Mountfield HP470 frame deck keeps coming off engine

[platforminc]

Hi All.

I have a problem with my lawn mower, whenever I use it, I find that the M8 bolt and nut which I have used to hold the frame/deck onto the engine keeps coming off, it makes using the lawnmower a nightmare, what causes the nut to come off is the vibration of the mower. I have used over 12 nuts now, and they only last about 5 minutes.

I believe I am using the wrong kind of bolt/nut.

Any ideas please ?

 

[just pumps]

Either a Nylock nut (section of plastic stops it vibrating loose) or Locktite nut lock.

 

[Burnerman]

As above....do you think the mower vibrates excessively?
John

 

[platforminc]

As above....do you think the mower vibrates excessively?
John

Not really an expert to say it vibrates a lot, I am just a normal user.
I did a mini service the other day, drained the oil, changed the plug and also filter. I have a new blade, just not had time to replace it also.
When the engine is loose, it becomes hard to maneuver and move around, when its all bolted down, the tyres roll effortlessly and the grass cut is even.
When it is loose, I have to use a feet to hold it down, one hand to pull the starter and one hand to hold the handle thing. you dont want to know what i go through a times.

 

[platforminc]

It vibrates so much so that a 40mm bolt gets its nut off in less than 5 minutes.

 

[Burnerman]

Nyloc nuts are the usual fitment...assuming the bolt thread is good you shouldn't have any more problems.
I just asked about the vibrations because I get lots of machines like these in with bent crankshafts after the user has clipped a stone. You can check this when you replace the blade....start the thing up, lever back on the handles and watch the spinning crankshaft. Just don't lose the woodruff key if you take the blade shoe off too!
John

 

[platforminc]

Sorry for my ignorance here, which bit is the crankshaft ?
Yes, I have clipped stones a few times.
Is it very hard to take off the blade, as my blade probably needs a replacement by now.

Nyloc nuts are the usual fitment...assuming the bolt thread is good you shouldn't have any more problems.
I just asked about the vibrations because I get lots of machines like these in with bent crankshafts after the user has clipped a stone. You can check this when you replace the blade....start the thing up, lever back on the handles and watch the spinning crankshaft. Just don't lose the woodruff key if you take the blade shoe off too!
John

 

[Burnerman]

The blade should have one central bolt (91/16 or 14mm) conventional thread. This secures the blade to an aluminium shoe which also has two pegs to locate the blade. The shoe is keyed to the crankshaft and will pull off, if it's not rusted in place!
It's a trick to run the engine with the blade and shoe off.....any bending of the crankshaft is pretty easy to see if it's out of true.
John