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[JamesV6CDX]

Beemer again.

With the "crank tdc locking pin fitted" the crank can still be spun a fair few degrees each way to the point it's not that accurate. Guessing an Ill fitting pattern tool (laser).

With it fitted, the highest piston 1 will go is flush with the block.

Without it fitted, piston 1 will go a bit higher and protude from the block a couple of mm.

Does that mean the TDC locking pin is not true TDC?

I always thought TDC was when the piston was as far as possible from the crank ?

[Field Marshal Dr. Opti]

Beemer again.

With the "crank tdc locking pin fitted" the crank can still be spun a fair few degrees each way to the point it's not that accurate. Guessing an Ill fitting pattern tool (laser).

With it fitted, the highest piston 1 will go is flush with the block.

Without it fitted, piston 1 will go a bit higher and protude from the block a couple of mm.

Does that mean the TDC locking pin is not true TDC?

I always thought TDC was when the piston was as far as possible from the crank ?

'Top dead centre'. So I would have presumed the same as you, James.

[STEMO]

The phrase 'Top dead centre' would suggest that the piston should be at the top of it's travel, as you say, James. But I wouldn't want to definitely say that is the case here. How many degrees do you reckon between the two positions?

[Field Marshal Dr. Opti]

On my smoky old 2 stroke bikes from the seventies I would simply poke a screwdriver through the plug hole to find TDC. Later on I would use the more accurate dial gauge.

[STEMO]

On my smoky old 2 stroke bikes from the seventies I would simply poke a screwdriver through the plug hole to find TDC. Later on I would use the more accurate dial gauge.

Yes, you liked poking holes even then. 

[Field Marshal Dr. Opti]

On my smoky old 2 stroke bikes from the seventies I would simply poke a screwdriver through the plug hole to find TDC. Later on I would use the more accurate dial gauge.

Yes, you liked poking holes even then. 

Yes.

Crude but effective, it worked well so long as you turned the engine over very slowly.

[Marks DTM Calib]

The locking pins are often not true TDC so I would not worry to much about the piston position (compromises being made regarding the cam chain setups etc).

More important to moving the crank to the centre point of the two extremes which can be achieved with the ill fitting crank locking pin in place.