TDC marks confusing me...

[Tommys86]

Hey chaps - struggling to determine TDC#1. I have the mark on flywheel bottom side but struggling to make sense of the top side window and "OT" doesn't appear to be there but I have some other markings - do you think this is set? I've also got a long stick in #1 spark plug which is indicating it's up but there's as much precision in that.

Cheers

Tom

 

[Tommys86]

 

[Cater_Racer]

Looks right Tom

http://www.clarks-garage.com/shop-manual/eng-13.htm

 

[Dan944t]

Tom if the stick is right up and that mark is there I’d say your there.

Have ve you got a dial indicator?

 

[Tommys86]

Yeah the bottom lines up ok but the comments on Clark's doesn't prefer this option

"If you have trouble locating the TDC mark from above, there is a 5 mm wide groove in the flywheel which can be used to locate TDC as well. It will appear in an opening in the bottom of the clutch housing near the starter. When the groove is centered in the opening the #1 cylinder is at TDC. Personally, I don't care for this method because if the groove is not centered in the opening, the timing can be off [FONT=symbol"]± 1 tooth."

That said I do feel mine is centered.... just cant make out the top bit :/

 

[Dan944t]

This time round I used a dial indicator to atchieve too dead centre.

normally I’ve gone by the book method too but wanted to do it my own way this time when I rebuilt the engine, and there’s no more precise way than with a dial indicator from cylinder 1. I have noticed it starts way faster now than ever I believe due to the timing now being spot on.

there not expensive to buy now online and takes any guess work out of you want to be bang on like I wanted to this time round.

atb
daniel

 

[Tommys86]

Thanks Dan - is that like a long dti needle you'd read off the top of the piston? I might have a look what's about thanks!

 

[Dan944t]

Hi tommy, here you go mate you’ll need the magnetic base so it doesn’t moove anything metal on the engine bay.
I used a 1/2inch extension down in cylinder one and set the dial indicator up so the needle was resting on the top of the extension and turnt the crank by hand very gently and it will display the minutest if movement, so you can go back and forth and get the very Top dead centre.

I actually engraved a made a new mark on te crank pully so that from now on I shall go by that, *Note that I have custom piston and Conrods so it was inportant for me to get this right as my new pistons are very slightly smaller in height ect.
Heres a pic i just found for you on Ebay very cheap

https://imgur.com/a/a3Qj6TY

Atb
daniel

 

[Tommys86]

Hi Dan been thinking about this - did you ever get a "flat spot" where you get the smallest of crank movement but zero dti movement? And if so did you favour one side I.e. on the up to zero OR on the other side zero to down. Technically both being zero but slightly different?

Or third answer - Tom you're completely over thinking this...

 

[Dan944t]

Hi Tom,

im exactly with you on this, which is why I wanted to do it this time with the dial indicator as doing it as per the porsche workshop is always gonna be vague if you want to know it’s precise.

i actually decided I would set up as soon as it hit the highest spot and not on the way down if that makes sense so that im timed at the first very begining of the highest point.

Soon as i turn the key it fires up I’d say 40% quicker than before when I’d use the marks in the flywheel.

atb
daniel

 

[zcacogp]

Tom,

I think your photos are upside-down but I also think you are just about there. I've marked one of them up but I think you are within a fraction of a degree of being spot on. FWIW, the 'OT' on the flywheel on mine is not stamped in the same way as the 'OT' on the flywheel pictured on Clarks Garage. Just to help, someone has been there before you and put a helpful blob of tippex on the flywheel so you know you are in the right place (I've done exactly the same with mine as peering into that hole in the bellhousing is not easy).

Someone who is clever will be able to explain the maffs of the movement of a piston as it approaches TDC but it's to do with Tan x tending towards 0 as x tends towards 0 - i.e. the movement will be infinitesimally small as you move the crank past TDC. Go with the mark if you can as it will be more precise.

I can't imagine that this is the first time you have done this job but the balance shaft belts always confuse me more than the cam belt.


Oli.