Anyone know about fixing this mower engine damage?

Page 1 / 2
-bookzone-, Mar 18, 5:45am
The bolt holding the blade has sheared off about 5mm below the shaft lip.

Is this a relatively straightforward repair - getting the bolt out of the shaft?

I don't have the tools to do it myself, so who's best to do such a job?

The town I'm in only has two auto mechanics, as it's only small. Would they be able to do the job, or is an engineering firm better?

And what's the likely cost?
jmma, Mar 18, 5:50am
What sheared it off, may have sheared the flywheel key as well. Probably need to get shaft checked as that might be bent, but can be straightened OK.
Mechanics in small towns should be up for the job.
Note = If it is a Firebrand mower, throw it away!
-bookzone-, Mar 18, 5:54am
Not sure what caused it to shear, as it just dropped off while cutting flat grass. It has, in the past, hit a number of hidden objects, so it's probably finally given up the ghost.

Flywheel key is still ok, and the mower was cutting just fine until the blade dropped off.

It's a 3.5hp Briggs engine.
jmma, Mar 18, 5:56am
Yes, try your Mechanics, or if there is one an engineer may be better.
-bookzone-, Mar 18, 5:58am
Thanks!

Any idea of the cost of this type of job?
tamarillo, Mar 18, 6:07am
How old is yours and was it going well?
Putting a new one is tempting don't you think?
-bookzone-, Mar 18, 6:14am
It's only six months old. The whole mower only cost about $220. It's one of those Morrison-made mowers sold by Mitre10.
-bookzone-, Mar 18, 6:32am
I think (hope) it was just due to getting a few hard 'hits', a few of which stopped the engine. The bolt was, however, on really tight from new, as I found out when I tried to remove the blade.

Could it have been over-tightened when the blade was first put on?

P.S. What would it cost if someone like you did the job?
mechnificent, Mar 18, 6:46am
If the bit of bolt left in there is free in the threads you may be able to wind it out using a small punch and small hammer to gently tap it around in circles. being careful not to distort the threads out so they jam on the walls of the bolt hole.
If it's too tight to turn then it will need drilling and an ezyout being used to wind it out.
If it's rusted or distorted and jambed in there it might need drilling right out and then a tap running down the hole.

Depending on what is found it could take ten minutes. or an hour.
-bookzone-, Mar 18, 7:09am
Thanks for that. It's a fairly new engine, and I only undid the bolt about a week ago when I replaced the blade, so it shouldn't be too complicated to get out, I hope!
mechnificent, Mar 18, 7:16am
If the bolt broke off a bit rough or crookedly you might be able to turn it with something like a screwdriver or small diameter rubber hose pressed against it. I've got broken bolts out occasionally just by putting the end of my finger against the broken stub and turning it like that. Since it's not rusted, now that the load is off the thread it should turn really easily.
muzz67, Mar 18, 7:20am
If it's only 6months old,, take it back to mitre10.
mechnificent, Mar 18, 7:24am
If there's a bit of broken bolt higher than the rest you use that and a small punch to tap it around, using the punch near the outer diameter but not distorting the bolt into the threads. Just get the punch to grip a little and gently tap, tap it around in circles, swapping from the left and hitting towards you for a few hits, then on the right and away from you for a hew hits.
If you try to just keep tapping on the one place on the bolt it will eventually bind against the threads, then you tap on the opposite side of the bolt, which pushes it away from the threads it's jammed against. till it starts to bind again and they you swap sides again. Sometimes you have to give just one gentle tap on one side to move it across and around a tiny fraction, and they you tap the other side of the bolt to move it across and around another tiny step.
yz490, Mar 18, 7:31am
sounds like a dangerous occupation mowing lawns at your place! . Yes might just wind out if you're lucky & hope so. Wonder if a poor quality bolt had been used from new but unlikely. Will be hard to drill if real high tensile. Drill a little way in & ummm tap an old screwdriver in & try to just wind it out which should work if just sitting there & not tight or just lightly tap it around as someone said. Have had luck on all sorts of broken bolts & studs by sitting a piece of flat steel with a hole just big enough against end of bolt then arc weld it on & just wind it out, perhaps not quite that easy but works. Of course if the bolt's recessed up the shaft a bit i'd probably get the angle grinder & whizz a bit of end of shaft to get it flush then arc the flat steel on. That's my idea but just re-reading it you might like to try someone else's idea lol. Good Luck.
-bookzone-, Mar 18, 7:37am
The hole is only 10mm, and the bolt recessed by about 5mm, so not much room to move, so to speak. I doubt I'd be able to get at it enough to do much!

