As a newbie let me ask this question. About 2 months ago I set my timing according to Purdy Swoft method. And the car as far as I can tell seems to be running fine. And since I feel I set it correctly I am a bit reluctant to tinker with it. But I do notice these things. I can start it at full retard or full advance and I have no kickback. If I stay at full retard and increase the rpm it will not increase much. But after I come off of full retard a notch or two very little changes after that. In other words I am thinking my timing is a little retarded and I am not getting full benefit of full advance. Does this make sense to anybody.
Advance curve for rookies
- Thread starter BILL WILLIAMSON
- Start date
ctlikon0712
Well-known member
Let me be clear, I was not saying that everyone should run high octane gas in their model A. However if you are running a high compression head (say over 6.1) and you experience knock, a higher octane will stop the knock, allow you to run more timing and the engine will run slightly cooler. Will you make as much power? No, except under the situation where your engine knocked before, you will be able to run with more advance up that hill or loaded down. It is a tradeoff. I wouldn't expect better gas mileage either.
Pat martone--std head # A-6050A has 76 psi,4.2 CR. So-called "police head"#A-6050B with large B on top has 110 psi,5.2 CR. Model B head with 3-bolt water pump#B-6050 has 90 psi,4.6 CR.On my B engine with 5.9 CR,I never advance more than 3/4 down the quadrant and always retard a bit going up hills & never give more throttle than needed on hills.In very hot weather you have to retard it a bit more.On a B engine,I like to use the A dist as I have no problem adj the timing manually.
Purdy Swoft
Well-known member
My guess is, if the distributor is in good condition, it could be one of four or five things. You don't actually have it set the way that I describe, You probably still have clockwise backlash, could be not enough gap at the points ( I set at .022), You are not getting full advance in the window of the distributor cap body, (may need to loosen and rotate the steering column tube so that the spark control linkage will have full movement, if you are running 2 tooth steering column). The cam gear could be off a tooth or two in connection with the crankshaft, Or it could just be improper use of the spark lever.
If all else is good and you actually have the timing as I describe you should have the most advance that you could get by with at full advance of the spark lever. If the engine is stone cold, you may sometimes be able to crank the engine with the spark lever fully advanced, but not after the least bit of \warm up. Crank the engine with the spark fully retarded. when the engine cranks, pull the spark all the way down, or it may go dead. When the engine warms a bit, it will idle with the spark fully retarded with a chick ah lunk sound, but probably won't idle with full retard until slightly warming the engine.. After very slight warm up the engine will slowly rev, but very slowly... When the spark is fully advanced the engine should have crisp throttle responce... I wouldn't really expect any difference in the way the engine responds at full retard , or two or three notches down the quadrant, the response will be very slow.
When I got my first model A, in 1960 there was a lot of people still alive that had driven the model A as regular transportation in years past. The general consensus was that you crank the model A with the spark up and drive it with the spark down. I have never had a problem operating my model A's or old Harleys (that I use to have) in this manner. I still have the model A that I got in the spring of 1960 and it is still running the original standard size babbits that came from the factory when it was new.
None of this is to say that the spark should never be used when driving. If you like to slowly chick ah lunk about on trails, tlke I do with my sept 29, you will notice after some experience that the engine will run better and pull hills without lugging and bucking, with the spark slightly retarded. This is the type of roads that had to be driven when the model A was new. The owners manual describes such situations as sand beds and listening for timing knock and slightly retarding the spark on hills, because those were the conditions of the day and the engine should never be lugged. Sometimes when takeing off you may experience chatter (bucking). In such cases, slightly retarding the spark will relieve the chatter and as you accelerate you will slowly advance the spark while building speed.
With todays good roads, higher octane fuel and faster driving, very little use of the spark lever is needed. Creepy take offs and really slow speeds can easily get you run over in this day and time. With faster speeds and more vehicles on the main roads (big trucks), I try to drive 50 mph for my own safety and not to be a problem for other people on the road. Fifty mph seems fast enough but if more speed is needed to get out of the way, a properly tuned model A should run faster, but only briefly, in my case.
Some like playing with the spark so much that they probably wear the notches on the quadrant smooth in a single driving season, as another guy said on this thread. I have never counted notches while useing the spark. It is more less an aquired feel that you need to develope with experience.What you are trying to avoid is lugging (bucking, mostly in high gear) and timing knock. Common sense is most important!!!! With some of the warnings about running at speed with full advance go way to far and scare the hell out of the inexperienced. I have run at speed with full advance at speed for over fifty years with NO problems. People that run their cars with the spark retarded, usually can't be helped and they usually wonder why they are running hot,and why the exhaust manifold is turning red.
