Sprockets

[kinsler33]

My 49cc eBay Chinese motorized Schwinn has been great fun, but (and I've asked about this before) it's having a tough time on hills, is always eager to stall when the clutch is engaged with any but the most delicate touch, and the top speed that it eventually achieves is terrifying, at least for someone as old as I am.

It clearly would like a lower gear ratio. Right now the front sprocket is 11 teeth and the rear is 44 teeth. I've ordered a ten-tooth front sprocket that may or may not help a great deal, but I've had less luck finding a suitable rear sprocket, which I guess ought to have maybe 46 or 48 teeth.

After reading this forum I've done some housework on the engine, sealing the carburetor to the intake pipe with Permatex blue RTV and the intake pipe to the cylinder with Permatex Indian Head gasket shellac. And although it's not recommended I also sealed the exhaust pipe to the cylinder with more Permatex blue RTV, for the old exhaust gasket fell to pieces. (I've since ordered two extra exhaust gaskets.) I pulled the cylinder head off, pulled up the cylinder barrel, sealed the bottom of the barrel to the crank case with the blue RTV, and torqued the head bolts down properly.

A ride up the local test hill revealed that the engine ran far more smoothly, quietly, and reliably, but that its power was still insufficient to get to the top without vigorous pedaling. It seems clear that the gear ratio must be altered to something less than its current 4:1.

(One other discovery: the blue Permatex RTV seems to have worked rather nicely as an exhaust pipe sealant, though the exhaust temperature far exceeds Permatex recommendations. I thought it would burn up, but it seems fine.)

So, questions:

>>Is a 48-tooth to 10-tooth (that is, 4.8 : 1) gear ratio reasonable for someone who was just scolded by his doctor (geriatric) for an excessive body mass index? Or should the poor performance of the current 4:1 ratio be blamed on some fault in that little engine?

>>Where can I find a 9-hole 48-tooth rear sprocket? (It doesn't help that I'm a cheapskate, either.)

>>And, this bicycle came with a three-speed hub, an Austrian copy of the Sturmey-Archer. Because the rear sprocket from the kit wouldn't fit over the 3-speed hub, I installed a rear wheel with a single-speed sprocket. But I've since seen a clever rear-sprocket mount that doesn't use the rubber spoke pads but which clamps to the hub instead. Are these worth considering?

Any advice, helpful or otherwise, will be appreciated.

Mark Kinsler

 

[bakaneko]

You should probably tell us the bike wheel size, your weight, and the approximate hill grade or sense of it. You can find cheap rear sprockets on eBay for about $10-15 from a US shipper depending on the rarity of the sprocket. Having a single speed on a hill is probably what is killing you. Even hardcore cyclists need a wide range of gears to get up tough hills.

 

[kinsler33]

Whoops. The wheels are 26 inch--the old British EA3 lightweight size--and I have ballooned to around 190 pounds. In earlier days I was barely able to pedal (no motor) up the hill without having to walk the bike. One problem is that the pavement is very bad, so maneuvering is required while you're climbing. I can get up the hill with the motor and a reasonable amount of pedaling--I wouldn't expect to zip up to the top with 49cc's.

There are a multitude of 36-tooth rear sprockets for sale, and I don't know why. I did find a 48-tooth sprocket on Amazon for $25.00, so that may be what I'll get. A ten-tooth front sprocket is presumably making its way over the Pacific, and I'll try installing that to see if it improves matters significantly.

I still have my old rear wheel complete with its 62-year-old Austrian 3-speed hub (a copy of the Sturmey-Archer AW) and after some consideration have decided to rebuild it with a coaster brake, heavier spokes, and the 48-tooth rear sprocket. As it stands, the bike's caliper brakes aren't real adequate even when dry, so the coaster brake would seem to be the best idea.

Thanks for your help.

Mark Kinsler

 

[bakaneko]

https://www.ebay.com/sch/i.html?_from=R40&_nkw=motorized+bike+48t&_sacat=0&LH_PrefLoc=1&_sop=15

There are a variety of sprocket size to choose from online. I would put that 10T sprocket on first and then check to see how it fairs. Nothing is worse than putting multiple upgrades on and having to diagnose performance issues. One of the things I did with my motorized bike before my electric was to just put it in idle and bike manually for exercise. The idle gives a little boost and you get a workout for decent speed... LOL

 

[FurryOnTheInside]

I would put that 10T sprocket on first and then check to see how it fairs.

I agree!

 

[crassius]

48T and 56T are available (I buy from BGF on ebay, but there are other places)

the hills here are like walls, so I never see any 49cc bikes - swapping to a 66cc would be best choice