1984 Honda Aero NH125 Rebuild

[zpb101]

I know this is a 50cc forum but, I can't find anywhere else where there seem to be people that are knowledgeable about Honda Aeros.

I found a barn fresh Honda Aero in pretty good shape a few weeks ago. Tags were 1988 so, it's been sitting for awhile.

I pulled her apart and did a bit of work -
wire brushed surface rust on frame and primed with a rust primer and then painted with a black frame paint
cleaned and relined the gas tank with a KBS kit
replaced the petcock
found a NOS carburator that included the dreaded bystarter on eBay (didn't need a new carb but it was a package deal with the bystarter)
cleaned and painted the rims
replaced the tires with Michelin S1s
cleaned and repainted the muffler

I had it running pretty well but, after 100 miles or so I have an issue - when I start accelerating the belt starts spinning/squealing before it catches on the drive. I opened the drive casing and there seem to be two issues. On the rear drive wheel clam there is some rust and pitting - this may be causing the belt to not catch but, not sure why it would start being an issue after 100 miles. The other issue is that the belt seems really loose. I thought the belt was supposed to be pretty tight. The rear drive clam seems to be compressing all the way. Visually, the belt doesn't seem to look that bad.

So, finally, my questions -

After sitting for 20+ years, did the belt stretch after a few 100 miles use? And a follow up - it doesn't seem that the belt - 23100-KJ9-003 - is available anymore. Has anyone found a viable replacement?

Also, is there a tension bolt on the Aero? I can't seem to find one.

Thanks so much for your help in advance.

[Wheelman-111]

Greetings:

Welcome. Nice resurrection.

Yikes that belt looks loose. I recommend first you Search and ascertain that you have the correct belt for the model. It's just possible that some P.O. couldn't/didn't bother finding Honda-san's Prescribed Part and just fitted something pretty close. The Bear is our resident NH125 Guru, but I gather he's off somewhere pouting instead of setting us poor Schlumps straight with his rapier wit. Anyway, I see a new belt in your future, and maybe a new spring behind the clutch.

There's no "Tension Bolt" but the squeezing force of the spring loading the rear pulley sheaves should force the belt almost all the way to the rims of that pulley, AND jam it tight between the fronts. Springs have been known to grow softer with time, heat, and open-close cycling. Coupled with the hard, brittle Ozonated rubber wearing quickly on the sandpaper pulleys, the tension at the FRONT pulley quickly became insufficient (as the belt wore narrower) for it to keep a grip on it. That could be the whole problem rat thar.

I have yet to see a belt "stretch", because the fibers encased in that molded rubber are pretty resistant to tension. (But that doesn't mean the whole thing isn't delaminating.) But they do become slippy as they get too narrow. A temporary solution is to reduce the boss/shim dimension at the front pulley.

[zuphilius]

Aero 125 is 23100-KJ9-003

Looks to be almost the same number, with an "A" thrown in there.

[motormike]

Welcome zpb101...your belt is correct and probably the original.
Without a doubt, it has become narrower due to the rusty pulley faces.
IT IS wore out and only replacement will help.
Some Honda dealers may have some NOS belt laying around, but they're not easy to find and very expensive.(about $92.00)
The dimensions of the OEM belt are: 794 X 18 X 30.
Explanation 794mm long; 18mm wide; 30 degrees sidewall angle...
Rather than pay HUGE money for a belt I could never find, I have installed a belt with slightly different dimensions.
New belt measures: 799 X 19 X 28...here is the link to my purchase> http://cgi.ebay.com/ebaymotors/ws/eBayI ... 1097490159 ....this seller has relisted these belts and it appears he has several.
The shipping time was very fast.
I have now put several hundred miles on this set-up and find that it is working well.
Take-off will indicate a small amount of slip, but seems to be decreasing as the belt angle scrubs off to fit better in the pulleys.
I recommend doing maintenance on the variator while you are already inside this side cover.
I have switched to Dr. Pulley sliders and you can see the thread here... viewtopic.php?f=3&t=24940
Good luck on getting your 125 straightened out and back on the road...
Use the search window on this site for additional 125 info.
Post your questions and we will help as needed...

[zpb101]

Thanks so much for the information.

I have some information on finding a new belt. I have been having an ongoing conversation with Bando/Erlandson trying to find a comparable belt. Here is what I found.

OEM belt is - 794mm long; 18mm wide; 30 degrees sidewall angle

Bando/Erlandson still makes a belt that measures - 788mm long; 18mm wide; 30 degrees sidewall angle - other than the 6mm length difference - the rest is an exact match. Model is - DBYA3KJB and was made for a 92-01 Yamaha Jog.

I am going to order one and I'll let you know how it works. (less than 30 bucks on ebay).

