Establishing actual TDC...

I always use the positive stop method for establishing punto morto.
Gary Bobileff

 

Can you explain your method a little more clearly (if you were actually calculating "degrees of crankshaft rotation per piston VERTICAL travel" -- this value goes to infinity at TDC because the piston vertical travel is 0 at TDC -- so it wouldn't be useful).

If you are using the dial indicator to detect the two (different) angular positions of the crankshaft where the piston is some distance, "X", below its maximum height, and then saying that the angular position of the crankshaft at TDC is halfway between those two positions, that would be mathematically equivalent to the piston stop method.

 

You can find tdc with a dial indicator as you noted, same way you find L/C on a cam. But a stop does the same thing and is quicker and easier.

 

I'm actually a little disappointed -- when you said that you were "calculating" the slope of the piston motion vs crankshaft rotation function and then using those calculations to predict the TDC location, I thought to myself "what black magic is this?". Good thing -- otherwise, we'd have to burn you as a witch

 

This is the method that I use with a degree wheel. I will install the piston stop and rotate the engine in 1 direction until the piston makes contact with the stop. Take the reading on the degree wheel then rotate it in the opposite direction until it makes contact again. now take the 2 readings subtract them then divide by 2 then move the indicator that many degrees to find true TDC.

Example CW rotation stops 18 degrees ATDC
CCW rotation stops at 22 degrees BTDC
22-18=4 4/2=2

Now move your indicator at the degree wheel 2 degrees towards BTDC
You are at true TDC.

 

James,

Do all production ferraris have symetrical cam lobes?

 

I can tell you that cam lobes for Ferrari cams A-138766, A-138767-R, S-139232, and S-139233 are symmetrical. At my request, Web Cam read my four cams from my 1994, 348 Spider on a program called "Cam Pro Plus". The camshaft is centered in a fixture with a sensor riding on the lobe. Cam is then rotated, and the data is transmitted to the computer where it is then available for review. The information obtained from this program is available in data form and/or can be displayed graphically in an easy to interpret table. These two pictures are from cylinder 8A exhaust lobe. “A” is the first lobe closest to the belt pulley on exhaust camshaft 5-8. 8B would be the second lobe from the belt pulley. Next in line would be 7A then 7B and so on….. After comparing all lobes (4 cams, 32 lobes) they differed not in lift or duration but in phasing relative to each cylinder. Regrinding will correct this. I guess it must have been a Friday at the Ferrari camshaft department when my cams were indexed and ground. 1 degree camshaft error is 2 degrees crankshaft. These errors are ground into my camshafts from the factory that could never be corrected without regrinding. Now, does it really make a difference????? I don't know. If I didn't need to repair a chipped lobe, I never would have known.
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good point - asymetric lobes will crater this method.

Sorry though - can't answer your question!

mackb61:
Did your re-grind cure the out-of-phase?
What kind of heat treat was done after the grind?

Are you sure the out of phase was not intentional by Fcar?
Perhaps they are accounting for load related torsion in the cam stick at high rpm?
The cams are likely ground by robot & as such, an error of this type would seem unlikely.

It would be interesting to note if the phase change was progressive as you measured lobes further from the pully.

Rgds,
Vince

 

It would have been interesting to see after the regrind whether there were dyno differences. Also, did web regrind or weld and regrind. I did not think there was much on the base circle to grind as is. I used Webcam back in my 308 days and they did nice work back then. Luckily I have had no used for their services in the last 20 years!

 

my numbers may be off here - I am working from memory...

Fcar TR says set the lash at .050 before using a degree wheel to confirm the cam position. If i read your graph correctly, that puts first contact well above the heel of the cam. likely chosen as a point well above the heal, to make first contact a point that is very easy to acertain.

given the symetric profile - why spec the .050 lash? wouldn't .075 work just as well?

presumably, they spec .050 as an 'easy' value that is well above the heal.

am I missing something? is .050 an important value for some reason?

Rgds,
Vince

 

Did your re-grind cure the out-of-phase?
I haven't gotten the cams back yet. Maybe by the end of the week. Web Cam told me cams would be "spot on". I believe we were talking +-1/4 of a degree. When I pick up the cams I will read them again and compare.

What kind of heat treat was done after the grind?
Are there different processes to heat treat a camshaft? I never inquired as to how heat treating is accomplished. Heat treating at Web Cam is done out of house.

Are you sure the out of phase was not intentional by Fcar?
I don't believe so as all the cylinders would be off. Not all of mine were off.

Perhaps they are accounting for load related torsion in the cam stick at high rpm?
Never thought along these lines. But again, if this were true, I believe all cylinders would be off.

The cams are likely ground by robot & as such, an error of this type would seem unlikely.
The cam grinders I've seen have some sort of input from the operator. Remember, 1994 vintage.

It would be interesting to note if the phase change was progressive as you measured lobes further from the pully.
If I had the data in front of me I'd look at that right now. I believe there were two cylinders off on intake 1-4, One cylinder off on Exhaust 1-4, One on Exhaust 5-8, and all OK on Intake 5-8. We're talking .5 Degree at cam worst case.

Rgds,
Vince

 

It would have been interesting to see after the regrind whether there were dyno differences. Also, did web regrind or weld and regrind.
I was told at the time I dropped them off that they could grind out the imperfections. No welding was necessary.

I did not think there was much on the base circle to grind as is.
I was told .002-.003 would clean up the cams. Wasn't a problem with my cams. I hope they didn't have to go any farther than .003. I think it would be close.

I used Webcam back in my 308 days and they did nice work back then. Luckily I have had no used for their services in the last 20 years!
I've been going there 25 or so years, and I trust them. I was surprised they had the masters for my cams. They haven't steered me wrong yet! Plus they gave me a free hat and shirt. I'm easy.

 

Thanks for the time & reply!
Rgds,
Vince

 

Not sure, but all the road car cams from the 60's-90's era cars that we have checked do. Not sure about 355 and later.

 

This is exactly what I do

 

Vince -- Your memory is off F typically specifies 0.5 mm (.020"), not .050", but the reason is as you noted in both cases -- to move off the heel a little bit to where the slope is not zero.

 

only off by one order of magnitude.... what's a few thou anyway...
rgds,
vince

 

Actually they are a little more accurate than I previously thought, 1/60th of a degree or 1 minute.​

 

In a motor a few thou is the equivalent of a mile. Too tight and you have a stuck motor, too loose and it will rattle and fall apart on you.

When checking lobe centers a few thou can result in a cam that is slightly retarded or advanced. This can cause rough running, loss of performance. On some sport bike engines a cam that is slightly mistimed can cause the intake and Exhaust valves to contact each other during overlap.

 

Thanks!
That's good information to know....
Rgtds,
Vince

 

PS: be sure the belts are on when you find TDC....

Rgds,
Vince

 

A piston stop is nice, but I always thought you weren't supposed to turn these engines backwards?

 

Ferrari specificly reccommends backing up the engine a few degrees while setting cam timing. See the exerpt from page B46 of the 308QV/328 Workshop Supplement manual.

The important requirements for safely backing up the engine are that the CAM BELTS MUST BE PROPERLY TENSIONED & the TENSIONERS LOCKED DOWN.

Otherwise you're risking having a cam belt jump teeth or even come off (ask me how I know). At that point if you're unlucky you'll tap a valve with a piston with expensive consequences!!!
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