Finding TDC with head on?

carl

carl

True Classic
In view of my post below about ignition timing, I want to verify the block mounted TDC indicator is correct. Anyway to check actual TDC of #1 piston with the head on? I would think the old stick in the spark plug hole would not work well with the angled plug. And yes I know there is a mark on the flywheel but it's a bitch to see (oddly enough not hard at all to see on a 128).

carl
 
I have done it with a dial indicator before....

You need one with a lever arm on it that can indicate at an angle versus a plunger type. I set up my magnetic base and indicated through the spark plug hole.

I was looking to verify my marks, and did.

Ciao,
 
You'll need a piston stop and a degree wheel

You'll have to buy/make a piston stop and print out a degree wheel from a website (I used photo paper stock because it was stiffer and and the glossy didn't suck up my oily fingerprints) Here's a pic of the piston stop I made from an old spark plug.

Degree Wheel here
http://www.gabma.us/tools/DegreeWheel.bmp

DSCN3639.jpg



DSCN3640.jpg


Before installing the piston stop, use a paper clip to make yourself an indicator. With the engine at the ballpark TDC, install the degree wheel with some packing tape to the crank so that it is close to zero on the paperclip indicator. Screw the piston stop into the spark plug hole and remove all the other spark plugs for ease of rotating the engine. ENSURE the piston is in the DOWN position before putting in the stop. After the stop is installed and have your degree wheel ready, rotate the engine SLOWLY and gently until the piston stops against the piston stop (LOL). Note the number on the degree wheel. Then rotate the crank in the other direction SLOWLY until you gently hit the bump stop in the other direction. Rebend the paper clip until you can get the numbers to be the same at both bump stops (43 1/2 in both pics below BTDC and ATDC) then remove the piston stop and the TDC will be 0 degrees. To speed this process up, some math may be involve to check how much to move the paperclip. Do not adjust the piston stop!

DSCN3644.jpg


DSCN3645.jpg


You can now accurately position the TDC on the car
 
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The flywheel mark is easier than...

carl said:
And yes I know there is a mark on the flywheel but it's a bitch to see (oddly enough not hard at all to see on a 128).
Click to expand...

The flywheel mark is easier than the other approaches being discussed, really it is. Use a shop mirror, and you'll find find it easily enough (unless your flywheel happens to be 180 degrees off, in which case it'll find BDC).
 
Thanks

As noted by others, that's a nice write-up. I think I figured out my detonation problem. I'm running quarter tank of the 5+ year old gas and 1/4 tank of new low test. I'm betting my resultant very low octane rating is what is causing the pinging and run-on. I'll know in the next day or so when I fill the tank with 91 or 93.

carl
 
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