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If running an original 3-bearing crank & high compression head I'd stick to 8 degrees.
Peter's method for checking advance sounds fine but another way is to set up a DTI against the side of the rotor arm, just requires a small calculation to translate the deflection into an angle.
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Thank you for the replies and information. As the information about 12 degrees advance seems to be a little suspect and not widely known, I shall leave the the holes be, at 8 degrees.
All I need to do now is to ascertain whether the slight amount of wear in the bushes is enough to cause timing problems or not.
Thank you.
Jamie.
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Location: Deepest Frogland 30960
Car type: 1933 RP Standard Saloon
Possibly not timing issues but very likely ignition ones as the points gap will be variable. I had a DK on my RP that had detectable, but not excessive wear on the shaft bushings and ignition was very erratic. I changed it many years ago for a Bosch 009 from Willie McKenzie and it has run pefectly ever since. I keep the DK, refurbished, as a spare.
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Thank you, Reckless. I confess that I meant points gap, rather than timing: poor terminology on my part. I shall look for some new bushes or turn some up and ream them if I cannot find any.
Regards,
Jamie.
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Location: Hampshire UK
The Lucas Data which I have seen suggests that the early DK4As had a rather cautious centrifugal advance range of 3 degrees (6 degrees crank) and the later/replacement ones 8 degrees (16 degrees crank). The two springs are of equal strength, so the advance increases more or less linearly from 500 to 3600 engine RPM. Total advance will of course be determined by your choice of static setting, but about 20 degrees total is a good starting point.
Austin handbook advice in 1934 for the recently introduced Ruby was a starting point static setting of 1 1/4 to 2 inches at the flywheel before TDC (14 to 22 crank degrees). Unfortunately, this was a repeat of the full advance setting from the manual distributor days and incorrect for the auto advance distributor. It must have caused no end of trouble. By 1936 the advice was was a static setting of 3/4 inch before TDC (8 crank degrees) - this may have been intended for the 3/6 degree distributor. In 1937 the advice was was 1/2 inch (5 crank degrees) which seems likely to suit the 8/16 degree distributor.
I don't know where the Cornwall article figures came from, but they may have included the static advance.
One thing I have never seen discussed is the effect of the 1937 head design. There is a "squish" area above the piston with a very small clearance. One would think that this gives more turbulence near TDC than the LC head, in which case the requirement for ignition advance is reduced.
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20-08-2020, 09:45 AM
(This post was last modified: 20-08-2020, 09:52 AM by Chris KC.)
"The Distributor Doctor" is the only source I know of for bushes and advance springs.
The bushes should be oilite; contrary to popular advice it can be reamed but do so with a sharp /new reamer and use it sparingly. Pre-soak in engine oil and don't forget to drill the hole for the oiler after fitting...
John, I shudder to think how many cranks that advice may have taken out. One thing to remember though is that 'proper' petrol used to let you know it was over-advanced by audible pinking; in fact I used to set my ignition by driving up Slapton Ley and advancing till pinking occurred, then back off a bit. Nowadays it is possible to run with massive over-advance with no 'hints' for the unwary.
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Austin company post war books give the late static timing as a conservative tdc. Timing must be judged by perfromance not noise. On my RP when stock moving the manual timing over a vast range had a marked effect on noise but the speed remained unchanged; 50 mph.
Whether auto distibutors have the appropiate springs is anyones guess. Those with time to spare can arrange an old motor mower or choke control as a manual override . Give driver something to play with when grindinging up hills.
