This site is driving me nuts! not you FBB, great writeup. I just spent a few minutes writing up a technical reason for using a dial gauge instead of the piston stop method and the submit button didn't submit but blanked out, aaarggg!. here goes again, the timing system employed on these motors uses a gear drive to turn the drive cogs. the 'lash' between the teeth and the helical design of the gears will cause a loss of translation from rotation. the gears employ thrust washers because the cut of the gear will try and 'thrust' the gear along it's axis before it rotates. so when traveling CCW to use the piston stop method there will be a few degrees of crankshaft rotation without camshaft translation. just my 2cents, and now back to our regular program...
Hi Scott, how does this effect change the reading of TDC? There is no camshaft cog drive / camshaft in the line. To my understanding it is stop -> piston -> rod -> crank -> degree wheel When it comes to degreeing the camshafts, you are completely right. You can feel the play and read it on the gauge. Regards Harry
Right, you'll have TDC on the crank with either method however by going CCW the cams will no longer be correct, and yes you can adjust the camshaft directly but if there is still slack in the gears it'll continue to be off until it is removed. I prefer to keep going CW and watch for when the dial gauge stops and note the degree's then watch for it start again, note degrees and divide the two for TDC. then continue CW until I get back to the divided degree mark. going CCW to me introduces error as the engine never rotates that way when running.
The crankshaft balancer bolt is directly screwed into the nose of the crankshaft, and the flywheel is directly connected to the opposite end of the crank. You turn the bolt, the flyweel rotates simultaneously. The pistons and connecting rods are directly connected to the crank, thus there are no gears creating any residual slack or backlash to be of any concern. You turn the crank, the pistons more directly in unison, there is no backlash anywhere to be of concern. You can rotate the crank either direction and the pistons will directly follow suit. Locating TDC by rotating the crank fore and aft against a piston stop causes no discrepencies because no virtual play exists anywhere. The camshaft index alignment mark is on a portion of the cam that is approximately 1.25 inches in diameter, or about 3.925 inches in circumference. There are 720 degrees of engine crankshaft rotation to rotate the camshaft once, thus one degree of crankshaft rotation is equivalent to moving the camshaft index mark 1/720th of rotation, or, .00545 inches, or, about .13 of a mm. Thus the difference in a figure of exhaust closing at 33 degrees ATDC, or at 44 degrees ATDC, is equivalent to moving your camshaft index alignment mark about .060 of an inch, or about 1,5 mm. The cams belt drive sprockets are gear driven off the crank through reduction gears. Valve timing indications should always be accomplished following normal forward engine rotation, never backing up, because of belt slacking and gear backlash. If you do back up, be careful that the belt does not crawl over the sprocket teeth. Backup far beyond the point you want to measure, and resume the correct forward rotation to remove all belt slack and gear backlash before you resume measuring. Always double check valve timing with four complete forward rotations of the engine with no reverse backing to confirm your marks. The 255 HP Euro 308 vs the early 240 HP US carb cars have a valve timing variance of 4 degees, equivalent to moving the camshaft index mark .020inch, or about 1/5th of a mm. I dont know if thats worth 15 horsepower, but it does show we need to be awfully damned accurate if we truely want the car to perform like a gnats a$$.
I like to use the dial guage to take up the slack everywhere including the crank/pistons etc. Perhaps you are correct that the piston/con rod/crank slck is of no consequenece but I don't know enough to agree or disagree with that. What I can tell you is that on motors I have played with rebuilt etc. I could always feel some play with my hand. I have never measured it but I can feel it. So I want this play out of the equation. As to the 720 degrees cam degrees vs 360 on the crank it is the cam that is moving the valves so in my line of thinking I'm not as concerned about the gross movement of the crank as much as I am on the movement of the cam. If you do your same math 360* on the cam instead of 720 and figure the mark size you are at 0.25mm which as I have said earlier in this post is very easy to see. So you nee to be precise in your mark line up but as Ernie has said earlier as well marks on cam is definately good enough as long as you have confirmed cam timing at least once with a degree wheel. I have over 50k miles on my motor and many race miles with no wear issues which have changed my cam timing relative to my marks. The only reason I degree cams is because 1) it is easy 2) it confirms timing markes and 3) maybe I want to alter valve overlap for some percieved gain in power. And sure be accurate for the 1/5 mm but that is 2 thicknesses of a hair very easy to see or feel. Pull a hair out of your head and chew on it. You can easily feel 0.1mm.
Just a word of caution, when setting cam timing on the 308, the crank damper must be properly installed. If not, the driving sprocket on the crank that turns the 2 cam drive sprockets will be free to float and will cause erratic cam timing numbers. (Just went through this while timing a friend's engine). I do not know if this is the case with the 348.
