Author Topic: advance or retard??  (Read 9091 times)

Offline emilios

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advance or retard??
« on: 12.12. 2009 11:08 »
Hi
Im going to set ignition timing on my 1956 plunger A10..
I have a manual advance/retard magneto...so i want to be sure where is the correct position for
full advance...
I also want to understand it..advance is when we have spark much before tdc and retard closer to tdc??
i hope foto helps..
Thanks
1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Online muskrat

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Re: advance or retard??
« Reply #1 on: 12.12. 2009 11:53 »
Yes that is right. Timing is set at full advance. Standard for A10 is 3/8"" before TDC which is 35 degrees. You may find it pings under load at this setting so retard a few degrees till pinging stops. Easy with a manual setup.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline a10gf

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Re: advance or retard??
« Reply #2 on: 12.12. 2009 12:09 »
Quote
advance is when we have spark much before tdc and retard closer to tdc
Correct. And retarding when starting means spark occurring close to (or over) TDC, which prevents ignition in the cylinder with piston on it's way up suddenly reversing and breaking a leg on the kickstarter.

With the mag cam housing you've got, full advance is when the cable is not pulling on the cam (= the cam is pushed fully down by the spring in the cam housing). So full advance is position 2.

A10 GF '53 My A10 website
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Offline emilios

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Re: advance or retard??
« Reply #3 on: 12.12. 2009 13:10 »
Thanks guys....
a10gf are you sure that full advance position is position 2 ???
Is yes that means i have a problem with my BSA M20... *sad2*
Cause when i put engine before a year i set ignition with lever at position 1..that means full retard..idint know...
and bike had no power at hills...thats why...i was planning to dismalte engine after A10..
But running M20 for a year with retard ignition will propaply need a rebuilt engine anyway *conf*
Thanks god for that forum...

1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Offline a10gf

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Re: advance or retard??
« Reply #4 on: 12.12. 2009 15:52 »
I know nothing about m20, mag-dyn? Can be the other way. There are k2f's with cable output on left or right hand cover side. LH = no pull advance, RH = pull advance.

On your left mag cable output, no pull on cable = the cam ring pushed CCW towards the points' rotation direction = opening earlier = advance.

Look at it closely & think over how it all works (movement of cam) relative to the pistons' position, this will help you a lot in getting good timing control.

A10 GF '53 My A10 website
"Success only gets you a ticket to a much more difficult task"

Offline MG

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Re: advance or retard??
« Reply #5 on: 12.12. 2009 19:59 »
Hello emilios!

a10gf and muskrat are absolutely right. If the lever is pulled back toward the rider, the ignition is retarded with your magneto. Take off the primary chaincase cover, mark one tooth of the crankshaft sprocket and make a matching mark for TDC on the inner chaincase,  slowly turn the engine in its working direction and look at the magneto breaker contact. When you move the advance/retard lever, you will notice the difference in ignition timing.
When setting the timing put the lever to fully advanced position. I would recommend 33-34deg BTDC with the iron head A10.

about your M20: driving with retarded ignition does not necessarily badly damage the engine. Usually the worst thing that can happen is a burnt exhaust valve due to the higher temperature of the exhaust gas (and exhaust pipes turning blue rather badly). So if it is running fine and the power output is ok when timing is set correctly, I don't see the necessity of taking it apart, unless you just enjoy doing so  *smile*

Check over how the advance/retard mechanism works, check and set timing and you are fine.

imho the best way to set ignition timing properly is using a timing disc and cheking with a timing light, which both are available for small money nowadays.

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline emilios

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Re: advance or retard??
« Reply #6 on: 12.12. 2009 20:26 »
Thanks guys..
Im waiting a new mag gear from draganfly and i will set ignition next week..
Thanks again
1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Offline chaterlea25

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Re: advance or retard??
« Reply #7 on: 13.12. 2009 19:00 »
Hi Emilios and All,

On most M20's B31's that I have worked on the advance lever works in reverse to the A10!

The usual reference is, "slack (loose) wire advance" on A10's and most competition magnetos,
"Tight wire advance" on M20's B31's etc (ie.lever pulled)

Hope this helps
John O R
1961 Super Rocket
1963 RGS (ongoing)

Offline emilios

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Re: advance or retard??
« Reply #8 on: 14.12. 2009 17:02 »
Thanks John
That helps a lot...
1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus