Film-Tech Forum ARCHIVE: Flywheel timing belt snapped

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Posted by Jon Morgan (Member # 3059) on 08-23-2005, 12:37 PM:

So I'm having a bad day...

At the beginning of a show today a belt snapped on one of my projectors (Simplex 35). It appears to be the timing belt that runs from the projector motor to the flywheel. I'm about to call and order some more right now, and I'm going to do my best to get a tech out here tomorrow, but we've never had a reliable projection tech at this theater (yeah, yeah, I realize that's bad, but it's a long story).

Anyways, what would have caused this? I'm assuming it's just something that happens over time (this belt has been on the projector for at least 1-3 years).

Any advice?

Posted by John Pytlak (Member # 331) on 08-23-2005, 12:43 PM:

Do you inspect your belts on a regular basis, looking for wear or physical deterioration? Any obvious wear points or misalignment, seen by belt debris at the wear point? Does the mechanism driven by the broken belt turn freely, without drag or binding?

I'm sure others will chime in asking for more details.

Posted by Gordon McLeod (Member # 33) on 08-23-2005, 12:50 PM:

turn the machine over by hand to make sure it has not siezed up causing the belt to break

Posted by Dominic Espinosa (Member # 2122) on 08-23-2005, 01:02 PM:

Is the old belt brittle? Does it have cracks?
Also be conscious of the belt tension. I don't imagine you could do more than stretch it slightly but you'd be more likely to ruin the bearings.

Posted by Monte L Fullmer (Member # 2797) on 08-23-2005, 02:26 PM:

Any fabric and rubber toothed belt will age over time by drying out and getting brittle. The same with our belt in our overhead cam cars-either import or domestic. Reason for mandantory belt replacement at a certain given time.

Simplex belts needs to be inspected at least once weekly, especially the round tooth variety-being that they are much stiffer than the older, thinner flat tooth variety.

If cracks are showing up on the flat outer surface of the belt, time for the changeout. When you get that "tech" out there, have him do a complete machine imspection of all the belts and do the replacement necessary.

(and this goes for the ones who have the Christie 35/P35GPS models as well: mandantory belt checks and changeout every year)

Too bad you don't know how to change one, or both of them out, for it's only a 20 minute to a half hour job to do, if one is trained properly on the procedure and proper tools at hand.

Luckilly, it was the motor belt, not the drive belt, or if it was the other, you'd have a good mess on your hands.

I've done changeouts inbetween showings.

-Monte

Posted by Brad Allen (Member # 470) on 08-23-2005, 04:59 PM:

Jon, the flat style "timing belts" for the Simplex 35 can be purchased at any good auto parts supply store. About $12.00 each.

Posted by Mark Gulbrandsen (Member # 72) on 08-23-2005, 08:26 PM:

quote: Monte L Fullmer
Simplex belts needs to be inspected at least once weekly, especially the round tooth variety-being that they are much stiffer than the older, thinner flat tooth variety.

If cracks are showing up on the flat outer surface of the belt, time for the changeout. When you get that "tech" out there, have him do a complete machine imspection of all the belts and do the replacement necessary.

Reeally, why piss off customers for the sake of 30 dollars worth of belts. I replace belts every year if the theatre is running all 6 or more shows a day and every two years if running less than that.... Its just not worth loosing a show, refunding or handing out passes, and pissing everyone off including yourself.

Mark

Posted by Frank Dubrois (Member # 3042) on 08-23-2005, 10:51 PM:

How about belt dressing? Would that helped improve the belt strength and possibly prevented this?

Posted by Monte L Fullmer (Member # 2797) on 08-23-2005, 11:54 PM:

Belt dressing is usually okey for the "V" belts, but not as well for the toothed belts. "V" belts are made for extreme tightness, whereas the toothed belts can't be run as such. Toothed belts will bust in a heartbeat if run "fanbelt" tight-in as well as being excessively noisy when operating-being so thin.

But, I'm never crazy in "cheating fate" or, "doing things half-assed" - if a belt approaches the need to be changed, do it. Don't crimp on additives to lengthen the life of such items.

-Monte

Posted by John Pytlak (Member # 331) on 08-24-2005, 07:49 AM:

"Belt Dressing" does NOT strengthen a belt or reverse deterioration. It is usually just a solvent that increases the friction against the pulleys to reduce slippage and noise. Using a solvent on a belt may actually hasten deterioration.

