New 49cc POS HT Bicycle Motor

DaveC

DaveC

Member
Ok, got the new 49 cc from BGF. Started to tear it down to bolt on the upgrades taken off the 66. Cylinder head comes off. I notice the head studs are of a much higher quality than the ones supplyed with the 66. They even got rid of the acorn nuts and are using the longer version of the nuts they use.

I get the jug off only to notice the mating surfaces top and bottom of the jug are un-machined! :/ The bottom is getting RTV Silicone so no big deal. Top gets the sandpaper-on-glass trick to at least grind it down flat. With my Puch head the compression should be in the 10:1 CR area. A good, flat gasket surface is a must.

They have a cast mounting strap now, getting rid of the stamped flat strap. Looks like it ought to hold better than what they had. Either that or it will just crack and bust :P
 
Re: New 49cc POS HT Motor

Yup. You do have to open the holes in the Puch head for the bigger M8 bolts on the 66 but it worked, no problem. I have a 49 cc and a 66cc head, except for the hole size they line up perfectly. The Chinese made the 66 on a 49 bottom end and they did nothing that would drive the cost up so they use the same machining for both. Which is why a 66 vibrates way more than a 49. They hung a bigger piston on without changing the balance, thus vibration.
 
Re: New 49cc POS HT Motor

Just get a 66 jug and piston. I'd drill and tap the block for SBP M8 1.00 head studs. The compression would be high but you could drill the 49cc head studs holes to fit, too. Use a new top and bottom gasket, new rings.

Be prepaired for the increase vibration. 66's vibrate real bad because you have to get them balanced and that's expensive which is why the Chinese don't do it.
 
Re: New 49cc POS HT Motor

DaveC said:
Ok, got the new 49 cc from BGF. Started to tear it down to bolt on the upgrades taken off the 66. Cylinder head comes off. I notice the head studs are of a much higher quality than the ones supplyed with the 66. They even got rid of the acorn nuts and are using the longer version of the nuts they use.

I get the jug off only to notice the mating surfaces top and bottom of the jug are un-machined! :/ The bottom is getting RTV Silicone so no big deal. Top gets the sandpaper-on-glass trick to at least grind it down flat. With my Puch head the compression should be in the 10:1 CR area. A good, flat gasket surface is a must.

They have a cast mounting strap now, getting rid of the stamped flat strap. Looks like it ought to hold better than what they had. Either that or it will just crack and bust :P
Click to expand...

You're talking about the rear mount right? I saw one of those on a SkyHawk 80. I didn't have any trouble with it, but I was a little concerned about it cracking too. It didn't so far. My thoughts on it were, it looked strong enough, but was an exact fit for some seat posts, but not others. Since it's cast it can't be bent in or out for a better fit, but you can sand or grind it for a little more room if you needed to. I'm guessing it will probably be ok.
 
Re: New 49cc POS HT Motor

Dang thing never ran and I sold all of my Chinee stuff off and got a Morini. I'm looking for a different bike for it, though. Don't think my aluminum Mongoose Paver is up to it. A steel frame/rims crusier would be a better bike in my opinion. Prefer one with handlebar brakes but I can add those.
 
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