Update 1/23/12: In the spirit of taking one for the team -you kind reader being ‘the team’, and the ‘taking one’ is me in the form of admitting to not fully considering this subject before I wrote about it, I am writing this update. It will be open ended and hopefully draw further discussion…
The result I was hoping for has finally happened: those with more knowledge/experience than me (Tom, Rick -thanks) have chimed in in the comments section -(though Tom, I think ‘inexperienced’ is a better word than ‘sloppy’). The question of the cam timing had been bothering me since I wrote the first draft of this post -I even made a table to try and figure out what I was missing, but now it seems to be approaching the obvious. For those that are spectators, or as inexperienced as me, this is what I have been thinking and why I have been thinking it.
Background on the subject:
This is the valve timing chart from the factory printed Giulietta Technical Specifications book. Note that this timing is always based on crank position. There are many versions of this chart for the many models over the years.
Figure 2. The cam part numbers from the factory Giulietta parts manual. Note that there are only 3 different cams listed: a common intake/exhaust cam for ‘normal’ models and intake and exhaust specific cams for performance models (Veloce/SS/SZ).
The Valve timing steps from the factory Giulietta shop manual. This only works for putting together engines where the parts all came together from, and were marked at the factory.
Courtesy of the fine folks at Centerline Alfa. Stock cam specifications.
Notes on Cam timing from an Alfa Ricambi catalog of unknown date but probably from the 80’s.
Second page of cam timing discussion.
Specifications of some cams available from Alfa Ricambi in the old days.
These were found on the Alfa BB. If you scale them so the semi-circle is the same size as the cam cap and print them, you can mark your caps for the desired duration. Care needs to be taken with timing chain tensions.
The timing marks on the cams are cut in pretty seriously, making me believe they are applied by a machining step during the manufacture of the cam. I have read that they indicate 90° from the lobe center -clockwise for the intake, counter clockwise for the exhaust.
The timing marks on the cam caps appear to be hand stamped -probably after the cam timing is set on the new engine, making them arbitrary in the event of a cam model change.
An aside: Looking at the valve timing chart (figure 1) and the parts book (figure 2) shows some interesting things. The Veloce’s and SS/SZ’s share cams (same part numbers), yet they have different clearances and there-by durations. A Veloce with a clearance of .375 – .40 mm gets an intake duration (at the crank) of ‘opening begins’ at 34° before TDC to ‘closing ends’ at 63° after BDC, and an SS/SZ with a clearance of .275 – .30mm gets an intake duration of ‘opening begins’ at 46° before TDC to ‘closing ends’ at 65° after BDC. So, since the valves are all the same between models, the clearance determines the duration of the cam, and approximately .1mm of clearance ADDS a total of ~14° (at the crank) duration for the intake Veloce cam.
A lot of questions are raised by the above paragraph. Are the cam timing marks for a Veloce engine aligned to the normal mark defined by the flat base of the cam cap? If not, are there other factors, other tolerances that add up and necessitate the placement of a timing mark that is not the same as a normal mark? I suppose there is enough tolerance stack-up in the engine to result in a ‘normal ± x°’ mark on the cap being the set mark. Does this makes the idea of ‘normal’ a nice, symmetrical and potentially meaningless idea? If so then my set up in the first installment was incorrect.
All this is compounded by the info that the cams are only adjustable in 1.5° increments (if Pat Braden is correct).
Where am I? Oh, yeah. So, my Sprint has a) a head that is not original to my engine; b) non-original cam caps that were chosen because they offered the right fit; c) cams from a 72-74 FI 2 liter engine; d) cams that are, as of a few weeks ago, timed to what I defined as the ‘normal mark’.
So, if indeed there is a degree tolerance in the engine making the ‘normal mark’ arbitrary, my cam timing is still off by some amount.
So if I’m right in what I wrote above, up next is setting the cam timing to the crank per the recommendation made for my cams which would be 114° intake and 102° exhaust, which means my exhaust is about right and my intake is retarded a bit based on the shankle gauges compared to the ‘normal’ set up below.
I hope this helps and I hope those with more knowledge than me comment to help me become enlightened.
Original post 1/11/12: I was hanging out at Jaan’s shop today and he related an interesting story about cam timing and a recent Giulia 101 1600 engine rebuild to me and, based on a recent chance to drive my Sprint, told me he’d gladly check the cam timing in my car, thinking it might be out since it didn’t pull very well from still. I told him the head was set up by Norman Racing Group at great expense, and I triple checked the cam to cap timing marks when I put the engine together, but he persisted and I though ‘hey, a legendary tuner wants to do some gratis work on my Sprint -why not’.
I acted as sous chef and he did the detail work.
This is what it looked like when I pulled the valve cover off. Timing chain is nice and tight. Cam lobes point where they should when the marks on the cams align to the marks on the cam caps. Looks good to me. Jaan instructed me to pull the cam caps with the timing marks off. There is another little problem visible here, look carefully -no, it’s not the wonky radiator hose.
Honestly, does this look as good to you as it does to me?
I bet one or two of you are looking at this and shaking your heads knowingly. This is a factory Alfa tool, it measures the degree off of normal that the cam timing marks are. Normal is defined as the machined face of the head and normal means the mark is perpendicular to that face. If the mark was correctly applied, the marker would point to zero. This intake cap is marked 6 degrees advanced.
This should give you a sense of how it works. The little blade at the top splits the center of the mark and the bottom shows clearly the angle of the mark.
You have to admit that based on this, the alignment of this exhaust cam looks perfect. Turns out this cam cap is marked so that the timing is 5 degrees retarded.
So in summary, it turned out my exhaust cam was retarded about 5 degrees and intake cam was advanced about 6 degrees. We marked the true center mark on the caps, retimed the cams, put it all back together and it starts much easier pulls WAY better off idle. I used to have to slip the clutch a bit to get it going and now it just goes. At the other end of the rev range it runs about the same.
How does your car run? Jaan says he’ll mark your cam caps correctly for $25. I guess you could mail them to me and I’d handle the action if you want.
This is what you were meant to see in the first picture. The coolant is seeping through these head plugs. I wondered where the coolant was going -every time I checked it it was a little low. I guess a little alumaseal is in my future -not sure how else to deal with it without it being a serious undertaking.
Lesson here is, you think you can trust factory markings… it’s not your fault.