I want to sharpen the cutting blade on the petrol mower ( Briggs and Stratton engine/Lawnflite SP mower ) but how do I lock the engine so that I can remove the nut that holds the blade in place ?
Thanks Brian
You can get a gadget that replaces the spark plug to lock the piston etc. However, IIRC the nut/bolt that retains the cutter is sometimes of left hand thread. In either case a ring spanner of good fit and a sharp blow from a mallet *in the right direction* should do the trick. Also IIRC, some mowers have the direction of removal marked upon the head of the nut/bolt. HTH GS
on 11/01/2007, snipped-for-privacy@btinternet.com supposed :
You should not need to. Isolate the ignition, to make sure it cannot start - pull the plug cap off. Then use a well fitting ring spanner get the engine on compression and give the spanner a clout with a mallet. Be aware that these bolts are usually of a thread which tightens in the opposite direction to the blades normal rotation so it cannot unscrew itself in use.
Doesn't one hold the blade, obviously taking care to not hold it in such a manner as it can hurt you? (can't remember how I did mine though).
cheers, clive
Hold the blade?
There is a way, if you are prepared to go to the trouble of making it (for present and future use): Make a "piston stop". Using an old spark plug, remove the insulator and central electrode (brute force is probably required). Then find a piece of rod (of suitable length) that will be a _tight fit_ in the body of the spark plug. Brazing it in would be better, but not essential.
Sylvain.
Ignore the ideas of a "Piston Stop" as I have seen the results from others when they give too much pressure (Usually in the wrong direction of rotation for the LEFT HAND nut) which results in a holed piston.
Use a piece of 2"X4" timber wedged across the end of the blade against the casing (Care to be taken if the casing is plastic) to restrain the blade from rotating. NOTE If you turn the engine.machine upside down or further than 90 degrees to work on it expect some difficulty restarting after the oil has gone past the rings and into the combustion chamber. Had many a Greenkeeper find out that a restricted compression piston being pulled by a pull start results in very sore fingers at the T piece pull start when it locks or kicks back ;-)
In other words, the nut is loosened in the same direction as the blade rotates.
It's much better to free the nut by impact than by hauling on the spanner, but for maximum impact the blade needs to be held against a really solid stop like a C-clamp over the grass skirt. That also give you a hand free to keep the spanner from flying off.
If you think the grass skirt couldn't stand it, that mower is not worthy of your DIY skills.
Yes. Fit the spanner on the nut so that there is a slight angle between it and the blade, and squeeze the two together.
I have a vague memory that Soddes Law says that (for undoing) you have to fit the spanner angled just behind the blunt edge and squeeze gripping the sharp edge.
If its like my old Hayter, you don't..hold the blade steady and do the impact thing on the nut. Its keyed to the shaft.. If its a tapered fit to the crank, you are in doggy doo.
Or a bent conrod.
Thanks all, if it's just a "jam the blade" type job then no problem !
*( touch wood)*Brian
That explains why it's blunt - wooden blades won't work terribly well :-)
cheers, clive
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