Finding TDC

[rpellicer]

Hi everyone.

I've been reading some posts, and I noticed a couple that recommended the "finger in the sparkplug hole" method of finding TDC. Although it is great for verifying that you are on the compression stroke, it is not very accurate if your trying to verify timing marks or trying to accurately time your engine. A better way is to get a piston stop that threads into your sparkplug hole (about 10-15 bucks from Summit.) Pull all your spark plugs (to make sure you rotate the engine smoothly, compression in some cylinders can make the engine spin abruptly.) Use the "finger" method to make sure #1 cyl. is on compression stroke. Back it off abit. Install the piston stop in the plug hole. Slowly turn the crank until the piston touches the stop. Mark the damper where the "0" is on the timing tab. Rotate the crank the other direction until it stops again. Mark damper again. Take a measuring tape and find the midpoint between the the two marks. If it coincides with the notch on the damper, you're good to go. If not, make a permanent mark (scribe or something), or place a timing tape with "0" on the midpoint.

Hope this is informative (and isn't redundant.)

 

[79Beast]

I see what you're getting at, and it's good info. I think most folks use the "finger over spark plug hole" trick on engines where the damper is properly marked and they just want to be sure that they're on the compession stroke and not exaust stroke.

 

[big_truxx]

Ive had to use the finger method before also used a plasic straw to see when the piston was all the way up. finger kinda hard to do alone. but you have a very good point there.

 

[R72K5]

good point yes but rarely would ever have a problem where you didnt know for sure you were on #! TDC compression, if both valves are closed then youll get the compression, IE what is the whole point of this

good lcuk

 

[rpellicer]

One of the threads I read brought up the possibilty of mismatched timing marks from having different timing tabs on the timing chain cover or a slipped outer ring on the damper. I had the latter happen to an Impalla I used to have a while back. In any case, if timing marks aren't accurate, your ignition timing could be off several degrees from what you think it is.

 

[dyeager535]

Thats why you find compression stroke, hook up a timing light, leave ignition on, and rotate the engine until the timing light fires. #1 TDC.

 

[big_truxx]

the timing light will actually work w/o the engine running?

 

[dyeager535]

Yes, because the coil has power in both start and run.

 

[big_truxx]

Yes, because the coil has power in both start and run.

Cool beans!! Thanks. that's one of them little tricks that will come in real handy :Grin:

 

[rpellicer]

The timing light technique is also great for setting static timing - setting timing up when you do a fresh distributor install. Keep an eye on timing marks when #1 fires, and adjust distributor accordingly. That way you are very close to where timing should be when the engine is first fired up.