Checking and setting 308 Cam timing

Those "event" specs are with a theoretical valve clearance of 0.5 mm (which is much larger than the normal operating clearance) so either:

1. actually change the shim to give the 0.5mm clearance -- then the "event" occurs with the first (and last) detectable motion of the bucket, or

2. measure the existing operating clearance, and the "event" occurs when the bucket deflection = (0.5mm - the existing clearance), or

3. put in a thin flat shim (between the bucket shim and the cam lobe so the clearance is 0 -- like you're measuring the operating clearance) -- then the "event" occurs when the bucket deflection = 0.5 mm

Also, you should really measure all three events (opens, midpoint, and closes) as a way to verify/check/be a little more sure about your results. I.e.:

1. If you measure the opening is early and the closing is early = maybe you do need to move the sprocket, but

2. If you measure the opening is early and the closing is late = either something is wrong with your set-up/method, or your camshaft lobe is not stock.

With your present method/set-up, are you also measuring that the intake is closing way late?

 

There is an alternative way of checking the timing. I assume that you checked and adjusted the valve clearances to within the specified range. Regardless of the clearances, fully open will always be the same, i.e., the center of the lobe. So if you measure to that point, when the valve is fully open, you can judge whether it is properly timed.

With the depth gauge on the shim, rotate the engine slowly and determine the point on the degree wheel when the valve is no longer going down. Note the degree. Then keep turning the engine slowly to the point where the valve just starts to move up. Note the degree of that point. Midway between those two degrees is the exact middle of the lobe. Do that for intake and for exhaust on #1. If you are anal, do this a couple of times to verify that you are coming up with the exact center of the lobe of each cam.

Now, if I did my math right, your intake valve should be fully open at 96* ATDC at the mid-point of the cam lobe, and the exhaust fully open at 89* BTDC. This is not the absolute most accurate way of doing this, but it should give you a very close estimate if you are verifying that the cams are timed properly. Because it is not dependent on setting all the shims to .050, you can do it with the cams properly shimmed for operating clearances.

Both cams should be very close to those numbers, within a degree would be great. If one or the other cam is off by more than a degree or 2, I'd be concerned and you may need to reset the cam sprockets, which can be a real PITA.

Hope that helps.

 

It's a LARGER clearance for checking the occurrence of the opening and closing events -- and, no, you would never operate the engine with such clearances in place (and as I tried to describe, you don't actually have to set this larger clearance -- but doing so is OK mathematically). It has to with the shape of curve for the valve movement vs the crankshaft rotation angle. At the normal operating clearance, the slope of this curve is almost flat when the valve just starts to move -- so it adds a lot of uncertainty to the measurement. By increasing the clearance, or pushing the valve in a little bit first (i.e., the 0.5mm - the normal clearance), you move up the curve a little bit where the slope isn't so flat so it's easier to repeat the same angle for the same lift.

 

People mention that they check the valve timing with the engine in, but I have never seen a picture of the set-up for measuring valve lift for the front exhaust cam. I had a hell of a time getting something in the space between the shim and the firewall. There must be a better way than what I did. Anyone care to take a picture of what they used for this and share?

 

But that is why the shims are supposed to be within a very tight tolerance range when set for operating the engine. If you use the "factory" procedure and set the shims on #1 and #5 at .5mm to measure open and close, you still have to change them back to the operating clearance before starting the engine. It seems to me that they use the .5mm to assure that the measurements are consistent on all engines, since valve clearances for operation can actually vary within a range of a few thousandths.

 

For those of you plan to adjust your own valve clearance, this might help.
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How do you set the clearance to .5mm to check timing without it also varying by a few thousandths?

 

Just to add yet another demension to the cam dynamic. As a rule of thumb, every thousands of an inch of valve clearance equals 1 degree of cam timing. By adjusting the valves up or down you can change the cam timing several degrees. Now we know that Ferrari gives us a specified valve clearance and that should be followed. However there are some that have changed the valve gap and modified the cam timing with adjustable sprockets. Just food for thought.

howard
tr0768

 

With difficulty

Seriously, I think the wording was a bit of a mis-translation, and was really meant as a mathematical statement rather than an action to be taken -- i.e., by measuring the existing clearance (which you can do to the nearest thousandth) and then deflecting the bucket by a distance of (0.5 mm - the existing clearance), the contact line on the cam lobe that is touching the shim is in the exact same place that it would be if the clearance was perfectly adjusted to 0.5 mm exactly and the bucket is just starting to move. JMO.

 

Anybody know where I can get a set of valve shims for the QV?

 

Start with GT Car parts in AZ, then try MotorKraft in Indianapolis. They have quite a few in stock. That's where I got mine.

JIM

 

No, it's a correct translation.

The factory training is to actually setup that 0.5mm clearance.

