| Author | Message | ||
| Phil Hughes (Ferrarifixer)
Junior Member Username: Ferrarifixer Post Number: 127 Registered: 7-2003 |
Trust me Jeff, your cams have a symmetrical opening and closing ramp. Your calculation of the max open period is correct for the inlet, can't remember seeing your exhaust calc? If you choose to do the 0.50mm clearance method you MUST have the clearance at exactly that, the entry from base circle to opening ramp, and exit after, is far too vague to try and guess from deducted values relative to desired clearance. It is non linear. The shims can be got out quite easily. Get the cam to a position where the lobe is almost directly opposite the shim, pry the bucket down with a smooth edged lever about 3mm or so. If you feel resistance it is the valve touching the piston so dont push too hard!!! Place a carefully sized square shouldered "ex screwdriver" on the very edge of the bucket, between it and the cam shaft to hold it down enough for shim clearance, and then remove your pry bar. The shim can now be flicked out with compressed air (put a rag over it to stop the oil going in your face, and losing the shim!). Dont lever it out as you may damage the area around the bucket, causing it to tighten. Then, measure the shim and use the info to compare your actual clearance to your 0.50 requirement shim. You should check all the clearances, as they tend to close up with valve seat wear, rather than go large due to cam/bucket wear. You may end up needing 20 shims or so, or a bit of swapping around and only 5 shims if you're lucky! Check the spec in your owners handbook and/or w/shop manual. I remember there was a change of spec between some of the TR family, so double check. Good luck, and keep us posted. | ||
| Henryk (Henryk)
Intermediate Member Username: Henryk Post Number: 1149 Registered: 8-2001 |
While I have never degreed a cam, I have replaced belts on a couple of Ferraris. I have used the marks on the cams, with no problem. If the cam was off, then I would use the dowel pins to correct.......rotate the crank several revolutions, and if they still align.....as they had in my cases, I considered it done. Even if one can do it exact with degreeing,isn't one limited by the dowel pin placement, on the final setting anyway? I agree with JRV about the many variables, and it seems that by trying to degree the cam, even MORE variables crop up!!!!!!! Are we making a simple task impossible?????? You are convincing me more and more that, when I do my TR major next year, that I will just go with the simple route, and leave degreeing to the drag racers. Just my 2 cents. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 2342 Registered: 11-2002 |
>>But as I go round and round, I'm getting the impression that perfectly timed cams are just a dream, or pure luck. Too many variables. With belt stretch and lag due to the camshaft rotational drag variations caused by various valve springs, cam drive pins adjustable at only 2.5 degree increments, and the difficulty of measuring valve clearances, and getting the indicator vertical to the lifter motion,<< Sounds like the built in slop I referenced earlier...{  } All/Any degrees 'unless specified otherwise' would be crank degrees. Usually denoted as degrees of rotation...which reference engine rotation... >>Problems abound, like the famous 0.5mm clearance. To get this would require removing a shim(s) and using "something" that would result in the clearance.<< I would suggest , since this is your first time, and like you mention chocked full of variables and pitfalls, that you order some shims to give you the correct 0.50 (46,49,51 { }) and follow the procedure directly from the book. Also imo, the degree wheel should be mounted on the Flywheel, rather than crank pulley for reasons of precision.. I'd bet in the end the marks will line up with inperceptable differenc, however since you are this far along, it would be a shame to not complete the full timing procedure and loose out on this chance. Best of luck. JRV | ||
| Bill Sebestyen (Bill308)
Member Username: Bill308 Post Number: 515 Registered: 5-2001 |
Jeff, Concerning 0.5 mm clearance for cam timing, you might want to measure the existing clearance and subtract this distance from the 0.5 checking clearance. Then, just check the cam timing at a lifter height equal to the diffenence. As an example, suppose you measure the existing clearance to be 0.1 mm. Subtracting 0.5-0.1=0.4 mm. So now you mount your dial indicator to register on the lifter and rotate the cam until you get a lift of 0.4 mm. This should be the point of opening for timing purposes. Continue rotating the cam through maximum lift until the height is again at 0.4 mm. This should be the point of closure for timing purposes. You still need to mount the dial indicator parallel to the lifter bore to make the measurement work. The contact point on my dial indicator would unscrew to allow fitting of extensions. I found a suitable piece of wire, actually I think it was a piece of coat hanger, cut a piece to a suitable length and bent it to an angle that would touch the lip of the lifter and still allow the axes of the dial indicator and lifter to remain parallel. I then threaded one end of the wire with a die and screwed it into the dial indicator stem. I hope this helps. | ||
| Jeff Green (Carguy)
Member Username: Carguy Post Number: 488 Registered: 10-2002 |
As many know I'm attempting to properly "time" the cams on my TR's motor. It is proving to be a very frustrating task. I'm tempted to just eyeball the cam/cap marks and just go with that. The mark on the cam is slim, and the notch in the cap is wide, this allows up to about 8 degrees of crankshaft (4 degrees cam travel) travel while keeping the cam mark within the cap notch!! I did a better plotting of the intake lobe shape, and it appears that the closing ramp is more "gentle" than the intake ramp, with vertical changes being less over the same rotation as on the opening ramp. And the closing ramp is longer by about 10 to 15 degrees crankshaft travel. Problems abound, like the famous 0.5mm clearance. To get this would require removing a shim(s) and using "something" that would result in the clearance. And to get vertical with the dial indicator is practically impossible. Two fellow fchatters have made great suggestions. 1. To make the clearance "zero" and then use the values above 0.5mm travel. 2. To make a special offset pointer for the dial indicator. Great suggestions! Make total sense to me. But as I go round and round, I'm getting the impression that perfectly timed cams are just a dream, or pure luck. Too many variables. With belt stretch and lag due to the camshaft rotational drag variations caused by various valve springs, cam drive pins adjustable at only 2.5 degree increments, and the difficulty of measuring valve clearances, and getting the indicator vertical to the lifter motion, I'm about ready to chuck the whole idea. Quesion: The manual states the cam events tolerance as +/- 1 degree. Is this in camshaft rotational degrees or crankshaft degrees? I am not convinced that even after degreeing the cams that they will be closer to ideal than the builders marks show. I'm not licked yet, just taking a breather. I would welcome any opinions and constructive criticism. Thanks; Jeff |