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Old 09-23-2019, 02:55 PM   #1
Tablemaker
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Default Can the TDC pin be off by 90 Degrees?

Ever since I got my 31 A from my father, it has been ďRunningĒ without the exhaust/intake manifolds flush minted to the block. In other words, the engine was been running without a flush seal on the third and fourth cylinders.

After installing a brand new pair of intake/exhaust manifolds, with copper gaskets, I now have backfire during acceleration and deceleration.

I suspected the car needed to be timed. Iíve timed the engine without relief. I now suspect that the timing gear could be off by approximately 90degrees.

I followed some advice to identify TDC for cylinder 1 (by taking off all spark plugs and watching the four cylinders rise and fall)

What Iíve found, is that the timing pin more closely aligned to TDC for cylinder 2. *AND*, if I set the timing according to when cylinder 1 is physically at TDC WILL CAUSE massive backfire.

Iím at a loss in how the engine even runs using the timing pin (since #1 cylinder in already at the bottom of the stroke) and why I cannot even get the engine running when I use what I know to be TDC for #1 according physical inspection.

Can anyone help me get my fathers car running the way it should?

Many thanks,
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Old 09-23-2019, 03:38 PM   #2
wmws
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Default Re: Can the TDC pin be off by 90 Degrees?

The first thing I would do is take the timing gear cover off and be sure the timing marks between the timing gear and the crank gear are in alignment. Something is not right there.
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Old 09-23-2019, 03:42 PM   #3
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Default Re: Can the TDC pin be off by 90 Degrees?

Thanks @wmws. Will remove parts tonight and send photos in the morning.
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Old 09-23-2019, 03:54 PM   #4
Dick Steinkamp
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Default Re: Can the TDC pin be off by 90 Degrees?

Quote:
Originally Posted by Tablemaker View Post

After installing a brand new pair of intake/exhaust manifolds, with copper gaskets, I now have backfire during acceleration and deceleration.

I suspected the car needed to be timed.
Was it backfiring before you changed the manifolds?

If not, just changing the manifolds didn't change the timing...Perhaps you changed/adjusted something else at the same time?
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Old 09-23-2019, 04:24 PM   #5
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Default Re: Can the TDC pin be off by 90 Degrees?

I too am thinking the timing gear alignment is off.
Assuming you were using TDC on #1 during compression stroke.

Last edited by Patrick L.; 09-23-2019 at 05:05 PM.
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Old 09-23-2019, 04:27 PM   #6
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Default Re: Can the TDC pin be off by 90 Degrees?

It was backfiring before changing the manifolds, but it was not as bad. I suspect the reason was because only the first two cylinders where operating properly.
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Old 09-23-2019, 04:45 PM   #7
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Default Re: Can the TDC pin be off by 90 Degrees?

Tablemaker lets do a little review here:
We are working on a 4 cycle engine. Intake, Compression, Power, Exhaust, in that order.
With 1 spark plug out, observe the INTAKE Valve.
#1 Piston at the top AND when it starts down the INTAKE Valve should begin opening,i.e.INTAKE Stroke.
When the #1Piston comes up, this is the COMPRESSION Stroke. When it reaches the top (TDC) the spark plug is fired, driving the piston down,i.e. POWER Stroke.
When the piston comes back up it is on the EXHAUST Stroke and is ready to repeat the 4 cycle process when it reaches the top.

If you set the timing with the #1 Piston at the top on the EXHAUST Stroke the engine will be 180 degrees out of time and will backfire..
Have fun!
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Old 09-24-2019, 06:08 AM   #8
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Default Re: Can the TDC pin be off by 90 Degrees?

Mag - Thanks for the reminder. The piston will be at the top of the twine twice per cycle.

How do you know if the piston is at the top for the compression stroke?
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Old 09-24-2019, 06:11 AM   #9
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Default Re: Can the TDC pin be off by 90 Degrees?

Also, I took the cover off last night and the timing gear DOES align with the mark on the crank.

Since the marks line up, how is it possible that #1 piston is not at the top of a stroke once I spin the engine to align with the timing pin?
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Old 09-24-2019, 06:47 AM   #10
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Default Re: Can the TDC pin be off by 90 Degrees?

You may want to remove the distributor cap and watch the rotor as you find TDC. True TDC the rotor wil point to #1.
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Old 09-24-2019, 06:48 AM   #11
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Default Re: Can the TDC pin be off by 90 Degrees?

