Posted: Sat Jul 07, 2007 10:19 am Post subject: Ign timing on USA M38 Jeep.
I have a 1950 M38. The Ign is std waterproof 24 volt, etc. The engine starts immediately and idles OK after a warm up. The points and plugs are new. Power, under load, seems to be about std for the genre.
The question is... The manual calls for static timing at 5* BTDC.
I am timing it dynamically (with engine running) with a timing light. I assume there is some secondary advance kicking in from the centrifugal advance dist because with much less than 18* BTDC...the engine does NOT idle well. I am using the pointer that bolts to the timing cover as a reference for TDC.
So...is there a 'value' that is perhaps more 'realistic' than 5* BTDC...or am I making a shambles of it?
5 Deg BTDC is the standard timing point either method. There is no vacuum advance to skewer the setting and if your centrifugal advance is coming in at idle RPM then your springs are too soft. To be sure your centrifugal advance is not making your initial 5 deg setting impossible to attain then disable it and set your dynamic 5 deg BTDC. Then enable your centrifugal advance and recheck your idle timing. If the timing goes too far advanced again at idle buy two new springs.
The centrifugal advance (Governor) chart is C2-P2 and at 650 crank RPM's centrifugal advance should be "0". At 750 RPM centrifugal advance should just be starting at "1" degree. At 1650 RPM you should have 5 degrees additional centrifugal advance degrees. At 2950 RPM you should have the max additional 11 degrees centrifugal advance. When you consider the original 5 degree BTDC initial setting you should see the following total degrees advance per crank RPM's:
Correct idle speed for this engine is 600 RPM. I would say you have either worn springs in the centrifugal advance or you are attempting to time the engine above 650 RPM. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
That is some answer Wes, I will have to print that out and add it to my manuel as the TM I have doesn't have that bit in.
On another note,
they have just built a bronze statue of your avatar Andy Capp in good ole' Hartlepool (his home town) UK just down the road from where I live.
It occurs to me they must have cleaned up his accent from his native tongue as in our copies the characters had a pretty strong local twang as I remember.
Very few M series vehicle specific service manuals address the major repair and overhaul of the electrical accessories. These were addressed in a specialized manual.
Auto-Lite (WWII) TM 9-1825B dated Jan 1944
Auto-Lite (Post WWII) TM 9-1825B Dated Nov 1952
Delco (WWII) TM 9-1825A Dated Jan 1944
Delco (Post WWII) TM 9-8627 Dated Jun 1953
These are indespensible when trying to maintain any M series vehicle. Delco manufactured replacement starter, generators, voltage regulators and distributors to Army milspec for the M38 and M38A1 so if you have a mix of Auto-Lite and Delco you'll need both manuals.
This specialized manual system also applied to Carbs, fuel pumps, brakes, and so on.
Hello Dave,
Yes Andy was a favorite of mine from childhood on. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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