Drive Belt Tension Changes When Hot

[ZR1Dan]

Hi Guys,

2016 Road Glide Ultra. Did a rear tire change, reset the belt tension using the HD tool, and following the manual instructions. Ease-peasy. Rolled the belt to 3-4 different locations, all the same tension. Go for a ride and 50 miles later I stop for a picture. Randomly decided to finger check the belt tension. It's tight. Like guitar string tight. No deflection at all, way overtightened. I nurse it home, and reset it while hot/warm. Easy-peasy again. Bike cools overnight, and now it's loose. Like really floppy loose, I can move it an inch or more with a fingertip.

Too be honest, I've always set the belt cold, and only rechecked it at a 5000 mile service while still cold. Never needed to adjust it between services.

So, what gives? Does the heat cause expansion causing it to be guitar string tight? Is this normal, and I just never noticed?

[Ohio HD]

Everything expands with heat. The belts teeth expand, then they push away from the sprockets, so they get tighter.

Adjust the belt at ambient temperature. And ambient temperature should be in the 40° F and up. 

[kd]

The sprocket diameters grow / expand with heat also.

[Coyote]

The sprocket diameters grow / expand with heat also.

This.   

[Ohio HD]

Kevlar has a small negative coefficient of expansion in length when heated. That and the size change in the teeth makes the belt tight.

[rbabos]

Everything expands with heat. The belts teeth expand, then they push away from the sprockets, so they get tighter.

Adjust the belt at ambient temperature. And ambient temperature should be in the 40° F and up.

At least in my v rod due to mile long swing arm, I shoot for 75 -80* ambient as my optimum adjustment temp. Huge difference between 40 and 75* in the measured result comparing the two . Using this one temp gives me repeatable numbers in tension, otherwise I'm chasing it all over due to the tension measurement moves with the ambient. Colder temps adjustment, the tension will be too tight in hot weather and visa versa. It really is amazing how much tighter the belt gets once up to operational temps. This can take out that trans bearing eventually, yup even the v rod can suffer that. Factory spec is too tight to be bearing friendly if set to the minimum.
Ron

[smoserx1]

So, what gives? Does the heat cause expansion causing it to be guitar string tight? Is this normal, and I just never noticed?

Does on mine, always has.  215000 miles on bike, 3rd belt (second one did break at 70K). Tranny has never been touched.  The opinion on this are all over the place.

[Norton Commando]

So, what gives? Does the heat cause expansion causing it to be guitar string tight? Is this normal, and I just never noticed?

Does on mine, always has.  215000 miles on bike, 3rd belt (second one did break at 70K). Tranny has never been touched.  The opinion on this are all over the place.

Mine, too.

It's completely normal.

[Schex3x]

I've always said it's overlooked how much the belt tightens when the bike warms up after enough miles ridden, I believe that's a cause of some bearing problems,, primary bearing race walking, wheel bearings, main drive gear bearings, Harley's spec is simply too tight for me.

I have a tension gauge, but rather use my finger while sitting on the bike, I know from experience what my cold and hot belt tension should feel like. roll the bike a little, check, repeat.

Something else overlooked is if the bike has shocks with more travel, hence more sag setting, how much weight was on the bike when the sag was set?, big difference on belt tension when bike is loaded 1 or 2-up, loaded for a road trip, etc.

[rbabos]

I've always said it's overlooked how much the belt tightens when the bike warms up after enough miles ridden, I believe that's a cause of some bearing problems,, primary bearing race walking, wheel bearings, main drive gear bearings, Harley's spec is simply too tight for me.

I have a tension gauge, but rather use my finger while sitting on the bike, I know from experience what my cold and hot belt tension should feel like. roll the bike a little, check, repeat.

Something else overlooked is if the bike has shocks with more travel, hence more sag setting, how much weight was on the bike when the sag was set?, big difference on belt tension when bike is loaded 1 or 2-up, loaded for a road trip, etc.

