On one occasion a wayward horseshoe found my lawnmower. I replaced the blade and the blade mount because the shear pins had done their job. I had trouble finding the right blade, though, because when I replaced the blade with the 22" proudly displayed on the mower deck, I could hear the slight "chirp" of the blade kissing the shield. No matter, I put in a 21" blade and I was on my way. As the years wore on, so did the mower, every so often a blade mount would crack, and at one point I had to replace the handle because it had sheared off from vibration. About 7 years later I was replacing another cracked mount, and as I rotated the blade around I found that the crankshaft was horribly bent.
Now it all made sense, the smaller blade, cracked mounts, and the handle breaking from vibration. I wished I had known about straightening the shaft with a pipe, rather than just taking the mower to the curb.
Ray, that's a great solution. I suspect the lawnmower makers might be interested. On the downside, it makes their product a little more expensive, and also stops them from selling new mowers to people who own rock gardens.
I agree: The pipe method is a great solution. I have to admit, my son hit a rock a few years ago and I could never get the crankshaft quite right (close, but not satisfactory). I eventually ended up tossing the mower and getting a new one.
I love it when the simplest fix can overcome a design flaw in a product. Still, you think there would be some kind of safeguard against this sort of thing! I don't have a lawn that needs mowing, so I don't use a lawnmower. Have modern mowers been adapted so they don't succumb to something as simple and common as a rock?
I straightened the cranshaft on 2 mowers that way. I put a dial indicator against the end of the shaft and keep bending it little by little until the indicator reads <.002". It doesn't take that long, and you quickly learn how much force and movement is required with that particular pipe. Just keep the same pipe around for next time.
FINE! You deserve the title of a "TRUE ENGINEER" because you used the proper tool to achieve that "magical touch" on the pipe straightener that probably took the old repairman an entire lifetime to develop. I have an inexpensive (cheap) chinese dial indicator I bought at Harbor Freight tools. It has paid itself many times because by using it for many tasks (like properly finding the best disc brake rotor orientation). It has saved me a lot of money. I even carry it with me when I go to a tool store, where it helps me find the one article with the straight shaft in ten or so (the other nine were not truly straight!).
I, too, live in a rural (although non-farming) community where fixing tools and machines is common--or used to be. Glad to say I don't have a lawn to bother with. But we do like to repair our stuff, or take it to the local fixit guy. There's something really satisfying about not throwing things away, and especially so about fixing something yourself.
Exactly Ann! Unless we keep that excellent "Fixit" mentality and transmit it to comming generations, it will be completely lost soon. Trashing any slightly damaged article is a despicable practice promoted by lazy and dumb people that justify themselves saying "I have enough money to pay for a new one". Another thing to have in mind, is that many items that were fabricated years ago were better made in respect to robustness and better designed too, and deserve to be fixed. The recent trend of intentionally designing for a short life and "throw away" mentality is consuming too much resources already, and recycling is not always completely "green" or efficient as prolonging useful life.
The "Fix-it" culture is totally dead in this country. I've maintained that position for decades. And, the younger generations have NO interest in repairing anything. They've been effectively indoctrinated by very cunning advertising that it IS more efficient to buy a newer, "more improved" product than to repair the existing one.
Try to explain the logic of repairing an item INSTEAD of landfilling that for a replacement to someone of this era. It is a physical impossibility, BUT that same person will sport a "Green" bumper sticker on their vehicle...... Hypocracy to the nth degree!
I forgot about TECUMSEH small engines....... They were the parent company to CLINTON & POWER PRODUCTS brands...... The CLINTON logo was an old stylized Indian arrow head, and the TECUMSEH logo was a likeness of the Indian Chief, Tecumseh. I remember exchanging several CLINTON engines on equipment back in the 1950s because the original engines just wore out in short time. POWER PRODUCTS used to make a series of 2 stroke cycle engines.... found their way into the go-karting craze, along with MacCULLOCH & WEST BEND.
We put a WEST BEND 2 stroke cycle engine on a machine. It was a replacement for another failed engine. The crankshaft was so hard that it had to be sent to a special machine shop which could cut a keyway slot with special tools. The local machine shop could not accommodate our needs.
Fixing a bent crankshaft on a lawn mower which runs at 3600 RPM is a bad practice. I've seen what happens when tractor mounted mower blades make an unanticipated dash for freedom and the damage has been significant. Once a cast shaft has been bent and cold-straightened you have no idea whether a crack has developed or not. Magnaflux and penetrating dye require the motor be disassembled and once you are that far into it, it's easier and cheaper to just replace the motor. A replacement motor still supports the repair-not-replace philosophy, plus you don't need to spend months recovering.
