Author Topic: Pinking and issue  (Read 841 times)

Offline BSA500

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Re: Pinking and issue
« Reply #15 on: 27.10. 2018 09:27 »
What is the timing set to now?
I'm not sure now 5/16 keeps popping up in my head but I think 3/8 is the one I read for a a7ss. Confusing me trying to get my head around is 3/8 more retarded than 5/16

Online muskrat

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Re: Pinking and issue
« Reply #16 on: 27.10. 2018 09:48 »
G'day BSA500  *yeah* *yeah* *yeah* persistance pays off.
Timing for an A7SS is 3/8" btdc = 38 degrees with the auto unit wedged to max advance.
Mate, I'd be looking for a new nut for the auto unit. And even then use a little vasso on the taper till you get the timing set up just right in practice before you clean and do it for good. It tends to move when tightening so you can guesstamate the movement and incorporate it into the position before tightening the nut.000000
Clear as mud, right?
Cheers
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Offline BSA500

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Re: Pinking and issue
« Reply #17 on: 27.10. 2018 10:08 »
Quote from: muskrat link=topic=13398.msg111237#msg111237
date=1540630113
G'day BSA500  *yeah* *yeah* *yeah* persistance pays off.
Timing for an A7SS is 3/8" btdc = 38 degrees with the auto unit wedged to max advance.
Mate, I'd be looking for a new nut for the auto unit. And even then use a little vasso on the taper till you get the timing set up just right in practice before you clean and do it for good. It tends to move when tightening so you can guesstamate the movement and incorporate it into the position before tightening the nut.000000
Clear as mud, right?
Cheers
I am pretty good at putting the atu on without moving the armature it's my only talent. I will check the timing tool to see what I last set it to. I perm marked it. I am I right thinking 3/8 is more retarded than 5/16. I may have cocked up last time. Don't know why used 5/16

Online Black Sheep

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Re: Pinking and issue
« Reply #18 on: 27.10. 2018 10:17 »
3/8 is more advanced than 5/16. I use 5/16" on my A7. Less likely to pink on 5/16".
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Online Greybeard

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Re: Pinking and issue
« Reply #19 on: 27.10. 2018 10:44 »
3/8" is 6/16" so larger; more advanced.

Offline BSA500

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Re: Pinking and issue
« Reply #20 on: 27.10. 2018 11:06 »
Dammit. So if it was set to 5/16 say what should I aim at to retard a little. I know a degree disc is a good way and I have one I am just not fancying taking the primary case off. I have only just got it leak free.

Offline Swarfcut

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Re: Pinking and issue
« Reply #21 on: 27.10. 2018 11:30 »
  Don't forget that these piston height figures are a rough translation of the true angle of ignition advance, published back in the day for the average backyard mechanic, working on a stock motor., running on the available fuels of the day. Anything you do to modify from stock will affect the optimum ignition timing. That includes the fuel.

  With the reduction of octane rating and removal of anti knock lead, no wonder we have problems.  I would try things as they are with a swig of octane booster.  Otherwise it is trial and error, setting it retarded and advancing until it just pinks, then retard slightly. That's the best you will get.
 
  Swarfy.

Offline BSA500

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Re: Pinking and issue
« Reply #22 on: 27.10. 2018 11:34 »
Not easy then  *smile*

Online RDfella

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Re: Pinking and issue
« Reply #23 on: 27.10. 2018 13:14 »
BSA500 - if you've set to 5/16 it should not be pinking. Are you sure the advance unit is jammed at full advance when you're setting the timing?
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Offline BSA500

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Re: Pinking and issue
« Reply #24 on: 27.10. 2018 17:02 »
Lots of careful checking when I put it back together.  It's a reconned atu and magnetic so careful setting up.

Online muskrat

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Re: Pinking and issue
« Reply #25 on: 27.10. 2018 20:14 »
G'day BSA500.
As Swarfy said, any deviation to std of the time will mean differences in ignition timing. Higher compression makes the bang happen quicker so slightly retarded timing is needed, higher octane fuel burns slower so a little more advance is needed.
 Two ways to combat pinging is to retard ignition or pour more fuel in (richen the carb settings). By adding octane boost to a certain extent is like retarding the ignition a tad without touching the timing.
Cheers
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Offline BSA_54A10

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Re: Pinking and issue
« Reply #26 on: 28.10. 2018 12:14 »
Your magneto fires when the points open .
SO increasing the points gap will cause the points to open earlier thus advancing the spark.
The reverse is also true decreasing the points gap retards the ignition.
Forth the purpose of working out the ideal tuning, you can cheat by changing the points gap.
When you have found the opening that causes the engine to run best, pull the plugs , rotate the engine to give the .002" opening and mark the piston stick.
Remember to do it on both cylinders.
If the two marks are different , use the shortest ( least advance ).
Then reset the points to 0.012" and time the magneto using your measurement stick.

It is very common for the cam to be different left to right  .
There are a lot of articles about stoning the cam to make the cylinders timed the same left to right.

AS others have already mentioned the numbers BSA published are only correct for 1950's fuel.
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