Author Topic: Pinking (pinging)  (Read 9142 times)

Offline beezalex

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Re: Pinking (pinging)
« Reply #15 on: 31.10. 2009 11:51 »
First of all, we need to clear up what CAUSES "pinging".  What we're really talking about here is detonation and it occurs when the combination of pressure and temperature in the combustion chamber exceeds the spontaneous ignition point of the fuel.  To prevent the fuel from detonating you can do three things:  Lower the pressure, lower the temperature or change fuel to one that has a higher ignition point.   Lean mixture causes excess heat, so you first need to make sure that your mixture is correct...mainly on the needle. Going too rich can alleviate pinging, but it's a formula of diminishing returns and eventually causes carbon buildup which causes an even higher propensity for pinging.  Get your timing right (too much advance can also raise heat), get your mixture right, then if it still pings, decarbonize and polish piston crowns and combustion chamber.  Also, remove any sharp edges from around the valve cutouts on the piston.  This removes localized hot spots and origin points for detonation.  This has worked for me 100% of the time that I have done it.  If, however, this still doesn't do it, you can lower the compression ratio by either changing pistons, installing a spacer under the barrel or installing a thicker head gasket.  1 mm lowers compression by about 1 point.  This has also worked for me in the past until I realized how effective massaging the chamber was.

Good luck.
Alex

Too many BSA's


Offline mike667

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Re: Pinking (pinging)
« Reply #16 on: 31.10. 2009 16:37 »
First of all, we need to clear up what CAUSES "pinging".  What we're really talking about here is detonation and it occurs when the combination of pressure and temperature in the combustion chamber exceeds the spontaneous ignition point of the fuel.  To prevent the fuel from detonating you can do three things:  Lower the pressure, lower the temperature or change fuel to one that has a higher ignition point.   Lean mixture causes excess heat, so you first need to make sure that your mixture is correct...mainly on the needle. Going too rich can alleviate pinging, but it's a formula of diminishing returns and eventually causes carbon buildup which causes an even higher propensity for pinging.  Get your timing right (too much advance can also raise heat), get your mixture right, then if it still pings, decarbonize and polish piston crowns and combustion chamber.  Also, remove any sharp edges from around the valve cutouts on the piston.  This removes localized hot spots and origin points for detonation.  This has worked for me 100% of the time that I have done it.  If, however, this still doesn't do it, you can lower the compression ratio by either changing pistons, installing a spacer under the barrel or installing a thicker head gasket.  1 mm lowers compression by about 1 point.  This has also worked for me in the past until I realized how effective massaging the chamber was.

Good luck.

 excellent points as always alex!

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Re: Pinking (pinging)
« Reply #17 on: 31.10. 2009 19:15 »
Good one Alex, indexing the plug can also help.
Cheers
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Offline nigeldtr

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Re: Pinking (pinging)
« Reply #18 on: 01.11. 2009 18:17 »
I hope this fits with the thread ? if not sorry!

I have been looking around to buy a Road Rocket, but I have been put off a little by the problems associated with high compression, and racy cams. Does it really make that much difference to performance (cam ? compression) especially as I will probably not keep the engine bubbling at the sort of revs where a racy cam comes into effect?

Your experiences and advice on what to look out for would be greatly appreciated.

Regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

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Re: Pinking (pinging)
« Reply #19 on: 01.11. 2009 19:13 »
G'day Nigel,
                It does make a difference to performance BUT. A highly tuned motor puts more stress on its components and needs a bit more fettling to stay tuned. Factory settings go out the window.
Start with a std model and work your way up if you want more go later.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Online chaterlea25

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Re: Pinking (pinging)
« Reply #20 on: 01.11. 2009 19:18 »
Hi Nigel,
Dont worry!
Normal well tuned and sorted Rockets and Super Rockets are extremely flexible and willing!
Mine will pull away from low revs in top gear without complaint.
They are nowhere as fussy as a tuned single cylinder bike
HTH
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline a101960

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Re: Pinking (pinging)
« Reply #21 on: 01.11. 2009 20:00 »
Agreed. the engine is not some highly strung inflexible unit that is a liability for every day use, but it is quite noticeable when it does come on cam. Regarding my own engine I have today removed the 420 main jet and fitted a 430 that I have yet to try out (the weather today has precluded that). I will let you know what improvement there is or not as the case may be as soon as I get the opportunity.

Richard

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Re: Pinking (pinging)
« Reply #22 on: 01.11. 2009 22:45 »
dont forget to mark the 1/4 incriments on the twistgrip
Richard

Offline a101960

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Re: Pinking (pinging)
« Reply #23 on: 06.11. 2009 21:02 »

Following on from from what I originally said about the pistons in my engine here is a picture of them from when I stripped the top end down to de-coke it. What compression ratio do you think that they are? could they be 9:1? I know that it might be hard to say from a picture, but I thought that it might be worth asking the question anyway.

Online Brian

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Re: Pinking (pinging)
« Reply #24 on: 06.11. 2009 21:24 »
To quote from the Hepolite catalogue,

6.5 - 1      Concave
7.25 - 1     Flat with valve pockets
8.5 - 1      Flat bevelled with valve pockets
9.5 - 1      Dome stepped with valve pockets


Yours are 8.5 - 1 

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Re: Pinking (pinging)
« Reply #25 on: 06.11. 2009 21:32 »
Hi, a101960
The pistons look like the GPM pistons???, I think they are 8.25 or 8.3 to 1
More importantly it looks like one cylinder is running differently to the other???
The nearest to the camera is black and sooty while the other is not!
Check the ring gaps, even though there is no evidence of blow by on the photo
Check the valve guide clearances, look for oil leaking down a guide in the ports,or for a loose guide in the head
Also check if the ignition timing is the same on both cylinders
HTH
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline a101960

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Re: Pinking (pinging)
« Reply #26 on: 06.11. 2009 22:30 »
There was indeed a problem with the valve guides. The inlet guide was lose in the head. The head has now been overhauled by the Cylinder Head Shop. The valves and guides were replaced and new seats fitted. That is why there was such a build up on the crown. Oil was getting in due to the lose guide. You might not be to amazed to know that before the remedial work on the head was done there was a lot of blue smoke emitted from the exhaust pipe, and oil consumption was quite high. The smoke has now gone and oil consumption is virtually nil. I very rarely need to top the oil level up now. I have still not had a chance to see how the bike goes on the 430 main jet. I must say that it is a relief to learn that the compression is relatively modest. I am not sure what make the pistons are. What I do know is that they are Italian. Thanks for your help.

Online Brian

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Re: Pinking (pinging)
« Reply #27 on: 06.11. 2009 23:35 »
If they are Italian there is a very good chance they are GPM and GPM pistons are amongst or even arguably the best you can buy.

Online chaterlea25

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Re: Pinking (pinging)
« Reply #28 on: 06.11. 2009 23:50 »
Hi again, a101960
You may find that a reduction in jet size will be in order!
This is because the new guides will have a much closer clearance to the valve stems
this very much reduces air leaking down the guides,
Did you get the guides with the oilseals fitted?
Cheers
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline a101960

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Re: Pinking (pinging)
« Reply #29 on: 07.11. 2009 09:30 »
The reason that I have fitted a 430 main jet is because no matter what I do with setting up the timing it pinks under load most specifically when going up gradients. What happens is I will hit the gradient in top gear doing about fifty or sixty say, and as I open up to maintain speed then the pinking starts. As I said at the start of this thread I have altered the timing so many times now without relieving the problem that I am totally lost as to what to do about it. It just seems logical to me to try the next size up main jet, especially in view of the fact that I always fill up with premium 99 octane petrol.