pull cord sping on McCULLOCH TM 250?

Hi Stuart,
A fiend of mine recently asked about an old T 250 chainsaw of 1960s vintage. The recoil spring appeared to have broken and the cord would not retract. He had removed the recoil housing cover and the recoil unit itself but could not work out how to remove the rope pulley from the housing as there are no obvious holes or fixings. Looking at the item, you have the pulley whose shaft runs though an alloy housing and terminates with the slotted lug that engages in the cam starting mechanism. Looking at this plate i found a directional arrow with the word "off" indicating the lug could be removed by unscewing in the direction of the arrow, clockwise I think it was, anyway the problem is how do you grip the pulley to prevent it turning whilst unscrewing. The temptation is to grip it in the jaws of a large vise risking cracking or damage etc. I however used an old motor mechanic/plumbers trick of wrapping an old fan or timming belt into the pulley groove, pulling the bellt only through the jaws of the vise an whilst keepig tension on tightened the vise onto the belt only which nipped up nicely gripping the pulley with the belt only and preventing it from turning. Then using a suitable piece of iron bar into the slot on the engagement dog a suprisingly small amount of effort had it unscrewing in the direcrion of the arrow. This belt use is similar to strap or pipe wrenches used to separate threaded pipes or remove oil filters.

Inside I found the recoil spring had indeed broken close to the end that locks by slotting into the pulley centre. I remade this end by heating the spring end to red hot with a small blow torch which allowed the hardened spring steel to be worked in to the required shape, I then reheated the repaired end to a dark cherry red colour and quenched it in a bucket of cold water this process though not as good as the original, restores most of the sringiness and hardness, if you don`t, the steel previously heated to a red heat loses its hardness and as result the repaired end won`t last as long, offcourse if you can get a replacement part you don`t need to do allthe above metalwork.

I was probable fortunate in the lug unscrewing as easily as it did it had been sprayed the night before with wd 40 penetrating oil, if I had too ,I would also have used a little gentle heating of the lug and/or a tap on the iron bar if required.

When you get the item coming apart note the positon of the two nylon bearing bushes that support the pulley shaft in the housing and remember the risk of melting them if you decide to use heat.

On reassembly I did not use the belt to hold the pulley, I simply threaded the lug on in the opposite direction until it was snug put the small iron bar into the slot and gae the bar a sharp light tap wtih a hammer. I believe it did not require to be tightened any further as when the whole assembly is put back onto the side if the chainsaw the pull start direction and rotation of the engine is in the direction of always trying to tighten it.

I nearly forgot, when reassemblig the recoil unit; turn the pulley a couple of times to put some spring tension on the rope which you have been careful to wind on in the correct direction, this will ensure the rope recoils fully onto the pulley rather than having it with a loose end hanging.
Hope this is useful, a manual for this chainsaw would have been handy, Cheers, Alan.

Alan Paice
April 2007