when is tdc not tdc?

[dave]

got this 1.9 ahf engine, took head of set it to tdc by fly wheel tdc, but when removing head noticed piston if a few mm down from tdc, move it to top and fly wheel mark don't line up no more.

when putting back together do i set it to real tdc or fly tdc?

 

[fingers99]

Odd. what's an ahf?

I wonder if the mark isn't "really" TDC, but some other er, mark?

 

[dave]

hmm maybe i should have used the oem mark, car all back together but dont start

 

[sludgeguts]

If that's a timing mark it will be set to a couple of degrees before tdc to account for the split second delay between spark, ignition and complete combustion so that by the time full combustion occurs the piston is on/about to start the downstroke to accommodate the expanding combustion gases. In which case, the piston will be slightly below tdc with the marks aligned but the mark may well be referred to as tdc because it's as near as makes no odds & no-one would ever know without removing the head.
Also, is it possible to have the piston at tdc on the combustion stroke with the cams looking at tdc on exhaust stroke?

 

[fingers99]

Also, is it possible to have the piston at tdc on the combustion stroke with the cams looking at tdc on exhaust stroke?

Well, not for all pistons.............

 

[dave]

its a diesel not sure if that makes any difference? if its not raining tomorrow the boy is coming round and we will set it all up again using oem TDC. piston was about 1.5cm down the bore though on that setting

 

[fingers99]

I do think it may be a "this is it" mark, rather than TDC as such.

 

[GrandeGuy]

http://www.contitech.de/pages/produkte/antriebsriemen/kfz-ersatz/docs/ti/00_003_en.pdf

 

[dave]

well its defiantly( thats not the right word but one i want dont come up on spell checker) timed correctly now, fuel comes out when i crack injectors but it still don't start i can see air bubble in clear fuel line it wont self bleed and battery keeps going flat trying to hand bleed, i tried a tow start but it seems the boy don't have a clue how to tow start a car:bang:

 

[Stilo man]

If the timing is all sett make sure the battery is fully charged and get some easy start and spray down inlet pipe and keep spraying while somebody winds it over if it starts and runs then youve got a fuel fault if it doesn't then There could be a fault with maf sensor or other stuff.

 

[dave]

cars long gone now.