Exactly. Many never even think of that. Where you are in the swing arm arc effects tension and where that position is, should be considered for setting the belt tension. Generally the belt gets tighter with load in most bikes, to a point. This again depends on shock length. A shorter shock, it might get looser with load. Boils down to understanding what ones setup is and working with that for adjusting, not just blindly following the SM as being gospel.
Ron

[ZR1Dan]

Thanks for the input guys. I'll reset it to the loose side of spec today, and ignore it when it's hot. I was just shocked how tight it was, it felt like it was a steel bar when I was poking at it. Sure seemed like that would play hell on bearings, not to mention trying to pull the rear end out of alignment with all that tension on one side. Also, FWIW, I've found the belt tension changes very little, if at all, when the bike is on a lift vs, on the ground. That surprised me a bit too...

[Hossamania]

Check your manual, but I thought tension is set with a rider on board.

[Coyote]

The belt tension changes a huge amount on my 12 RG from laden to unladen.

[Deye76]

IME tighter is better than loose. Loose belts will spit teeth, have seen it on more than one occasion. One would have to crank it down hard to affect bearings/seals. Using a tension gauge, ambient temps, to adjust, have put 350,000 + miles on rear drive belts, solo, 2 up fully loaded, you name the scenario, no problems. I also don't drop the hammer until everything is heated and expanded.

[Ohio HD]

The belt tension changes a huge amount on my 12 RG from laden to unladen.

[Ohio HD]

IME tighter is better than loose. Loose belts will spit teeth, have seen it on more than one occasion. One would have to crank it down hard to affect bearings/seals. Using a tension gauge, ambient temps, to adjust, have put 350,000 + miles on rear drive belts, solo, 2 up fully loaded, you name the scenario, no problems. I also don't drop the hammer until everything is heated and expanded.

[Ohio HD]

Check your manual, but I thought tension is set with a rider on board.

Depends on the bike. Some yes, some no.

[ZR1Dan]

Check your manual, but I thought tension is set with a rider on board.

It's changed through the years. Manual on my 16 says, "Measure on side stand or upright, saddle bags empty, no rider or luggage". I know on previous Road Glides I've owned, it's been different. I did the work with the bags off, on a rack with the wheels off of the ground, and torqued the axle. Once I sit it down and rechecked it, it didn't change, which surprised me...

[kd]

Loose belts are a death sentence and will leave you on the side of the road somewhere.   

[hardheaded]

I've always set my belt tension cold at the loose side of spec, within spec but at the loose end of it.  It gets damn tight when it's warmed up after a long ride.

[ZR1Dan]

Thanks for the input Guys.

I set it to spec, a fat ½" as 9/16" is the loose end of the limit. Did it on the center stand this time, rear wheel on the ground. Double checked it on the side stand after rocking it back & forth in gear, and bouncing it a few times. Measurement stayed the same. Going for a ride here in a bit, get it nice and warm and recheck it hot. I'll post those numbers for the curious, or for someone that searches this thread in the future.

Thanks Again for everyones input. I love this site, great info that gets to the point...

[MikeL]

I bought my 2007 Ultra used with 4800 miles.The dealer serviced it before I bought it. I checked over the bike and found at room temp cold the belt was as tight as a banjo string. Anyway I adjusted it to my spec of a close to half twist. No chirping on decell or werring at highway speeds.

[ZR1Dan]

Went for an 80 mile ride, same day we hit our first 100* temps. Pulled in the garage and measured it hot, radiator fans were still running. it's right at ¼" deflection with 10 pounds pressure now. ⅜" is the tight end of the spec cold. I'm within ⅛" of that hot, so I'm calling it good and not going to mess with it anymore. It is amazing how much difference the belt "feels" between 9/16" and a ¼" though. The difference is night and day.

Thanks again for the help, beers on me...

[mkd]

had the same experience when adjusting belts, i always adjusted to the loose end of the spec. don't know where i heard or seen it but somewhere i heard that a rule of thumb on the belt is to grab it mid point with your thumb and pointer finger and twist it from vertical to horizontal. it should just rotate 90 degrees with a good amount of effort.

[rbabos]

had the same experience when adjusting belts, i always adjusted to the loose end of the spec. don't know where i heard or seen it but somewhere i heard that a rule of thumb on the belt is to grab it mid point with your thumb and pointer finger and twist it from vertical to horizontal. it should just rotate 90 degrees with a good amount of effort.

90* ? Maybe if your name is Dwayne Johnson. Most of us struggle at 45* LOL.
Ron