Posted by Mark Gulbrandsen (Member # 72) on 08-24-2005, 08:58 AM:

Belt dressing usually reduces wear on the pulley itself. At Joe's suggestion I tried Film-Guard on a couple of sets of Christie belts and it does eliminate all belt shedding and doesn't seem to be detrimental to the belts either.....

Mark

Posted by John Pytlak (Member # 331) on 08-24-2005, 10:44 AM:

The "belt dressings" I was referring to are the aerosol ones containing solvents like naphtha, perchloroethylene, acetone, etc. --- definitely can harm deteriorating belt materials.

Posted by Monte L Fullmer (Member # 2797) on 08-24-2005, 12:10 PM:

quote: Mark Gulbrandsen
tried Film-Guard on a couple of sets of Christie belts

...LOL...I used to do that continually at the 21 complex that I used to work at - got a noisy belt, just open up the back, turn on the motor, zap FG on moving belts and instant quiet.....until I figured out the proper belt tension on these beasts, then I eventually quit the practice.

When it was time for belt change, those belts that were FG'ed, still had a bit of a rubbery feel instead of being dry-even the shutter belt wasn't all beat up as they are normally after the 6 month usage.

Posted by Brad Allen (Member # 470) on 08-24-2005, 03:54 PM:

What is the proper tension on a flat belt on a Simplex 35?

Posted by Wolff King Morrow (Member # 2226) on 08-24-2005, 04:02 PM:

It would help if Strong actually made a guide booklet for doing this work. I had to use Monte as a guide writer for my instructions (thanks bro!).

Posted by Tracy Bellar (Member # 3049) on 08-24-2005, 04:19 PM:

I don't know this model projector. But, I have seen on Centurys the motor mount bolts loosen and put to much tension on the belt. Then the belt streaches a little and then the motor gets a little crooked and cuts the belt.

Posted by Louis Bornwasser (Member # 3063) on 08-24-2005, 07:02 PM:

Proper tension: just barely tight enough that you have a little bit of lost motion when you rock the motor flywheel back and forth. Too loose and teeth skip; too tight and undue stress is placed on shafts and bearings. (Even gears have some lost motion.) Louis

Posted by Monte L Fullmer (Member # 2797) on 08-25-2005, 01:28 AM:

..I use the technique of the quarter-inch deflection: pressing down on the section of the belt that is between the two sprockets with your finger. Deflection distance is when there is the quarter-inch looseness when pressing down in the middle between the two sprockets before the belt that is around the two sprockets begin to tighten.

-Monte

Posted by Wolff King Morrow (Member # 2226) on 08-25-2005, 01:57 AM:

BTW Monte, just did a belt change-out using your guide you wrote me. Did everything to the letter including alignment and the quarter-inch tension trick. Everything worked like a charm and your guide was almost flawless in detail (step 2 had the wrong allen wrench size, but this was easily corrected).

Thanks again for you help. I honestly would have had no clue without your guide! [thumbsup]

Posted by Jon Morgan (Member # 3059) on 08-25-2005, 10:17 AM:

Everything's been taken care of guys, thanks for the comments.

And yeah, this belt was incredibly brittle. We'll be checking them on a regular basis from now on.

It's times like this when I wish I wasn't such a projection n00b.

Posted by Monte L Fullmer (Member # 2797) on 08-25-2005, 12:43 PM:

Glad to be of help, Wolff.

Which allen size did I goof up on since I was typing that out from memory's sake and sometime myself, I'll pull out the wrong allen blade from my Xcelite screwdriver set, when doing the belt change.

I bet it's the allen size in either removing the outer pulley, or the allen size that loosens the bearing from the driveshaft.

I always get those two messed up at times.

Did you spin the two shafts -drive shaft and scanner drum shaft- to see how these bearing feel and sounded?

thx-Monte

Posted by Wolff King Morrow (Member # 2226) on 08-25-2005, 01:36 PM:

It was the belt tensioner pulley set screws. I recall you had them listed as 9/64, but they were actually 5/32.

I checked the shafts for bearing wear after I got the old belts off, but everything spun smooth with no noises or vibrations. The old belts were riddled with cracks. Thanks again!