Finding TDC or Waiting For Godot

[Guest]

The enigma of TDC is such that achieving it is oft a trick.
My lightbulb went off this morning while gazing at my headless block. Rather than bump the starter, or try to re-affix a bolt to the crank from which I can turn from, why not just put her in fourth gear (she is on blocks) and very easily turn my rear wheel back and forth and watch my dial gauge do its thing.

 

[Mickey Richaud]

Way to go there, Estragon! :wink:

 

[Brosky]

Once again, necessity is the mother of an inventive mind. Sort of para-phrased, but you get the general idea.

 

[DNK]

Been doing that for years on the old cars. One thing,just like it is easy to go past the spot when you turn by hand it tends to move easily past that point when you push it

 

[Guest]

Been doing that for years on the old cars. One thing,just like it is easy to go past the spot when you turn by hand it tends to move easily past that point when you push it

Should be able to move it back and forth, right. The crank will turn backwards with no effort? Talking smidgens of movement here, especially when using the dial gauge.

 

[Dave Russell]

As long as the head is off, check into the "positive stop" with degree wheel method of finding TDC. Much more sure & accurate than dial indicator.

Also, you really should use the degree wheel & dial indicator to check cam timing when you replace the cam.
D

 

[DNK]

Used to rock back and forth. of course a little easier (maybe) on a Cortina with an outrageous Formula Ford motor.

 

[70herald]

I picked up a big socket which fit the nut on the end of the crankshaft. Very easy to move the engine back and forth. I used it both while assembling the engine (to find TDC) and later on to set the valves. Much easier than pushing the car back and forth.

 

[Guest]

I picked up a big socket which fit the nut on the end of the crankshaft. Very easy to move the engine back and forth. I used it both while assembling the engine (to find TDC) and later on to set the valves. Much easier than pushing the car back and forth.

Yisreal, the car is on jack stands. I can just reach back and turn the tire like a steering wheel. Or let the wife do it.

 

[Tinster]

Morning Bill !!

I've been up since 4:30 AM AST doing some yellowfin tuna
research. What miserable local time did you get of bed
this morning? 3:30AM??

Raining cats and dogs here.

d

 

[70herald]

I can just reach back and turn the tire like a steering wheel. Or let the wife do it.

You must have really long arms and an angel for a wife. :laugh:

Using the socket, you really have much more accurate / easy control over positioning the engine. After all, even in 4th gear, you still have the ~4:1 ratio from the differential in between the tire and the engine you are turning over.

 

[Twosheds]

I'm like Dave Russell. Seems to me that a dial indicator will find Top Center but not Top Dead Center. Due to the few degrees of crank rotation that do not move the piston because of slop.

We used to have a tool (I forget its name) that screwed into a spark plug hole and stopped the piston on its way up. You then zeroed the degree wheel. Then you backed up the prop... er, crank 'til the piston hit it again and noted the degree mark.

Top Dead Center was half of this degree mark.

The fact that you were still moving the piston up when it hit the stop meant that all the slop was taken up.

 

[DrEntropy]

Hard to do if the head's already off, John. :smirk:

The same thing CAN be done with the dial indicator and degree wheel, it just takes more patience to achieve. A bar attached to the top of the block (head bolt hole) with a "stop" hanging into the bore is a good surrogate... *hint-hint*

 

[JFS]

Bill, If I remember correctly, Godot never shows; however, TDC can be had

 

[Twosheds]

Hard to do if the head's already off, John. :smirk:

Silly of me.

 

[swift6]

A bar attached to the top of the block (head bolt hole) with a "stop" hanging into the bore is a good surrogate... *hint-hint*

Such as this...

The two outer bolts are to attch to the deck of the block, the center post is the stop.

 

[TR3driver]

But you still need a degree wheel (or careful measurements on the rim of the pulley/damper) to find TDC. The stop only gives you two points equally spaced on each side of TDC.

Of course, as noted, so does the dial indicator, except with it, they are NOT evenly spaced.

 

[vettedog72]

TDC accuracy on the TR6 may be limited by the tolerances of the crankshaft or some other factors like rod length, piston pin to piston top. As dumb as this may sound there is some significant slop with these parts. I recall the decking procedure brings these tolerances to light. If your motor is apart measure the deck to piston top on each cylinder and you will see the dofferences; you may be able to eyeball the differences in heights