View Full Version : timing belt of Bport, what does it time?

06-18-2012, 10:12 AM
The clutch dogs on my Bport seem to be worn hence the rotational play on this short vid I made. These dogs (I think) drive the high speeds. My question is, what does the timing belt keep in time. Is is just a speed reduction? I have searched and studied drawings but no help.


A.K. Boomer
06-18-2012, 10:27 AM
Im thinking your talking about the quill feed.

My machine is a hand wheel quill feed so I can't verify...

06-18-2012, 10:30 AM
It's only a "timing belt" if it "times" something. Long before anyone used one for a camshaft toothed belts were in use and properly called "Gilmer" belts. Their lack of slip is a property that makes them valuable in many applications.

06-18-2012, 10:51 AM
Those are useful in a situation where there is little or no belt tensioning adjustment.

06-18-2012, 11:09 AM
Yes the answer to your question is that is what drives the low speed reduction. If your dogs are worn some one at some time probably had the head apart and did not get it aligned properly.

A.K. Boomer
06-18-2012, 11:39 AM
So what drives quill feed is it gear? or maybe worm gear?

06-18-2012, 12:20 PM
On http://www.machinerypartsdepot.com/site/1478157/page/552090 there is a diagram of the parts I am speaking of. Part no. 25, 23, 20. It is called a timing belt pulley, timing belt, spindle pulley hub respectively. I can't see where it times anything.

The clutch dogs that are worn are under the spindle pulley hub(i think).

Thanks for the help!

A.K. Boomer
06-18-2012, 12:36 PM
Oh I see - yeah that's massive,
Duckmans got the goods...

and im thinking both tdmidget and toolguys right on too,

It's not easy access and it's a guarantee no slip, they may call it a timing belt though.

06-18-2012, 12:38 PM
The clutch dogs are engaged in high speed, not low. i.e. - direct drive, not though the bull wheel. The "timing" belt doesn't time - just drives the bull gear for low speeds. No tensioner so it uses the teeth for grip.

Worn clutch dogs are very common. Worn pulley bearings (no lube), incorrect pulley bearings after a "repair" (they are supposed to be DB ground - preloaded), years of heavy interupted cuts and not making sure they are locked correctly (turn quill by hand until they drop) before applying power all contribuate. The usual symptoms are "rattles" in high gear.

As mentioned above, the top casing need to be aligned when assembling. Easy stuff - loosen 3 bolts, run it at 1000 rpm, and tap/whack it around with a big rubber hammer for minimum clutch noise.

06-18-2012, 05:34 PM
The timing belt, or cog belt, doesn't time anything. It just uses the cogs to give it a more positive grip on the pulleys. (cog pulleys?)


06-18-2012, 07:50 PM
My mill has the same problem and I've been wondering about it for quite some time. Have you tried emailing the video to the guys at http://www.machinerypartsdepot.com/ to see what they think? I'd be interested in the answer as well.

Rich Carlstedt
06-18-2012, 09:45 PM
The timing belt has nothing to do with your issue.
The timing belt is used for a back gear reduction of the spindle for lower speeds. It is controlled by the small handle on the right side, just below the belt cage. I believe it was the first one you moved.

The noise you have is very common. It is the result of wear on the spline of the spindle, and/or the internal spline on the Dog Clutch.

It only shows up on interupted cuts usually, especially with fly cutters
You can replace the parts $$$ or, if it bothers you, add a "snubber" to the spindle nose.
The snubber is nothing more than a spring loaded cork, but it will stop the racket if it appears.


For BP replacement parts, you may want to look at
High Quality Machine in Ohio

Edited. Senior moment- I had pulley and not clutch internal spline, which is correct as Lakeside pointed out

06-18-2012, 09:50 PM
Yes, Richard is correct. The dog clutch has slightly tapered sides so unless extremely worn will "settle" into contact. The splines of the spindle AND/OR the INTERNAL mating surface in the lower dog clutch wear and make the rattle. I have had BPs where the spindle splines, internal spline and dog clutch were worn. Sure made a racket... hard to image a previous owner let it get that far, but...:(

06-18-2012, 11:14 PM
Guys, I really appreciate the help. When I get some extra time I might take a look. I'm hearing some noise using larger EMs, not just with fly cutters so it might be worth a couple afternoons. If I find a work around I'll update so others might know.