Degreeing cams

I wish Peter would make and sell some of the cool stuff that he has.

The center lobe method is very simple:

1. you assume that the profile of the lobe is symetrical
2. you assume that the center of the lobe is the point where maximum lift is found
3. you calculate where that point is by the diagram / information provided by Ferrari
4. You ensure that the maximum lift is right at that point on the crank
5. You are done, no need to adjust the valve to 0.5mm

 

If you can use a little math, you don't need to replace the shim at all. If your present clearance is .229 mm (.009"), when the deflection on your gauge is .271 mm (.0107"), the "event" occurs (i.e. .229 +.271 = 0.5 mm). This is exactly the same point on the cam lobe as having a 0.5 mm physical clearance, and saying the "event" occurs when the gauge motion starts or stops.

 

Thanks again,

I appreciate all the help. Mitchell, So I assume that if I use the center point method that I would have my intake cam a 12° ATDC on my degree wheel below? and for the exhaust cam 2° ATDC.

Steve,

That is what I was trying, my friend Peter is from BC, so I just assumed that his indicators were mm. If I use your method and and set the dial at zero, what reading would I need to get to .0107. Since my dial gauge is in .001", isn't .0107 one complete revolution +?. I apologize I have never used one of these before and even more confused as my whole time with the Ferrari I have tried to think in mm's.......... If you help me with the first calculation I am sure I can figure out the rest.

Please all bear with me.......

Rob
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No, each small division on the dial gauge face is 0.001" -- so 1 revolution is 0.100". The jpeg describes where .0107" is located relative to zero (or it could be on the other side at the 89.3 mark depending on your test set-up -- i.e., if the needle goes CW as the shim moves down = use 10.7; if the needle goes CCW as the shim moves down = use 89.3):
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Robert,
I remember you said that your cam has been reworked. I have no idea what was done to it. Assuming that your cam profile is still the same as the stock 308GT4 you posted on post 139 above, then this is where your cam timing lobe centers are found:
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Just finished reading the whole thread. Getting ready to embark on this road during summer. Obviously, different engine in my case, but the principles remain the same for TDC.

Thanks for all the great info.

Ciao,
George

 

Friends,

I have moved my part of this thread to the 308 section:

http://www.ferrarichat.com/forum/showthread.php?p=140483743#post140483743

I have had some complications and did not want to extend this thread with my personal problems. I am hoping that all or some of you especially the experts will check it out and give advice as needed,

Thanks again for all your help.

Rob

 

+1!

 

Can someone help me out with this? I'm really struggling to understand what this is saying.

When you first crank clockwise, what's the relevance of stopping at .050? I assume just an arbitrary number? when you then go counterclockwise, why .090? Again, just an arbitrary number to be certain it went back the other way plus took out the slack? And here's my big question, when you the go clockwise back to .050, why would the degree wheel change from the original 12 degree reading to -10 degrees? I don't get why it wouldn't go back to 12 if you're at the same spot on the gauge.

Please forgive my ignorance, but I've read this probably 50 times and just need a few gaps filled in the description.

 

I think Carl has a typo in his procedure. Try this (credit to ISKY cams for this C&P):

Rotate crankshaft and this time on the way up to TDC compression, stop exactly .200 (dial indicator reading) below the maximum piston travel. Now read the degree wheel; if for example, it reads 40 degrees before T.D.C., continue rotating slowly on up to T.D.C., over the hump and down the other side, keeping thumb firmly on piston. Watch dial indicator closely, and when it reads exactly .200 down from T.D.C., stop and note reading on degree wheel. If you have a perfectly split overlap, it should read 40 degrees after T.D.C. If it doesn't, you have not found exact T.D.C., therefore you must try again.

MAKING CORRECTIONS
Split the difference (your error in degrees) by moving the degree wheel radially on the crankshaft. After you have made the adjustment, come around with the crankshaft as before, stopping .200 below each side of T.D.C. When you get exactly the same degree readings .200 inch below each side of T.D.C., you have found absolute Top Dead Center.

