How to find top dead center

I am trying to figure out how I can set my engine to top dead center (TDC). The bike is currently not running and I need to figure out a way to rotate the engine to achieve TDC and a method to ensure that the engine is indeed at TDC. Any tips would really help. Oh, the bike is a KZ650. Thanks!

Mine has a "T" mark on the rotating piece down where the points are. Turn the nut on the crankshaft end until the T lines up with the notch and that's it. Yours is likely similar, there is a mark somewhere to align. If the camshafts have not been disturbed, there are also alignment arrows on the camshaft wheels that are set at TDC.

You need a factory service manual because it has all that stuff in it.

Top Dead Centre Tool

There are various methods available to find Top Dead Centre (TDC). The most accurate being a micrometer or
as it is sometimes called, a Dial Test Indicator. However, even the DTI can't achieve accuracy much better than
1 deg. measured on the crankshaft. So what do you do if you want your TDC 'spot on'. Well here is a nice,
simple and cheap tool which most people will be able to knock up in about half an hour.
THE MATERIAL LIST
An old spark plug that fits your engine.
A piece of thread rod, approximately 10 cm / 5 in long.
A cutting tap with a thread to match the treaded rod.
A lock not with a thread that matches the thread rod.
A piece of wire (coat hanger) to act as a pointer

THE TOOL
Take the old spark plug and cut off the external electrode from the bottom
Then with a hammer and punch destroy the porcelain core so you are left with the bare metal body. Wear
eye protection as the ceramic tends to fly everywhere as you pound it out with a drift and hammer. Best
solution is to hold the spark plug up side down in a vice and drive the centre electrode back through the
plug body. Do NOT damage the plug threads.
Using a tap, cut a thread down the centre of the plug body. I found a 8mm or 3/8" thread was OK.
Round off one end of rod (see diagram). Screw the rod into the plug body and run a nut down the rod so
that you can lock the lot up.
File flat across the plug thread and the plug base (to allow an air passage when screwed into cylinder
head).




















THE METHOD
Rotate engine to just before top dead centre - the exact distance is unimportant, then screw your tool into the
cylinder head, unlock the locknut and screw the rod down until it touches the piston crown, relock the nut. The
important part is to stop the piston going over TDC, then place your degree disc on the crankshaft and fix a
pointer using the coat hanger wire. I use one of the clutch cover bolts to hold the wire.
Next turn the disc to where you think it should be, again accuracy is not all that important at this stage.
Now turn engine so that the piston is hard up against the rod of your TDC tool.
Look at your degree disc, lets assume that it reads 42 deg. BTDC (Before TDC) make a note of that figure,
now turn engine backwards until piston rises and contacts the TDC tool once again.
Holding the piston in hard contact look at degree disc, this time lets assume it reads 18 deg. ATDC (After
TDC).
Add your first reading (42 deg. BTDC) to the new figure (18 deg. ATDC), resulting in 60.
Divide 60 by 2 and you have 30 deg, so still holding engine against the stop rotate your degree disc to
read 30 deg. ATDC.
To check if you are correct, rotate the engine forward again until the piston contacts the stop and check the
disc - it should read 30 deg. BTDC.
Remove TDC tool and turn engine till disc reads 0 deg. this will be true TDC.
Edited from an article published at www.docv.org and accredited to John Withers, March 1986

Sorry Guys, I have this as a pdf but can't figure how to upload image, the twat a tron says wrong format:blink:

A Dial Test Indicator usually measures 0-.030", a Dial indicator usually measures 0-1", and a micrometer is just a different kettle of fish altogether (there are a "bunch" of different kinds of micrometers).

The usual way of finding TDC is with a dial indicator, and that will certainly get you closer than 1 degree if done properly.

The tricky part is finding exactly where tdc is...because the piston is very near the top of it's travel for several crankshaft degrees of rotation. One way to find tdc is to use a dial indicator, and note the pointer reading at about .050" before tdc, and .050" beyond tdc, measured in piston travel. Then the pointer position exactly halfway between these readings is exact TDC.

www.cadvision.com/blanchas/54pontiac/tdc.html

There is another interesting (and cheap) way of finding TDC using oil on that link.

I don't want to copy and paste the whole page though, so you'll have to go there to read it.

A dial indicator is not accurate enough for this. These engines have too much piston dwell at tdc.

The positive stop method is the only accurate way.


If you don't want to go to all the trouble to build the toodl,you can just order it.

Thanks for the info everybody. I think I will go with the "T" mark on the advancer. I will be rethreading my spark plug hole soon and I wanted to make sure that I was at TDC when I do it.

In that case, stick your pinky finger in the hole and see if you can feel the piston crown. I think it is a lousy idea to rethread the plug hole with the cylinder head on the bike... just too much non-metalic junk will fall on the piston but if you feel comfortable in your ability to get it out, its your bike. I just never get that comfortable feeling. Good luck. How much does a cylinder head gasket cost anyway?

If you grease your tap or thread chaser and keep cleaning as you go and regreasing it you can get most of the metal. Still not the best idea but if youre dead set against taking it apart its probably the best way to do it

wiredgeorge wrote:

In that case, stick your pinky finger in the hole and see if you can feel the piston crown. I think it is a lousy idea to rethread the plug hole with the cylinder head on the bike... just too much non-metalic junk will fall on the piston but if you feel comfortable in your ability to get it out, its your bike. I just never get that comfortable feeling.

Good point. Since the metal you are cutting from the head is aluminum, it can not be retrieved with a magnetic rod. It's just going to fall in there and hang around.

I will be using a "back-tap" tool that will not allow any shavings into the engine. The tap tool is threaded from the bottom to the top taking all of the shavings to the top right along with it. No worries using this tool. I just hope that my threads aren't so bad that I have to go with an insert. If that is the case then I will definitely pull the head.

Here is a demo of the back-tap tool.

HERE

I will be using a "back-tap" tool that will not allow any shavings into the engine. The tap tool is threaded from the bottom to the top taking all of the shavings to the top right along with it. No worries using this tool. I just hope that my threads aren't so bad that I have to go with an insert. If that is the case then I will definitely pull the head.