for this...none of them should tighten up anywhere on the rotation. Now on Simplex soundheads....most don't change the steel pinion gear when they change bronze gears and they should. It is amazing at how much longer a gear box will last when all three are changed (and properly lubricated).  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 03-29-2005 06:26 PM                        I agree completely with Steve. You can check for roundness by temporarily reducing the gear clearance and then rotate, slowly checking each tooth for tightness. If all are the same, then the gear is round where it counts: at the contact point. The outside diameter sometimes is bad but it rarely matters. I have had out-of-spec gears from all sources. It is my opinion that gear materials are not as durable as they once were. This is probably not you, but we find that most theatres do not grease the most critical gear mesh: the main drive. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-29-2005 07:16 PM                     quote: Louis Bornwasser You can check for roundness by temporarily reducing the gear clearance and then rotate, slowly checking each tooth for tightness. If all are the same, then the gear is round where it counts: at the contact point. The outside diameter sometimes is bad but it rarely matters. I couldn't disagree more about this. If the machine in question has more than a years running time on it then there is probably some wear on the main drive steel gear. Indeed, what does matter most to gear train longevity is the driving face of the steel gears. Look at the face of the teeth with a very high power lens to see the tiny grooves(actually teeth). These teeth gnaw away in a hurry at the new fibre gear. In the several hundred Centurys of all types that I've rebuilt I have yet to see a steel main drive gear that was not worn this way, unless it saw very recent replacement. The movement gears tend to wear less and the sprocket drive gears even less.... the load is progressively lighter on those gears but the main drive is taking the full load of the mechanism. Also, for the theatre owners sake you are there already making your service fee so why not do the job correctly and replace that steel main drive gear gear as well, Its but a small extra cost...... unless you had prevoiusly replaced it 2 weeks before. Yes, gear face wear is also VERY common in Simplex and RCA gear boxes, look at the driving faces of the worm gear carefully.... They don't use quality metals properly hardened like they used to for the original parts! Also, we have had pretty darn good luck with the new composite Wolk Century gears. They finally are making them correctly. and they also run ALOT quieter. DP-70 shutter gears are forthcomming in this new material from us soon. Mark @ CLACO  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-29-2005 09:59 PM                     The Wolk gears that are grey in color are indeed a longer lasting gear. In terms of time...changing out a main drive steel gear does indeed take substantially more time in the field than just the fibre gear. Also, when you replace the vertical shaft, you now have to once again realign three contact points (two feed sprockets plus the main drive) then bring all else back into alignment. Odds are you will start wearing other gears differently. Also, next on the hit parade is the GR-207 shutter drive...they get a bit of wear. If the intermittent drive wasn't really set up well it will have a narrow sweet spot now....where does it end? I mean, if the intermittent drive gear isn't worn too badly on the teeth it almost always has slop on the key...so lets change that too....and on and on and on. I'll stand by evaluating the steel gear and if it warrants, it gets changed, if not, it doesn't....I know I have not had to revisit that main drive gear any time soon. In general, the main reason I see main drive failures is due to lack of lubrication than anything else (aside from a bad gear train design). Once I pull something off a machine, all parts associated with that assembly get re-evaluated before it goes back...at that point the thing is in your hand. As to out of rounds...there was a period where we had to spin each new gear to check them and then check it in a mule to just to be sure the gear was any good. I guess we all have our ways that have served us.  |  IP: Logged

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