Table, put your hand over the #1 cylinder, or a light tissue over the cylinder when you are cranking it over. Before you do this it will be easier if you remove all of the plugs.

The top of the compression stroke will move the tissue or you will feel the air with your hand. At this point, both the intake and exhaust valve will be closed.

Make sure the piston is at the very top of the cylinder. At this point, the timing pin will drop into the hole as you are cranking it over.
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Old 09-24-2019, 11:05 AM   #12
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Default Re: Can the TDC pin be off by 90 Degrees?

""How do you know if the piston is at the top for the compression stroke?""

The INTAKE Valve has closed completing the Intake Cycle. When the piston comes up and reaches the top both INTAKE and EXHAUST valves are closed compressing the fuel mixture.
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Old 09-24-2019, 11:30 AM   #13
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Default Re: Can the TDC pin be off by 90 Degrees?

With the front cover off, and marks on the gears aligned, no pistons are at TDC, this is normal. If the timing is off by 90*, it will not run at all. Don't know what to tell you where to start, so many things to check. Suggest you find a local A guy with experience. Good luck!
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Old 09-24-2019, 11:39 AM   #14
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Default Re: Can the TDC pin be off by 90 Degrees?

Quote:
Originally Posted by Tablemaker View Post
Also, I took the cover off last night and the timing gear DOES align with the mark on the crank.

Since the marks line up, how is it possible that #1 piston is not at the top of a stroke once I spin the engine to align with the timing pin?
Can you post a picture of your timing cover?

There are Model A covers and Model B covers. The timing hole is in a different location on the B cover. It's not 90į but it makes a big difference.

http://www.fordgarage.com/pages/timingcovers.htm


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Old 09-24-2019, 11:45 AM   #15
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Default Re: Can the TDC pin be off by 90 Degrees?

May not be the timing . I doubt that the engine would even run at all if the timing was set on the number two cylinder . If the gas adjusting valve (*GAV) is set way too lean it will cause backfire. Check the GAV , try opening the GAV on the choke rod a bit to the left to richen the mixture at the carburetor . As for timing, if the backlash at the distributor cam is on the wrong side when the cam screw is tightened it will effect timing . In other words when the timing pin drops in place , adjust the points cam so that the trailing edge of the rotor tip is pointing exactly at the number one spark plug connection in the distributor cap body with NO clockwise backlash . Backlash is free rotational movement in the distributor shaft , in this case . Wear increases backlash . Some may have as much as one half inch of rotational backlash , some may have little or no backlash . When the cam screw is tightened , NO clockwise backlash should be allowed to remain at the points cam . Counter clock wise backlash will have NO effect on timing because the distributor rides on the clockwise side of the backlash when present . when present . I always check and adjust points gap because gap effects timing .Ford specs for points gap is .018 to .022 . More gap advances less gap retards . I usually set mine at the wider gap of .022 .
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Old 09-24-2019, 12:00 PM   #16
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Default Re: Can the TDC pin be off by 90 Degrees?

As for CAM timing , there is only one way that the cam timing gear can be installed without alteration of the two holes in the cam gear . There is a slight offset to the holes on the cam gear . I once saw where a person had rat tail filed one of the holes larger in an attempt to get the cam gear on . The person that rat tailed the hole , obviously didn't see the offset in the cam gear holes .

Last edited by Purdy Swoft; 09-24-2019 at 02:54 PM.
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Old 09-24-2019, 12:51 PM   #17
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Default Re: Can the TDC pin be off by 90 Degrees?

You might still have a leak in the manifold check for that. Good luck Frank
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Old 09-24-2019, 04:01 PM   #18
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Default Re: Can the TDC pin be off by 90 Degrees?

OK, before putting the cover back on enlarge the timing pin dimple so its easier to find.
With the sparklers removed turn over the engine until #1 piston come to near TDC on compression stroke. Try to find the dimple with the timing pin. Once found, thats TDC on compression and the timing can be set.
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Old 09-24-2019, 04:09 PM   #19
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Default Re: Can the TDC pin be off by 90 Degrees?

Thank you for all the help. Specially appreciate the detail on where the pistons should align when the timing gear and the cam are aligned. Also appreciate the help on how to tell which stroke the piston is on (Power vs intake)

I will post photo tonight of the timeing gear tonight and the alignment pin
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Old 09-24-2019, 05:15 PM   #20
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Default Re: Can the TDC pin be off by 90 Degrees?

Basic timing: rotate engine, find the dimple, pull the dist cap, retard spark, set point gap, adjust dist cam........done.
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