Hey

There was a thread in the general chat area about rear pulley bolts getting sheared or coming loose.

Which made me think how the setup works.
Ok...the motor on a Dyna is made to jump around on rubber mounts...while most everything else stays still....for the most part.

If the motor is jumping around while connected to a solid mounted rear pulley....what is supposed to give?.....the belt?

Is the belt supposed to give like a rubber band when the engine is yanking on it? Plus...if your belt is way tight...isnt that a recipe for disaster?

Just wonder what kind of pressure is applied to the rear pulley?...to make some bolts shear off.

Murph

 

First of all, in reference to the post about the guy shearing off his rear sprocket, there had to be some underlying issues for this to have happened in the first place. After all, how many other issues have you heard of this happening under normal circumstances?

Second of all, the motor shakes around on the Dyna's because it is allowed to do so by the HD designers. These motors aren't counterbalanced.

Last, the drive belt, being made of rubber, would absorbe more shock. And be able to flex a little better than a chain drive system. And belt / chain tension is absolutely critical for propper operation of either of these drive systems.

 

First..I didnt look for people who had bolts seared...just heard it happened.

Second...I also already know these motors are rubber mounted...on some shIIty motor mounts....which causes issues eventually. Also been hearing of guys shearing motor mount bolts...is that designed by the engineers also?

Last...I know a belt gives more than a chain.

Now Im back to the original question.

Also...Ive built rotaries for laser scanners before....we used Kevlar belts...and they were tensioned according to their tight spots....if they were too tight...they would fock up the $1500 bearing real quick like.
Wouldnt this system ...rubber mounts...belt.....be yanking on the bearings in a bad way also? ...More so if the belt was too tight or over tensioned?

I got a seal leak in a 97....belt was waay tight when I picked it up....pulling hard on the pulleys.

 

OK man, simple as this. I've worked in industrial maintenance for 15 years. Had many hours training on propper set-up and maintenance of drive systems. We have big electric motors set up on shock absorbers to take the initial stress of start-up. The HD motor doesn't shake enough to cause any type of belt misalignement problems. And the rubber belt is elastic enough to better cope with the stress of "off the line" acceleration as apposed to a chain drive system. And there is no need to worry about any type of engine shock unless you are planning on "heavily modifying" the engine.

Belt /chain tension on any system is critical.

Ride your bike. Maintaine it well. And have FUN.

 

McMurphy, the front of the swingarm is mounted to the engine/transmission assembly, not the frame. So there's not a lot of relative movement between the drive pulley and the rear wheel pulley when the engine bounces around.

Rear pulley bolts typically shear from improper installation.

 

Ok...the swingarm is not mounted to the frame...that takes the engine movement out of the equation.
My motor looks like it gonna jump out of the frame sometimes...mostly at idle.

I guess Im stuck on the belt tension...as it pulls the rear pulley towards the motor.

These belts are kevlar... not made to give. Different than a rubber belt on a generator. I also understand the pulley has a slight angle to help the belt track straight.
We used to use a sonic belt tensioner for our kevlar belts to measure the frequency of the belt for tightness. Pulleys would spin if too tight...bearings would fail....excessive vibration.
I was wondering if the previous owner caused my leak issue with having the belt way too tight...not sure how many miles he put on it that way...the thing was screaming for help(squeaking).
Guess Ill read up on the design...I know the belt systems we used was almost the most critical part of the build...along with the bearings.




Thanks!

 

That's an interesting way of doing it, not unlike what a lot of people do to check for loose spokes.

So I just went out and "bonked" my drive belt, and got 98 hz (that's a G natural for you musicians ). Now I just need you to come up with a proper-tension frequency spec for me.

 

And an expensive device to read it. Way Over Thinking going on here.

Go out and buy a service manual and a belt tension guage.

 

I seemed to me that FXDWG12 WAS answering your ORIGINAL question.
My answer would be, just don't over-tighten the belt.

 

There's an app for that.
(And it's free.)

+1