So my lawnmower (20" murray w/Briggs & Stratton engine, 1999 or 2000)will not start. When I try to turn on the engine using the pull cord, it stays "tight" and I can't pull it any farther. Tried to turn the blade by hand (with the plug disconnected) and it won't budge. So I'm trying to figure out if I've got something economically fixable like a stuck blade brake or a sheared crankshaft key, or if it's toast. There is oil in it; doesn't look very good (I think I last changed it 2 or 3 years ago ). Any input would be appreciated.

7/16/2012 7:47:52 PM

they're $50 on craigslist

run to failure

7/16/2012 7:59:29 PM

gas and match

7/16/2012 9:38:19 PM

I once had a Murray riding mower seize up on me after hitting a root a few times. It's done for.

7/16/2012 10:36:24 PM

the safety bar on the handle hooks up to a brake on the engine. Maybe the cable is messed up and the brake won't release?

7/17/2012 12:12:15 AM

I can see that when I move the bar, it puts tension on a spring which causes a series of levers to move. So neither the cable nor the spring are broken. However, since I'm not sure exactly what sort of mechanism the blade brake is, I don't know what those levers in turn activate.

7/17/2012 1:05:30 AM

blade brakes?


sheesh.

7/17/2012 8:56:47 AM

Hitting obstacles causes a lot of bent crankshafts. Really common in Hondas but can happen to a lil briggs too.

7/18/2012 1:30:37 PM

I really doubt it has blade brakes. Most basic mowers just cut the engine when the "safety lever" is released. Not to say they don't exist, because I'm no expert, but I've never seen a basic walk behind mower with blade brakes.

Blade brakes are employed mostly by riding mowers so when you disengage the PTO it stops the blades rather quickly. However it's not a "lock" it just tensions the mower deck drive belt and wouldn't behave like a seized engine.

With a direct drive walk behind w/o a belt, what kind of mechanism would they utilize for a blade brake? I'm curious now.

7/18/2012 1:45:07 PM

^This is a good point you have. It does indeed cut the engine, I thought perhaps there was something else that stops the blade from spinning immediately, but I could easily be wrong. No expert, obviously.

So then the options seem to be sheared crankshaft key (if it has one of those, will be taking the top part of the engine apart tonight to find out), bent/broken crankshaft, or (the simplest one) cylinder has gotten full of gas when it got turned one way or another. Pulling the plug ought to tell me this (haven't been able to do that yet as I didn't have a socket or wrench available. Damn all my tools being in Virginia. Now have borrowed tools.)

7/18/2012 5:01:54 PM

we used to run 5 hp briggs racing kart engines w/o a flywheel key b/c we didn't want the stock timing and i guess we were just too cheap to buy the offset keys. we'd just torque down the flywheel nut to some value i can't remember.

7/18/2012 7:28:25 PM

sounds like junk to me. go and try to find a cheap/used professional walk behind. there are usually lots of "landscapers" going out of business this time of year because they got in over their heads thinking they'd get rich. as a homeowner if you buy one of these (even if used) you'll be set for life just change the oil occasionally

7/18/2012 7:33:12 PM

So upon further investigation the blade would turn in a 90 degree arc, though sometimes it took a good amount of force to get it to start. Took apart the top of the engine then found I didn't have a big enough socket to remove the nut holding the flywheel down (using borrowed tools) so I couldn't go that far into it. Discovered I could move the flywheel 90 degrees in either direction by hand but no further. But sometimes it would bind up at one end of the travel and I'd have a hard time getting it to go the other way. Flywheel and blade move in concert so the crankshaft isn't broken, but does it sound bent? I also have an issue with the little piece that causes the pull cord to engage with the flywheel, but I don't know what it's capable of causing this issue.
After bolting it all back together I got several clean pulls on the cord, though I couldn't get the engine to fire. Then it bound up again.

As to the blade brake issue, I found out that at least on this model, letting go of the handle switch not only cuts power to the engine, but also applies a friction brake directly to the side of the flywheel to cause the blade to stop faster. So it does have one. But it's not stuck, in fact it operates just fine.

7/19/2012 1:38:22 AM

throw that shit away

7/19/2012 11:50:09 AM

At this point I'm almost past "get a new one" and into "I want to know what's broken to satisfy my curiosity".

7/19/2012 12:51:42 PM

how did it first get in this condition? did you finish mowing one day, put it away, and then come back to it the next time and it was bound up? did it bind up while you were mowing?

7/19/2012 8:14:42 PM

At the very end of mowing the last time I clipped a rock. Like the very end, I was trying to mow around a shed rather than pulling out the string trimmer because it was getting dark. So I decided I was finished at that point. I'd hit similarly sized ones before and thought nothing of it, so I just put it away. Then, the next time I came out, no go. So I figured it had screwed something up but depending on what you hit and how much contact it makes with the blade, seems there are a variety of things that can happen.

7/19/2012 11:14:54 PM

did you cut it off after you hit the rock or did it just quit running on its own?

7/20/2012 4:47:19 PM

Truth be told I don't remember. This was 3 weeks ago.
The heat kept the lawn pretty much in order for a while, until the rain came and encouraged the weeds to come out of hiding.

7/20/2012 11:17:41 PM