Hi everyone, I hit a hidden metal bar with my lawn mower and although at the time I did not felt any change on it, after I used another couple of times it started to shake a lot. I had a look at the blade and it looks ok, not bent and no marks but the Crankshaft is bent. I have a couple of questions. Apart from the vibration, does it do any other harm to the machine if I still use it with a bent crankshaft?
I guess it may be possible to straight it up, but how weak would it make the metal? and is there any other part that may be damaged as well?
The best to do I believe would be to replace it, does anyone have an idea what would cost?
If the crank breaks and the blade flies off, you maybe minus a few toes or even a foot.
Take it to a good lawnmower shop, they might be able to put a new crank it n the motor, but it might not be worth the $ to do it, if it is an older mower.
skin1235,
Apr 6, 3:14am
even the warehouse sell mowers with the same engine as that, should last just as long too, last time I looked t was about $299 for the 148cc models
nick2707,
Apr 6, 3:21am
Biff it mate - it's rooted
pretinha,
Apr 6, 3:21am
That's what i paid, not long ago actually, less than a year. No, when I first hit the bar it stopped but I had no problems re starting and as far I could tell it was just as the same as before. I them used once again, and the today after I had mowed half the lawn I noticed it was vibrating a lot. I removed the oil and gas and put mower on its side. Removed blade and checked blade, them I attached a point rod to the mower just touching the crankshaft end, when I turn it I could see a gap was created between the rod and the shaft. It was actually visible when turning but I used the rod just to prove.
pretinha,
Apr 6, 3:25am
Is it possible to buy just the crankshaft that is bent? Would you know?
skin1235,
Apr 6, 3:25am
yep, its bent, time to replace it, being only a year old it maybe covered by your contents insurance
nick2707,
Apr 6, 3:36am
For the cost of replacing the bent shaft, bearings and seals - you're better off with a new mower - or one off Trade Me as someone suggested.
pretinha,
Apr 6, 3:42am
Believe it or not, but I don't have content insurance ! Bugger!
skin1235,
Apr 6, 3:46am
its possible to buy another motor for it, the price is more than anew mower, buying a crank would not be cheap, expect approx $200 then more for gaskets seals and bearings etc, again its cheaper to buy a new mower, take the wheels off the old one, and put the old engine in the shed, parts are never cheap, in fact even the body would be good to hang onto, 6 years down the track you could fit your going engine to the new body - the wheels and bodies are usually first to go ( if you avoid hitting great lumps of steel etc)
skin1235,
Apr 6, 3:47am
x1
not sure if it would be covered anyway, a lot of shed contents are but lawnmowers?, for damage?, maybe fire or theft
mrfxit,
Apr 6, 4:52am
1st: Not easy getting a bent shaft out of these if it's bad. 2nd the shaft end bearings are simply bored through the block so can't be replaced (no bearing shells) 3rd: They can be straightened in situ but often bend easily next time they get a half decent whack. 4th: If a rebuild is preferred, it's better to use your motor to rebuild another block. 5th: Brigg's engines rebuild really easy even with s/h parts & if done properly will last for many years.
kiwitech1,
Apr 6, 2:47pm
You can buy a brand new B&S 148cc engine for $200 from here:
Tks mate. I am guessing that comes with the CrankShaft with it?
So, should I keep using the old one with the bent crankshaft until it blows the motor, or because its bent it may cause the crankshaft to break sending the blades flying. its not that bend, but enough to cause a shake on the engine, I still can turn the pull cord with not much effort.
thank you,
cantabman1,
Apr 6, 3:40pm
Agrees, once the shaft is bent, the motor requires a complete strip down and repair or replace.
kiwitech1,
Apr 7, 3:08am
Personally, I wouldn't risk it.
$200, or a (possibly) serious leg injury from some part of your mower when it fails? Not worth it!
shakespeare6,
Apr 9, 5:01am
Most lawn mower shops can true them up with a jig if it is not to bad. I've done it my self flipped it over spun it till the bend was up and hit the shaft with a big ball pen hammer couple good wacks till it was true, got it pretty straught except the last swing of the hammer I missed the shaft and went right through the crank case.
joaopnz,
Apr 13, 4:30am
But is this make it safe to use after? I have been to a mower shop and he told me he could fix if not too bad of a bend but reading comments above it sounds like it can be dangerous, or is it only dangerous if done by someone with no experience or knowledge of what they are doing?
skin1235,
Apr 13, 4:39am
no arrogance intended - that so called expert in the workshop has no way of knowing what has happened inside the metal, no way of knowing if it is a simple flexing bend or a tearing bend, he can give it a few smacks and proclaim its all good to got, the science of metals say he has no idea if it will fly apart next time you fire it up, or where it will fly apart
if it were taken to a proper engineering shop it can be xray'd and crack tested before and after, can even be cut to get to a tear and welded up again
and would cost more than a new one anyway, their result can only be nearly as good as new, not better than new
joaopnz,
Apr 14, 4:19am
True that. I guess to pay 150.00 for him to "fix" I would be better off buying a new motor for it for 200. Keep the old one for parts or even put on trademe for parts only.
sr2,
Apr 14, 5:17am
Good advice there fixit mate but could I add a proviso to #3. I've straightened a few B&S cranks in situ with a piece of pipe and a DTI. Despite being a rather sordid piece of engineering (to say the bloody least!) the results have always been surprisingly successful. I can't see a broken crankshaft being a safety issue, any balancing, oiling, etc. issues usually cause those old B&S motors to have a big end/conrod failure and poke a leg out of bed.
alfred011,
Apr 14, 5:23am
Those crankshafts are soft and can be straightened easily you just remove engine from chassis then attach it to a steel plate then you wind a bolt against crankshaft opposite side of bend , bend it a bit then rotate crankshaft find out how much of the bend has gone ,bend again until bend has gone ,takes about 1/2 hour .
mrfxit,
Apr 14, 5:25am
No worrys at all. Have seen a couple of snapped cranks in about 40 years & those were an unknown history at the scrappys.
Had a couple straightened up when I was contracting & it didn't take much to bend them again + the extra wear on the crank bearings. More often then not it's the big end that lets go or the blade holder bolt shears off from vibration & hard hits.
LOL heres a giggle for you. That motor that I busted last month (mentioned on this board) also had a sheared crank key, (blade holder key). Top key was fine. Motor always ran well but I did notice it was getting gutless over the last year.
joaopnz,
Apr 15, 4:30am
Thanks for that,
But, does it make the metal soft, causing it to break? And i guess if it fails the blades would just go out flying.
alfred011,
Apr 15, 6:14am
I have not seen any snap off after straightening them ,they are not made of hard steel ,the way they wear on the bearing surfaces where they run in aluminium cases show how soft they are that was why most mowers today are fitted with flail blades swinging on bolts is to stop crankshaft damage like the old style bar blades caused.
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