Film-Tech Forum ARCHIVE: crazy motor pull

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Posted by Paul Montz (Member # 3741) on 04-29-2006, 09:28 PM:

[Confused]

ok i could just be really stupid and overlooking something but my drive motor for my christie slc p35 siezed, so i switched it with my spare projector. got it all hooked up the same and started it up worked fine for around ten seconds, then it started to pull the film through the gate to fast and it started rubbing in the gate. I dont think its jumping because its bunching up under the gate towards the ultramitten. if there is a info posted somewhere else please direct me, or if any help can be given it would be much appreciated [Confused]

Posted by Monte L Fullmer (Member # 2797) on 04-30-2006, 08:39 PM:

..being a P35 unit..did you get the belt path done correctly for all three belts

..and that you know that you have to do the shutter belt first, then the outer double sided belt, then the inner belt - for proper tension of all three belts?

Here is the Christie P35 manual for you to reference all of this.

Posted by Eric Robinson (Member # 2966) on 04-30-2006, 11:22 PM:

Agreed Monte, sounds like a belt issue. If you have some belts which are not meshing with the belt pulleys then you may have belt slippage. If your belts are too loose, you may experience some belt pulleys which slip a few teeth during startup. This can cause loops to get too small or too big depending on where the slippage is occuring.

I was once told by a projector tech. that you should find an area of belt where the belt distance between two belt pulleys is greatest, then use your fingers to twist the belt in the middle of the two pulleys. If you are able to twist the belt by 90 degrees from original position and no more, the belt is of proper tension. This is assuming of course you are using twisting power of a normal human being. I think this becomes sort of a judgement call.

Does anyone else have a better way to phrase or spec this? Please?

Posted by Paul Montz (Member # 3741) on 04-30-2006, 11:39 PM:

thanks, shortly before reading this i found it was a little bit of belt slippage in the wheels behind the motor. but the information on wich belt to do first is extremely helpfull.

Posted by Monte L Fullmer (Member # 2797) on 04-30-2006, 11:50 PM:

That 90 degree twist technique was used by certain mechanics when replacing timing belts in car motors.. for I've done that as well. You'd twist to the 90 degree mark before tension is taken up by the twist. Doesn't matter here on the 'human strength' condition.

You can do this method, for I've done it as well with the P35 belts. But, I rather do the old fashioned way of the quarter-inch deflection between pulleys before the belt begins to tighten...by pressing on top of the belt inbetween any two pulley sprockets. This way, you're right by the adjuster pulley to make the final snug on the allen screw, do the test again, then snug down the remainder of the allens...

With the shutter belt is completely different: you'd pinch the belt right in between the two pulleys and the correct tension is when the teeth of the belt are just barely touching without putting force on the pinching.

You have that "T" handle allen driver on one of the allens of that upper jack shaft assembly ready to be turned to snug that allen when the pinch felt good. Then the other belts come into play - outside first, then inside.

Then, comes the shutter timing to be the last...with the cross being dead center of the aperture opening. Have the shutter loosed on the shutter shaft, with the intermittent sprocket set with the correct number on the tooth as center, have that "T" handle allen on one of the screws of the shutter, swing that shutter to where the cross is dead center to the aperture, then reach around from the front and grab that "T" handle and snug that allen down. Then, you can go around to the back side and tighten both screws down and make your final check.

-monte

Posted by Frank Dubrois (Member # 3042) on 05-03-2006, 01:35 AM:

I've had this same problem in the past. Turns out, when i put on the outer timing belt, it wasn't exactly flush with the pully. It took me forever to find it because even though I felt the belts to make sure they were on correctly, as soon as it turned over, the belt started sliding off.