I wouldn't have went this far with my rambling, but you asked and I believe that this is the sort of thing that Bill was refering to when he started this thread!!!
Last edited:
Purdy I think you did answer my question. I was thinking that if I went to full advance at idle or slow speed I would get some kind of knock or problem and after it is warm I do not have that. I do have the chunk lunk at idle and retard and so again I think I am ok. The engine is running fine and I have plenty of power so I will leave well enough alone. I think some of us just read and want to tinker to hopefully make ours perfect. Thanks.
KR500
Senior Member
I agree with Bill Williamson in that explaining at 500 rpm idle it takes so many milliseconds to fire and cook a charge of air and gasoline. Well at 1000 rpm given it still takes so many milliseconds took fire and cook a charge of gasoline you had better fire and cook it sooner, like before TDC to extract the power. The way it was explained to me many moons ago. The engine extracts the power from the super heating of Nitogen gas in the cylinder of which at least 74% is nitrogen.
Mike V. Florida
Well-known member
And if you go too soon when it fires the expansion of the gasses will try to push the piston the other way causing stress on the bearings, knocking, "kick back".
BILL WILLIAMSON
Well-known member
Absolutely, my man!
Gotta' listen & feel out your machine so's you know when she's runnin' HAPPY!
A lot like keepin' your HONEY happy, listen a lot, don't over do it, and say "YES DEAR"
----often!Bill W.
SAJ
Well-known member
Great thread. Just to add a little more without getting too complicated. The burn has to start at the right time relative to where the piston is, as stated. But it also has to be a smooth burn that travels throughout the mixture and expands gradually as the piston moves downwards and the volume above it in the cylinder increases. If the spark is too advanced before TDC, the pressure and heat build up will be so great, as the expansion tries to force the piston back down, in the direction it is coming from, that the mixture reaches its “auto ignition point”. At this temperature and pressure it becomes a detonation, with all parts igniting from the heat and pressure at once, instead of a smoothly advancing flame front occurring and moving through the mixture to points remote from the spark plug. This gives serious spark knock and will destroy bearings, pistons and other components which are not built strong enough in a petrol engine to resist these instantaneously high forces.
Diesels work like this, so are built far stronger, heavier (and slower revving). No spark plug, just compression ignition like the petrol detonation just described..
Detonation knock can be initiated by too much spark advance, glowing carbon in the cylinder, weak mixtures, red hot valves due to running very retarded ( causing too early ignition from not enough advance!), poor (low octane) fuel and many other things, not necessarily applying to a Model A.
So definitely do not persist with an engine that pings or knocks – especially a higher compression one.
I have a Snyder 5.5 to 1 head and it will not take more than 29 Degrees advance on hills, before making really loud detonation noises. Extra power cannot be felt with more advance, so I mechanically limited the total advance to 29 deg. with my lever right down, in case other people drive it and over advance it.
This is a simplified version of a complicated subject and I apologise to combustion engineers for taking a few liberties in my description!.
Regards
SAJ in NZ
Diesels work like this, so are built far stronger, heavier (and slower revving). No spark plug, just compression ignition like the petrol detonation just described..
Detonation knock can be initiated by too much spark advance, glowing carbon in the cylinder, weak mixtures, red hot valves due to running very retarded ( causing too early ignition from not enough advance!), poor (low octane) fuel and many other things, not necessarily applying to a Model A.
So definitely do not persist with an engine that pings or knocks – especially a higher compression one.
I have a Snyder 5.5 to 1 head and it will not take more than 29 Degrees advance on hills, before making really loud detonation noises. Extra power cannot be felt with more advance, so I mechanically limited the total advance to 29 deg. with my lever right down, in case other people drive it and over advance it.
This is a simplified version of a complicated subject and I apologise to combustion engineers for taking a few liberties in my description!.