Very interesting. I do not remember this being a problem on 308 2v or 308 qv I have done. I assume you are talking about the slack created by crankshaft endfloat and the pitch of the cam gears. I have not done this in a while but I do not think proper placement of the dampner prevents or controls any crankshaft endfloat. Furthermore you would need to kludge your degreewheel if you leave the dampner on. On 348's you can get the T-belt off with dampner on. So dampner off makes the most sence to me. Each of you will need to evaluate and correct for the individual quirks of your motor set-up. Myself and others in this thread have posted about making sure all readings are in the driven direction and that any backing up ccw be done well past the predicted timing marks or dial guage reading so that once driven cw all slack is taken up. This produces stable reproducable data. This holds for all motors. Is this what you mean?
FBB, Pauls right, the dampner acts as a 'thrust' washer. the helical cut of the gear will force it forward on the crank snout since it free floats. I noticed that as well and made a note to have the dampner back on for timing. as it thrusts forward the timing gears won't rotate and the whole mess will be off.
FBB, one thing I wanted to add, is that I fully understand your idea about 360 degrees vs 720. I just felt it was better to show actual valve timing degree information which is always degrees crankshaft. But heck, just getting people to change thier belts more often and keeping it as simple as possible will be a great help. The truth of the matter is that any of these cars will run "OK" if you just put them on the marks. Its looking like the earlier cars would gain the most from really zeroing things in, whereas the later cars are pretty accurate to start with and doing all of this is just redundant. You know, this timing gear vs balancer thrusting the cam drive gear forward thing, this is interesting. On my other crank that gear never slid off, and I never pulled it, its on tight as he11. I sent the crank out to be checked and polished and its still on there, I think I would have to press it off. I was advised to leave it alone and not mess with it. But if some later cars have slip fit gears I guess its worth showing everyone a way that would cover all the cars. I guess we would need a longer bolt with a sleeve to back up between the dial and the balancer, or a short sleeve to fit over the crank backed with a big thick washer.
O.K. here is the second way to degree cams which avoids all the problems I discussed earlier. My first to start this thread shows the calculations for how to get installed lobe centerline from the Ferrari specs of opening and closing on intake and exhaust cam. Degreeing cams by the Lobe Centerline method: Still TDC is the referrence point. Looking back at the first page you can see that with limited Ferrari specs the proposed installed lobe centerline can be calculated. How you calculate it is given on the first page. Again set-up the dial guage rig on the #1 piston intake valve tappet at TDC. Crank motor CW and watch the dial guage for max lift. This is a very hard transition to find but no more difficult than finding the clearance ramp to opening/closing ramp junction. Here the degree wheel points to 109.5 degrees perfect as calculated. Image Unavailable, Please Login
Doing the same thing with test rig moved to the #1 exhaust tappet gives 111.5*. This is done on the 5-8 bank with #8 piston in TDC and all the numbers and marks line up perfectly. This a great method of degreeing cams because it is faster. Also, the tappet lash does not matter. How Ferrari determines their specs does not matter because the math calculation will always work. If a hydralic valve tappet is used and the real height/lash of this is not known it does not matter. Notice that lobe centerline is the centerline of the cam relative to the crank so the number on the degree wheel is in crank degrees. There is no division by 2 as in the open/close method. Therefore it is read directly off a generic degree wheel. Now isin't that easy? It takes no time at all so why not do it. There is no mystery and anyone of you who can change a waterpump can degree your cams. So I guess no one will be beating their chests over doing it anymore since you can see right here how amazingly simple it is. I have checked cam timing by 1) cam marks, 2) installed clearance open/close method, 3) lobe centerline method and Everything lines up spot on by each method proving that our marks can and in many cases are dead on and that either method will give you excellent results. Image Unavailable, Please Login
So why degree cams? 1) confirm all marks and timing are spot on. 2) on 4 cam motors you can change the lobe separation angle where these max lift peaks are relative to each other. This can alter or tune how an engine responds for how a driver likes his engine to respond just like adjusting rollbars or tire pressures tune a cars handling. So what happens if say the #1 intake cam opening reads 34* instead of 28* at the degree wheel or 115* with the lobe centerline method? This means the opening is off by 3 cam degrees or about 1 tooth of the timing belt. The intake cam needs to be moved to get the number of degrees as specifed in the open/close method or the lobe centerline method. Bring the motor to TDC and line up all the marks again. Loosen the cam pulley nut and remove the locking pin from the cog. This is easy on the 5-8 side and difficult on the 1-4 bank because you cant push the pin out from the back. I use a rhoades chisel dental tool to work behind the chamfer of the pin head and pry it out. You can fine grind 2 chisels and pry behind the chamfer 180* apart do the same thing. Now barely hand tighten the cam bolt so the cog does not fall off. On the 1-4 intake cam you can grab the cam towards the rear with a vice grip plier and a rag and turn it CW or CCW as needed. On the other cams there is a 10mm hexnut you can turn the cam by. Loosen the cam bolt and feel for the free hole that will allow reindexing of the locking pin. Becareful holding the cam since the tension on other valves will cause the cam to snap out of your hand. I use a matchbook cover under a cam journal cover to lock the cam gently until I am ready to turn it. Then I lossen the cover turn the cam and lock it down again. Now I reindex the locking pin. This is why I start everything at TDC with cam marks on so that I always have a point of referrence. If the cam jumps I can always start over from the base cam marks. Set the test rig back up and check the results. This may take a few trys to get perfect. Degreeing cams takes little time if the marks are on. It is this monkeying around to be exact that takes time. So that's it, I hope it was worth it to you all. Image Unavailable, Please Login Image Unavailable, Please Login
Fatbillybob, thank you. Printed out and in my workshop manual binder for next years major service. Curious, the manual shows timing differences for Euro and US spec motors. Are the cams the same? Have you tried the Euro spec timing in your race 348? What is the power advantage gained? I understand the Euro timing would possibly cause a cat US car to fail emissions. Thanks again, John.
