Engine Vibration & other fun stuff

Creative Engineering · #1 (**permalink**) 10-28-2008, 06:41 PM

Hello all,

I'm working on a new build and decided to tear down my BGF engine to see how these are made...all I can say is Oh Boy what a mess. photos below.

I dial indicated the crank, photo below, the run-out is .015" symetrically on both sides. No wonder they vibrate. The Chinese have added extra weights to each crank half, I've never seen this before. All I can figure is that they used a crank from a smaller engine, and filled the void between the case and crank with added material that is fastened with machine screws. I will be making a new crank for this engine. I wll not be making crakshafts for resale.

I remember a post regarding "rusty" con-rods. As I had figured it's copper plated to prevent case hardening along the beam. You only want the bore of the big and small end hardened.

All-in-all it's really not a bad engine, there's plenty to work with. I don't know how they can make them so inexpensively!

Jim

Bike parts

tyrslider · #2 (**permalink**) 10-28-2008, 09:37 PM

Do you think you could true and balance the crank? Or not worth the effort?

FileStyle · #3 (**permalink**) 10-28-2008, 10:16 PM

hope you keep us informed of the progress , looks like its gonna be something really nice when your done!

Creative Engineering · #4 (**permalink**) 10-28-2008, 10:56 PM

tyrslider,

It would be possible to balance the crank as-is. The crank in this engine is a conglomeration. I wouldn't even consider balancing it. It will be less trouble for me to make a new one. I worked on and tuned a lot of moto-cross bikes as a kid in the 70's. I'm not sure how this crank came to be, but it looks like the factory acquired a stock crank from another factory and then modified it with added weights to work within the engine case they had. I have no idea if other factories have cranks that are made from solid pieces...i.e. no added parts screwed to the crank. The crankshaft should be two "solid' matching pieces.

filestyle1,

Yes I will! I started an email to you this morning and my computer crashed...the classic blue screen with Gibberish and reboot...I had to get to the shop! I'll try to get you some pics in the morning.

Best Regards,
Jim

Finfan · #5 (**permalink**) 10-29-2008, 12:33 AM

Jim:
I WANT your garage/shop!!!!!

Creative Engineering · #6 (**permalink**) 10-29-2008, 09:39 PM

Finfan,

Yes the shop is fun!!! But sometimes it's also a burden...rent, power bills...etc.

Me and the guys like making products, but we also have to cover our bills every month.

Jim

jburr36 · #7 (**permalink**) 10-30-2008, 12:25 PM

I like to do machine work myself and I excel at solving problems. All I have is a cheap mini lathe with a milling attachment. Not the most accurate setup but well enough for these kinds of engines. At least it's not like my good old days when I was using a drill press to turn metal. Man! That wasn't fun at all.

jburr36 · #8 (**permalink**) 10-30-2008, 12:34 PM

I've got at least 7 diferent mod projects lined up for this china engine. Some I hope to sell to make money so I won't go into detail but I know you guys would go crazy over it just by reading the complaints/problems here.

I think it's awesome that some of us enthusiasts make aftermarket upgrades to make these engines better.

Motoschwinn · #9 (**permalink**) 10-31-2008, 06:16 PM

Anyone considered a big bore kit? They made these for VW's and they sold like crazy for years... 85cc sounds about right doesn't it?

Andyinchville1 · #10 (**permalink**) 10-31-2008, 08:29 PM

Great Thread....Since you are making a crank anyways, How about a stroker?.....Simply place a machined piece (spacer) under the cylinder, add longer studs....Wallah....Instant REAL 80+ CC power!!

Andrew