Another Australian piston bites the dust

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Another Australian piston bites the dust#10409

By Norm - Wed Mar 14, 2012 11:47 am

- Wed Mar 14, 2012 11:47 am #10409

 Simon,

        The 68.75 one pulled the piston in half, the one with the hole was travelling much slower, 2 Bullets busted the same day gets a bit confusing.

Another Australian piston bites the dust#10410

By MadMike - Wed Mar 14, 2012 1:03 pm

- Wed Mar 14, 2012 1:03 pm #10410

Good  morning everybody. I don't wish to appear contentious but I have seen speeds of 90+, over 90, and 110 kph quoted in this posting. Well that's between 56 and 68 full size imperial miles per hour!

Now my Norton Model 50 (the 350cc single for those that don't know Nortons) with its 83000 miles on the clock since its last rebuid in 1976/77........yes 36 years ago, will cruise at those speeds all day and it did on Saturday, Sunday and yesterday. It doesn't overheat and it certainly doesn't eat pistons. So what is wrong with the bikes refered to in this posting? Modern bikes, even made in India, should be able to cope with these sorts of speeds. I am somewhat confused. I would like to offer some help and advice based upon my motorcycling and engineering experience but I simply cannot understand what causes piston failure like this, unless these are simply one off cases.

Another Australian piston bites the dust#10411

By MadMike - Wed Mar 14, 2012 1:12 pm

- Wed Mar 14, 2012 1:12 pm #10411

Me again.

Having zoomed in on the photo in the initial posting I note that the piston crown is very clean and there is no trace of any carbon deposits. Was it cleaned off before the photo? The hole looks for all the world like a result of a weak mixture. A hot plug is umlikely to do that sort of damage but when combined with a weak mixture it may exaserpate the problem.

So mixture setting and timing setting are the most likely causes, as others have said. However I do not understand why pinking should occur after a fast run, unless the engine needed a decoke. None of mine exhibit that sympton.

Another Australian piston bites the dust#10417

By ChrisD - Wed Mar 14, 2012 5:42 pm

- Wed Mar 14, 2012 5:42 pm #10417

Gentlemen

I haven't  damaged a piston quite that comprehensively but I have seen one exactly like that.  The 500 Classic had been ridden ~1000km with a badly advanced ignition.  Spitting and barking it must have been.

ChrisD

Another Australian piston bites the dust#10425

By Norm - Wed Mar 14, 2012 7:50 pm

- Wed Mar 14, 2012 7:50 pm #10425

 Mike,

      The holed piston out here is rare but we have been pulling the tops off pistons for years although it has eased off over the last couple. The OEM piston was junk, run them past 10,000 ks and you were on borrowed time but the one I have sitting beside the computer is a JP, first one I have seen do this and it only has 4,000ks on it

Another Australian piston bites the dust#10428

By MadMike - Wed Mar 14, 2012 8:59 pm

- Wed Mar 14, 2012 8:59 pm #10428

Norm, sorry but please indulge me. Have you a picture of one of the pistons with the top "ripped off" plus a picture of the fracture on the piston crown as well? Also again my ignorance of things specifically RE but who or what is JP?

A piston crown coming off is almost certainly a component problem but what causes the detachment? It sounds like a partial seizure may have occured. Is the crown detaching around the wall of the piston or simply within the crown area?

Another Australian piston bites the dust#10434

By Dennis C - Wed Mar 14, 2012 9:55 pm

- Wed Mar 14, 2012 9:55 pm #10434

Hi Mike

JP are a piston manufacturer based in Australia and reputedly make high quality pistons.

It would appear that the Indian made Enfields are attracting people to this type of bike who are now learning the lessons which some of us British bike affectionados  learnt many years ago.

Personally I think this is great as the modern car/bikes leave nothing to learn, you just repair them by computer.

Another Australian piston bites the dust#10437

By Beezabryan - Wed Mar 14, 2012 10:21 pm

- Wed Mar 14, 2012 10:21 pm #10437

this is a decapitated Bullet piston, happened on the Fosse on our way home from a splendid weekend in the Cotswolds

Looked like this when I removed the cylinder head

http://i50.photobucket.com/albums/f340/ ... eld001.jpg

 but when the barrel was removed it looks like this

http://i50.photobucket.com/albums/f340/ ... piston.jpg

Took me a little time but with careful fettling it was as good as new

http://i50.photobucket.com/albums/f340/ ... on1001.jpg

Hope there are no folks here with a humour shortage like the silly buggers on RealClassic some years back.

Another Australian piston bites the dust#10438

By Beezabryan - Wed Mar 14, 2012 10:23 pm

- Wed Mar 14, 2012 10:23 pm #10438

sorry did not do that too well !

I meant to address my post to His Madness and mention the loss of forward motion occurred on the Fosse not a million miles from Mad Manor

Another Australian piston bites the dust#10440

By Alan R - Wed Mar 14, 2012 11:29 pm

- Wed Mar 14, 2012 11:29 pm #10440

------------ oh look !! >>>>> a squadron of pigs, flying in formation ( He-He). Never mind the smiley-smiley but I'm with you all the way on the humour front. Picture No 2 is why I have just put my hand in my pocket and bought a nice forged piston from "H".   8.5CR with a plate giving 7.5CR and big dollop of peace of mind.   Guys, how do you load those pictures up ?  CAST ALUMINIUM is just not meant to be in this type of operating scenario. From my Apprentice days the Instantaneous Moment of Inertia at TDC for a piston of this size at 5,000 RPM is in the order of "X" TONS !!!!Honestly.  