Any small engine/lawnmower experts out there?

[wkilleffer]

Hi everyone,

I have a question about odd behavior from my Craftsman 21" pushmower. It has a 4.5 HP Briggs engine and is equipped with mulching and bagging capabilities.

Last year, I hit a piece of metal in the yard. This resulted in a bent crankshaft and broken blade adapter.

I had the crankshaft straightened at a local small engine shop, and the engine seems to run like it did before the incident. I went down to the nearby Sears Essentials, but they were out of blades and blade adapters. A nearby hardware store had them.

The person at the hardware store said that the mower should be able to use an adapter with a star-shaped fastener, which would allow me to use a readily available blade with a star shaped hole. I bought them and installed them according to instructions.

Everything seemed ok for about 10 minutes, and the mower started making a knocking sound. I checked the oil, but all was ok. I looked under the mower, and the blade adapter had fragmented. I took it back and got another one, and it's done the same thing. I gave up on getting the yard mowed today.

Now, this can't be normal. It doesn't seem likely, but could the engine be causing this?

Also, since it's a Sears-branded mower, is it going to require Sears parts? I've known them to require that on some things like this in the past, but I was hoping to avoid a trip to the mall.

Also, could this have caused any more engine damage?

Thank you,
-Bill

 

[aeronca65t]

While I can't offer any expert advice, I'll be happy to provide some amateur advice. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

I'm suspicious of your "bent crank repair". Generaly, it's been my understanding that if a Briggs crank is bent, it's scrap.
If nothing else, you may want to remove the spark plug and remove the blade. Then put the mower on it's side and turn the engine over slowly....see if the crank is turning "true" or if it is wobbling.

 

[wkilleffer]

Well, I didn't come up with the idea of getting it straightened on my own. It was suggested by one of the shop employees at the local Ace Hardware, and he told me to try the place where I took it.

I asked the owner if he could do it, and he said he could, but offered no guarantees that it would be a perfect fix. In fact, he couldn't promise that the crank wouldn't break when he tried. It seems to be running smoother and not surging.

I am kicking myself over this, because if I had seen that metal while going over the yard before mowing, this would have been avoided. The mower has a service contract, but that doesn't cover bent cranks. The repair center wanted almost $180 to fix it, when I only paid $150 for the mower.

I'll use your method to check and see if anything looks strange. Just seems odd that a problem like mine could be breaking blade adapters.

Thank you,
-Bill

 

[mailbox]

Are you sure the adaptor is seated against the bottom of the crank? What kind of material is it made of? Where exactly is it breaking? It sounds like it's not seating against the crank and ripping itself apart. If the crank was bent, the adaptor may not be bottoming out. I have several steel adaptors that might work better if you need one. Let me know. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[Harry_Ward]

Re: Any small engine/lawn mower experts out there?

As mentioned previously,
First disconnect primary wire and remove the spark plug! Switch ignition off and make sure fuel line is off. You can clamp a rod or some other type of straight edge from the edge of the deck to the side edge of the crank shaft and pull the cord slowly and see if there is any run-out or in and out movement on the shaft to the straight edge end. If you see no deviation in the crank replace the blade and on a level surface turn the blade back wards or carefully have some one slowly pull the rope and see if you have any deviation on the horizontal plane of the blade. If you do have deviation, you have a bent blade, or blade holder. Most B&S lawn mower engines have a shear key in the flywheel to prevent bending of the crank when striking objects. I'm seriously not implying this is the case but some not so reputable lawn mower repair shops will tell you the crank is bent and replace a $1.50 shear key with about a half hour of labor. Although occasionally a very solid impact will bend them occasionally. It also sounds like the local hardware part may not be a correct fit and is hitting the deck and breaking, orrrr the crank is indeed still bent.

Here is the direct link to Briggs and Straiten Engines. Plug in your model and code number and hopefully a .pdf file will open with your engine parts diagram for direct order.

https://www.briggspowershop.com/BriggsAndStratton/advancedsearch.aspx

 

[wkilleffer]

Are you sure the adaptor is seated against the bottom of the crank? What kind of material is it made of? Where exactly is it breaking? It sounds like it's not seating against the crank and ripping itself apart. If the crank was bent, the adaptor may not be bottoming out. I have several steel adaptors that might work better if you need one. Let me know. /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

All good things to check. I'll make a trip to the real Sears store tomorrow and see what they might have as well. The parts that have broken were made out of some cheap-looking alloy, so a steel one might do the trick. I'll let you know.

Thank you,
-Bill

 

[Rob_T]

Bill,

I work at a Outdoor Power Equipment store. As a rule when a crank is bent its trash. I generally costs more to repair than your typical Sears mower is worth.
Blade adaptors are not interchangable, each manufacturer has their own style.
They are made of "soft" metal to help minimize damage to the crank, in the event of hitting an immovable object.......in theory. Go to a mower shop, where
the staff is knowledgeable, as thats all they do. They should be able to match up the correct blade and adaptor for you. We stock the more popular ones, even for brands we don't sell.
That being said, I would suspect the crank is still at fault.

Cheers,

Rob