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flywheel key broke ?


Boofhead's Avatar
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07-04-09, 01:54 PM   #1  
flywheel key broke ?

Hi, I have a 20 year old Briggs & Stratton walk behind lawn mower, it use to be my dads mower so for sentimental reasons I am trying to get it working again.
Yesterday I put new oil in it, new plug , new petrol , check it for spark and it was good, so I tried to start it, it did kick but at the same time the whole blade assembly come off the bottom and it of course mad a hell of a noise, I checked it out and just the bolt must have been loose, so i bolted it back on tried to start it , now it feels like its got no compression as the pull rope has no strength in it and just spins the flywheel with no effort at all.
So my question is, in your opinion could the flywheel key be broke now and if so how the heck do you get the nut to undo, I have tried very hard but with no success.

thanks in advance for any help.

 
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07-04-09, 02:04 PM   #2  
Pull the spark plug out and see if it has any compression. Sounds to me like a broken rod or stuck valve.


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07-04-09, 02:06 PM   #3  
Does pulling the rope now cause the blade to spin?, or not?

 
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07-04-09, 02:45 PM   #4  
Yes, when the flywheel moves the blades move as well at the same time but takes no effort to pull the rope.
How do you know when there is compression when pulling the plug out ?
thanks for your help guys

 
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07-04-09, 03:44 PM   #5  
It makes no differance if the spark plug is in or not, i just pull the cord so easily, seems no resistance in the pulling of the cord.
and with the plug out I put my finger in the spark plug hole and felt nothing whilst pulling the cord.
something major guys

 
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07-04-09, 04:06 PM   #6  
See if the piston is moving. If it is, then something is broke that drives the valves, or a bad valve, or some tiny screw or carbon chunk lodged under the valve, or loose head, or bad head gasket, or break in the head.

 
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07-04-09, 04:55 PM   #7  
ok, thanks for help, much appreciated

 
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07-05-09, 02:37 PM   #8  
Back again guys needing your help, I took the mower apart and can see what is wrong, the piston rod is broken into pieces and was able to pull the piston & broken bits of rod out.

Now to be able to replace the broken piston rod,
is it a hard job, does it require a mower mechanic to fix it ?
I am very willing to give it a go if I can do it, I don't care how long it would take me.
Another problem might be getting parts for a 20 years Briggs & S'.
thanks in advance for any advise.

 
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07-05-09, 08:48 PM   #9  
You can fix it if it didn't ruin the rest of the engine. Was it out of oil? Look at the rod journal on the crankshaft and see if the crankshaft is ok. Check the block all over and the lower part of the cylinder. Did it hit and crack or creak any parts of the block? What about camshaft or crankshaft bearings in the block and sump cover? Is the cylinder in good shape or does it have scratches in it?


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07-05-09, 10:30 PM   #10  
Thanks for your reply, no it had oil in it, I will check all what you have mentioned, the cylinder appears to be ok, probably better still get the local mower mechanic to check it out and get his opinion as well if it's worth fixing or not.
thanks very much for all your help.

 
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07-06-09, 07:03 AM   #11  
Make sure your mower deck itself is not the next thing to fall apart. My neighbors rotted right through until the mower came apart in halves the other evening! Compeletly rotted out from all the wet grass under there for years.

Also make certain there are no block cracks that oil can come out of.

I can't imagine trying to do a complete tear down on some mower where often you can find them for sale used for like $25-75.

And I'm curious why that thing flew apart like that. I do not work on mowers for a living, so I'm not certain of the frequency of repairs by repair type. But this seems like this would rank up there as fairly rare. You'd think someone had been running that machine without oil in the past, causing other damage. Then again, I suppose on some old mower that some apart has to be the one to fall apart first. But I'd be sort of thinking there would have been issues first with the carb/diaphram, pull rope, or electrical system failure first.

 
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07-06-09, 01:06 PM   #12  
Hi ecman51, It is solely sentimental reasons why I wanted to get this mower going again as I mentioned in my initial post.
I am not sure of the history of the mower as its been passed around the family but I do recall my brother getting the piston rod fixed a few years back.
I am retired with plenty of time on my hands these days so it's sorta a challenge for me to try to fix it, I do fix most things I put my mind to, but have no prior experience with small motor repair
as of yet.
So it depends if the rest of the motor if it is good enough to repair the piston rod, if so I will or look around for another second hand motor to whack on it.

thanks for your help.


Last edited by Boofhead; 07-06-09 at 01:10 PM. Reason: added info
 
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07-06-09, 04:31 PM   #13  
Posted By: Boofhead So it depends if the rest of the motor if it is good enough to repair the piston rod, if so I will or look around for another second hand motor to whack on it.

thanks for your help.
In all honesty,..If someone took the motor off of their mower and was selling it.....They know its worth something....I would try to find another complete mower, with a motor comparable to your horsepower, from someone who will let it go for peanuts, because it is taking up space in the garage.... You can probably find a dozen or so on any given week, in your Local Classified ads, for under 100$. Then you can enjoy the challenge and satisfaction of building "Super Mower" by swapping parts between the two..and keep your sentiments

Just for thought......My current mower is a hybrid of 3 or 4 parts units, which I gathered from junk and trash piles( Cost me nothing), and my grandfathers Sears and Roebuck 10 HP, purchased new in 1970...It might be kinda Funny looking, cuz the motor is to tall for the deck, and the pull cord only comes out 8 or 10 inches, but it runs like a top, and is virtually unstoppable. And by the way, it is now self propelled..

 
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07-06-09, 11:56 PM   #14  
Hi Unclediezel, that is a great idea, I will be doing that for sure.
I just checked the mower for the year of manufacture and it is 1977, it has been around for a while too
thanks for your help

 
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