Model A Ford - Precision Timing and Finding Top Dead Center
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- เผยแพร่เมื่อ 16 ก.ค. 2024
- This video teaches two methods for setting spark timing on the Ford Model A to arbitrary values, e.g., 19° before TDC or 5° after TDC. It also teaches some techniques for finding the top dead center point as accurately as possible without removing the cylinder head.
The first method involves calculating a length of arc around the crankshaft pulley and then offsetting the crankshaft from TDC by that amount. The second method involves calculating a length of arc around the distributor cam and then rotating the cam by that amount.
Update (thanks RK): If your car has the original pop-out ignition switch (and I mean a true original), when setting the timing using a multimeter as shown at 21:16, you must set the ignition switch to on. When in the off position, the original pop-out connects the point arm to ground, which makes the multimeter method not work. This means you need to work fast - don't leave the points closed with the key on for more than about 30 seconds.
I've heard two critiques of this video. First, "the vast majority of Model A owners don't need to know how to do this." That is correct, but it is a question that comes up frequently, so here is the tutorial.
Second, "this video is way too long, no one will watch this." I like to be comprehensive. Use the chapter headings below to skip to the part that interests you. I won't be offended.
Chapter headings
0:00 Titles and a silly animation I made to fill time
0:40 Review of Model A timing basics
3:07 Overview of two precision timing methods
7:36 Finding top dead center as accurately as possible
16:31 Step by step method to set timing by rotating the crankshaft
21:16 Finding the spot where the points open using a multimeter
25:40 Step by step method to set timing by rotating the distributor cam
41:45 Some caveats about how much precision is really feasible
43:25 Verifying your results with a timing light
44:57 Measuring ATDC timing indirectly
46:58 Closing thoughts - ยานยนต์และพาหนะ
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That's the most informative video for precision timing a Model A I have watched yet!
Considering the timing is controlled by a lever it doesn't have to be precise, just close. With the timing lever all the way up and the plate all the way retarded, set the #1 piston to what you consider 12*-15* ATDC. Then adjust the points cam to when the points just start to open.
What needs to be precise for optimal performance is is the points gap, best measured and set with a dwell meter to 52*. One degree of dwell = one degree of timing. I never tried one on a positive ground car before but I'm sure there's some way to do it. Starter speed is enough to set them just recheck after it's run a bit.
I have a lot of rotational slop in the point cam. LIke 3/4 of an inch. When I stop the engine, it is usually in the middle of that slop, not at one end or another as folks say.
I am getting a lot of coughing and vback fire as I press on the gas peddle.
My first thought is, you might have a centrifugal advance device installed in the valve chamber. Have you had the car a long time? Have you had the valve cover off?
You always know you're in for a thorough in-depth explanation of the topic when it's alexiskai doing the upload!
I have a question - maybe you know the answer: The instructions that come with the insert main bearing kit states that
"29° of advance is the point of no return". Anything more would result in bearing damage, they say.
Does that mean full advance is no longer allowed? Sure, I can set the distributor to stop at 29°, but in my experience, that'd make it a sluggish gas-guzzler at higher speeds.
Or do they perhaps mean 29° of distributor advancement (which would result in 58° crank advance which I wouldn't want my engine to experience anyways)?
Best Wishes
Adrian
The short answer is, yes, full advance is not recommended and hasn't been recommended for decades. If you've been habitually running the car on 40° spark advance, that might be one reason your babbitt bearings broke down in the first place.
29-30°, or about 3/4 advance on the quadrant, is the total timing recommended for the stock Model A engine and cylinder head by most experts I've seen. The Model B distributor uses 32-34° total timing. The Phillips/Nu-Rex automatic advance uses 30° total timing.
Although the Model A manual states that the spark advance should be placed all the way at the bottom of the quadrant for "high speeds," it's unclear what that means, and with modern fuel there's no reason to think we need to stick with that particular directive.
You have several options for setting a 29° total timing with the stock distributor. You can make a little clamp that fits on the quadrant at the proper spot. You can follow the instructions in this video and set your initial timing at 10° ATDC, which would shift the advance curve to place the bottom of the quadrant at roughly 29° BTDC. Or you can modify the distributor body to prevent the upper plate rotating more than 14.5°. In any of these scenarios, you would ideally want to verify your total timing with a timing light.
By "thorough in-depth" I assume you mean "incredibly long and pedantic and usually involving math," which is correct. That is my brand and I'm sticking with it.
@@alexiskai Very important intel, I'm glad we talked about it!
In fact, I had set my ignition to fire one notch after TDC (that ought to be 3 degrees if memory serves me correctly), which seemed to make the engine alot happier at higher speeds.
It would of course also mean full advance would be 37° before TDC, which indeed would explain the bearing fatigue.
You, sir, just saved me from possibly blowing out my fresh insert bearings.
Thanks awfully!
@@alexiskai But that's the thing I love. Most people would end at "the faster you go, the more you advance" - but I already knew that. You mention all the little things that are valuable to know about, especially when driving the car more than for the annual ice cream run.
@@AstraWerke Your description is broadly accurate, although in general there isn't a strict link between notches on the quadrant and degrees of timing. The linkage between the hand control and the upper plate goes through several steps, which all incorporate some degree of flex and spring. The axis of upper plate rotation is offset from the axis of control rod rotation, and the levers are a different length. This means that a notch at the top of the travel can translate to a different number of degrees of timing than a notch in the middle or at the bottom. And of course every car is different, etc.
Glad I was able to help you out, I've enjoyed your videos immensely.
Muy bueno!
