Need New Crank- Any Advise?

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supercub

New Member
Nov 1, 2012
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New London, CT
I searched around and found some good points but need to make a choice- My motor is from boygofast and is about 3 years old. The crank lower rod end failed, locked up after about 20 miles. Now I read that the bgf cranks are bad. Also, that some other seller's cranks have different small rod end diameters and rod lengths.
My questions are, who sells the best quality cranks, and which would fit up to my 66/80 engine? I will measure the rod length and small end diameter and post.

Also, I recently brought another BGF engine but haven't tried it yet.

Thanks
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
There's nothing actually wrong with BGF cranks... The problem that I've found with his engines is that someone at the factory in China often installs too many shims behind the main bearings. (between the flywheels & case bearings).

When you remove all the case bolts from the engine, the two case halves don't quite touch each other, then they force the two case halves together with the engine bolts & put sideways stress on the main bearings, (which causes them to fail).

I've found that BGF engines are actually very fast & reliable if you take them apart & remove those shims before starting them. ;)
 
Last edited:

biknut

Well-Known Member
Sep 28, 2010
6,631
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Dallas
It didn't have any shims and the mains are fine.
None of my three BGF motors had any shims either. An X, a T,and a Z. All three had badly out of true cranks. I bought 3 different replacment cranks, from three different vendors, and all three were out of true also, and only one had anywhere near correct balance.

I have to agree though, that the BGF motors have good power as long as they last.

Many of the other parts on the BGF motors are good quality. I now use the BGF motors I have as a spare parts supply.

If you have a BGF motor I would recommend not reving it above 6000 very often.

I've been a lot happier with Flying Horse motors. They seem to have better cranks, but some of the other parts have seemed less than great. I have swaped out some parts from my BGF motors, to my Flying Horse motors.

It seems like different factories focus on different parts of their motors. Flying horse on their cranks, and bearings. BGF on their gears and shafts. No body seems to care that much about assembly.
 

supercub

New Member
Nov 1, 2012
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New London, CT
Every bearing was loose in the case bore and every shaft slid out of the bearing. I can see where the shafts have wear from spinning in the ID of the bearing. If I buy another BGF crank, can I expect it to fial fast, or it is a better bet to go with a flying horse? In both cases, I don't know for sure if they will match up.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
Every bearing was loose in the case bore and every shaft slid out of the bearing. I can see where the shafts have wear from spinning in the ID of the bearing. If I buy another BGF crank, can I expect it to fial fast, or it is a better bet to go with a flying horse? In both cases, I don't know for sure if they will match up.
My BGF X motor's crank had so much runout that the crank bearings outter race wobbled back and forth in the case half, and wore out the hole the bearing was pressed into. When there got to be enough wear, the flywheel started scraping the crankcase, making a really nasty sound. The motor still ran though lol.

All I can tell you is out of 4 Flying Horse motors, all of them had good cranks and were smooth running. On my last Flying Horse motor I thought the big clutch gear had a little too much slop in it, so I replaced it with one out of a BGF motor that seemed a little tighter to me. None of my Flying Horse motors have ever cratered on me. The assembly however, has been just as bad as any other brand, but if you take the time to look it over you can correct sloppy assembly.
 

supercub

New Member
Nov 1, 2012
56
0
0
New London, CT
I see that bikeberry sells cranks but I don't know if they are flying horse, although they sell their kits. The crank comes without the covers, would the bgf ones change out onto the bikeberry crank? The listing doesnt give journal sizes but my small rod end is 14mm, crank journals 15mm, and rod journal spacing is 85mm.