HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Comments
View Comments: Threaded|Newest First|Oldest First
didymus7
User Rank
Platinum
Very Similar
didymus7   3/8/2012 9:44:09 AM
I had the same thing happen to my 1985 Toyota Camry (albeit much more expensive).  Luckily I was just pulling out from in front of my hour when the car stalled and refused to restart.  I had the AAA tow to the local garage where they said the timing belt slipped.  They replaced the belt and everything was find for a few months.  Then the same thing happened again, this time I was two blocks from home.  This time I had it towed to my brother-in-law's garage.  The replaced the belt but also replaced both idlers.  Never had a problem with the timing belt again.  And I never went back to the other garage, either...

Dave Palmer
User Rank
Platinum
Innocent bystanders
Dave Palmer   3/8/2012 12:09:29 PM
This story is a good example of the fact that often the part that breaks is not the real problem. Sometimes, it's just an innocent bystander.  This is important to remember in failure analysis.  The impulse is always to focus on the part which broke, and try to find something wrong with it.  But it's important to look at the entire mechanical system, rather than just one component in isolation.

Alexander Wolfe
User Rank
Blogger
Re: Innocent bystanders
Alexander Wolfe   3/8/2012 2:03:45 PM
Very nice diagnosis, and it's true, as Dave says, you have to check all the parts connected with the problem. Often, like in medicine, the failure point is a symptom, not the cause. This reminds me of the stuff the guys in Gold Rush on Discovery have to deal with all the time with their second-hand back loaders.

ab3a
User Rank
Platinum
Re: Innocent bystanders
ab3a   3/8/2012 4:13:10 PM
NO RATINGS
Indeed, I had some doubts when the first belt broke because it looked worn. I had no idea of how long it had been in service. There were no tell-tale squeals or squeaks so I assumed it had to be the belt.  But when a brand new belt with only a couple hours on it broke, I knew something wasn't right.

These bearings are actually one of those press-fit things that slide in to the idler puly wheel. It's "sealed" so that you can't lubricate it easily. Given how much dust and grass clippings go flying around, I'm not surprised that the mowing deck manufacturer used them. And in general I get five or six years of service out of them before I get nervous and just replace them out of prophylactic care. 

It's cheaper than a new belt (and I get about three seasons out of a belt).

 

Rob Spiegel
User Rank
Blogger
Re: Innocent bystanders
Rob Spiegel   3/8/2012 4:21:40 PM
NO RATINGS
That makes sense replacing the bearings now that you know what is causing the belts to break. Seems like a flaw in the design, though, that the bearings would wear out so frequently.

ab3a
User Rank
Platinum
Re: Innocent bystanders
ab3a   3/8/2012 9:38:00 PM
NO RATINGS
Actually, I don't know for a fact that the bearings are worn that far. The galled bearings may well have been original equipment from the 1970s (I discovered this problem in 1997). That's not too bad, really.

My caution is because it's cheaper to replace this stuff than to wonder if it's going to bite me again. I know what these bearings feel like when they're new and when I begin to detect some play, I replace them out of caution. I don't think they're bad yet. However, since I'm not certain how far I can go with the existing bearings, I replace them on the theory that it's cheaper to do that than to buy a new belt.

Keep in mind that I'm not working with a micrometer here. I'm servicing this thing in my barn with just hand tools (socket wrenches, a bottle jack, screwdrivers, etc.).

 

Jake Brodsky

Rob Spiegel
User Rank
Blogger
Re: Innocent bystanders
Rob Spiegel   3/9/2012 2:20:37 PM
NO RATINGS
Yes, that makes sense, Jake. You're doing the preventative maintenance way in advance in order to avoid a costly emergency maintenance. 

Rob Spiegel
User Rank
Blogger
Re: Innocent bystanders
Rob Spiegel   3/8/2012 4:08:58 PM

Good point, Dave. That's really the lesson here. Fixing what broke doesn't mean you have addressed the problem. There are a number of medical conditions that are similar, where attending to the symptoms actually hides the real problem. 

 

Mydesign
User Rank
Platinum
Wear & Tear and Lubrication
Mydesign   3/8/2012 11:02:25 PM
NO RATINGS
Jacob, good if the ball bearings are gone, ofcource there should be some play while rotating. This play can cause more wear and tear, which may end up in replacing the associated components/parts. So it's always better to have a periodic check take for lubrication and wear & tear for the moving parts. Otherwise it may end up in a mess.

kleetus
User Rank
Silver
Re: Wear & Tear and Lubrication
kleetus   3/9/2012 10:28:31 AM
NO RATINGS
Very good article for maintenance! I too have several tractors on the farm for chores from lawn care to mowing the pastures. Something I have noticed going missing from most operator manuals these days is the trouble shooting section, or at least any trouble shooting beyond if it doesn't run check the gas tank....

Having purchased a set of factory service manuals with every car/truck I own, they at least (Ford anyway) have a very in depth trouble shooting portion for each major assembly. Proper diagnostics can go a very long way in fixing the problem right the first time once and for all. A great example is the rear axle... if you look at the number of descriptors of sounds describing conditions discovered while driving you'll know what I mean. Clunk, howl, whine, whoop,  are just a few of the many adjectives that describe subtle differences in what's really going on in that rust covered cast iron box between the rear tires.

