Very curious. I have had one of these units for about 20 years and I never had this sort of an issue. I have a number of the different tools and the clamping system works fine.
The drive is via a flex shaft so alignment is not an issue. The only thing that I can imagine is that the coupling clamp is not being tightened sufficiently.
I just replaced the power head on mine and noticed that it had a somewhat larger knob on the clamp. I never gave it much of a thought since it never seemed to take much to clamp it securly but maybe I am stronger than some folks!
Basically after 20 years it has been a solid design. I did initially have my doubts.
The same set up is sold under a number of different MTD brands. I believe that the last time I looked at impliments they were generically branded as "Trimmer Plus". The Ryobi Expand-It seems to be the same system.
I agree completely. Even though my engineering discipline is essentially electronic, I could conceive of several better ways to design that coupling. But, as you pointed out, they probably would have been a little more expensive than the one that they used. I have noticed, while shopping for a replacement for the TroyBilt unit, that the newer models have a slightly different design of this coupling, but is does not appear to be much more rugged than mine. I haven't really studied the new ones in much detail, but the changes they made in them may have decreased the problems that I was having.
A proper coupling would have made a world of difference. The coupling you described sounds like a rigid one. It's inexpensive, sure, but it's also cheap. A proper coupling (maybe a jaw coupling?) might have made all the difference.
I have to say something nice about MTD too. I have an MTD snow thrower that's nearly 20 years old. I can still buy parts for the machine, and some parts, like the auger bearings, are so common that Ace Hardware carries them. I'm not saying that MTD doesn't have any monkeys, but they didn't let them work on my snow thrower.
Thanks to all who responded to my post about the TroyBilt trimmer/weedwacker. I did not know, prior to buying this unit, that TroyBilt was a part of MTD. After this experience I agree with most of the suggestions and comments that have been made.
However, as bad as my experience with this equipment has been, I must give a lot of praise to the MTD Customer Relations Department. After several phone calls about the problems that I was experiencing, they agreed to give me a refund for most of what I had invested in the unit. This was an unexpected conclusion to the situation and worthy of a large vote of thanks to MTD for being sensitive to the concerns of unsatisfied customers. While I can no longer recommend MTD products due to potential design problems, I do want to congratulate them on their commitment to satisfy their customers. By the way, I also have a Cub Cadet utility vehicle, again that I had no idea was made by MTD, and have had minimal problems with it after 5 years of rather hard use.
For the problems of the slipping coupling between those changable sections, the solution that I suggest is a good application of a permanent threadlocker compound, such as LokTite. You will need to get the correct type, since there are several choices. But that stuff held the engine sprocket on a snowblower in place even with the key missing. The downside is that you would not be able to take the thing apart, which I would not regard as a problem if it were mine.
My Troy-Bilt chipper/shredder was made by MTD, and looks just like the YardMan. I lost count of the sheetmetal repair welds on it. Thanks Dad, where ever you are, for teaching me how to use a gas welding torch.
On the last McCullough trimmer I had, the shaft housing came loose and caused the inner flex shaft to break. I threw it away since it took a half hour to start it anyway. That's another once great brand that went down the tubes.
Alas, MTD demonstrates one result of billion dollar take-overs. I can't swear to it but I believe all lawn mowers and snow blowers sold by the big-box stores are MTD. They change the livery but the guts are the same. Multi-purpose tools are usually a compromise and they do neither well. A weed whacker is supposed to be light and easy to use, not so with a brush cutter. I trashed a dual-purpose Echo for the same problem, the twisting motion of the brush-cutter head caused damage to the shaft and ultimately destroyed the tool. The purpose built Stihl brush-cutter is way too heavy to weed-whack but works very well for its intended use.
I was reading the original article, remembered all the problems I had with my Stihl (it might even be an FS45, household version). I've put 3 carburetors on that thing, so far, at $30+ each. The dealer told me the same thing about ethanol, boutique fuels, and on & on. It led me to the conclusion that I needed av gas, or something like that. Now I see from your post that might have worked.
That dealer went out of business not long thereafter.
I ended up getting a different machine altogether, but I might try some racing fuel on a new carburetor on the Stihl machine. The carburetors are quite easy to swap out, for people who always have another $40. Not me.
In many engineering workplaces, there’s a generational conflict between recent engineering graduates and older, more experienced engineers. However, a recent study published in the psychology journal Cognition suggests that both may have something to learn from another group: 4 year olds.
Conventional wisdom holds that MIT, Cal Tech, and Stanford are three of the country’s best undergraduate engineering schools. Unfortunately, when conventional wisdom visits the topic of best engineering schools, it too often leaves out some of the most distinguished programs that don’t happen to offer PhD-level degrees.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.