TDC -- Top Dead Center -- Timing Pin ???

H

H. L. Chauvin

Well-known member
1. This Model A engine's timing gear's timing pin hole location being off by as much as approximately ten (10) degrees as opposed to a few degrees may be rare; however, this is a report on an engine's no. 1 piston being approximately ten (10) degrees advanced when the timing pin immediately first hits the bottom of the hole in the timing gear.

2. Have installed a new "repro" timing gear, a new "repro" camshaft, combined with an original Ford crankshaft & an original Model A timing cover, the correct positioning of the crankshaft gear to timing gear was verified. (Was told by an experienced engine rebuilder that locations of new "repro" cam shaft pins & new "repro" timing gear pins are not always exact, not to even mention the hole in a new "repro" timing gear often being off.)

3. Just one (1) easy method to find exact TDC is to get a dial indicator with a magnetic base, (under $14.00 at Amazon,com); a 1/2" PVC pipe "plug", (under $1.00 at Hole Depot); a 1" long scrap piece of wood cut round to fit in the open end of the PVC plug; a length of regular metal coat hanger; & the stainless steel timing indicator currently sold on e-bay for $30.00 or the one sold by Model A vendors, or a degree wheel.

4. Tightly fit the wood plug in the PVC pipe plug, drill a hole in the center of the PVC plug & the wood plug a little larger than the diameter of the coat hanger. Pass the coat hanger through the drilled hole -- bend the bottom 90 degrees with a long radius bend to insert in the spark plug hole & rest on the top of No. 1 piston, , & bend the coat hanger top at 90 degrees above the PVC plug with a doubled backed hemmed edge to receive the dial indicator point.

5. Sand bottom circumference of PVC plug to fit snugly in the 7/8" no. 1 piston spark plug hole. After dial & wire gauge is set up, rotate engine until timing pin slips in to find where dial moves from approximately 0 to approximately 70 -- with these (2) piston up & down readings, TDC will occur in the middle, e.g., a dial reading of 35.

6. What caused this suspicion of correct timing?

After setting the timing on this particular engine in the conventional method with the timing pin:

A. Noticed with the timing pin setting, the engine was kicking back now & then while starting with a Model A distributor, with spark handle advanced downwards about 1 or 2 notches.

B. Next, noticed with the timing pin setting that the engine was kicking back every time with a Model B distributor while starting when timing set even at about 12 degrees BTDC.

7. After marking "0" on the crankshaft pulley when at TDC, & using the stainless steel timing indicator, everything appears normal.

8. Timing gear is metal, so may drill correct timing gear hole if oil pan is removed in future.
 
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In a way I guess you were fortunate to have only a minor problem of readjusting ignition timing with just the timing pin hole was incorrectly positioned.
It would have been major problem with incorrect valve timing if the offset lugs were incorrectly located on the gear wheel.
 
A few years ago, I bought on eBay a 18" lighted battery powered flexible fiber optic scope. It's only about 1/4" in diameter and bends easily. I think I paid about twenty five bucks for it. It works great for seeing exact TDC of a piston, looking at valves and seats, and possibly other areas that you may want to look into. (gas tanks). I think many professional mechanics may have them also.
 
Hi Patrick,

Thinking just like you, that was the first thing I checked, i.e., is the embossed area around the timing pin "round" like my (4) other A timing covers that I've had for 55 years, or elongated around the timing pin like my B timing cover.

It is an A cover.

Also, were it a B cover, it would be a minimum of 15 degrees advanced on the crankshaft in lieu of just 10 degrees.

Never saw conventional timing pin type timing on a Model A engine off this much.

Car also came with a "Police Head'".
 
its my understanding that the piston is not actually at top of stroke and there is aprx an 1/8 inch more of travel before it does reach it to which the timing is being set at for spark. i have checked with the head off and found this to be true of my engine ,i set my timing as instructed here and in several books ,and do not have a problem with timing at all. so if you set your timing at the point in which the piston is actually at top , how does that affect the actual timing ? is it than more retarded spark or??
 
H. L. Chauvin said:
Hi Patrick,

Thinking just like you, that was the first thing I checked, i.e., is the embossed area around the timing pin "round" like my (4) other A timing covers that I've had for 55 years, or elongated around the timing pin like my B timing cover.

It is an A cover.

Also, were it a B cover, it would be a minimum of 15 degrees advanced on the crankshaft in lieu of just 10 degrees.

Never saw conventional timing pin type timing on a Model A engine off this much.

Car also came with a "Police Head'".
Click to expand...


I just thought I'd mention it. Something sounded odd, the 'B' cover should allow for about 19º so your 10º just seemed strange. Maybe this is why these engines are all different when it comes to lever position.
 
Being as you are trying to determine TDC with a bent wire through the spark plug hole, do you know that the piston rises .032 or sometimes more above deck height?? Checking for TDC through the spark plug hole is not a good way to set the timing!
 
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Hi Purdy,

Sincere thanks for mentioning that tops of pistons rise above decks. however in already knowing this, & already taking this into consideration, the TDC wire method mentioned in message no. 1 worked well.

1. After bending the wire 90 degrees below the vertical, insure that this horizontal part of the wire going inside the combustion chamber not only sits flat on the deck, but also extends to close to the center of the top of the piston.

2. When this horizontal part of the wire is sitting flat on the engine deck, (with piston set below engine deck), & the dial caliper is sitting on the top of the top hemmed 90 degree wire, set the dial caliper at "O".

