Methods to find TDC?

Is this what fbb was stating when he said he uses ferraris method to time his engine??

 

Ok so he is timing with lobe center instead of lift.

 

I find the cam center then piston TDC center with before and after tdc readings. Do it again forward backwards until you repeat results several times. I was taught by Iskendarian this way so been doing it that way forever.

 

Dave, should not the start of the dwell. It should actually be the center of the dwell. Like I said in the other thread as you approach TDC all the "slack" in the crank/rod/piston system is pushed one way, in compression. In theory, the piston would stop just as it reached TDC. If you were to stop there, then rotation in either direction would (should) not move the piston until all the "slack" was taken out of the system in tension as the crank pulled the piston down. The dwell is symmetric about TDC. As we were discussing, the issue is the lack of sensitivity of the piston motion to crank rotation around TDC and the resolution of what every dial indicator was used. Or, as Grant noted, approach TDC for both directions, and average the values observed. If they are the same you pretty much nailed it. If the are difference, there is some uncertainty.

There is no doubt that the piston stop method is a more reliable method. The dial gage method is fine but it's based on measuring linear displacement at the point it is least sensitive to angular displacement thus prone to possible error.

 

Some thoughts, Ferrari , I would not believe what they say if tongue came notarized. When it comes to racing you do whatever you can to stay ahead even if that means supplying slightly less accurate info to the public, public meaning anyone except the race engineer's.

 

No. Ferrari's method is spelled out in the WSM. That's what I do. RifleDriver refined what we peons know by cluing us in on Ferrari's position of TDC over a decade ago.

That is the way I used to time Ferrari motors. I have found it just isn't as accurate in that using Ferrai's lift in fractional mm's yields more changes in cog pin positions that would be needed using the classic Isky method. Does it matter? I don't know. All I know is the effects on the cog pin positions. I assume Ferrari has a reason and I just accept it. When I cam time my corvette racecar I do it the old chevy way.

 

Correct. My experience 1st is like Tim's Isky statement. An engine is an engine. Why can't I time a Ferrari motor using the Chevy method? On top of that the chevy method was giving me really nice dead nuts marks lining up. I have admitted to that. I also admitted to RD and DH not really telling my why I was misguided but on the right track. I think you are just where I was years ago because I've just been playing with these cars longer. When DH told me I had a "good start", I understand him now. If you do the 2 methods you will see. I don't know why there is a physical difference or if the difference matters but there is one. Therefore, I just do it Ferrari's way.

As another datapoint I raced my 348. I took the belt out annually and camtimed it every year because my car lived at redline. I messed with different timing and never gained an advantage on my stopwatch which is the only thing that matters in racing. If there was power to be found "timing" I did not find it. It may be there but it wasn't for me. This datapoint would also imply that if we are off a few degrees from Ferrari's specified timing maybe it just dosen't matter that much. That said I still Cam time Ferrari's way...everytime. I walnut shell my head's intake every major. I send out my fuel injectors to be cleaned and balanced every major. My labor is free. Fixing Ferrari's and racing are my hobbies. I can spend a little more on other stuff that maybe others can't who have to budget for labor costs.

 

Going to have to try it. I'll put on some BBQ maybe pastrami and have you stop by

 

Carl said it made a difference in pin position and I believe that. That being said were the differences consistent.
And were the differences the same so did ferraris way advance both intake and exhaust, opposite, or provide more overlap just for my own curiosity?
Thanks Carl

 

This is the way I see it. As you rotate the crank towards TDC, in either direction, the crank is pushing up on the con rod which pushes up on the wrist pin which pushes up on the piston. Looking at the crank-conrod bearing the clearances, neglecting any oil film, the crank journal would be forced against the conrod as shown to the left with all the bearing clearance at the bottom. As the piston comes to TDC, it will stop. Before the piston can start to move down, the crank must rotate sufficiently so that the crank journal contacts the bottom of the rod bearing, with all the clearance at the top, as shown at the left. So, regardless of which way you rotate the crank, TDC will always be at the point where the piston initially stops. Call that as the start of the dwell if you like. If you continue to rotate the crank in the same direction, it can be rotated by some angle, alpha, before the crank journal moves to the position as shown to the left, and the piston start moving down. Call that the end of the dwell, if you like, and the dwell angle is alpha. But if you were to stop the crank exactly at TDC you can then rotate the crank in either direction by alpha before the piston would move down. The angle would be the same regardless of the direction of rotation and is defined by the amount of rotation to move the crank journal down by approximately the bearing clearance. In other words, if exactly at TDC the crank could be rotate +/- alpha degrees w/o the piston moving. Whether you wich to define the dwell as alpha or 2 x alpha is a matter of semantics. However, if you define TDC at the point where the piston stops are you approach TDC from either direction, then that is indeed TDC, to what ever accuracy you can measure it, and it will be the same position you would find using the piston stop method, again to within the accuracy of the measurements. The only difference will arise from how accurate you can determine the angle at which the piston stops compared to measuring the angles where the piston hits the piston stop. One is limited by the sensitivity of the dial gage used, and the fact that as you approach TDC the piston movement become insensitive to rotation of the crank. The other by the accuracy which you can read the degree wheel.

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Just reading through Brian's old comments. Where he says other manufactures define TDC as 1/2 way through the dwell and Ferrari defines it as at the start. I think that becomes a matter of how the dwell is defined. If the dwell is defined by the point where the piston stats to move down when rotated CC and CCC, that is, twice the dwell that you would have if you define the dwell based on where the piston stops and where it stats to move down again when rotating in the same direction, then TDC should be the same in both cases. But it should be obvious that if you define TDC 1/2 way between where the piston first stops and where it starts to move down you would be off. How much? Based on my calculation of piston movement about 1 degree.

I think you can say there are 3 methods here. 1) used a piston stop method and TDC is 1/2 way between the two angles measure. 2) Use the Ferrari method and TCD is where the piston initially appears to stop. 3) find the angles where the piston starts to move down when the crank is rotated in each direction and TDC is 1/2 between.

Noted that Brain also said,

The way I read that is belts swaps are fine if you have confidence that the cam timing was done correctly previously.

 

How you figure? If you are rotating the crank in either direction and Ferrari defines TDC as the point where the piston first stops, that is TDC. Time for another picture.

 

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or if the crank is rotating clockwise.

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