I had a mechanic put a 383 in my 86 z28 over the winter and I find out that he never marked where top dead center is. I'm still a noob at this stuff. Well car isn't running up to par any my friend think the timing is off. They tried to use a timing light but found out about the lack of a mark.

How do you find out top dead center when you don't have it marked?

The mechanic has moved out of state so I can't ask him.

 

with heads off i use an indicator, with heads on piston stop in spark plug hole. when you find TDC mark it with timing tape, or paint if you want to go the cheap way

 

if you want to buy a piston stop, its pretty easy.


the stop is a bolt that screws into the #1 spark plug hole. screw it in there.

turn the engine one way until it hits the stop.. mark where the needle/timing pointer is.

turn the engine over the other way until it hits the stop... mark it again.

the space exactly between thoes two marks is TDC.


its more accurate if you have a degree wheel on there, but its accurate enough for setting timing and such this way..

 

i would use my finger and make sure your on the compresstion stroke that where the dumb piston stop dosent work well...take the 1 plug out then put your finger over the hole bump motor over till you fell pressure/compression then line up the timing mark on the ballencer to 0 now your at tdc #1 on compresstion no question......

 

The timing mark is notoriously inaccurate. That's one reason for doing the piston stop or dial indicator thing: is to see where the mark has wandered off to this time.

The other methods of finding TDC work fine on either the compression stroke or the exhaust stroke. The piston does not care what the valves are doing, as far as finding TDC.

Of course, if you merely mark your crank damper's inertia ring with your new-found TDC mark, then tomorrow when the blob of spooge that loosely associates it with the crank decides to wiggle around like Jello again, your new mark will be just as wrong as your old one used to be.

 

Where do you make your marks?

Is it on the balancer? If So do you mark TDC between where the marks are closest or farthest apart.

 

You make a fine mark on the damper in line with the zero mark on the timing tab for each direction that the piston contacts the stop. Then, make a white mark on the damper exactly between those two marks to use as your timing mark.

Is your engine actually missing the timing tab, per chance?

 

If your talking about the little jagged piece connected to the timing chain cover than yes, I am missing that.

 

In that case, you need to go down to the parts store and buy one that attaches using two front cover bolts. Then go through the procedure outlined above to "set" it to the damper.

You'll have to know the diameter of your damper.

 

1)So buy a timing tab and attach it to the timing chain cover.

2)Take the number one spark plug out and place a piston stop in it.

3) Turn the motor over until it hits the stop.

4) Mark that spot on the balancer, the mark should be on the highest point of the balancer streight up.

5) Turn the motor the other way and mark the balancer again.

6) measure the distance between the two marks from the direction I turned the motor. Divide that number in half and mark that distance spot on the balancer between the two spots.

7) Turn the motor so that the "middle" mark is streight up, it should be at TDC.

8) begin to adjust timing on the distributer.

If any of this is wrong tell me. This is what I understand of what everyone has told me.

 

So is this all right?

 

That's correct.

Note that the #1 piston and #6 piston will be TDC using this method. This does not mean the engine will be in the #1 firing position.

 

this confuses me and i would like to get the concept. when you hit the bump the fist and second time, are you not at TDC both times, or is that just "close" to TDC? because then if you found the exact middle between those numbers, would that not be BDC?

 

you're CLOSE to TDC one way.

then CLOSE to TDC the other way.

the lines will be fairly close together.... the exact middle of them the short way is TDC


the middle of them, on the otherside of the dampener (the long way) is BDC.



heres a quickie pic.

red line is pointer. its pointing at TDC.
blue line is where the pointer was pointing when it hit the stop each time.
yellow line is BDC

notice how its easy to measure TDC with your eyes... but not BDC.... (heh, looking again, its off annyway... but you get the idea)

 

I have found it helpful to file a small groove where TDC is on the balancer if the existing mark on the balancer does not match up to your new pointer. Paint the groove white, and if for whatever reason the paint gets messed up down the road, you will still know where TDC is without going through all of this again.