Assembly defects, with pics & other stuff

Hey guys,

This thread is for technical reference only. It is intended to be an aide to the end user as well as the resellers of these kits. It is not for the benefit of pointing fingers and naming the resellers of these particular engines, (so please don't ask). The resellers do not want the factories to ship them scrap engines. They want thier business to prosper, and I want them to prosper as well.

I think we should all, as a group, set a simple precedent:

Resellers:

Take care of an obvious manufaturing defect...whether you offer a warranty or not! You are the one dealing directly with the factory, not us. We buy a product from you fully expecting a limited life span...don't expect us to deal with your manufacturing defects in the first few miles of use...It's not reasonable.

End Users:

If you cobble-up part of your kit, don't blame the reseller! They aren't Wal-Mart! It is already common knowledge that the fasteners should be replaced. To expect a reseller to replace your engine because you broke off a stud is ridiculous!

Loss of power:

The first 2 pics below show an engine that was disassembled due to a major loss of power. The bearings were installed backwards with the seals facing inward towards the crankshaft. The bearings got so hot due to a lack of lubrication, that the seals melted and clogged the bearings. The bearings were completely seized. The crank was spinning in the inner races of the bearings. The crank journal and the inner races were blue. It just goes to show how a simple error in assembly can cause major problems.

Excessive gear noise:

The next 2 pics show the clutch gear of a bike that was used for 3 hours. I didn't even need the gear puller to remove the hub. It fell off once the nut was removed. The countershaft taper was not correct to the taper of the hub. The same was true for the sprocket on the opposite end. I didn't even need the puller to remove it! It just fell off. The entire countershaft assembly is scrap.

The CAD graphic at the end shows how the gear hub is assembled. It is easy to check this on a new engine. Simply remove the gearset cover and check the gear for any excessive play. I have a new engine on the shelf that was assembled without the 2mm ball bearings shown in the graphic. The gear can be moved up & down, or side-to-side about 1/16".

Jim

Excessive vibration:

The photo below shows a crankshaft with the weights removed. The bolt hole pattern for mounting these weights are 120 degrees apart. The cut-outs for balancing should, of course, be postioned at the rod big-end. One of the weights on this crank had been fastened, "clocked", 120 degrees out. I'm certain that this is why some engines vibrate so much more than others.

Jim

eDJ said:

Jim,

From what you've seen of the insides of the motors, does it seem like the design
is satisfactory for a service motor that can give 20 to 35 mph performance ?

I seem to remember you indicating you thought the materials and machining of the
case etc were OK whereas the cylinder and porting left much to be desired.

Is it more of a question of better training for those who put these motors together,
along with better inspection, and quality control ?

Perhaps a definitive manual for how to do a complete tear down and rebuild would
be what's most needed now for the markets outside of China. Even if it were set
up online as an eBook.

Click to expand...

EDJ,

Yes, the design is fine for its intended use. From what I've discovered the majority of the problems are caused by improper assembly.

As a means of high speed manufacturing, the castings are die cast. This results in a superior casting when compared to sand casting.

Most of the engine internals are fairly good...totally serviceable. This has to be taken in the context of what we are paying for. A 70cc engine is capable of producing 15HP reliably, so one could say that this Chinese engine is junk. All things considered they really aren't that bad. If the parts are made to the intent of the design, and assembled properly; this engine should provide years of fun.

The engine that is shown above with the countershaft problem is a recent exception. A new local customer came in this week to have me check what he thought was excessive gear noise. He was certainly right, and it's a good thing he didn't ride it any more than he had. The entire countershaft assembly is scrap. I replaced the countershaft, and gear assembly with a new one I had here at the shop. We'll see how the rest of it holds up.

"Is it more of a question of better training for those who put these motors together,
along with better inspection, and quality control ?"

This is it! 99% of the problems would be resolved if this were done. It would take so little to train someone to assemble these properly. One day, tops, to train 30 assemblers in a class-room type enviornment.

Same thing for the quality inspectors...One day of class room instruction: combined with the simplest collection of standard measuring tools, and a few custom gauges would make a world of difference in the finished product.

I have just about enough material...photos from tear downs, to put together an assembly manual. I plan on doing this eventually and putting it up on my website for everyone to use.

Jim

Large Filipino said:

So to fix it you just moved it back 120 degrees? That particular crank still in use or is it sitting with parts? And how hard or easy was it to dissasemble the engine that far?

I'm truly appreciating your work.

Click to expand...

Large,

Yes, simply bolt the weight back on clocked in the right position. This only applies to an engine that is vibrating EXCESSIVELY. If it's just a little worse than usual, it is unlikely that this is the problem. When the weights are clocked wrong the engine will REALLY vibrate.

This crank will be balanced with new weights that I will manufacture here, and then used in one of my new engines.

It's easy to disassemble these engines, with one exception; the magnet. On some engines the magnet for the magneto is really stuck to the crankshaft. There isn't enough room between the magnet and the case to get a typical puller to work. The crank is small in diameter on this end, and easily damaged. If the magnet is stuck, you must be patient. A combination of PB Blaster, or Liquid Wrench, and two small flat blade screw drivers behind the magnet wil eventually get it free. Again, you can't rush this. If you try to force it, the crank will end up permanently damaged.

As long as you have the universal puller tool that comes in some kits and is available at DAX, the tear down only takes about 1/2 hour; if the magnet isn't stuck.

"I'm truly appreciating your work."

Thanks, I figured from some of the posts I've read lately that this info may help others to diagnose problems and/or be a bit more equipped to describe a warranty claim to thier reseller.

Jim

Bob K said:

That's an outstanding bit of "number crunching" there , Jim !
Have you had time to do an estimate between the weight differential
suggested by your simulation and the cut-out volumes of the
stock flywheels ( balancer wheels/crankcase stuffers? )?

Bob K

Click to expand...

Bob,

As part of that process, the computer has already given me this info. It's like a virtual machine shop that compliments my physical machine shop.

Jim

Thanks Guys,

The customer that came in this week, (clutch gear photos in the first post), had figured that his engine was too noisey; but he wasn't sure why. He had pulled the clutch cover off and noticed that the clutch gear was loose, but figured it was normal since the engine was "new". Had he rode it much longer, it would have been totally ruined.

I'm hoping that this thread and the posts that follow will help others prevent major failures. If you catch some of these problems early on, they are completely repairable. It is up to us to be as knowledgeable as possible in order to get the most enjoyment out of these MB's.

Jim

You're welcome EDJ,

I've been planning on putting up a bunch of, (help/how to), stuff on my web site for everyone to use. Thinking about it; maybe instead of waiting to finish the, "full boat", project I'll put up the info as I write it.

Thank you for the link...I will have to put this together with software that I am familiar with for now. Time constraints don't allow me to get too engrossed in the presentation, but I promise it will be laid out in a concise manner that will be beneficial.

Jim