Taylormade

Finding TDC on a flathead six

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Getting ready to start the motor on my 1932 Dodge Brothers DL six and have run into a bit of a problem.  I'm trying to find TDC to get the timing set up correctly.  I know the best and obvious way is to remove the plug over number six cylinder and put a rod into the hole and watch until it reaches the top of travel.  At this point it's TDC on one and six, then I check the tappets and if both are down on one, one is ready to fire.  The problem is, I can't get the damn plug out.  It's made of brass and seems to have fused to the cylinder head.  It has a screwdriver slot cut into the top, but any attempt to turn it out with the correct size flathead screwdriver just chews up the brass.  Naturally, I have the engine nicely painted and don't really want to burn the finish off by heating the area up.  It's a fine thread plug and there seems to be enough sticking out of the cylinder head to get a pair of vice grips on it and try to turn it, but I'm sure it would totally tear up the plug.  Are they still available or am I going to get myself in deeper by destroying it?

 

Any other methods of finding TDC accurately?  I can turn the engine with the crank and watch the tappets until they are both down on number one, but there is a lot of slack and I don't think I can get that accurate a reading.  Same with putting a finger over the open spark plug hole to feel for compression.  I swear there were timing marks on the flywheel when I was putting things together, but I can't see a thing through the timing port hole on the bellhousing when I think I'm close to TDC.  I have the sinking feeling I'm going to have to get that threaded plug out of the head to make this work.

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The thread is a standard 1/4" pipe plug so far as I know. If you get the plug out you should be able to get a replacement at any auto parts store or hardware store. I don't think I have ever seen a brass one with a screw slot, they were all standard square head pipe plugs. But have not worked on one that old.

 

There is an alternative if you don't want to mess with it. Get or make an adapter that screws into the spark plug hole and put a balloon on it. Turn the engine till the balloon blows up to its largest size. This is not precise but gets you in the ballpark, then you line up the timing marks. By this method you know you are on the compression stroke.

Edited by Rusty_OToole (see edit history)

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I got the plug out with vice grips.  As I feared, they tore up the plug pretty badly, but it was already damaged, as the slot was in poor shape before I even touched it.  It's still usable in a pinch, but I'll try and find a new one.

 

IMG_7626.jpg

 

This allowed me to put a small diameter rod into the opening.  Obviously, the rod rests on the top of the piston and as you rotate the crank it's easy to find TDC. 

 

IMG_7622.jpg

 

I'm glad this worked out.  Before I was trying to guess at it based on the lifters going down.  It turned out I was about ten degrees off doing it that way.  Using the rod, the mark on the flywheel showed up (I knew it was on there!) and I can now see the ignition setting and  the TDC setting.

 

IMG_7628.jpg

 

And I discovered I actually lucked out and got the distributor in correctly.  At TDC the rotor is in the one o'clock position.

IMG_7630.jpg

 

So, adjust the valves, set the timing and I'm ready to fire her up for the first time.

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I believe that the rotor should be pointing to the number 1 cylinder.

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Everything I can find says one o'clock for the number one cylinder to fire.  There is a detailed description of it on the P-15 D-24 web site and they say one o'clock for one and seven o'clock for six.  My wiring diagram also shows it in the one o'clock position.  If this isn't correct, my engine rebuilder did not index my oil pump correctly.

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Anyone who wants to do this, I suggest you NOT use a plain wire or rod. It is possible for it to fall into the cylinder and the only way to get it out, is take the head off. It is better to use a screwdriver or bend the rod into a T shape.

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Using a vernier calipers on the depth gauge is the method I use.

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4 hours ago, Taylormade said:

Everything I can find says one o'clock for the number one cylinder to fire.  There is a detailed description of it on the P-15 D-24 web site and they say one o'clock for one and seven o'clock for six.  My wiring diagram also shows it in the one o'clock position.  If this isn't correct, my engine rebuilder did not index my oil pump correctly.

Just make sure when you put the distributor cap back on that the rotor is lined up with the spark plug wire that goes to cylinder #1. Then you know you have it right.

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48 minutes ago, Joe Cocuzza said:

Just make sure when you put the distributor cap back on that the rotor is lined up with the spark plug wire that goes to cylinder #1. Then you know you have it right.

THAT is what I meant to say.

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18 hours ago, Rusty_OToole said:

Anyone who wants to do this, I suggest you NOT use a plain wire or rod. It is possible for it to fall into the cylinder and the only way to get it out, is take the head off. It is better to use a screwdriver or bend the rod into a T shape.

 

Probably a good idea, Rusty, but I didn't have a screwdriver with a shaft that was long enough and still small enough to fit in the access hole.  The rod I used is plenty long enough to not come near falling in and is almost exactly the diameter of the access hole, so there is no sideways motion that might cause it to slide to the side and fall in.  Right after I took the photo, I wrapped tape on the top of the rod just to make sure.

Edited by Taylormade (see edit history)

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If its long enough it cant slide in unless you had the wrong piston or one with a hole in it.

The rod you used looks plenty long for the task.

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Glad you got it sorted, this is an oft repeated problem with side valve engines, where a probe over the piston is not going to work because the spark plug hole is over the valves, not the piston, hence the need for a removable witness plug which is invariably corroded in place; by the way in your case just cut an appropriate length of similar threaded bolt as a replacement, cut a slot in the top and screw it in.

 

So a couple of other points to make when you cant determine TDC with a probe and you do have access to the valve lifters. At TDC #1,  both the inlet and exhaust lifters should be slack, that is no tension on the valve springs (valves are closed), at the same time (with a 6 cylinder) the #6 lifters should be rocking - exhaust just closing and inlet just opening. So in summary, turn the engine by hand in direction of rotation and watch the movements of the #1 and #6 lifters, it takes a little finessing and you may have to go a couple of rotations to get it right but in the end you will be within a few degrees of correct positioning, the emphasis needs to be on watching the #6 lifters rather than #1, and in the case of an OHV watch the rocker arms.

