8 replies to this topic

[JamesAlexander]

Hi folks,

I’m in the process of changing the cam on my ‘92 998 and I’ve found that the dizzy is firing on number 4 piston when it is at dot to dot on the cam/crank sprockets.

I’ve checked for movement in the push rods and there is no movement at cylinder 4 and slight movement on 1 and similarly when I rotate to TDC on cylinder 1 the dot on the cam sprocket is 180 degrees out and there is no movement on the pushrods on cylinder one.

 

So I am right to assume the dizzy is in the correct place for the firing stroke but someone has taken off the sprockets and put them back in with dot dot firing on cylinder 4?

 

The dizzy does point to the cylinder that has no movement photos show dizzy firing on 1 and the cam ting sprockets and dizzy firing on 4 and the sprockets.

 

If I just rotated the dizzy 180 degrees then I believe I would then not be sparking on the firing stroke, I guess it doesn’t matter much as I’m taking the sprockets off to change the cam so can put back in using dot to dot at TDC on 1 but I just wanted to check if my engine had been messed about with by a muppet!

 

Cheers for your thoughts!

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[imack]

What you have is completely normal and correct. Dot to dot is firing on no.4, dots 180° apart and rotor arm pointing at no.1 cylinder is correct.
Just one of the A series peculiarities.

[mad4classics]

Don't get hung up on firing stroke the dots set TDC on number 1 cylinder at the start of the 4 stroke sequence. i.e. the next stroke for cylinder 1 is the induction stroke.

[JamesAlexander]

Many thanks for your answers! Turns out I’m the muppet then! Ha! So does this mean that when I take it off I just move it to dot to dot then remove, then put back on the in the same position?

Thanks again!

[mad4classics]

Many thanks for your answers! Turns out I’m the muppet then! Ha! So does this mean that when I take it off I just move it to dot to dot then remove, then put back on the in the same position?
Thanks again!

Escentially yes. However, call it OCD but I like to see both rockers free on number 4 to set true TDC.

[JamesAlexander]

Does this mean that you take it off with the dots 180 degrees apart and put back on the same way mad4classics? Thanks for your help!

[timmy850]

It doesn’t really matter how you take it off, as when they are lined up dot to dot the crankshaft is at TDC on 1/4 cylinders (when the woodruff key is up), and you just rotate the cam till it lines up

[mad4classics]

Does this mean that you take it off with the dots 180 degrees apart and put back on the same way mad4classics? Thanks for your help!

As long as you don't rotate anything or disturb the position of the cam or crank sprocket in the timing chain!!! The dots gave you the correct setup in the first instance. I just like to see the dots line up whenever I'm taking things apart; gives me a nice comforting feeling knowing it's absolutely spot on and there's no doubt.

Edited by mad4classics, 18 June 2023 - 04:35 PM.

[JamesAlexander]

Great thanks all, appreciate the help, got the new cam in today and now just need to check the timing is ok with the protractor.