The 0.5mm clearance setup goes back to the early '50s DOHC V12s, & is still used on the newer engines. Was discussing this with a 30+ year Ferrari technician when I saw it unambiguoustly described in a F40 WSM & he confirmed that he was trained to do it this way by an ex Ferrari F1 team technician:

You replace the shim on the front valves of each bank with ones selected to just let a 0.5mm feeler gauge thru. If necessary a shim is ground down on a surface grinder to give minimum clearance. Since the engine is never run with these setup shims, in theory you could even make setup shims out of a hard Al like 7075.

 

I don't dispute that the training may have evolved (or is it devolved) into doing the cumbersome physical action (since it doesn't require using any intelligence and is more easily stated), but I'd still say that it is unnecessary (and the mis-translation, or simplification, if you prefer, occurred between the Eng. Dept. and who they were trying to explain it to, rather than just in the language translation from Italiano to English). If someone handed you a bare camshaft and asked you to measure it, is your only option to find a corresponding engine so that you can set the clearance to 0.5 mm exactly before measuring it?

 

Lobe ramp profile variances are greater in the transition area one to the next than one might think. I change the shim. With a max. allowable variance of 2 degree's (Thats from the printed spec, not a notch!) on a TR exhaust cam being the difference between the Cats living and not, accuate figures and settings are a must.

Lobe contours off the transition from heal to lobe are quite consistant and is the reason to check it further up the ramp.

 

But isn't it the same spot on the cam lobe wether you turn the cam for .5mm lift with no clearance or if you set the gap to .5mm and turn the cam for first signs of lift? Is it still not .5mm of lobe lift either way? And so wouldn't that spot on the cam be exactly the same spot?

I don't get the difference.

 

Speaking of lobe, shouldn't the lobe be pointing perpendicular from the tappet?
This pic shows that it's not. Does this make any Diff? Thanks.
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Mike,

In that the cam lobe is postioned on the "base circle", the clearance "should" be the same as on the perpendicular axis. For my money, I always set the cam lobe perpendicular to the tappet before checking the valve clearance....

David

 

Ok Thanks David

 

Thanks to this and everyone who has contributed to the other cam setup threads I've been studying... I've just done my '88 328 (60K miles/ timing belts so old they're floppy loose), and need some help to close out:
After finding TDC with the bump/stop method on cylinder 1, all 4 cam marks were DEAD ON - not close, but dead on. That's nice, but since these are only assembly marks, I'm not satisfied, so, using the lobe center method, I've degreed the 4 cams with these results (note: of course, I can't measure fractions of a degree - the fractions come about because of the mathematics of locating the lobe centers):
cyl 1 Intake +1/2 degree from spec
cyl 1 Exhaust -1/4 degree from spec
cyl 5 Intake dead on to spec
cyl 5 Exhaust +1.5 degrees from spec

Question is: using pin/sprocket, belt teeth, etc., what's the best I can achieve? is it +/- 1/2 degree, +/- 1 degree, or what?

Second question: is 1.5 degrees worth trying to improve? (car was running 'fine' before, but had occasionally lit up the slow down light)

Many thanks for any/all who care to weigh in.

ZOOOOMZ

 

Personally, I would leave all alone.

There is no way to get 1/4 or even 1/2 degree accuracy on whatever degree wheel you are using. You are dreaming up that number. The belt tension alone gives you +/-1 degree.

The only possible exception that I might (might not will) make is the cyl 5 with 1.5 degrees off. In order to adjust this, you have to remove the cam sprocket from the cam, move it 2 belt notches over, re attach the belt, re-tension, and re cam the whole thing.

In my opinion, leave it alone if it ran well last time. You are not going to get much performance from this.

Last, is the engine out of the car? How did you set up the dial indicator over the exhaust cam on the front bank? No space ...

 

There's space, you just have to be clever with how you set up your dial indicator. While there's definitely not enough clearance to use a standard dial indicator holder on the front bank, there are other ways to get the dial indicator in appropriate position. I used a threaded rod with the same diameter and thread pitch as a spark plug (M12 x 1.25) and screwed it into cylinder #7 and then used this to clamp my dial indicator to. You need to make sure and create a vent hole in the threaded rod so you don't build up compression in the cylinder as you're turning the engine over.
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That is a clever little tool for mounting your dial indiacator. Great job.

 

Thanks for your quick responses!

Yep, agree, we cannot 'measure' fractional degrees, with the wheels we can fit on our engines... as I mentioned in my post, the fractions are an accident of mathematics, calculating the lobe center by dividing the close-open by 2... however, I'd consider those fractional errors to be artifiacts, and I see those three readings as 'dead on'.

Thanks for the guidance on the 1.5 degree one.

The engine is in the car; I used a dial indicator setup from JEGS, setup of which I'll post a pic or two later today (not at the home computer right now). I used a crossbar spanning two of the cam cover studs, and had only to move one hose out of the way, near the firewall. Wish I'd had one of those sexy spark plug threaded posts, though - that would have been quicker to setup!

Thanks again for your quick responses!