Author Topic: Kymco AK 550 belt tension check  (Read 783 times)

rjs987

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Kymco AK 550 belt tension check
« on: November 09, 2021, 11:30:19 PM »
Took some time today to remove the plastic final drive belt (timing belt) guard and test the belt tension with my force belt tension tool. I needed to get a benchmark for when I do any rear wheel or belt maintenance and need to re-tension the belt.

I was not about to spend the $800+ the Kymco officially recommended sonic belt tension tester, or the $600 that it costs on eBay.

This is the tool I bought to do the job. They are available from several sources and for different prices and especially from Harley dealers since those bikes are what this tool is most often used on.

http://www.amazon.com/gp/product/B01M2ZHHNX/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

I figured $16 was low enough that I would take a chance on only doing it this way. This tool has an L bracket that is exactly as wide as the belt on the AK 550.

Had to refer to the service manual to see how to remove the belt guard. There are actually 4 pieces to the belt guard. Two pieces on the upper half, inner and outer. Two pieces on the lower half, inner and outer. ONLY THE LOWER HALF NEEDS TO BE REMOVED. The lower outer guard was easy. 2 bolts are easily seen and there are snap hooks along the bottom edge where it meets the lower inner guard. These snap hooks are not as fragile as on other scooters I’ve worked on.

Pic 1 I show that I used a # 5 hex bit on the 2 bolts that hold the lower outer guard.

Pic 2 is that lower outer belt guard removed. You can see the 2 bolt holes that hold it on. One toward the rear end and one at the front end.

The inner bolts are a 10 mm socket bolt and are harder to get to. There is also a washer with each bolt. The one toward the rear is easier but still needs a short extension for the ratchet handle or a long socket to get to it since both bolts are recessed. Pic 3 is the first bolt removed with the socket I used.

Since my pictures are too big and the forum does not allow more than 4 per post I'll continue in the next post.
« Last Edit: November 10, 2021, 01:37:40 AM by rjs987 »
/bob
2022 Kymco AK 550 Super Touring Extreme in Matte Deep Blue
RETIRED - US Navy and Air National Guard and civilian career

rjs987

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Re: Kymco AK 550 belt tension check
« Reply #1 on: November 10, 2021, 12:08:40 AM »

Continued from post 1.
The forward inner bolt is a real bear to get to. It is located exactly next to the tire and I had to search for just the right extension that was not too long yet long enough to get to it. This bolt is also recessed so an extension is also needed. I used my ratchet to loosen the bolt and then wormed my fingers back there to turn out the bolt.

Pic 4 shows the lower inner belt guard and you can see the 2 bolt holes.

Now for the belt tension check. Everything I was reading says to measure the distance between the front and rear belt sprocket centers and check belt tension using the force tool at the mid point between those centers. Most of the articles I read also stated that someone should be sitting on the bike to compress the rear end as it would be while riding. I am guessing there are two reasons for this. One is that the front sprocket may not be exactly centered at the pivot point of the swing arm so the tension may be different if it is not compressed as when riding. The second reason may be to prevent the rear wheel from turning slightly while checking the tension. On this scooter the front sprocket is centered at the pivot point of the swing arm so that doesn’t change tension on the belt. The pivot for the swing arm rotates around the drive pinion shaft for the forward drive sprocket. Also this scooter has a parking brake that will prevent the rear wheel from turning while pressing on the belt on one side or the other. So I proceeded to do this check while the bike was on the center stand.

I set up my tape measure to stand up so my hands were free to test the tension and also take the pictures. The belt at rest, including the thickness of the tension tool L bracket was set to be at the 1 inch mark and as I pressed up on the force tension tool I measured up from there looking at the bottom of the tool L bracket.

Pic 5 is what it looked like.

The deflection of the belt is checked when pressing up on the end of the tool until the plunger gets to the 10 pound mark. You can see here where the midpoint is where the belt should be checked. Set the tool on the belt just below the space between the Kymco label and the front of the insert with that logo on the swing arm. I checked the belt in several places by turning the wheel one quarter turn and checking the belt. Then another quarter turn and check the belt again. Then repeat. I did this every quarter turn of the rear wheel 6 times to get an average reading of belt tension deflection.

