Cylinder Head Refit Question - Updated

billy_bob · Post by **billy_bob** » 04 Aug 2004, 18:51

Hi All,
The head has gone to the engineers to get skimmed and I have been trying to familiarise myself with the refit procedures. Mostly, things seem fine but I have come accross something I don't understand ...
Haynes says I need to turn the crankshaft (which is currently locked at TDC) until the pistons reach bottom dead centre (BDC) and then keep going until all pistons are half-way up/down their stroke. Why?
Currently the injector pump is locked at TDC, as is the crankshaft, and camshaft (before dismantling for skimming) was also locked at TDC. With the timing belt off, won't turning the crankshaft put everything alse out of alignment?
I'm confused [:(]. Can anyone shed light on this, please?

bxbodger · Post by **bxbodger** » 04 Aug 2004, 19:11

Very strange indeed! To put everything back it all needs to be in matching positions to start / run, i.e. everything at TDC, or whatever....are you sure you have read it correctly and not missed something?- if its put back together with all at TDC except the crank, then it certainly won't start like this.

billy_bob · Post by **billy_bob** » 04 Aug 2004, 19:21

Re-read the refit head section and it seems to be!
I'm confused and don't really want to start loosing TDC with the camshaft sprocket not in place and everything else freed from the timing belt.
If refitting was going to mean not using TDC then why was it important to find it while dismantling?
HELP!!!

Mosser · Post by **Mosser** » 04 Aug 2004, 20:09

Haynes is wrong, dont take your locking pins out !!, i found the same problem when i was rebuilding my 406td cylinder head, i did hours of research and in the end came to the conclusion that haynes messed up (no suprise there though!!), just refit the head leaving the camshaft out, then put the sprocket on the end of the camshaft and line it up with the locking screws before putting the caps on and torqing the nuts

billy_bob · Post by **billy_bob** » 04 Aug 2004, 20:33

Thanks Mosser - that sounds a bit more like it!

Robin · Post by **Robin** » 04 Aug 2004, 22:07

I think I can explain the misunderstanding here. Haynes are wrong in this instance though. It was always considered good practice when replacing OHV heads to put pistons at half way to avoid any risk of clamping down open valves on a piston head at TDC. All very simple on non OHC engines.
This is a typical example of the Haynes proof readers not being engineers/muckanics/enthusiasts etc. Best wishes and good luck. Got mine to do when time permits!! R

AndersDK · Post by **AndersDK** » 04 Aug 2004, 22:30

bb - stop worry and get in line with Mosser & Robin, where I also would be to find [;)]
then you'd pretty soon be a king - bb king [8D]
it would not be smart to loosen all set axles at this stage [;)]

billy_bob · Post by **billy_bob** » 05 Aug 2004, 00:35

Feel even more relaxed now ... [8D]
Thanks for the advice everyone.
Hopefully I won't be singing the blues too soon!

carl · Post by **carl** » 07 Aug 2004, 00:02

With an ohv engine you are unlikely to have disturbed the cam timing so you can bolt up without having to worry. With an ohc engine you could put the head on with the cam in the wrong position. as long as you make sure the cam is in the same position as it was when the head came off you will not have a problem. So Haynes are just safeguarding you from making this mistake.I do not understand Robins reply. Why would the cam timing be different when replacing a head with push rods? sorry if I`m being a bit thick.

Robin · Post by **Robin** » 07 Aug 2004, 01:41

Carl, the practice was due to the possibility of fitting the head before you timed up the camshaft which was possible with the older OHV units. This could then allow the head to be bolted down with a piston at TDC and a valve wide open on the same cylinder.
A bit of belts and braces really. Hope this helps, Robin.

carl · Post by **carl** » 11 Aug 2004, 03:00

Sorry if I come across as a bit of a pedant here. I assume that when we use the term ohv we are talking about pushrod engines, in which case what is the difference between an "older ohv engine" and a modern push rod engine(say Ford Endura)?. Why would anyone would fit a pushrod head with the cam drive disconnected?

TheWorker · Post by **TheWorker** » 11 Aug 2004, 03:42

the crank is locked with 1 and 4 pistons up then when the head comes back stick the sprocket back on and make sure its timed as well,i presume you have a diesel so the the hole lines up about the 7 o'clock position with a 13mm bolt into the head.the pump has two timeing holes at 12 and 4, again you can use 13mm bolts.
once the head is tightened down put a belt on and turn the crankshaft over twice by hand to make sure you have compresion and the valves dont hit the pistons,then recheck the timeing.simple.

Robin · Post by **Robin** » 11 Aug 2004, 22:20

Carl, not a pedant at all. Yes, I am referring to pushrod engines. The belts and braces bit goes back to basic training and advice that was popular way back from the 1920's in fact. It really stems from engine building not just head replacement.
Industrial and automotive engines would have a range of ancilliaries driven from the front end so it was accepted that you would not necessarily time up the camshaft until you knew what you were putting on the engine and which housings and chain would be used.
Many engines use the bolts that hold the rocker shaft as head bolts too. So it was easily possible to fit a head with a piston at TDC and the valve wide open.
More modern units tend not to use the head bolts for securing rocker shafts so the practice or advice is now rather dated but still relevant on older engines. Say pre 1970's. A bit of custom and practice that is rapidly becoming outdated I guess. Robin

oilyspanner · Post by **oilyspanner** » 11 Aug 2004, 23:46

As long as the cam is in the index position as well as the crank you can pop it back on fine. I have seen someone snap a cam if thats wrong.
Stewart

billy_bob · Post by **billy_bob** » 12 Aug 2004, 13:46

Billy here again with an add-on question!
Thanks for the advice everyone but now I need your help again.
I have gone with leaving everything at tdc and have refitted the camshaft. The centre and right (brake pump end) retainer caps for the camshaft fit flush to the cylinder head but the left cap (camshaft sprocket end) won't sit flush, i.e. there is about a 1mm gap beneath each face of the cap.
Should all three of the caps be flush?
Thanks, Billy [Paused]