[motormike]

Your effort has found an alternative belt that I will be interested in seeing the result.
OEM belts sometimes come up on ebay, last time in Europe somewhere and about $60 before shipping.
The belt I have chosen is used on some Kymco models and is not too hard to get.
Even though the difference on my choice is 5mm longer, it seems to be good considering the cost.
Yours is only 6mm shorter, so maybe you have found a replacement that will work better than mine.
I anticipate a slight reduction in the top end, but great take-off for yours....rock-on...

[Tyler VR]

I bought a 788x18x30 belt on ebay awhile back, it's some cheap brand. I haven't tried it yet because I got a new stock belt, but maybe I'll try it out soon. I'm sure if you found a bando belt the same size it will be a lot better quality rather than a cheap one like I got for $14 shipped.

[zpb101]

I will keep an eye out for an OEM belt but, hopefully the closely spec'd belt will work. I'm ok with losing some top end speed - I live downtown in a city so, zero-30 is what counts.

Thanks for the information on the variator and the pulleys. I'll be looking more into that and probably will have some questions.

I ordered a new NOS clutch wheel off of ebay - a little expensive but, the rust on mine is significant and will probably continue to grind through belts.


Love seeing the pics of the Gyro - I have a 1986 Gyro in my garage that I haven't started into yet...

[zpb101]

OK - big fail on the belt. I had said 'Bando/Erlandson still makes a belt that measures - 788mm long; 18mm wide; 30 degrees sidewall angle - other than the 6mm length difference - the rest is an exact match. Model is - DBYA3KJB and was made for a 92-01 Yamaha Jog. '

I got the belt today and it was 788 17 30 - it was way too wide for the Aero. I've contacted Erlandson because they gave me the wrong specs. Sorry if I misled anyone - pretty disappointed myself. I'll let you know what Erlandson says.

[motormike]

OK - big fail on the belt. I had said 'Bando/Erlandson still makes a belt that measures - 788mm long; 18mm wide; 30 degrees sidewall angle - other than the 6mm length difference - the rest is an exact match. Model is - DBYA3KJB and was made for a 92-01 Yamaha Jog. '

I got the belt today and it was 788 17 30 - it was way too wide for the Aero. I've contacted Erlandson because they gave me the wrong specs. Sorry if I misled anyone - pretty disappointed myself. I'll let you know what Erlandson says.

You say this new belt is 17 wide,
the stock belt is 18 wide,
17 mm is 1 mm narrower....
so not understanding.

[zpb101]

OK - so, now I'm really confused and this is definitely making me feel like a noob.

I got an 'OEM' belt today and tried to install. The 'OEM' belt is too wide to fit on the drive boss - you can't get the face drive on far enough to engage the gear. Thinking I must have done something wrong I made sure I was assembling it correctly.

So, then I pulled out the original belt and it is much thinner. (See pic)

Notice the same belt model number. Now I'm really confused. Any ideas?

[Wheelman-111]

Greetings:

It's just possible Bando made a typo, but I'm inclined to believe your original belt really is that worn.

To install, try the following.
Use Manly ZPB grip to separate rear pulleys fully. Stick something in between the sheaves to hold them open from the front. I use my handy 3/8" Socket Extension but any inanimate object will do.
Then you can pull the belt forward and spread the loop further away from the center of the crank. This will allow the outer sheave to seat onto its splines and the nut to be snugged down sans belt interference.

You can spin the rear pulley and watch the belt walk up the rear/down the front sheaves into a TIGHT position. See how it sits with respect to front/rear loop diameters. If it's nearly parallel, it's ok to add a thin washer between the crank shoulder and the pulley boss to widen the space between the front sheaves. However if the belt is indeed stock size - and nobody's swapped pulley bosses before you - the belt should be OK. Now revel in faster accelertion 'cause your belt ain't slippin' away all that monumental 125 Power.

[Tyler VR]

Any ideas?

I struggled for a minute when I was trying to install my new drive belt.

The trick I found was to first slip the belt on the clutch pulley (rear), then pull it tight making the belt sink down into the pulley. That should give enough slack to put on the outside varirator pulley (front) without the belt getting in the way.

[zpb101]

OK - you guys were right. I am really surprised how much the rust pitted drum shaved the original belt down. I got the belt on last night - took some work but, it went on.

Bike is running great - nice smooth fast acceleration right through 55 mph (might have gone faster but, I don't have a long enough flat run where I live).

As with a lot of people here - might be too many variables.
- new OEM belt
- 18g Dr Pulley sliders
- new clutch wheel

I ordered the new clutch wheel a few weeks ago from Thailand via ebay. You can see in the picture the pitting on the old one.

I put a little bit more money into this build *than I really wanted to - but, I really feel like I have a pretty much brand new scooter.

[motormike]

Congrats on the success....
Now think about this: CT chrome manifold, adapter, Mikuni 24mm flat-slide=65 mph