First, thank you very much for the write up. Now, here is the point at which I become confused. I understand that you turn the engine CW until your dial gauge reads .050" and your degree wheel happens to be at 12*. Then, you turn the engine CCW - your dial indicator is dropping back down to zero then to .090. You then turn the engine CW until your dial indicator reads .050" again. How can your degree reading now be -10*? If you started at 12* on the degree wheel and then moved the degree wheel back to your starting point (0 on the dial indicator) minus .010" or .090, and then turned the crank CW back up to .050" (or .060" inches of total movement on the dial indicator), shouldn't the degree wheel be reading somewhere close to 12* again? How can it be at -10*? I'm sure I must be overlooking something very simple but I would appreciate any clarification. Thanks, Scott
Let me try. Initially, based on the flywheel's PM1-4 mark, the degree wheel is set to 0. Presumably this close to but not quite at the real TDC for whatever reason, maybe the flywheel pointer is miss adjusted, maybe you're not looking at it straight on, maybe the flywheel mark really is off a bit. You want to find the real TDC: You rotate the engine CW until the piston peaks the dial gage & zero the gage. Then rotate the engine CW until the gage reads 0.050". Then rotate the engine CCW past the 0" lift reading, keep going CCW past 0.050" till you get to 0.090" on the gage. Then rotate CW from 0.090" till you get to 0.050" & note the degree wheel reading (in this example -10 degrees). At this point you still haven't gone CW far enough to get to the 0" lift point. Thus the two 0.050" reading points are exactly the same number of degrees on each side of TDC. ie: True TDC is exactly halfway between the -10* 0.050" reading point & the 12* 0.050" point, which is the 1* point. The same is true when you're measuring valve lift on each side of the cam lobe's maximum lift point to find the 'lobe center'.
Thank you Verell. It makes perfect sense now. You are essentially noting degrees of crankshaft rotation ATDC with the piston moving .050" and degrees of crankshaft rotation BDTC with the piston moving within .050" of TDC. You split the difference and have true TDC. You turn the engine CCW back as far as you do to make sure there is no slack interfering with your measurement. This is a correct statement? Thanks, Scott
Wow! This is certainly a very, very cerebral dissertation. Good job, FBB and others! You guys should try giving bar review classes! Two questions: a) I presume the exhaustive degreeing is more applicable to older engines due to wear from age and uncertainties of prior work. What is the position on degreeing newer engines-360 and up? b) I don't believe you said what you use to lock the driven cams for belt replacement.
I use that approach as well, but only because im focused on performance instead of idle quality and emissions and I only have dumb old carb 308 motors. I believe the reason the techs are so focused on actual opening and closing points has more to do with how they were taught and, they have to return the cars meeting strict emissions standards. At idle and at very low speed, the intake and exhaust timing is VERY critical. Move it more than a few degrees and you could have a car that is hard to meet emissions if not impossible. And as we move up to cars like the 355 and newer, they are so close to the edge, that being off more than a couple degrees can lead to cooked cats, holed headers, burned valves and smoked pistons. IOW, the OWM must be followed unless you are totally familiar with the outcome of doing things differently. The old carb cars can be all out of whack and still run okay and not hurt themselves (within reason). The later cars have much less tolerance for errors. I am totally comfortable screwing around with valve timing on a carbed engine. But if I was wrenching on a 355 or newer, I would want to be as absolutely precise as possible.
I did a quick search on the web yesterday and Crane Cams has a nice write up on degreeing cams. You can read their process at http://www.cranecams.com/?show=article&id=3 but a couple of points they make are: The lobe centerline method has the disadvantage of assuming that the lobe has a uniform profile, it doesn't. The lift is generally much faster than the close so you can get your timing off by several degrees using the lobe centerline method. They also note -- Important Tips to Remember When Degreeing a Camshaft: 1. You must always use the same type and size lifter that your camshaft was designed for. For example, you cannot use a .842" diameter lifter on a camshaft designed for a .875" diameter lifter. You cannot use a standard (flat) lifter to degree a roller camshaft. 2. Clean off any excessive lubricant from the lobes and lifters that you are checking. Thick oil, especially assembly lube (paste) can cause false readings to occur. Wipe the parts clean before checking, and remember to re-lubricate them when you are finished. 3. If you make a mistake and rotate the engine past the point you wished to take a reading, do not back up the rotation. If you do, any slack in the timing chain or lash in the gears will affect the readings, causing an error. If you miss your stopping point, just continue rotating the engine in the normal direction until you return to the desired point.
