Timing

[WPVT]

I had some problems with engine noise at higher RPM's, so I retarded the spark, and now it runs so much better and quieter. I tried retarding it more and retarding it less, and found what seemed to be the sweet spot. Now it's comfortable at 50 mph. 

I was curious, so I checked the timing with a light , and it was retarded 10 degrees at idle (400 rpm). So I put it back to 0 degrees at idle, as specified in the manual. Doing that gives me about 10 degrees advance at 1500 rpm. At 2000 rpm I can no longer see any marks, so it's well advanced at that speed. 

Vacuum advance is new, and centrifugal advance seems like it's working properly.  

 

I haven't road tested it yet, but I suspect I will be back where I was, with a very noisy engine at 40 mph. 

Why, do you suppose, would my engine run so much better with the spark retarded ? Compression is good, and it runs smoothly. No carbon on the plugs....steady vacuum at 18 or so. 

[kencombs]

It is possible the crank pulley and timing pointer are mismatched.   I don't know the history of your engine, but crank pulleys,timing covers and pointers often get changed during engine swaps.   They are not all the same over the years, yet the engine basics interchange.  Long way to say that I would first verify my TDC mark on the pulley.  remove the little pipe plug over #6 and use a piece of wire to find TDC accurately.  You can make new marks on the pulley if needed.

[WPVT]

5 hours ago, kencombs said:

It is possible the crank pulley and timing pointer are mismatched.   I don't know the history of your engine, but crank pulleys,timing covers and pointers often get changed during engine swaps.   They are not all the same over the years, yet the engine basics interchange.  Long way to say that I would first verify my TDC mark on the pulley.  remove the little pipe plug over #6 and use a piece of wire to find TDC accurately.  You can make new marks on the pulley if needed.

Thanks. I should have mentioned  that I did that a while back. The engine is original and un-tampered with.

[Merle Coggins]

Do yo have a timing light that can adjust to measure the advance? I suspect that one of your mechanical advance weight springs is bad and you’re getting way too much advance over 2000 RPM. 

[Plymouthy Adams]

finding TDC with the aid of a wire in the small hole at the #6 slug is not going to cut it for absolute TDC...the wire is merely a ballpark only.  The eye cannot see or detect with accuracy the small change in piston position over the degree changes before and after TDC.  You will need a degree wheel and a piston stop device to measure the piston location if you wish to set the pointer and pulley marks to coincide and reflect TDC.  

[kencombs]

37 minutes ago, Plymouthy Adams said:

finding TDC with the aid of a wire in the small hole at the #6 slug is not going to cut it for absolute TDC...the wire is merely a ballpark only.  The eye cannot see or detect with accuracy the small change in piston position over the degree changes before and after TDC.  You will need a degree wheel and a piston stop device to measure the piston location if you wish to set the pointer and pulley marks to coincide and reflect TDC.  

True, but when looking for mismatched parts, one doesn't need to be concerned with small differences, just be close enough to see if you have a left side pulley with a right side pointer

[Plymouthy Adams]

I agree, if you only wish to be in the ball park, then, batter up!   Watch for the curve balls.....?

[chrysler1941]

Are you sure it's retarded and not advanced. Tell us where your pointer is.

 

[WPVT]

47 minutes ago, chrysler1941 said:

Are you sure it's retarded and not advanced. Tell us where your pointer is.

 

I think I have this one right. It's as shown in your diagram, but more like 10 degrees, not 2.

[WPVT]

3 hours ago, Merle Coggins said:

Do yo have a timing light that can adjust to measure the advance? I suspect that one of your mechanical advance weight springs is bad and you’re getting way too much advance over 2000 RPM. 

My timing light is an older, non-induction type. I'm open to suggestions for a good quality up-to-date replacement.

An over-reacting centrifugal would possibly give me the effect I'm seeing. 

How much should the centrifugal mechanism advance the spark at 2000 rpm ? As I stated in my original post, If I set the timing to TDC at 400 rpm, it is advanced 10 degrees at 1500 rpm and at 2000 rpm it was well past the area with marks, far enough that I couldn't even estimate.  Isn't there a mechanical limit to how far it could advance the spark, even with bad springs ?  

If it is indeed a problem with the centrifugal advance, I could pull the distributor and have it checked and repaired, or.... just compensate by retarding the spark the way I did before. Even with the spark retarded 10 degrees at 400 rpm, it idled just fine. Bad idea ?

[Merle Coggins]

I don’t know if the specs changed for your C1B, but here is a look at the specs for a B-series truck. It looks like 21 degrees total. 10 degrees mechanical and 11 with vacuum. You might be able to find an advancing timing light hanging in the tool isle at your local parts store. They’re pretty common. It may require a 12v supply. If your truck is still 6v you could use any 12v battery  for a power source. 

 

[T120]

Excuse me for mentioning, Keep in mind the 1300 distributor RPM in Merle's figures represents engine RPM at 2600 RPM.

Edited September 10, 2021 by T120
Added, 1300

[WPVT]

If I have the truck in the shop and rev it up to 2000 rpm, am I seeing the full effect of both the centrifugal and the vacuum advance  when I am using the timing  light ? I'm not sure if 2000 rpm and no load would be a maximum vacuum condition or not.

Or should I be disconnecting the vacuum in order to isolate and test the centrifugal advance by itself ?  

[T120]

You should be reading the addition of the vacuum advance,( vacuum advance working correctly ), plus the automatic advance at a steady engine RPM.  In Merle's figures this would equal 21 deg. advance total at 2600 engine RPM for the Auto-Lite IAP-4101-1.

