Setting ignition timing on R24
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Autor Thema: Setting ignition timing on R24  (Gelesen 1485 mal)

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DanMay

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Setting ignition timing on R24
« am: 24 September 2018, 23:42:44 »

Hello,   I am trying to set the ignition timing on my R24, and as you may know there is no timing window or timing marks on the flywheel. The manual states (in German) a distance from what I believe is top dead center. Is this as simple as removing the cylinder head and bringing the piston down from top dead center by the prescribed measurement and setting the breaker points to open at that point?

Daniel
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Setting ignition timing on R24
« am: 24 September 2018, 23:42:44 »

Kurt in S.A.

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Re: Setting ignition timing on R24
« Antwort #1 am: 25 September 2018, 01:23:15 »

Interesting...no timing window.  I wouldn't think you'd need to remove the head, but rather use a measuring tool that screws into the spark plug hole.  These have a way of measuring the distance that the piston crown moves.  Seems like you could make settings based on that.

Kurt
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DanMay

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Re: Setting ignition timing on R24
« Antwort #2 am: 25 September 2018, 02:03:15 »

It is the same as the pre-war twins.  Some use a degree wheel on the flywheel, but you have to pull the transmission for that.  Vech marks the flywheel when he has it apart, and uses a bolt hole from the generator mount to peek in with a mirror.  Unfortunately there is no inspection hole on the singles.

I believe the specification is here:
https://cms.bmw-einzylinder.de/images/PDFs/unterlagen/handbuch/bmw_r24_serviceheft.pdf
But my German is bad.

For my 1938 R61, the specification is “.237 inches (6mm) before u.d.c”.  But I cannot find the same specs for the R24.

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Re: Setting ignition timing on R24
« Antwort #3 am: 25 September 2018, 02:25:51 »

Dan -

Typically, those measurements are circumferentially on the flywheel...or at least it's specified at say 6 degrees before TDC which can be converted to distance along the edge of the flywheel once you know the diameter.  If that's what is the spec for the R24, I'm not sure how one converts the up-down motion of the piston with rotation of the flywheel.  It's doable...just need to remember my Mechanics 101!   ;D

Kurt
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Borgward

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Re: Setting ignition timing on R24
« Antwort #4 am: 25 September 2018, 10:41:04 »

hi Dan,

you can find an simple conversion tool under
https://www.metriccustom.de/doku.php?id=umrechnung_zzp

attached picture shows the results for an R24 engine; i.e. an ignition timing at 42° corresponds to ~10.5mm before u.d.c.
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DanMay

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Re: Setting ignition timing on R24
« Antwort #5 am: 25 September 2018, 13:47:00 »

Thank you, that is very helpful information.  I knew of the formula (sk = hr*(1+pl/hr-COS(a)-SQRT((pl/hr)^2-SIN(a)^2)) ), but I was not sure of the values for the connecting rod length (pl).   

Do you know of the recommended amount of ignition advance on the R24 for the traditional (F) marks  (full advance) ?  Is 42 degrees/10.5mm the target ?

Daniel


« Letzte Änderung: 25 September 2018, 14:05:34 von DanMay »
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Re: Setting ignition timing on R24
« Antwort #6 am: 25 September 2018, 14:09:47 »

I just know the values forthe  R25 which has almost exactly the same engine:
there the ignition advance shall be between 38deg and 42deg.
I'm sure it is the same for the R24.

Hubi
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Re: Setting ignition timing on R24
« Antwort #7 am: 26 September 2018, 00:19:24 »

So I was actually able to attach a degree wheel to the crankshaft on the front of the engine, and find 5° before top dead center. Per the R25 manual, this is the location that you should use for static timing.

 Once I found 5° before top dead center, I installed a piston stop and proceeded to set the static timing per the R25 manual.

I will have to assume the mechanical advance is working properly to get me to the full ignition advance at higher RPM's.  I used a timing light on the advance and I can see the springs allowing the weights to reach full extension.





« Letzte Änderung: 26 September 2018, 00:40:02 von DanMay »
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