As for taking it back to Mitre10, I think it's more wear and tear (hitting a few buried rocks!), so probably not covered by warranty.
-bookzone-, Mar 18, 7:39am
It tightens clockwise, when I flip the mower on its side. That's the normal way, isn't it?
mechnificent, Mar 18, 7:50am
Yes they are a standard right hand thread, and unf threads. And since you just had it out it should come out easiiy.
As for taking it back to Mitre10. You will probably take more care and do a better job of getting it out than the handyman there that will have a go at drilling it and probably making a hash of the job. Try turning it with the end of a screwdriver ot use a nail to try and turn it . Put the tip of the nail near the outer edge of the bolt and aiming around the edge in an anti-clockwise direction. The first tap of the small hammer should be fairly straight down to start a small dimple the nail can grip , then the next few hits are at a lower angle to turn the bolt.
mechnificent, Mar 18, 8:05am
There is no harm in trying some other ideas first Outer. It can still be drilled later. and no spark eroder will be nessecary I'm sure. I've removed dozens of those bolts over the years.
And I've mostly got them out by tapping them around. not drilling.
-bookzone-, Mar 18, 8:10am
I've only removed the bolt once, and made sure not to re-tighten it too much, as my father was a mechanic, so I know about not over-tightening bolts.

It had one of those locking washers, as well.
-bookzone-, Mar 18, 8:18am
Anyway, thanks for all your help with this!

I think I'll try (very carefully) some of the ideas mentioned, but I'm definitely not going to make things worse by being cavalier about it!
mechnificent, Mar 18, 8:23am
The worst thing that you could do would be to try drilling it yourself and getting the hole off center. that will cause problems possibly. Try turning it as I suggested, and if it moves a little and then seems to stop, swap sides as I suggested. they do jam and bind up if you try tapping it around from one side of the bolt only. a little tap on alternative sides will get it out if it's going to come out easily. If not, get someone competent to drill and ezyout it.
alfred011, Mar 18, 8:49am
All vertical shaft B&S engines on rotary cut mowers are all right hand threaded and are 3/8 UNF thread it always pays to lubricate the threads and do them up tight they usually make a knocking noise when loose and will shear the woodruff key holding the blade boss on don't try and start it with out the blade fitted as it will kick back as it needs blade for the momentum as they only have alloy flywheels.Tip out the oil and petol turn mower upside down bore a small pilot hole right thru the bolt 1st ,put in some crc type product done the hole then drill hole out to 6mm use an easy out to wind it out ,it the worst happens and bolt wont move don't snap off the ezy out ,drill hole to tapping size for 3/8 UNF and use a tap to cut out the remains of the bolt might take 15 minutes to do job.
-bookzone-, Mar 18, 8:58am
Don't worry, I'm not going to do any drilling!

I'm just going to try the easier, more basic options of getting it to unscrew. If I can't get it sorted by doing that, I'll take it to someone who knows how.
jmma, Mar 18, 9:02am
Being a Mitre10 one, it will have split the driver and blade bolt worked loose and broke, seen it a dozen times. As the driver is a cheap alloy one, you will need to replace it, do that with a steel one.
It is not as a major job as most seem to make out.
Good luck (o:
mrcat1, Mar 18, 9:29am
I think from memory if its Briggs is 3/8th UNF, and is a high tensile bolt. And if your in Thames there's mower shops there that can deal with it.