Cam Timing !,3

[Derek Creasy]

  After an S1 re-build with an S2 head , it starts and runs well using the 28/66 inlet and 66/28 exhaust settings but the pistons “just” touch the exhaust valves as it gets warm .Can anyone suggest how far I should ideally advance the exhaust cam to be safe ; maybe 63/25 or even 60/22  ?

[lancialulu]

That should not happen! I assume you have 303 cams?

How thick is the head? From memory a Fulvia head is c 86.0 mm thick. (A last ditch solution would be to use a thicker head gasket).

The critical area for an exhaust valve / piston clearance is c10deg before tdc. I routinely see adequate clearance at this point. Maybe recheck valve timing?

[Richard Fridd]

 I had deeper pockets machined into the piston crowns. This was to accommodate alternative cam profiles.

            Richard

[Derek Creasy]

I loose fitted the head again today and checked all openings/closings and both cams have a 24* longer duration than standard so I can only assume they have been modified at some point .  This explains why the exhaust valve set at the book opening closed late enough for the piston to just touch it .  I will re-fit the head properly tomorrow and set the inlet to open at 28* btdc and the exhaust to close at 28*atdc .
 If I ever do anything like this again  (unlikely) , I'll also check closing points and not just the openings ! Huge learning curve .

[lancialulu]

The better way is to measure both opening and closing with a 0.4mm measuring gap, and calculate max opening point MOP. Then adjust timing to set the MOP to c 109 degrees. At c 10deg BTDC see how much clearance is when operating gaps are set. For HF and more radical cams gaps In is 0.2 and Exh 0.3mm. To see how much gap from piston to valve, wing in the tappet adjuster till valve touches piston (at c10deg BTDC for ex and c10deg ATDC for IN). One turn of the adjuster = 1mm

[RobD]

Derek, Have you considered reducing the valve overlap? Italian manufacturers often use quite a lot of overlap and in the real world potentially sacrificing a few BHP from the top end can be compensated by improved mid range drive. It depends what you're looking for of course but in my relatively limited experience the Fulvia responds very well to a slighter softer cam timing. Might be worth a try.

[Derek Creasy]

Thanks for your comments Tim , Richard and Rob .   I'll check those measurements today .

[lancialulu]

Derek you mention that the cam may have been modified. Are there any markings and is the base of the lobe (diameter across the base of the lobe) reduced from the standard 24mm?

[RobD]

Using the lobe centre method of measurement, the cams in my Fulvia are timed at 105, if I recall the standard cams are timed at something like 100.

[Derek Creasy]

Derek you mention that the cam may have been modified. Are there any markings and is the base of the lobe (diameter across the base of the lobe) reduced from the standard 24mm?

I am only assuming that they are not standard because of the increased duration  .  The odd thing is that when this S2 head was fitted on the S2 engine using the normal timing there was no problem (other than low oil pressure),  despite the new pistons in that engine having  smaller cut-outs than the ones in the  original S1 engine that I am now endeavouring to fit it to.  Could it be that the piston heights are slightly different as all measurements on the 2 heads are virtually identical . I can't see any marks whatsoever on either set of cams or measure the lobe in position , BUT----- what I can see is that the "heel" of the suspect cams is thicker than my S1's and also that the shaft casting faces between lobes are very different .  The S2 s are rough unfinished whereas the S1 s are machined smooth ; does any of this present any clues  ?

[lancialulu]

If the heel base of lobe is c24mm then this would be an un modified cam. S2 cams were not finished to same S1 standards… make sure you have timed to a MOP of 109deg BTDC using .4mm tappet gap. Measure opening and closing positions to calculate mop. Running gap should be 0.3mm for exhaust….

[Derek Creasy]

If the heel base of lobe is c24mm then this would be an un modified cam. S2 cams were not finished to same S1 standards… make sure you have timed to a MOP of 109deg BTDC using .4mm tappet gap. Measure opening and closing positions to calculate mop. Running gap should be 0.3mm for exhaust….

Thanks again Tim ,  I will check it like this asap .