Hitchcocks Forum

Another  'holy' Bullet piston, SIGH!


http://i81.photobucket.com/albums/j203/ ... piston.jpg

 And Leon,


      If I knew how to do pics I could show you the one I pulled out this afternoon,  it's 2 piece one, that is going to take a lot of araldite

Hi Leon


A hole like that is caused by a hot spot and used to happen quite often back in the 60s, the cause is usually either running too lean or more often too hot a spark plug.


That picture looks like a mixture of both as there is a distinct lack of carbon on the piston crown.


I don't know if you have the same problem there as in the UK with added ethanol in the petrol, but this also causes a hotter engine requiring a cooler plug to be fitted.

Hello Leon--------Oh dear,oh dear. What can I say to help ?? It's not a laughing matter, is it ?? As Dennis C noted--the crown looks very clean. Have you just done a top-end overhaul? Can you give us some details of the event itself ??  On the subject of Ethanol and spark plugs, as this mixture( E5---later E10, and in Brasil E25 ),   is effectively a "new" fuel with it's own, individual burning characteristics, shouldn't the vehicle manufacturers be advising on the appropiate plugs to n ow use ??  To all who are reading this----------------- Please DO look at Wikipedia "Ethanol", and "Methanol". Yes, the chemical bits are heavy going but just have a read of the reults of Ethanol combuston and it's exhaust gas properties. Norm, Leon---there is also mention of Australian laws with regards to these fuels.  In the meantime--------- I suppose Tig-welding a patch on is out of the question ?? ( Only joshing --- but, being an Enfield it might just actually improve things ?? )  Chin up old son---soldier on.  It's Sunday morning, 09.45, a big, red warm thing in the sky---I can hear the local bikers going off to the Welsh coast and I'm stuck here in the garage as well as you, Leon. Crack a tinnie mate & let's feel sorry for ourselves !!!!

 Alan,


    I's not Leons so don't feel sorry for him he is Lucky Leon. It was running 98 non ethanol fuel and has been having problems for some weeks with strange noises at 90+ kph The plug he was running was factory recomended. He had just fitted a 127 main jet because they felt it was running lean on a plug check. Problem is this bike is 2500ks away so little chance of checking what happened

The owner had complained about it making clacking noises at speeds over 90 kmph, and thought it might be pinking; so retarded the timing, this didn`t cure the problem, so a larger main jet was fitted with still no cure. The timing was then reset to the correct position, but it was apparently too late. I think  a movie could be made when this is all over. What  causes clacking?

You'd have to say it looks like a spark erroded hole. Almost as if he had a long reach in a medium reach head?


 

 Not good at the moment, piston holed was a JP I have a JP which pulled the top off last Thursday and after we studied it closely over the last few days no real reason as to why. Only thing I found out last night was that the bloke riding with him said they were sitting on 110kph and that was on his Suzuki speedo

That's 68.75mph by my reckoning. I don't think they cool well enough at that speed for any sustained period although if it was normal overheating you'd expect more of a collapse than a polite little hole in the top. 

Actually re reading this I agree on the cooler plug. I fitted a B7HS NGK rathervthan the B6HS that is the recommended heat range on mine as it would pink fearcely after a fast run. Dialing the static advance back to 7/16" before TDC full advance as opposed to 1/2" and the cooler plug made this symptom disappear. I also use the 95 octane fuel rather than the 91 although the 91 is fine in the Duc and that's 9:1.