 

Yes, it's fairly arbitrary -- you want to be far enough away from TDC so that the slope of the lobe deflection vs the crank rotation angle is not zero, but you want to stay in the neighborhood of TDC.

Yes, again somewhat arbitrary, but you don't need to overshoot by a huge amount -- just enough so that when you go back the other way to the 2nd .050" location, the components have moved enough to assume their same relative positions as during moving to the first .050" location.

He's using that just as an example of when things aren't quite right yet -- that's why he goes on to describing tweaking the pointer position by 1 deg (afterwhich, each side would measure 11 deg at .050" from TDC).

 

Oops -- had "cam" on the brain from the thread title, but should've written "the piston deflection vs the crank rotation angle is not zero" (but same principle applies to both).

 

To further possibly confuse, the process of clockwise/counterclockwise is because of dwell. At TDC the crank will rotate for a couple degrees while the piston "hangs" so to speak. This is due to geometry and can be calculated with trig, if so desired. So when using a dial indicator on the piston the gauge will stop reading at TDC but the crank can continue to rotate, so by measuring where it stops reading the piston movement on both sides of dwell we can divide that and get a very close approximation to true TDC.

So far on the Ferrari engines I've yet to find one where the factory TDC mark was not accurate.

 

I think I get it now. Is my mistake that in Fatbillybob's write up I didn't realize that the second .050 reading was on the OPPOSITE side of TDC? He says go back to .050 but I read that to be the same .050 when in reality it's the opposite side? You're measuring the same distance on opposite sides then splitting the difference to find TDC?

 

Where is the factory TDC mark on a 355?

 

If you are looking to replicate Ferraris timing specifications they never calculate dwell. To them TDC is defined as the time the piston arrives at top. I got that directly from the mouths at the engine department in Maranello. I asked it to be repeated with a good interpreter to be sure I was correctly understanding them and it is how they do it.

 

So, as soon as the piston arrives at the top, that is TDC. It does not matter if the piston stays at the top for the next 3 degrees?

 

There is a dot on the 355 crank pulley, and at TDC it should line up with a rib on the engine case, 2 inches behind it. Not an exact science. You are expected to have a degree wheel, indicator, and find it that way.

 

That's right, and as Brian pointed out, that's not the "Ferrari correct" way of finding TDC. It also only works if the cam profiles are symmetric, which most, but not all, engines were, prior to variable valve timing, etc.

Since everything else in Ferrari's procedure (lift @ degrees) is presumably based on finding TDC their way, it's probably going to throw off your overall timing if you set TDC to be the middle of the dwell, then proceed to use their "lift @ degrees" figures to set the cams.

 

Correct.

 

Probably a dumb question, but Ferrari's TDC is when it first arrives at TDC on the CLOCKWISE rotation?

Do the pros use the more widely accepted view of TDC along with Ferrari's specs for valve open and close or the first spot where the piston hits TDC?

Sounds like the view of "true" TDC could result in the timing being off 1.5 degrees?

 

Some profess to know more than Ferrari's collective knowledge in making these cars run correctly. I am not one. Doing cam timing their way has always served me well.

Maybe not a coincidence that many of them also have many cars with cat reliability issues and slow down lights. When you tune a motor to run close to the edge of cat temp heat, 2 or 3 degrees of cam timing can overheat a cat or just run hot enough to have premature failure.

The only way to get Ferraris results is to do it their way. Exactly their way.

No measuring max lift and redefining it as the "lobe center", no measuring absolute open and close times.

Use their procedure, set In Open and Ex Close and you are done.


If you like a different way, fine. Just accept that it will not end with the same result. That may be good or bad but not the same.

 

The "Ferrari way" is to end up with the cam timing to match the cam timing diagram or specification as listed in the workshop manual. That is the only end goal. The path to get there is not important.

 

That's funny! Old Luigi with a 10 pound sledge, some gum and a paperclip..