Hello all ,I have a 1983 yamaha 250 mono and have landed the sumpgaurd on a rock which has pushed the flywheel cover upwards and snapped off the top two screw bosses,or at least its forced the 6mm allen bolts up through the bosses wrecking them. My question is are the crankcases alloy or are they magnesium i can get alloy welded and make new bosses to weld on but will struggle if they are magnesium.I dont want to bodge the job with metalfillers,so if anyone knows it cant be welded i shall start looking for new crankcases, yes i now know i should have just had a standard cover on not an after market job because they give a bit. many thanks for all future replies.

Think youve got problems http://uk.youtube.com/watch?v=RPfUZ3lbEQ0&NR=1

Hello all ,I have a 1983 yamaha 250 mono and have landed the sumpgaurd on a rock which has pushed the flywheel cover upwards and snapped off the top two screw bosses,or at least its forced the 6mm allen bolts up through the bosses wrecking them. My question is are the crankcases alloy or are they magnesium i can get alloy welded and make new bosses to weld on but will struggle if they are magnesium.I dont want to bodge the job with metalfillers,so if anyone knows it cant be welded i shall start looking for new crankcases, yes i now know i should have just had a standard cover on not an after market job because they give a bit. many thanks for all future replies.

They are magnesium.

I wouldn't waste my time trying to repair these cases because they aren't pure enough to give a satisfactory weld.

Look on Ebay. Replacements are always coming up for sale, and luckily for you the flywheel cover is the cheaper of the two!

Think youve got problems http://uk.youtube.com/watch?v=RPfUZ3lbEQ0&NR=1

I thought - yeah I've seen that one, but then realised it wasn't the same one:

Another one pretty similar

I am pretty certain the crankcases are alloy and can be welded.

The original ignition cover is magnesium