Topic: TDC for CB750 (Top Dead Center Tool)

[CafeRacingMan]

I have bought a few dial indicator TDC tools for Honda 72-75 SOHC CB 750's.  None have a shaft long enough to adjust the set screw clear of the head so you an set the length of the TDC tool.  I also have the solid aluminum versions that simply stops the piston.

I am sure someone knows of a tool that screws into the spark plug hole with a dial indicator that can be set depth wise clear of the cylinder head.  In most cases you cannot get into the opening to adjust the set screw that adjust the length of the dial indicator.  Any advice is gratefully accepted.

The engine I am tearing down has a hot cam in it and degreeing the cam.

[madmtnmotors]

The way I understand it is the TDC tool is a simple piston stop. You rotate the crank clockwise (slowly!) until it stops, read the degree on the degree wheel, then rotate the crank (slowly!) counterclockwise until the piston stops, read the degree on the degree wheel and TDC is exactly halfway between those marks.

At least that's how I do it. 

[Airborne 82nd]

The way I understand it is the TDC tool is a simple piston stop. You rotate the crank clockwise (slowly!) until it stops, read the degree on the degree wheel, then rotate the crank (slowly!) counterclockwise until the piston stops, read the degree on the degree wheel and TDC is exactly halfway between those marks.

At least that's how I do it. 

Wilber Are you saying with something in the spark plug hole it does not matter how far in it is just turn slow look at the wheel when it stops then go the other way same thing and split the difference?

[kmb69]

Wilber Are you saying with something in the spark plug hole it does not matter how far in it is just turn slow look at the wheel when it stops then go the other way same thing and split the difference?

That's how it's done.

[DaveBarbier]

Since the spark plug holes are at an angle I would not really want to use a dial indicator with a thin plunger because it could bend and give you a false reading. A solid piston stop is probably easiest to use.

Make one out of an old spark plug.

If you're interested, I wrote up a degreeing how to on my build thread. Link in signature.

[Airborne 82nd]

Thanks to both of you I do like the tool will through one together and read your build thread.

[madmtnmotors]

Since the spark plug holes are at an angle I would not really want to use a dial indicator with a thin plunger because it could bend and give you a false reading. A solid piston stop is probably easiest to use.

Make one out of an old spark plug.

If you're interested, I wrote up a degreeing how to on my build thread. Link in signature.

My piston stop tool was made the same way. 

[robvangulik]

  I made this one many many years ago....

[Pat_at_APE]

If you try to use a dial indicator on the top of the piston you will find the crankshaft rotates many degrees with no movement of the piston at the top of stroke.  This leaves you guessing at TDC. 

Using a piston stop at mid stroke and reading the degree wheel in the method described is the only way to exactly find TDC. 

Cheers,
Pat at APE

[Airborne 82nd]

If you try to use a dial indicator on the top of the piston you will find the crankshaft rotates many degrees with no movement of the piston at the top of stroke.  This leaves you guessing at TDC. 

Using a piston stop at mid stroke and reading the degree wheel in the method described is the only way to exactly find TDC. 

Cheers,
Pat at APE

Good to know thanks Pat