Timing advance plate - Crab Distributor

glennpm

glennpm

Well-known member
Is the center mark of the timing advance plate 4° advanced when the plate is inline with the distributor case mark? I believe it is.


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I think that is what it is supposed to be . . . but I always have a TDC marker and an adjustable timing light to know what I'm really getting. I don't trust the distributor, the slot in the cam or anything else to be exact.
 
Glenn, please post the results of testing with your timing light, I'm curious how the stack up of tolerances and 80 years of wear have affected the distributor timing mark.
 
These days I typically advance a front mount distributor several notches more than factory spec and find the engine runs better. I suspect that is due to a bit of wear in both the front slot of the cam and in the drive tang of the distributor.

Today's fuel with octane higher than the 1930s, with a bit of alcohol in it, probably matters too.
 
I'm with 38 - usually I have to advance the timing and I always have timing marks on my pulleys (when I build engines). Usually, I try to get to 24 degrees (total) and that takes at least a few marks forward (clockwise).
 
Here you go ....

I set the distributor up using the static method shown in early bulletins and also on Van Pelts site. Note that this is a rebuilt distributor that I got from Drake or Carpenter decades ago. The 3/8" is a bolt not a drill bit.

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The result of this gave me ~7° advance on the Distributor adjustment tab.
I got a little pinging under heavy load. I then backed it off 1° and screwed the vacuum brake in a half turn by hand. It was loose. Perfect starting and road test.

I had a few years ago found TDC with the zip tie method, made a pointer and marked the belt pulley inside and outside the groove.
This picture shows the pulley at 180°. I notched the pulley and painted marks for TDC.


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This is the current adjustment plate position of 6° BTDC


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Drum roll ...


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Summary:

- Static distributor timing yielded 7° advance
- Changed slide plate down to 6°
- My dial type Craftsman timing light confirmed 6° at 500 RPM. My engine won't idle at 400 RPM. I like my idle about 1K
- 23° advanced at ~2,500 RPM



Glenn
 
Last edited:
Thanks for the report and the pictures. I find I usually have good results with the advance half way between the middle and the end of the scale, and run down the vacuum brake a few turns if needed to take care of any pinging. However, I have only worked on stock engines that are probably fairly tolerant of ignition timing.

Is this the engine the distributor is mounted on? My memory is your engine is a bit "turned up" compared to mine, which may make things a bit more sensitive to timing.
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Hi Glen. Is that the wide land side or the narrow land side?
I couldn't find the pics in the other thread.
 
38 coupe said:
Thanks for the report and the pictures. I find I usually have good results with the advance half way between the middle and the end of the scale, and run down the vacuum brake a few turns if needed to take care of any pinging. However, I have only worked on stock engines that are probably fairly tolerant of ignition timing.

Yes, that is a good choice Fred. I'll probably bump my scale up to 7° again. I decreased from 7° and at the same time that I screwed the vacuum brake in a half turn. My intent is to go up to 7° and then adjust only the vacuum brake if I still get pinging

Is this the engine the distributor is mounted on? My memory is your engine is a bit "turned up" compared to mine, which may make things a bit more sensitive to timing.
Click to expand...

Yes, that is my 59AB engine with these specs:
- 268 CI 59A block
- 4" Merc crank
- 0.400 Offenhauser heads
- Isky Max 1 cam
- Dual Stromberg 97s


Glenn
 
According to the big spreadsheet of compression ratios your engine is over 9:1, and if no relief over 9.5:1. Definitely expect it to be more sensitive to spark timing than the stockers I work with.
 
I had the heads off a flathead, so I went ahead and made a timing pointer out of a 1/4" stainless steel bolt, cut the head off of it and ground it to a point and threaded it into the timing cover so that point of it just came up to the pulley. Then I stuck a dial indicator on the top of the #1 piston and rotated the piston to TDC and marked crankshaft pulley with a felt marker. Then rotated the engine in the "opposite" direction and marked the pulley again. Right in between the two marks was the exact TDC. I took a file I put a little groove into the pulley for TDC. I had set the distributer points exactly like they showed in a 1948 Mitchells Motor Manual, using go and no-go feeler gauges and I set the timing at 4 degrees. Then mounted the distributor and it fired right up. Just for fun I wanted to check the timing with an adjustable timing light since I now had a timing pointer. It measured 0 TDC so it was off 4 degrees and I corrected it. But for only being 4 degrees off initially after setting it up on the bench like the book showed was pretty amazing. If you do have the heads off, make yourself a timing pointer so you can use a timing light.
 
Yes, it's good to have an accurate TDC mark. From my post #8


"I had a few years ago found TDC with the zip tie method, made a pointer and marked the belt pulley inside and outside the groove.
This picture shows the pulley at 180°. I notched the pulley and painted marks for TDC."
 
38 coupe said:
These days I typically advance a front mount distributor several notches more than factory spec and find the engine runs better. I suspect that is due to a bit of wear in both the front slot of the cam and in the drive tang of the distributor.

Today's fuel with octane higher than the 1930s, with a bit of alcohol in it, probably matters too.
Click to expand...


I have a pertronix solid state in my crab distributor and I want to adjust the timing plate - that little plate with the notches. I am having a heck of a time finding out which direction adjusts it how. If I'm facing the engine, which way do I push the screw and plate to advance or retard? Left or right? (Or up or down, depending on how you think of it.)
 
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