Regards
SAJ in NZ
Last edited:
lindy williams
Senior Member
This is going to be a daunting task and may not satisy anyone no matter how well done. How ever, any discussion for rookies should emphasize the dangers of over advancing the ignition. (beyond 28-30 degrees) while under a load, especially with a higher compression head. Some engine rebuilders are now giving warnings to this effect with their rebuilds. (Rich Falluca, Antique engine rebuilding, Skokie, IL)
About 28 degrees:
1. I know about a guy with an inserted engine who set it up with 32 degrees advance (ONLY 4 degrees over the recommended 28 degree advance and 8 degrees less than Model A full advance). Head was a police head at 5.2 as I remember.
This engine even had full pressure oil to rods and mains. But none the less the ROD bearings were pounded to the point of many small cracks in the surfaces and were loose.
This was a run from California to Oregon as I remember. He was fighting a strong head wind for most of the trip and with all the wind noise could not hear the knocking.
Rich at AER said max advance should be 28 and also said that 32 was too much when he was asked for advice as to what caused the problem.
2. Checkout the dyno pulls on the various websites, Stipe, Kelley, PIRANIOS etc. ... one thing you will notice is that most if not all dyno pulls limit the advance to 28 degrees. It is right there on the pull charts. Maybe there is a reason that all these folks limit to 28 degrees.
Nu Rex automatic advance distributor is limited to 30 degrees.
Now I only have 40,000 miles experience driving Model As since 1962 in similar conditions on daily basis. Head is the one "with the large B" ( also used a Thomas 8.25 and a 7.0 head for a short time but went back to 5.2).
In the 60's there were limited choices when it came to HC heads ... No Brumfield or Snyder heads. And Winfield, Thomas and others were big bucks and rare.
Long hard pulls up grades from 4 % to 7%. The road I drove alot goes from 5000 feet to 8000 feet in 20 miles. Sometimes the head winds coming out of the canyon are as much as 90 miles an hour. This is a strong headwind I would think.
Anyway sorry I caused such a ruckus!!
1. I know about a guy with an inserted engine who set it up with 32 degrees advance (ONLY 4 degrees over the recommended 28 degree advance and 8 degrees less than Model A full advance). Head was a police head at 5.2 as I remember.
This engine even had full pressure oil to rods and mains. But none the less the ROD bearings were pounded to the point of many small cracks in the surfaces and were loose.
This was a run from California to Oregon as I remember. He was fighting a strong head wind for most of the trip and with all the wind noise could not hear the knocking.
Rich at AER said max advance should be 28 and also said that 32 was too much when he was asked for advice as to what caused the problem.
2. Checkout the dyno pulls on the various websites, Stipe, Kelley, PIRANIOS etc. ... one thing you will notice is that most if not all dyno pulls limit the advance to 28 degrees. It is right there on the pull charts. Maybe there is a reason that all these folks limit to 28 degrees.
Nu Rex automatic advance distributor is limited to 30 degrees.
Now I only have 40,000 miles experience driving Model As since 1962 in similar conditions on daily basis. Head is the one "with the large B" ( also used a Thomas 8.25 and a 7.0 head for a short time but went back to 5.2).
In the 60's there were limited choices when it came to HC heads ... No Brumfield or Snyder heads. And Winfield, Thomas and others were big bucks and rare.
Long hard pulls up grades from 4 % to 7%. The road I drove alot goes from 5000 feet to 8000 feet in 20 miles. Sometimes the head winds coming out of the canyon are as much as 90 miles an hour. This is a strong headwind I would think.
Anyway sorry I caused such a ruckus!!
Last edited:
Pat Martone
Senior Member
How do I limit my advance to 28 degrees?
I do not know what lever "position" represents that number?
I have been starting the car with full retard (lever fully-up) and then moving it to about 3/4 down upon engine running, and only use fully-down when cruising on flat open road at 45+ mph. Of course, on inclines I try to make sure I am not lugging and I retard to about one-third to half-way down on the lever.
I assume this is an acceptable operation? (I have a standard head, transmission, and rear gears.)
I do not know what lever "position" represents that number?
I have been starting the car with full retard (lever fully-up) and then moving it to about 3/4 down upon engine running, and only use fully-down when cruising on flat open road at 45+ mph. Of course, on inclines I try to make sure I am not lugging and I retard to about one-third to half-way down on the lever.
I assume this is an acceptable operation? (I have a standard head, transmission, and rear gears.)
Pat,
Full advance is 40 degrees on a stock A. So 3/4 advance is 30 ... 28 is a little less than 3/4. All the notches were worn off my quadrant when I got the car so can not tell you how many clicks that is.
Pat Martone
Senior Member
Thank you, Benson.