I came up with a measurement of between 3/8 to 7/16 of an inch deflection depending where I was measuring. This is my benchmark for now.

This tool has 2 rubber O-rings. One you can see in the picture above to be used to mark deflection. I used the bottom of the L bracket instead but could have used the O-ring just the same. After doing this I am thinking it would be easier to see the O-ring so I may set that to a mark on the tape measure and observe the deflection using that as the marker. There is also an O-ring on the silver plunger shaft to make it easier to see the 10 pound mark. There are only the zero and 10 pound marks on this plunger since those are the only marks needed.

If tension is too loose the tool will deflect the belt more than what it should be. If tension is too tight the tool will not deflect the belt enough. In either case the belt will need to be re-tensioned per the procedure in the service manual. And then this procedure will need to be repeated.

When finished checking the tension of the final drive/timing belt then reinstall the belt guards in reverse order of removal.
« Last Edit: November 10, 2021, 12:11:07 AM by rjs987 »
/bob
2022 Kymco AK 550 Super Touring Extreme in Matte Deep Blue
RETIRED - US Navy and Air National Guard and civilian career

jermwars

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Re: Kymco AK 550 belt tension check
« Reply #2 on: November 10, 2021, 08:37:22 PM »
This is just a great deal...i owe you one. I had already done the math and decided it was worth it to buy the stupid $800 u-508.

Why on earth could such a tool possibly be necessary?? 

"Tension reading should be 1300~1700N (brand new, after running
1000~1400N)."

Surely specing with the method youve described and the tools commonly available are more than adequate to land within a range like that...it might be fun to buy the 508 and do some test comparisons if the seller is happy to take a return. See if a reading well outside the range will still result in 3/8" deflection @10lb 


22' KymCo AK550
07' Yamaha Majesty YP400

rjs987

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Re: Kymco AK 550 belt tension check
« Reply #3 on: November 10, 2021, 09:09:44 PM »
This is just a great deal...i owe you one. I had already done the math and decided it was worth it to buy the stupid $800 u-508.

Why on earth could such a tool possibly be necessary?? 

"Tension reading should be 1300~1700N (brand new, after running
1000~1400N)."

Surely specing with the method youve described and the tools commonly available are more than adequate to land within a range like that...it might be fun to buy the 508 and do some test comparisons if the seller is happy to take a return. See if a reading well outside the range will still result in 3/8" deflection @10lb


Let me know how that turns out.  ;)
/bob
2022 Kymco AK 550 Super Touring Extreme in Matte Deep Blue
RETIRED - US Navy and Air National Guard and civilian career

jermwars

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Re: Kymco AK 550 belt tension check
« Reply #4 on: November 10, 2021, 09:34:40 PM »

Let me know how that turns out.  ;)

I absolutely will.
22' KymCo AK550
07' Yamaha Majesty YP400

john grinsel

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Re: Kymco AK 550 belt tension check
« Reply #5 on: November 11, 2021, 12:18:43 PM »
Even if you are riding 30-40,000 miles a year, I would not worry about it!!   Just ride.

rjs987

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Re: Kymco AK 550 belt tension check
« Reply #6 on: November 11, 2021, 02:27:11 PM »
Even if you are riding 30-40,000 miles a year, I would not worry about it!!   Just ride.


Not worried at all about it here. Just needed to get a benchmark to be able to restore the proper tension when that time comes... whenever it is. Most likely after a tire change.
/bob
2022 Kymco AK 550 Super Touring Extreme in Matte Deep Blue
RETIRED - US Navy and Air National Guard and civilian career

jermwars

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Re: Kymco AK 550 belt tension check
« Reply #7 on: November 11, 2021, 03:05:54 PM »
Even if you are riding 30-40,000 miles a year, I would not worry about it!!   Just ride.

I was kinda worried when i saw we needed a tricorder to check the belt tension...:P
22' KymCo AK550
07' Yamaha Majesty YP400

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