I was thinking the same thing, Bob. Since this realtively high-end machine didn't have any protection, one wonders where else costs may have been taken out. I would be a bit nervous about the shaft giving up the ghost and some other time...and not only the next time the blade meets a rock.
@bob from maine: We regularly cold straighten hardened steel crankshafts as part of the production process, using a dial indicator to measure runout, as @Turbineman described. The crankshaft is held between centers and is spun around to measure the runout. The crankshafts are checked for cracks using Magnaflux, but someone doing it at home could use a can of Spotcheck.
In my experience, if you are straightening less than a certain amount of runout (depending on the shaft, but generally about .050"), you will never crack it, and if you have to straighten more than a certain amount (about .100"), you are 100% guaranteed to crack it. In between those extremes is a grey area, where you might or might not crack the shaft.
I would definitely not recommend trying to straighten a badly bent shaft -- or, really, trying to straighten a shaft at all, unless you know what you're doing. I also agree with @Davinci87 that you don't want to do this to a cast iron shaft. Trying to bend a brittle material is just a bad idea.
One process that might work on cast iron shafts with small amounts of runout is peen straightening. In this process, you use an air hammer to induce residual stresses on one side of the shaft, which causes the shaft to "grow" in that direction.
@OLD_CURMUDGEON's idea of heating up the crankshaft to make it easier to straighten sounds like a disaster to me. This will completely wreck the heat treatment of the shaft. You might be able to bend it more easily, but now your bearing journals will be dead soft. Good luck with that!
All of that being said, here is my own personal solution to bent crankshafts on lawnmowers.
A bent shaft on a mower usually means one end of the shaft stopped while the other end didn't. The 'fly-wheels' masses are at opposite ends of the crankshaft, when the blade stops, the engine fly-wheel continues to try to rotate causing a twist in the crankshaft. Fifty thousandths of run-out may represent only a few degrees of twist, or the crankshaft may be 75% fractured. The risk is significant.
Well, in shops that I have had familiarity with, that was the procedure they used very successfully. But, I didn't claim that it was a carte blanche solution, and certainly NOT for cast iron shafts..... nodular iron, yes! And, steel, of course. Furthermore, most small engine cranks are NOT seriously heat treated, so I disagree with you on that point. But, that also depends on the ultimate quality of the engine...... small lawn mower & outdoor power equipment engines are mostly considered "throw-aways" nowadays..... I have taken a file to the counterweights of these genre of engines, and the file penetrates very easily, so that adds more credence to their non-hardened state. They VERY well could be "spot hardened" at the points of bearings however.
I agree in principle with you. However, products are being designed to be non-servicable. Lawn mowers (for the most part) are still servicable items, but how many other devices are simply made to be thrown away. For example, I have a Bunn coffee maker that quit. I disassembled it to find out what was wrong to discover a set of thermal fuses. I tried to order these from Bunn, but no-way. I eventually (with great effort) found a suitable replacement.
The point is, I spent many hours on a $1 part and a $40 coffee maker. Ten minutes in Wal-mart would have replaced it. Young people are not as motivated or dedicated as I am to fix it (and economically I could not blame them as I am just stubbornly cheap).
How many Ipad/Android teardowns has DN shared? Were these ever put back together?
I have had that thermal fuse fail simply because I ran a second batch of coffee too soon after running a batch. The thermal fuse got a wire jumper and the thing worked another year before the heater finally failed. Yes, I understand the potential hazard of removing the fuse, but we never run the thing unattended anyway, so it was not a big deal.
Radio Shack still has a variety of these thermal fuses/switches. There are 2 in most coffe makers, the one for the hot-water boiler is actually a switch, and has a temperature rating on it, the other one is a one-time in-line with power fuse
I did not realize that Radio Shack carried those thermal fuses. But I don't know what temperature to buy, and my guess is that the RS ones would be on the low side. So instead, we unplug the coffee maker when we leave. In addition, it sits in a thick glass tray, sort of fire resistant. And the running control for that package is sort of electronic, so I hope that it does not fail in the "on" mode.
when the blade hits a solid ground object. But most owners either don't know about the the breakaway key or do not have the mechanical ability/ tool to fix the mower, so the mower gets quickly thrown out when the flyway key is broken and the mower will not run or runs badly after hitting an object.
Nothing in the average owner's manual about this either... (Sarcasically) It must be much too dangerous to even ~inform~ the mower user about the flywheel shaft key even to write "This is what could have happened but take mower to service shop because the shop will have special tools to fix it."
"Buy a new mower!" is what the mower manufacturers want.
I, however, have benefited from this by getting the supposed dead mower for free, removing the flywheel, installing a new key, and, bingo!, an almost new mower with low hours on it!