[WPVT]

1 hour ago, T120 said:

You should be reading the addition of the vacuum advance,( vacuum advance working correctly ), plus the automatic advance at a steady engine RPM.  In Merle's figures this would equal 21 deg. advance total at 2600 engine RPM for the Auto-Lite IAP-4101-1.

Thanks. My question is whether running the engine in the shop at 2600 rpm should cause the vacuum advance to be fully activated, assuming it is working properly and there are no vacuum leaks.   

Edited September 11, 2021 by WPVT

[greg g]

With steady state throttle position with basically no load, intake vacuum should be very close to idle vacuum 19 to 21 inches.

Edited September 11, 2021 by greg g

[kencombs]

As mentioned, vacuum with no load and most any speed will be high,  so the vacuum advance will be at max. 

 

For your testing purposes, I'd recommend disconnecting and plugging the vacuum line to isolate the two advance mechanisms. 

 

Keep in mind that at any engine speed under load,  the vacuum will drop.  How much is directly proportionate to the throttle opening and load.

 

Driving with a vacuum gauge in the cab will help visualize what is happening with the vacuum advance in actual use.  Helps develop good driving habits too once you see what happens to the vacuum under acceleration, and note that low intake vacuum is what opens the big jets in the carb.

[Tooljunkie]

I had my distributor apart, it was worn, and the weights were flopping around in oversize holes. No consistency whatsoever. The vacuum pot was leaking as well. 
timing after all the repairs was much more stable and easy to get it close. 
a friend online has a source for rebuilt vacuum canisters, got one from him. And a donor distributor gave me what i needed to replace worn out pieces. 
only takes a minute to see if mechanical is working/returning to base timing. Pull cap and turn rotor a couple degrees, should spring back. If you can turn rotor and let it go and it stays there, there’s wear. 

[greg g]

Can you post the source of the vacuum cans?  I imagine they need to be ordered by dist number.

[T120]

14 hours ago, WPVT said:

Thanks. My question is whether running the engine in the shop at 2600 rpm should cause the vacuum advance to be fully activated, assuming it is working properly and there are no vacuum leaks.   

Yes,if the  vacuum advance unit is working properly it will max out at 14 inches of mercury, (vacuum as presented to the vacuum advance unit = 11 degrees advance)

 The centrifugal advance will max out at 1300 distributor RPM (10 degrees advance).

These figures are for the distributor listed by Merle.

 Advance curves can be plotted for both the centrifugal and vacuum advance. If you have the number of your distributor,it's possible they may be available. ?

 

 

Edited September 11, 2021 by T120
added =

[JBNeal]

On 9/10/2021 at 10:53 AM, WPVT said:

... 

If it is indeed a problem with the centrifugal advance, I could pull the distributor and have it checked and repaired, or.... just compensate by retarding the spark the way I did before. Even with the spark retarded 10 degrees at 400 rpm, it idled just fine. Bad idea ?

additional information - Burton L Norton distributor repair

 

when I talked to BLN, they told me about the limitations of testing a distributor in an engine, and how they used a Sun testing machine to accurately refurbish distributors.  On one of my distributors that I sent them on a truck that had been parked for decades, the springs had oxidized and no longer had the same K-value.  They replaced springs with new, cleaned up and lubricated the mechanical advance, replaced the vacuum advance, etc and adjusted to specs...those flatheads came alive with that investment.

[Tooljunkie]

6 hours ago, greg g said:

Can you post the source of the vacuum cans?  I imagine they need to be ordered by dist number.

Shoot an e-mail off to halifaxhops@hotmail.com

Have your distributor number handy, and a photo of the arm that connects to breaker plate. He specializes in mopar distributors. 
mention i sent you. 

[WPVT]

 

I set the timing using a vacuum gauge, adjusting it until I got the highest vacuum reading at idle speed (500 rpm). I rotated the distributor until I got a steady 20Hg on the gauge. That seemed to be about maximum. Then I checked the timing with a light. It was about 8 degrees before TDC, read from the crank pulley.  At this setting, the engine idles fine but is very noisy above 40 mph. 

 

 With the vacuum advance disconnected, at 2600 rpm, the centrifugal adds about what it should, 10-15 degrees. I'm doing some estimating because it's beyond the marks, but it seems in the ballpark. 

 

So with the timing set by the vacuum method, at about 8 degrees BTDC, the truck engine is very noisy above 40 mph. I verified that the centrifugal advance is working properly. I retarded the timing to 8 degrees after TDC, and it runs great, like a zippy old 6 cylinder, no problem at 50-55 mph.

 

I suppose it's possible the vacuum advance could be advancing the timing way too much, but I doubt it's even mechanically capable of advancing it enough to create the situation I'm experiencing. 

 

Whatever the reason, 8 degrees after TDC seems to do the trick, with no ill side effects.  I wish I knew why. 

 

 

 

 

Edited September 12, 2021 by WPVT

[WPVT]

One final thought. The vacuum advance and the centrifugal advance seem to be working more or less properly, yet the truck engine runs much quieter at 40-50 mph if my initial timing is set at 8 degrees after TDC, which is quite retarded. 

Could it be that by retarding the timing I am simply masking the sound of a mechanically worn engine ?  I have good oil pressure, decent compression, etc., but it's too noisy (clattering) at 40 mph and above unless I keep the spark retarded.

[wallytoo]

if it runs better the way you have it set, i wouldn’t worry too mucn about it.  as long as you have adequate throttle response, and not a lot of black smoke (unburned fuel) out the tailpipe, run it.