 

With regard to misplaced distributors, a lot of time can be saved if you consider where the #1 spark plug lead needs to be when #1 piston is at the correct timing point. It doesn't really matter where the distributor or cap are placed, the critical element is with the rotor, wherever it is pointing when #1 is ready to fire, that's where the #1 plug lead needs to be positioned  in the cap; the rest are positioned to follow suit, such as 153624. So if you know which way the distributor rotates, position the other wires accordingly, it may look wrong asthetically and you may have to move wires to reach, but if the alternative is removing the sump and re keying the oil pump I know which option I would choose.

:D

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Thanks for the detailed advice hchris.  Regarding the position of the rotor, as I mentioned, I was glad to see it was in the one o'clock position at TDC, which is correct according to the owner's manual.  I had my wires on the cap in this configuration, so I won't have to adjust anything.

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I have a 1930 DeSoto CK6, and the only way to set the timing accurately is by finding TDC of #6 cylinder. I had a dial guage in my tool box for measuring cylinders. Created my own tool for setting TDC and then turning back the required amount for proper timing. Works like a charm!

IMG_1161.JPG

Edited by ckowner (see edit history)
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Excellent tool, no doubt that you could get pin point accuracy with it.

 

But the problem remains with getting that stubborn plug out without causing grief; the purpose in using this access point is usually associated with getting a starting position for initial ignition timing, different matter if we are talking valve timing. The fact still remains that there are other reasonably accurate ways to achieve initial timing.

 

Lets not forget that ignition timing settings are a guide to best engine performance, every engine is different, fuels are different to way back when, pulley timing marks are subjected to such things as timing chain wear, softened rubber in the crank damper etc. etc.

 

Summarising all of the above; setting the ignition timing is only a guide, you don't have to be precise at the initial timing point, the quoted figures are there to get you started and then the fine tuning can commence based on road tests, timing lights or vacuum setting (which I find most successful). 

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  The timing light is great, but the 1930 engine does not have a timing mark. To set Ignition timing the 1930 DeSoto Finer Six instruction book reads as follows:

 "The breaker points should be adjusted to .020" (.508 mm.) opening. The 1/8" pipe plug should be removed from the cylinder head above #6 piston and a gauge rod placed through the hole and in contact with the piston head. The crankshaft should be rotated until No. 6 piston is coming up on exhaust stroke and stopped when the piston is .009" before TDC. The screw which clamps the distributor timing lever to the distributor should be loosened and the distributor cap removed to see that the rotor brush is at #1 spark plug cable terminal. The distributor clamp screw should next be loosened and the distributor rotated in an anti-clockwise direction , as viewed from above, until # 1 cam begins to separate the breaker points. Before doing this the distributor rotor should be pressed against the direction of rotation to be certain that all backlash is removed. The clamp screw should then be tightened and the distributor cap reinstalled as well as the spark plug cables connected to the proper spark plugs and terminals on the distributor cap"

 It may be possible with modern test equipment to by-pass this process, but I decided to build this tool and follow instructions, and it works!

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I guess I'm lucky they decided to put a timing mark on the flywheel by 1932.  It makes life a lot easier.

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1 hour ago, ckowner said:

  The timing light is great, but the 1930 engine does not have a timing mark. To set Ignition timing the 1930 DeSoto Finer Six instruction book reads as follows:

 "The breaker points should be adjusted to .020" (.508 mm.) opening. The 1/8" pipe plug should be removed from the cylinder head above #6 piston and a gauge rod placed through the hole and in contact with the piston head. The crankshaft should be rotated until No. 6 piston is coming up on exhaust stroke and stopped when the piston is .009" before TDC. The screw which clamps the distributor timing lever to the distributor should be loosened and the distributor cap removed to see that the rotor brush is at #1 spark plug cable terminal. The distributor clamp screw should next be loosened and the distributor rotated in an anti-clockwise direction , as viewed from above, until # 1 cam begins to separate the breaker points. Before doing this the distributor rotor should be pressed against the direction of rotation to be certain that all backlash is removed. The clamp screw should then be tightened and the distributor cap reinstalled as well as the spark plug cables connected to the proper spark plugs and terminals on the distributor cap"

 It may be possible with modern test equipment to by-pass this process, but I decided to build this tool and follow instructions, and it works!

 

No argument with that, that's how the engineers of the day wanted it.

 

Without wanting to labor the point, I am saying that there are other factors today which could make a rigid timing setting less than ideal, modern fuel properties being just one of them and then of course, the wear and tear of an older engine with its knock on effect of timing gears/chains etc.

 

Establishing an exact by the book timing point is not absolutely necessary to have an engine run efficiently, its a starting point which can then be refined to suit the particular needs of any one engine.

 

As to not having a timing light, you might like to consider setting the timing with a vacuum guage, its a very reliable and accurate method of getting the best out of an engine with regard to ignition timing.

;)

 

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I purchased a brass slotted plug for my 1930 model 70 from Restoration Supply  1-800-306-7008 in California. Get one of their catalogs, it is loaded with special parts at reasonable prices. I've bought a lot of special screws and misc. parts from them. Fast shipping too.

 

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I would rather use an iron pipe plug with anti seize on the threads. They are cheap and easy to remove. The head is square and fits into a 1/4 socket wrench extension. The trick is to use the extension, and/or a 3/8 socket turned upside down and a ratchet handle. You need an 8 point or 12 point socket but this trick works great for all square pipe plugs and square brake adjusters.

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