[And customizing the mower by replacing the standard aluminum mower flywheel with a heavier cast steel one from a brush cutter mower (from the same type engine) provided a lot more root cutting fun prior to the flywheel key breaking away...]
Small engines have always had a flywheel key, and an aluminum one to boot to prevent damage to expensive parts. Key replacement has always been a common repair for blade impacts. In this case, however, the poster is talking about the blade adapter, not the flywheel. There are many different designs, some with shear protection and some without.
Lawnmowers use a lightweight flywheel because the blade also acts as a flywheel. heavier flywheels are used fo engines with low rotating masses on the output end, such as belt pulleys.
As a kid, I mowed a rock which bent the shaft and the blade on our mower. Attempting to replace the shaft was my first experience with 4 stroke engines. While I never did get the mower working correctly, I did learn about the inner workings of the engine which kickstarted my engineering desire to see how things work.
Straightening a bent crankshaft with a pipe may sound like a good idea, but keep in mind that the crankshaft is cast iron, not steel. CI is much less forgiving about being bent and bent back. Having a compromised crankshaft spinning a 21" steel blade at 3,600 rpm only 6" from my ankles is not particularly appealing to me. Especially on a mower with an aluminum or plastic mower deck.
I've been there, Davinci87. I tried stratightening a crankshaft with my own crude methods (not with a pipe). I used that mower in fear for a short time afterwards, then gave up on it. I had this nagging fear that if I kept using it, I would soon end up being about six inches shorter.
I am glad someone pointed out the dangers involved of simply straightening out a bent shaft. That is the key component of any engine and I seriously doubt that piece of pipe was actually able to put it in balance again. I really doubt the crank was cast, but was probably a forging, which forms the grain of the material into the stongest positions. A cast crank would not have a proper grain structure and would probably break before bending to any real degree. Anyway it is not just important that the shaft is almost straight when you have the flywheel inertia of an 11 radius flying about 6" from body parts.
Replacing the crankshaft is not an example of our throw away society any more than relacing a bent blade, which can also be straightened but at what cost if you now a have a vibrating piece of accident looking for a place to happen. Then if you live where I do you can run across the river and find some lawyer in Illinois to try and sue the manufacture's socks off.
Small mower crankshhafts can or cannot be formed using cast iron. Some may be nodular iron, and some, steel. I have been down this road with small engines for decades. One of the problems in a vertical shaft engine with a bent crank is removing the (aluminum) base plate from the shaft, even one with only a slight bend. Forcing the baseplate over the radius puts enormous pressure onto the bearing. In many small engines, these are not pressed-in roller bearings, but more commonly are simply pressed-in or cast-in aluminum bushing-types. They almost solely depend on the total immersion of lubricating oil for any expectation of life.
The BEST way to straighten a bent crank is to jig it in a lathe, determine the amount of runout, and then heat it sufficiently to anneal it and then "work" the bend out. Using pipes or other brute force methods is chancey at best.
Changing a flywheel for an iron replacement is also a dangerous endeavor, since it drastically changes the rotational inertia of the system. Replacing flywheel keys is far safer. I DO agree that it would have been a good design to include a breakaway key @ the blade end of a typical garden lawnmower. Years ago we had a large tractor-style mower. The mowing deck was approx 48" wide with three staggered, belt-driven blades off the main PTO. However, each blade also included a hub mechanism which included an easy-to-replace key in the event that a blade hit an immovable object. Even small tree stumps CAN bend a shaft, so it's NOT only large stones or rocks or bricks, etc.
Decades ago, small engine manufacturers DID carry replacement parts. Today, however, I doubt whether you can purchase any replacement items for a BRIGGS & STRATTON or HONDA small engine. IF you move up the ladder to engines included on industrial equipment, then the picture changes.
Does anyone remember CLINTON, POWER PRODUCTS, REO, KOHLER, WISCONSIN? They all made small engines. and are mostly all part of history today.
I don't know about Wisconsin ( a very good brand, along with Clinton, RIP.), but Kohler is alive and well. Check out the engines in the online catalogue of Northern Tool and Equipment.
In my younger years I went to the Clinton Engine factory technician school. We students were "drug over the coals". On final exam day, we spent the first 3 hours on a written exam. After lunch we were handed two pieces of Clinton powered equipment. I was issued a chainsaw and outboard motor. They both ran fine, but something was wrong with them only the examiner was aware of. We had to tear them down, find out what was wrong, write down the part numbers needed, go to the factory parts crib to get the parts, re-assemble the equipment and take them outside and test them.
