Is it possible to find TDC on a flathead with the cylinder heads on? I want to make sure that the distributor was installed correctly from the previous builder.
That's a good question. I had the same situation on my 8BA and to make matters worse there was no timing mark dimple on my pulley.
Not positive of the year of the engine but I think it is a 1949 239. It has 8BA on the cylinder head.
Could I just line the dot up on the pulley and just make sure the rotor is on the number 1 distributor lug on the cap? Could I still be off a tooth on the distributor gear?
Overhaulin, I think in your case if you rotate the motor so the rotor is pointing at the #1 plug wire and the timing dimple lines up with the timing pointer than you are good. I may be wrong. It is Monday morning.
I like your idea better. I may take an old distributor cap and drill a hole through the number 1 terminal to make sure I am right on top of number 1. Thanks!
I did mine with a zip tie, stick the business end down the spark plug hole towards the piston, turn engine over till it stops, mark pulley, reverse. Courtesy of an old HAMB thread.
You could mark the side of the dizzy at the #1 plug wire spot on the cap, remove the cap and rotate the motor. This also gives you a reference for future dizzy removal and reinstall.
Coat hanger down the spark plug hole. Get it to what you think is TDC and mark it then roll the engine the other way to what you think is TDC and mark it. between the marks is TDC. or you can actually buy a TDC stop ( about 7-30 bucks) that screws into the spark plug hole. or you can use a dial indicator again down the spark plug hole, get it close set it up and roll it, when the measurement starts in the other direction you have just hit TDC.
Interesting...I just found this idea on the web and it sounds pretty good. Someone also suggested maybe using a light oil vs. water. Had need to find TDC on number 4 cylinder and remembered someone mentioned a whistle being used. Don't have a whistle, but made up a simple fitting from an old sparkplug housing, attached clear tubing and ran it into a jar of water. Bubbles came out on compression, stopped at TDC and started ****ing up water immediately after TDC. I worked the crank back and forth slightly a couple times to get accurately centered. Easy to see the water level position inside the small tubing.
The zip tie method will work or take a piece of rope and insert thru plug hole and direct it towords piston. Same as zip tie (most people don't have a zip tie they big) rotate until it stops and then back again until it stops. Right in between you have TDC. But whats the point if it runs the distributer is in correctly i.e not 180 out or even off one cylinder. Timing maybe well off but the distributer is in correctly.
Find TDC accurately by interference, easy and accurate: http://www.jalopyjournal.com/?p=10940 On long rod, offset motors like Flathead and Small Block Chevy you can only get close by eyeball, dial indicator, or whistle. Interference method, heads on or off, is accurate and at least as easy. Then if you want you can easily measure off your whole curve...
Remember there is two tbc per crank rotation. You want the power stroke. The thumb over the hole, while you bump it, will get you there. Then you can narrow it down from there. Bump stop or a dial indicator with the head off will always be more precise.
Another method is to use an old spark plug with a pipe welded to it, as you would use to pressurize the cylinder. If you don't have one, not hard to make. Put some kid's bubble soap on it and turn the engine, when the bubble is biggest you are at TDC. This is surprisingly accurate.
Visual, dial indicator, and pressure ways are only accurate within about 2 1/2 degress on long rod/offset engines like Flathead and SBC...the pistom movement at top is effectively zero in that dwell period, even to a good indicator. See Yunick's discussion of this if curious... This is probably about as accurate as most factory timing tabs, and good enough if you are going to experiment to find happy timing, but interference method is considerably more accurate with the heads on method and probably approaches perfection in heads off method allowing measurement from farther down the cylinder where movement corresponds better with obsercation. Heads on method is as easy as any other, and since it gives sunstantially better results...
As far as I have learned .... MOST ACCURATE WAY to find ACTUAL TDC on any engine is ...... ALL PLUGS OUT of motor ...Insert a STOP thru spark plug hole ( allthread, long bolt, etc) ... turn engine over BY HAND until it contacts the stop..... MARK the balancer where it stops ( 0 degrees, 5, 10 degrees - whatever - just mark EXACTLY where the motor stops turning the best way you can ) Then turn the motor in the REVERSE DIRECTION and hit the stop again ... mark the balancer in that position ..... measure EXACTLY BETWEEN the marks and you have EXACT TDC ........ learned that right here on the HAMB ..... hell of a place -- huh ???
But on a Flathead Ford, you have to use a long, flexible tool because plug is not over piston. Best thing I have found is a BIG tie-wrap, using the buckle part as the stop. A thicker stop would be nice, but you are restricted to something that can go through plug hole and then over quite a ways until it hits far cylinder wall. Also, plastic is nice because it isn't going to scar the piston unless you are really strong and stupid. Thicker stop blocking piston farther down would give slightly more accurate correlation between piston TDC and Crank TDC, but it is still better than visual/pressure checking, and thicker requires removing head. Once you have head off, a simple strap with bolt as a positive stop allows deep reach. Old way, as in early edition of the Isky manual, used a dial indicator NOT to directly find TDC (NOT accurate) but to locate stop locations an inch down. Same as bolt process but harder and adds in possibility of mis-reading instead of giving you positive stop.
Hmm, that sounds good. I wonder within how many crank degrees it's accurate. Just from turning motors over with the heads off it seems there is several degrees around TDC where the piston isn't moving much.
The other day I put the plug fitting from my compression tester in the spark plug hole with a latex glove finger stuck over it. I had already marked the pulley with the positive stop method when I had the heads off, and just as Rusty says above it was surprisingly accurate. It would inflate as it approached TDC and deflate after, quickly enough that you could rock it back and forth and the sweet spot was right where I had marked the pulley. Good tip for a fast timing tab double check.
Since the original post I tried using a balloon instead of bubble soap, which works like the glove finger idea. It is more convenient but possibly less accurate. In my case I was trying to find TDC on the compression stroke, close enough to install a distributor. I 'fine tuned' the timing using the timing marks. The bubble or balloon method is close enough to get the distributor gear meshed on the right tooth.
the questions still lurk TDC Very Simple folks Disconnect battery ground if turning by hand remove No. 1 spark plug I plug a shop rag in the TOP of no 1 spark plug hole , screw driver works well remember your just blocking the plug hole not the cylinder below turn engine as soon as rag pops out it's TDC compression stoke. the Rotor points at No 1 at at Dist. cap, and spark plug wire install spark plug and Dist. cap and battery ground Start engine Adjust with timing light Works every time "she's crazy about a Mercury"
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