3. When one rotates the engine CW, the piston naturally rises above the engine deck, whereby the piston will push the wire upwards above the deck, thus moving the dial caliper tip upwards, whereby the caliper dial readings increase above "0" reading at deck height.

4. As one continues to rotate the engine, the piston will reach it's uppermost point, (TDC), & return downwards, allowing the dial caliper to return to the original reading of "0", e.g., at deck height.

5. As mentioned before above, if the highest caliper reading is say 70, then divide this number by 2, (i.e. 35) & TDC will be when the engine is rotated & the dial caliper indicates 35; hence, mark the crankshaft pulley when the dial caliper indicates 35.

6. Amazed to see 10 degrees BTDC with the timing pin; however, the following day, rechecked same with this tool while using the timing pin several times & kept getting this exact same reading.

7. Called a professional Model A racing engine builder -- he said he was not surprised -- he sees it often.

Hope this helps.
 
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H. L. Chauvin said:
Hi Patrick,

Thinking just like you, that was the first thing I checked, i.e., is the embossed area around the timing pin "round" like my (4) other A timing covers that I've had for 55 years, or elongated around the timing pin like my B timing cover.

It is an A cover.

Also, were it a B cover, it would be a minimum of 15 degrees advanced on the crankshaft in lieu of just 10 degrees.
Click to expand...

H.L.:
I am running a B engine in my Model A with an A distributor. Lately it seems to want to overheat fairly frequently. After seeing your post above I confirmed that I have a B timing gear cover (elongated boss around the timing pin). Apparently even though it seems to be timed perfectly and starts easily and really "Cadillacs" (ta-puckita puckita puckita) maybe it's too retarded since it has the B timing gear cover. I have an A timing gear cover from a spare engine in the barn - is the A cover perfectly interchangeable bolt-hole wise with the B cover? Hopefully so, then I can just change out the timing gear cover and re-time the engine which might end the overheating issue. :D

Fred
 
Some crank timing gears made in the 70ts were off a 1/2 a tooth from the key way. That could do it.
 
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I believe the covers are the same except for the timing pin location [ and marking] . The A has pin location at TDC where the B pin location is at 19º BTDC.
 
lookin-backtexas said:
...I confirmed that I have a B timing gear cover (elongated boss around the timing pin)...:D Fred
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You need to confirm the location of the timing pin hole as some "replacement" A covers had the elongated boss, but had the hole in the correct "A" location.

And Yes, the A & B covers are interchangeable bolt wise, and take the same gasket.
 
Fred, you probably know this but all timing covers with a oval boss for the timing pin aren't model B timing covers. Here is a picture of a model A service replacement timing cover. Note that the hole for the timing pin is at the bottom of the raised oval and is the same location as the timing covers that came on the model A when new. I learned this bit of trivia from Vince. I figure that Ford decided that rather than produce two different timing covers that the timing pin hole could be drilled and tapped at the upper part of the oval for model B use or at the bottom of the oval for a service replacement part for the model A. The timing covers are interchangable.
2896222-T400300.jpg
 
CarlG said:
You need to confirm the location of the timing pin hole as some "replacement" A covers had the elongated boss, but had the hole in the correct "A" location.

And Yes, the A & B covers are interchangeable bolt wise, and take the same gasket.
Click to expand...

Thanks Carl - I'll check it out and give you a report later.
Fred
 
CarlG said:
You need to confirm the location of the timing pin hole as some "replacement" A covers had the elongated boss, but had the hole in the correct "A" location.

And Yes, the A & B covers are interchangeable bolt wise, and take the same gasket.
Click to expand...

My car has one of these. I read they were factory replacement covers supplied after the A era. it has an elongated boss like a B cover but is drilled at the bottom of the boss for an A not the top like a B.
 
Purdy Swoft said:
Fred, you probably know this but all timing covers with a oval boss for the timing pin aren't model B timing covers. Here is a picture of a model A service replacement timing cover. Note that the hole for the timing pin is at the bottom of the raised oval and is the same location as the timing covers that came on the model A when new. I learned this bit of trivia from Vince. I figure that Ford decided that rather than produce two different timing covers that the timing pin hole could be drilled and tapped at the upper part of the oval for model B use or at the bottom of the oval for a service replacement part for the model A. The timing covers are interchangable.
2896222-T400300.jpg
Click to expand...

Purdy:
First, thanks for the "Purdy" picture. Mine is an original B timing gear cover with the hole at the upper part of the elongated boss.
Fred
 
Hi Lookin,

A few minutes ago just posted a new thread above on how to determine:

"Model A vs. Model B Timing Cover"

just in case one may have any questionable doubts about aftermarket, later Model, or original Model A or B timing covers.
 
Well, in case of discrepancies or doubts, there's always that audible "ACID TEST"
1- Spark up=that smooth, rythmical, TADA-TADA-TADA-TADA. (YES, I know sum of your cars speak diffurent wurds, or with a different "accent" but that's the way MINERVA said them, SO THERE!)
2- Spark 1/2 way down=A faster, smooth idle.
3- Spark all the way down=An even faster, but a "rolling" idle.

If you have ALL these sounds, you're "RIGHT ON" & don't DIDDLE WITH IT!
If you don't have all these sounds, you might have to do a small adjustment, either to the retard side, or the advance side, to obtain those "PERFECT" sounds. Bill W.
 
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