I never went to another mfr's factory school, but other students said that, compared to Clinton's school, all they had to do was skate through Briggs & Stratton and Techumsa schools.
As a kid we had a small engine on a yard vac with not much spark plug hole thread left in the AL cylinder head. We'd screw in the spark plug and start the engine to launch the spark plug like a bullet. Take cover!
The mower I have today is 30 yrs. old with the too-thin tubular steel push-handle attachment to the deck being the weak point. After the first couple of years I had no choice but to weld smashed 3/4" iron pipe in parallel to the tubular steel handle and down to the deck's anchor points. No problems since.
The problem is always that when the blade gets stopped instantly that the rest of the rotating mas twists until something is damaged. That problem is very obvious indeed. Many years ago, while I was still in high school and Kenedy was president, I came up with a simple, cheap, and very effective solution, which has saved me from lawnmower damage many times. Here is the simple solution: whenever I get a rotary mower with a gas engine drive, I remove the blade and the blade attachment adapter that is ke6yed to the crankshaft. Then I remove the key and put a dab of anti-sieze grease on the shaft, and reassemble it without the key in place. I tighten the blot and the job is done. When I eventually hit something that stops the blade the coupling slips a bit and often the engine stalls. ON quite a few of those occasios I have had to tighten the bolt. BUT the engine has never been damaged enough to notice. Using an aluminum key might also work, but using no key at all has proven itself to work quite well.
Of course if the blade ever comes loose during normal operation I would need to stop the engine immediately and tighten the blade, and that has indeed happened twice in 45 years. But that is a very small cost compared to having to replace an engine, since usually when the crank is damaged the lower bearing plate is damaged as well.
The key which connects the shaft to the flywheel on the top side of the mower engine is made out of a soft metal. Not aluminum but some type of alloy.
The flywheel, at least on Briggs and Stratton and out-of-production Tecumheh engines, is used for the engine ignition, timing, and balance. When the blade hits something, the key shears off, the flywheel keeps going and spins on the shaft. This takes the engine out of timing which stops the engine. If the flywheel hasn't moved too much, the engine maybe able to re-started to run badly but most of the time the engine does not re-start or run at all.
This is when most people give up now and scrap the lawnmower. The flywheel keys are able to be purchased at stores which actually handle small engine repair parts, usually not at big box stores which only have replacement maintenance parts.
This is where I came in to get the free mower. In one mower I got, the flywheel had sheared the pin but not moved enough to totally shut the engine down. But this mower had blade mount which the threads and locator pins had been damaged because the bolt had loosened up- probably a forgotten lock washer. The mower felt and sounded like garbage when it ran due to the off timing, loose and knocking blade, and vibration from the loose blade/off timing. I installed a new shaft key, got a brand new blade, and replaced the blade mount and with one from a another dead mower (which had sat outside for years getting water into the engine). The mower then ran like a charm! I used the stink out of it for about three years later giving it to a relative who is still using on a small lawn...
My point is that just simply removing the blade key will prevent damage to the mower when a rock or something stops the blade. And the fix of retightening the bolt is not that much work. Replacing the flywheel key is a lot of bolts to remove and replace.
It used to be that you could expect a "new" machine to out perform and last you a long time. I hate how things have become. You buy a "new" machine today and almost HAVE to expect it to break. What the hell happened to quality?
Just reminded me of a weedeater I bought a few years back. I bought a nice one thinking it would last me a very long time. I buy most of my tools for that very reason...they will last. That weedeater only lasted about 5 years and I BARELY used it. I've had the same problem with cordless drills...the batteries go bad and then it's cheaper to just buy a new drill than replace the batteries...if you can even replace them. It's a sad world we live in...lol Just buy more!!!!
I agree, Cadman-LT. More likely than not, any item you buy - especially small electrics or small gas powered machines - is designed to be replaced after failing. Repairability is not considered in most cases. Of course, some items (like my long gone '81 Citation) were too expensive to throw away but were a bear to fix. In general, most of today's vehicles are more reliable than those from the 70's and 80's.
I get a great amount of satisfaction from fixing things. Some people might find that as an acceptable way to recycle or to think green. The green I really care about is the green in my wallet.
I believe that if you polled most engineers, rrietz, approximately 90% would agree with everything you said here. Most engineers do the repairs to save money or because they secretly enjoy it, which is why many engineers are driving older cars. I can speak for myself here: Whenever I buy a new car (every 12 years or so), I feel like I'm being wasteful.
If I ever meet whoever put the engine into that Ciation car, I promise I will beat them up. Bloody their nose, break their arms or something painful, just to pay me back for all of the busted knuckles I received while changing the spark plugs or the back side of the engine. I really liked that car except for that and it made me hate it from then on.
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