Moby Belt Size Confusion

I know this question has been answered a million times, but I've searched and found different reccomendations for Moby belt sizes. I have a non variated 77. Can anyone tell me the best belt for that?

I need to rule out belt slippage from the power loss problem I'm having, so I really want to get the right size.

I've seen these referenced:




And for when the idiot at the autoparts store that can't do anything without the 20 year old computer system in front of him asks, what type of belts are these?



Moby Belt Size Confusion

The number designation follows that the last three numbers are the belt circumference... so 320 is 32.0 inches around. 4L means 1/2" wide which is what you want for a moby. I use a 31 or 32 on my 50V but the 31 seems to last longer since they stretch after a bit. I've not sure about the non variated ones, but a 31" should assure there is no slipping. Just make sure the starter pully and air box clear with the belt on.

They are often called fractional horsepower belts or industrial v-grove belt. Those will look like they have cloth wrapped around the outside, and are usually white or green.

If you can find a cogged belt with the cuts underneath, they tend to hold up longer. I have attached a pic of the cogged belt.

Good luck!



longer belt or shorter belt?

wow dude. thanks for the thorough answer. i put a 31.5" belt on and the "clutch issue" i thought i had for the past 6 months is fixed. almost.

originally, the bike was running at 30mph with a 32" belt on it. Something happened to that brand new belt for the short time it was on the bike, or something happened to the engine to make that belt not work properly.

anyway, i put a 31.5"belt on and it went from giving me only 5mph, to 25mph. if the problem lies entirely in the belt, do you think i would regain that extra 5mph by going down to a 31", or back up to a 32"?

the belts are $15, so i don't want to buy each and try it out. any thoughts?


Re: longer belt or shorter belt?

See Ya Moped Army /

Just to see what would happen, I installed a 31" belt on my Moby yesterday and it ran like crap. It was slow to accelerate and had a high speed miss. I put back the original 32" belt and it ran fine again.

Re: longer belt or shorter belt?

huh. so maybe that half inch is killing my extra 5mph. i'm glad you tried that experiment. now, do i really want to spend another $15 on a belt for a bike i'm selling?


Re: longer belt or shorter belt?

John Joedicke /

You should be able to get fractional horsepower belts that size for about 5 bucks. You going to a autoparts store? Try TSC (Tractor Suppy).

Re: longer belt or shorter belt?

i tried autozone, but the idiots behind the counter couldn't handle anything their computer couldn't tell them, as i predicted. it's funny how resistant people can be to thinking. the dude at pep boys at least had the wherewithal to measure some belts for me and get me the right one. but yeah, $15. i wonder if napa is any cheaper. i'm pretty sure there's a tractor supply store around here somewhere... i'll try to find it.


Re: longer belt or shorter belt?

Of couse not I went into Autozone and said Huh? I have to make parts for my '77 Kreidler and I don't need a belt I have a intenal tranny I can't believe you can't find a belt. trial and error. that is how I keep my moped running. I have a belt drive moped I don't know what it is going to restore it I will and I will have no problem because of my resources in my city

Re: longer belt or shorter belt?

Napa uses the 4L320 part number, so if you go in and ask for one, they will know what it is.

Also: the 4L320W they have is green and coated in Kevlar, which makes it a much more heavy duty belt. I got one for my moby and it works great

Re: longer belt or shorter belt?

ಠ_ಠ Jon Folks ಠ_ಠ /

I went in to advance auto parts, and they weren't really sure what to do, they were going to order me an L320 belt. Do you think its the same? I don't think it will be the right width.

Still missing 5mph

Well, I went from a new 31.5 to the closest to 32" I could get, a 31 7/8". Still only getting 25mph out of my formerly 30mph single speed Moby.

I checked the carb and the exhaust, all seems clean and clear.

The only thing left to do is to drop the engine and get into the cylinder to examine. I have no clue what's going on with this thing.


« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account