Going full circle here, I guess my point was that in lesser cost products (but we'd like to think even low dollar items would have the same attention as expensive ones) the basics of maintenance are often neglected or given much lower priority. Maybe it's so you spend more in repair parts which helps their bottom line, maybe because they don't care, or maybe because they just never took the time to really research it, but we, as engineers, really owe it to ourselves to sometimes take our jobs home with us to really ferret out what's going on to save ourselves added expenses later.

Some products aren't too bad if they go bad catastrophically, sometimes the repair parts are more  then the base unit, or it's just cheaper to buy a whole new one, like a weed eater for example, but a $5000 zero turn mower for example, that's a different story. And if that goes bad, say you loose a blade spindle, you don't want that to come flying out!

Oh well, good article for thought! Carry on!

OLD_CURMUDGEON
User Rank
Platinum
Re: Wear & Tear and Lubrication
OLD_CURMUDGEON   3/9/2012 10:38:16 AM
NO RATINGS
There was a tractor company in the mid 50s to maybe 70s that made light duty farm tractors.  They were called ECONOMY tractors.  It was a very simple design.  Used a 1 cylinder, 11 hp WISCONSIN air-cooled engine coupled to a non-synchromesh 3-speed manual transmission with the power being delivered to the rear end via an enclosed driveshaft.  It was rumored that the original tractors were designed w/ "left over" FORD MODEL "A" transmissions & rear ends, but I never confirmed that.

  The engine was horizintal shaft w/ it aligned w/ the major axis of the tractor.  The front end of the tractor featured a multi-shived pulley attached to the crankshaft.  Between the front wheels & the rear wheels there was sufficient room to hang a 48"{ wide mower deck w/ 3 blades.  The mower deck was fastened to the frame w/ clevis pins & locks and was relatively easy to attach & remove.  To power this mower, a very long V-belt was connected to the front pulley and changed from the vertical orientation to horizontal via idler pulleys.  The other end of the belt attached to the center 3-groove pulley connected to the center blade shaft.  Two much shorter belts connected the power to the outer blades. 

The two idler pulleys were DEFINITELY designed by the "bean-counting" dept.  In profile, they were two steel "hat sections" spotwelded together with a center boss area so that a roller bearing could be pressed in.  In theory, that would be sufficient, but given the closeness to the ground & the high dust (dirt, sand) content of the effluent from the blades, these idlers did not last very long.  And, considering that they were sealed bearings, there was no provision for any lubrication.

The three main blade shafts were designed by a mechanical engineer with experience.  They were housed in precision stancheons w/ a roller bearing at the top & a roller bearing at the bottom.  Additionally, there were very aggressive shaft seals at both ends, even though the pulley had a "skirt" feature so that the top of the stancheon was buried unside the pulley.  And, each one of these stancheons had a hefty ZERK fitting attached so that they could be greased periodically.

The idlers had to be replaced almost every mowing season which extended from early April into November.  While I investigated alternative solutions for these idlers, I could find no catalog items which could be readily adapted to fulfill the requirements, so we learned to live with it, and every year we'd go to the tractor outlet to buy at least two sets.... one for immediate use, one as spares.

William K.
User Rank
Platinum
Bad Idler bearings break big belt.
William K.   3/9/2012 8:37:47 PM
NO RATINGS
Finding adequate idler bearings is indeed often a challenge. There are a few good ones made for some automotive applications, though. Another choice would be to make your own, using good cam-followers and a machined pulley to press onto it. Probably using a good alloy for the pulley would allow you to do a heat shrink installation and produce a part that would last until something much more expensive wore out.

Of course the weak idlers were probably touted as a great cost reduction item, able to reduce the cost of a $1200 mwer deck by $2. That made somebody a hero, no doubt, but you paid the price instead.

Tim
User Rank
Platinum
Mower decks
Tim   3/10/2012 8:02:19 PM
NO RATINGS
I have had two good riding mowers that have worn out their mower decks well before the engine began to show any signs of wear.  We had a Briggs and Stratton mower that ran great, but after a few seasons, one of the two blades on the deck wore a hole on the side of the deck when it started turning off center.  Investigation showed that a bearing on the housing siezed up, but the shaft continued to rotate and basically destroyed the bearing housing.  The funny thing was that when I went to get the replacment housing and shaft and bearrings, the new design had a grease zerk as well as slightly more robust bearring.  The deck completely failed about a year later when the minimal powder coat paint gave way to a significant amount of rust.



Partner Zone
Latest Analysis
A Silicon Valley company has made the biggest splash yet in the high-performance end of the electric car market, announcing an EV that zips from 0 to 60 mph in 3.4 seconds and costs $529,000.
The biggest robot swarm to date is made of 1,000 Kilobots, which can follow simple rules to autonomously assemble into predetermined shapes. Hardware and software are open-source.
The Smart Emergency Response System capitalizes on the latest advancements in cyber-physical systems to connect autonomous aircraft and ground vehicles, rescue dogs, robots, and a high-performance computing mission control center into a realistic vision.
Tolomatic ERD actuator provides high-tolerance, high-force capabilities at a low cost to innovative medical therapy machine.
The diesel engine, long popular on European roads, is now piquing the interest of American automakers.
More:Blogs|News
Design News Webinar Series
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
6/25/2014 11:00 a.m. California / 2:00 p.m. New York
5/13/2014 10:00 a.m. California / 1:00 p.m. New York / 6:00 p.m. London
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Sep 8 - 12, Get Ready for the New Internet: IPv6
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


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.
Next Class: September 30 - October 2
Sponsored by Altera
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service