The original Ford spec was design when using the pin method on a new engine would be set 5 deg. Retarded (ATDC). This was for ease of starting with starter and safe method hand starting. Also the advanced would be 10 deg. for e every 1000 RPM or 30 Deg. at 3000 RPM. I have noticed that each notch on the advance lever is approximately 4 degrees movement. My old Sanp On timing light does read retarded. Hope this helps someone. On another note if you use a Mellory distributor you can set the total advance and curve and have a preferred base timing degree. Hope this helps someone
You're being too critical. Get it close and move the lever while driving to set the timing. That accurate of TDC is only needed if you are running distributor with a built in advance. If you are just toss the timing light on it - rev it to max advance RPM and set it with a timing light.
Nice, is your wrench a breaker bar? What socket size and depth will fit the crankshaft nut with its hooks for the original crank handle? 6 point, 12 point, deep or not?
On my car, the ratchet nut was all torn up, so I removed it and installed a standard bolt. The bolt has a 15/16" head, which is small enough for me to get a breaker bar and socket onto it inside the engine bay as you see in the video. If you still have the ratchet nut, you have two choices. First, you can buy a crank wrench from the vendors or at a swap meet. This is only way to adjust the ratchet nut from inside the engine bay. Second, you can buy a 1-3/8" socket (some aftermarket ratchet nuts are 1-1/4", so check first) and a 6" extension. You put the socket on the ratchet nut and then you run the extension through the crank hole in the radiator shell. Then you put a breaker bar or socket wrench on that and turn it from outside the engine bay. It works fine and actually is more convenient for this operation because the fan doesn't get in the way.
Regarding which socket to get, either 6-point or 12-point will work, but 1-3/8" sockets can be a pain to find. This one *might* work? www.amazon.com/ARES-14008-36mm-Profile-Filter-Socket/dp/B09QVCHRYP/
This is pretty funny
I noticed you're running a Marvel-Schleber (Sears All-State, Johnson 2405) carburetor. I guess you like them? Seems some like them others despise them?
Some say they're a fuel guzzler. Any thoughts or opinions?
I've found a source for parts...Renners Corner
I haven't developed carb repair skills/tools yet, and I had persistent trouble with my Zeniths, so I opted for a Marvel rebuilt by the late Jim Bullock. It's had one problem, which is that the GAV driver (which consists of two spot-welded pieces) came apart. Bought a replacement from Dave Renner and it's been trouble-free ever since. Always starts, never stalls, just solid. Idles down to 300 rpm. I don't track my mileage, so it certainly is possible that it's not as efficient as the Zeniths, but fuel is a small part of my budget. On my project car I'm going with a Stromberg 81, so it's going to be awhile if ever before I get around to learning the ins and outs of the Zeniths.
You don’t need to use all of that complication to establish TDC.
1. Just set points at widest tolerance and use your cam TDC dimple for mechanical engine TDC it is more accurate than guessing tdc from piston position.
2. Set advance lever where you want TDC and adjust point opening there.
Done
This isn’t a space shuttle adjustment you just need to be able to set the timing to TDC or after for start.
After the engine is running you are adjusting timing by seat of the pants anyway.
After initial setup point wear slowly retards timing until you readjust the point gap.
There is no precision in the adjustable part of the system
You are
Measuring with a micrometer
Marking with a grease pencil
Cutting with an ax
That method does work well for most people. This method is for the small percentage who need a way to repeatedly time an engine to a specific degree value. If you don't need to do that, I agree - use the timing gear dimple and then set your spark lever as desired.
I don't agree that the timing gear dimple is more accurate than taking visual readings and averaging them. You're relying on the gear manufacturer to place the dimple with a tolerance of 1mm or less, and there's no way to be sure that your pin dropped into the center of the dimple rather than slightly off to the side. Taking visual readings ensures that you're measuring the position of the piston itself.
Where did you get your plug wires?
I made them, using Model T parts from Snyder's. They carry something very similar, pre-made, as part #T-5029-BS. However those wires are a lot longer. I bought the wire and the brass connectors separately, cut the wire to the length I needed for each plug, and used a large pair of pliers to bend and crimp the connectors.
Thank you@@alexiskai
I'm trying to time my engine and having no luck. When I find top dead center and adjust my distributor cam till the points just begin to open my rotor is 1/4 inch from pointing to the post in the cap, Hope this makes sense. I know it must be something simple but I can't figure it out,
It sounds like your points are not in the stock position. Can you confirm: is the upper plate fully retarded (arm against the passenger side of the gap)? Are you using the V8 points? Are you using the Nu-Rex upper plate?
@@alexiskai Thanks for the fast reply, yes the upper plate is fully against the pass side of the cap. there original style points, and no way to move them. I'm pulling my hair out with this one.
@@oldknuckleheademmor4791 That’s weird - I mean there aren’t many elements involved here. Upper plate, points, cam, and rotor. Gotta be one of those. What caused you to need to re-time it?
@@alexiskai I just got this car and figured I'd time it before trying to start it. When it is at top dead center the rotor is to the left of the contact point on the cap, Its like the points need to move counter clock wise but there non adjustable. Thanks again.
@@oldknuckleheademmor4791 Yeah this one's gonna be hard to troubleshoot without photos. If you want to continue, I suggest starting a thread on fordbarn.com or vintagefordforum.com so you can add photos. The folks on those forums will have you sorted out in a jiffy.
why work in mm?
I guess because the math is easier to do in your head, and with digital calipers you can get the readout in any units you want.
No way is this need the Model A runs so good without all this B-sh@t
That's correct, this level of precision is absolutely unnecessary for anyone running their Model A in a stock configuration.
You lost me!
Sorry to hear that! Let me know where you got lost.