Timing centrifugal advance

M

meteorgray

Member
I have a new to me 31 which has a high compression head and a centrifugal
advance distributor. It starts and runs just fine but sometimes at speed I am
getting pre ignition. What is the best way to set the timing?
 
Who is the maker of the distributor? Do you have a timing degree indicator, like the one Nu-Rex makes, installed?
 
If you are getting pre-ignition, retard it a bit, maybe 5 degrees.

Each engine is slightly different so there is no magic number. It is a matter of experimentation. You will need a degree wheel on the front pulley and an indicator arm and a timing light. First read what advance you have at a high idle, about 1,000 rpm. Then adjusting the timing for about 5 degrees less advance and go for a drive. If you do not have pre-ignition but the performance is the same then you are finished. If the performance is down a little then advance the timing about 2 degrees and go for another drive. Keep experimenting until you are satisfied with the performance. The timing will be different at different rpm's so try to read the advance at the same rpm. Use the hand throttle at the same place each time.
 
I don't know the maker of the distributor. I did install a timing indicator for the crank.
Just looking for information from you guys so I know what to do. Nkaminar has some
good advice, so I will start there when I get a chance. Thanks
 
nkaminar said:
If you are getting pre-ignition, retard it a bit, maybe 5 degrees.

Each engine is slightly different so there is no magic number. It is a matter of experimentation. You will need a degree wheel on the front pulley and an indicator arm and a timing light. . . .
Click to expand...

nkaminar,

If you don’t have “. . . a degree wheel on the front pulley and an indicator arm and a timing light . . .” is it possible to set the timing at TDC by moving the Spark advance Lever down 3 or 4 clicks and then moving the Spark Advance lever up to the top when running the car?

Not my idea, but I think I read in another thread that this would work when you have a centrifugal advance and a high compression head.

David Serrano
 
Sure, anything is possible. Give it a try and then go for a drive to see if it worked. The proof is in the pudding. A high compression head needs a lot less advance than the original head.
 
Most Mod A motors with a high comp head don't need much advance.
The trick is to limit the amount of advance in the distributor.
I start with max 20 degrees (crank) and set initial timing to TDC.
The curve is not so crucial but you need 0 advance at 600 rpm and full in about 1300-1500 rpm. This means the springs are probably not what came in the dist.

As someone mentioned, you can back the timing off (retard) and test. I have a coupe that likes about 3 degrees retarded to start and runs about 18 degrees total.

YMMV, John
 
Yes and no
You have 50cu in per cylinder and if you are making hp you will feel the power pulse

All of the engine combinations are different and require different timing
The more efficient the chamber and cr the less timing required to perform
I have a Miller that likes 50degrees total advance and the race car that makes more than double the hp only needs 26 degrees

I have ridden in cars with too much advance and it is obvious but some drivers can't tell

A 4 cyl engine will have an inherent disadvantage in vibration from the offset acceleration of the pistons and the stroke length
Add into that a less than rigid crankshaft without counterweights and you get the idea

John
 
Richard,

The Burtz Engine makes little to no difference, it is just an air pump. The ports as I understand have been improved some but not sure about flow and cylinder filling in the shadows (areas that no flow occurs or fuel reaches). Again, this is dependent on the chamber shape.

The Snyders head is probably a Tod Buttermore casting. More than likely a shallow "B" chamber or a Winfield style.

All this said, starting point should be about 22-25° max advance.

I would make changes after driving and do not be surprised to find it runs more efficiently by retarding a couple degrees.

J
 
That is the beauty of manual advance. Mine is limited to 28 deg, but I back off a bit at 55 on level ground, because it sounds better.
 
Bruce has brought up a good point. The Model A was produced with a manual spark advance via the lever on the steering wheel. The new owner was taught how to control the timing for various conditions such as going up a grade or cruising down a level road at a moderate speed. The operator was the engine management computer. The automatic advance does not control the timing as well as an experienced operator.
 
Question : with an auto timing advance dizzy and you get spark knocking/preignition when it happens how do you stop it ? With a manual advance you just retard a couple of clicks and continue on your way up the hill, passing , pulling through muddy roads . Also sometimes I will open the GAV a quarter turn .
 
UPDATE, Alexiskai I believe it is a Nurex distributor. Nkaminar I retarded the advance a
few degrees and it seemed fine after a short ride. I will give it a longer run when I have
time. Thanks to all.
 
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