Finding "good" TDC easily

[roadrun_fr]

To change a CCT we have to find the "good TDC" for each cylinder.
For one cylinder, the good TDC is when the intake and exhaust valves are closed (no tension on valve spring) : end of compression stroke.
the "bad" TDC is at the end of exhaust stroke (exhaust valve opened).
We can see these two different TDC at the fly wheel (FT mark for the front cylinder).

At 6th gear, turning the wheel, we'd be able to feel the compression stroke (difficult to turn the wheel) of the two cylinders.

If we know which cylinder fires first ccw, we can know which cylinder is at compression stroke and then know which cylinder is at "good TDC".

Checking FT or RT mark at the fly wheel would confirm us that we are right for the corresponding cylinder... isn't it ?

Is there a way to find TDC ?
Which cylinder fires first ?
Does the motor run counter-clockwise ?
Motor is a 90° vtwin but, what is the timing between the compression stroke of the two cylinders ? 1/4 turn, 3/4 turn, 1-1/4 turn, 1-3/4 turn ? cw, ccw ?

Do all these things make sense ?

[Ians98VTR]

any chance of that in english

[roadrun_fr]

Front and rear share a common journal for the connecting rods. So front and rear are always 90 (270) degrees apart.
Engine spins forward, so TDC for the rear is 270 degrees after TDC for the front.

So timing goes like this:
Front "good" TDC at 0 degrees
Rear "good" TDC 270 degrees later
Front back at "good" TDC 450 (360 + 90) degrees after rear TDC.
TDC referring to the compression strokes.

Front :
0° : Front at "good" TDC, both valves closed, end of compression stroke, FT Mark
180° : Front at BDC, end of explosion stroke
360° : Front at "bad" TDC, exhaust valve opened, end of exhaust stroke, FT mark
540° : Front at BDC, end of intake stroke

Rear:
90° : Rear at BDC, end of intake stroke
270° : Rear at "good" TDC, both valves closed, end of compression stroke, RT Mark
450° : Rear at BDC, end of explosion stroke
630° : Rear at "bad" TDC, exhaust valve opened, end of exhaust stroke , RT mark

[Ians98VTR]

thanks for that,should be quite straight forward now

[sirch345]

thanks for that,shoud be quite straight forward now

You did ask for it

[Pete.L]

So Roadrun
you have now answered your own question of "what it the firing order?"
Just after the compression stroke it goes bang
and as there are only two pots I bet it goes front,back,front back,front back,front,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontback,front back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontback..cough!front back,frontback..splutter,frontback..bang!
Well it is a V twin

[RAINMAKER]

Pete.........just how bored are you

[roadrun_fr]

[cupasoop]

So Roadrun
you have now answered your own question of "what it the firing order?"
Just after the compression stroke it goes bang
and as there are only two pots I bet it goes front,back,front back,front back,front,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontback,front back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontback..cough!front back,frontback..splutter,frontback..bang!
Well it is a V twin

Mine must be broken, it goes back, front, back, front........... Do you think this will cause problems?

[Pete.L]

Only if you shoot off backwards down the road Cuppa!

Paul- yep!!

Pete.l

[Stormin Ben]

So Roadrun
you have now answered your own question of "what it the firing order?"
Just after the compression stroke it goes bang
and as there are only two pots I bet it goes front,back,front back,front back,front,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontbackfront,back,front back,frontback,front back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontbackfront back,frontback..cough!front back,frontback..splutter,frontback..bang!
Well it is a V twin

Mine must be broken, it goes back, front, back, front........... Do you think this will cause problems?

<national stereotype mode engaged>
Its not an Italian import is it mate?

Ben

[cupasoop]

<national stereotype mode engaged>
Its not an Italian import is it mate?

Ben

Wish it was......might make me ride like Rossi

[iggy1966]

Wish it was......might make me ride like Rossi

yeah FRANCIS rossi