Timing advance plate - Crab Distributor

[glennpm]

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.

[Bored&Stroked]

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.

[glennpm]

Thanks B&S.


I have a TDC marks and a pointer and plan to check tomorrow.


Glenn

[38 coupe]

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.

[glennpm]

Stay tuned Fred :-)

[38 coupe]

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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.

[Bored&Stroked]

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).

[glennpm]

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.



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.






This is the current adjustment plate position of 6° BTDC




Drum roll ...





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

[glennpm]

Oh, this is with regular ethanol gas, 87 octane.

[38 coupe]

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.

[Mart]

Hi Glen. Is that the wide land side or the narrow land side?
I couldn't find the pics in the other thread.

[glennpm]

Originally Posted by 38 coupe

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.

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

[glennpm]

Originally Posted by Mart

Hi Glen. Is that the wide land side or the narrow land side?
I couldn't find the pics in the other thread.

Hi Mart,


I edited the photo in my post above for clarification and fix the "3/8" bolt" error.

[Bored&Stroked]

Nice looking engine Glen - I bet it runs really well!

[glennpm]

Originally Posted by Bored&Stroked

Nice looking engine Glen - I bet it runs really well!

Thanks and it does! LZ gears and Columbia make it a pleasure.

[38 coupe]

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.

[glennpm]

Yes, it is 9.33 with factory relief.

[Flathead Fever]

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.

[glennpm]

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."