Generic MD 1000 and HD 750 ebike model discussion

So, I found what’s broken, 2 parts.
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I have to say that my bike down shifts much easier since the cable was replaced and the cable guard shortened. There is still a good amount of resistance but carpel tunnel inducing pressure is no longer required. I'm sure all the pressure required to shift is what broke those parts.
 
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cracked the seat post...
 
That is really weird but obviously a catastrophic failure of the seat post tube. Send your photos to Yeili and see what they say.

It does look like the seat post tube failed at the bottom of the seat post. My seat is even higher than yours and @210lbs I should be putting even more pressure on that area. I've got over 1000 miles on the bike and ride it pretty hard but mine looks fine. The weld on mine looks better than yours so that might have been a contributing factor. Please let us know how the resolution process with Yeili goes.
 

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Is it possible that your seat post was shortened because a longer post would not go past the ( very poor ) welds? That's what it looks like to me.
 
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Is it possible that your seat post was shortened because a longer post would not go past the ( very poor ) welds? That's what it looks like to me.
The post does goes past the weld. I can't get the seat post out of the broken bike. I talked to leili and they sent the photos to the frame builders. The said it's because the seat post is too high so it's my fault, see photo of the black bike they sent me. As you can see in my photo, I only have it up like 2.5 inches (only a 30 inch inseam). They offered to send me a new frame but I have to pay for shipping plus it won't arrive until summer.

I'm going to check the welds on the other 4 bikes. The weld does look poor compared to rmks
 

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The post does goes past the weld. I can't get the seat post out of the broken bike. I talked to leili and they sent the photos to the frame builders. The said it's because the seat post is too high so it's my fault, see photo of the black bike they sent me. As you can see in my photo, I only have it up like 2.5 inches (only a 30 inch inseam). They offered to send me a new frame but I have to pay for shipping plus it won't arrive until summer.

I'm going to check the welds on the other 4 bikes. The weld does look poor compared to rmks
With this comparison pic I see the problem. Due to the lower enlarged tube the extra lower length of post does nothing to stop the upper part of the post from moving. This is going to happen to a lot of these bikes.
 
With this comparison pic I see the problem. Due to the lower enlarged tube the extra lower length of post does nothing to stop the upper part of the post from moving. This is going to happen to a lot of these bikes.
I had a feeling when buying these bikes that would be a weak spot. I am going to get a professional welders opinion on it. Also it doesnt seem to make a tight fit on the seat post like my normal bikes do.
 
I had a feeling when buying these bikes that would be a weak spot. I am going to get a professional welders opinion on it. Also it doesnt seem to make a tight fit on the seat post like my normal bikes do.
I had a feeling when buying these bikes that would be a weak spot. I am going to get a professional welders opinion on it. Also it doesnt seem to make a tight fit on the seat post like my normal bikes do.
There are minimum insertion marks on the standard seatpost and yours is well within that limit. My Suntour NCX suspension seatpost requires a sleeve shim that is 4" long and that shim helps reinforce the area. I recall some frame building photos that show the seatpost tube going an inch or so into the box below that contains the motor controller. As you can see from the photo, the 400mm suntour seatpost is considerably longer than the stock seatpost. Although below minimum insertion mark, my seat is much higher than yours and that creates more leverage on this area. After 1000 miles, mine seems very solid.

The hand welding done on these frames will lead to issues like this and with COVID as a mitigating factor, QA might not catch the problem. I like your idea of having an expert welder look at this and with a little creativity, I bet this can be made better than new. It is a hassle but such is the issue with these types of bikes. Hopefully Yeili will pay to have it repaired.
 

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The hand welding done on these frames will lead to issues like this and with COVID as a mitigating factor, QA might not catch the problem. I like your idea of having an expert welder look at this and with a little creativity, I bet this can be made better than new. It is a hassle but such is the issue with these types of bikes. Hopefully Yeili will pay to have it repaired.
While not pretty, the weld does not appear to have failed. Unless the seat tube extends and is supported in the boxed section of the frame, I think Reed may be on to something. It will be interesting to see where this all goes. Could be a serious design defect.
 
So is this a design flaw that will eventually happen to all the bikes over time and would a seat post shim as stated above help reduce the chance of it happening?
 
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