Sure, we could argue cam lobe wear, lifter wear, valve tip wear, pulley wear but these are all incidental at best. Given stock geometry, the lowest increment of adjustment is 1.5 degrees, so to your point of total tolerance of 2 degrees, the best it's going to get is within 1.5. And, given the methods for measuring the lifter travel and the "eyeball approximation" of the indicator travel coaxial to the lifter, other measurement errors can be introduced. And, the wear on the drive pulleys will be so incidental, if you estimate a wear of .005" on diameter, that will not effect the calculations much at all.
Just wanted to be the 101st post in this dead horse... Get your motor running Image Unavailable, Please Login
First, I am aware of how Ferrari states to set timing. I am also aware from reading posts here by members and pros alike that there is disagreement on how to find TDC to start with. As for belt tension, how much do you think the belt length changes with tension? Say 100#? I've measured it. Cam wear. If there is enough cam wear to effect timing there are bigger problems as you do or should know. Example: Assume for argument that the cam wears symmetrically. (I realize that it doesn't.) Say the opening ramp is warn such that the cam needs to be rotated in the advance direction by 2 degrees to obtain the Ferrari spec'ed lift. The result is not correct timing as now the angle of max lift has been advanced 2 degrees. (The max lift won't be as great due to wear, but it will likely be at the same position. And, if the position changes due to wear timing isn't right anyway.) Additionally, since the closing ramp is also warn, the effect would be that the valve now closes 4 degrees early, in this example of symmetric wear. So if there are wear problems, adjusting cam timing to compensate is just a sucker's game. As for sprocket wear, please. The system is a fiber belt on a hardened steel sprocket. What's going to wear?
Agreed it shouldn't change much at all on lock/swap but for how often it's done I'll gladly check it every time.
John, I have not read this carfully but you are "engineer right" and dead wrong at the same time. Think about what you engineers do. You come up with theory and solve a problem. The result is an engineered system like a timing system. But rarely are you the ones to test them in the field. It is the technician who comes back and says xyz does not work regardless of how the engineering is sound. That happened all day every day with the apollo to the moon. If what I say does not happen we would not of had the incremental babay steps that was mercury and gemini. Insteed we would have just done it all on paper and 1st rocket would have gone to the moon. This camlock issue is alot about theory and a lot about what happens in real life. You can learn so much more about the process by physically doing it. Here is another example: look back to the dark days of the 308 belt changes. We had similar discussions but the 308 is very tolerant of off timing. Soup d'jour was lock and swap. Even back then I promoted unpinning cogs so they would free wheel to gain accurate belt tensioning and accurate belt relaxation over a belt's entire length to improve accuracy. This is another area where the dreaded matchbook cover was important. You see while your engineering is right what happens in real life is a differicult to manipulate folded hard new belt with memory in the folded position. Often the no remove cam bolts crowd would place the new belt on a appear to be 1/2 a tooth off. But the engineering says it can't be. The problem is the hard folded belt unable to stretch onto the cogs. So when 1/2 a tooth off which way do you turn your shaft became yet another assembly wholly war. When people started to unpin the cogs and easily index the belt the lightbulb started to go on when they realized that now sometimes you were not in the same cog hole as before yet nothing moved from tdc or the shafts. We are talking very little play of a cog to be in hole 1 or hole 2. People then started to realize that proper cam timing was a pretty precise issue and doing all this the ferrari way took out all kinds of guess work and assumptions. Try doing this a few times (hopefully differnet ways) and you will have a new appreciation for life beyond the engineering.
You might want to read what's been posted more "carefully" And, if you knew John and I at all, you would realize we are both very hands on engineers. I spent exactly zero time of my career dedicated to an office only environment - I've always been on the floor and in the office.
OK, Carl, so here is one for you: The procedure is to time the motor (bank 1) off # 1 cylinder. So, say we just did that and it's as perfect as it can get. Now, let's say we proceed to repeat the procedure (for sake of investigation and verification) at #2, #3, and #4. Do you think the same exact results will be found at each cylinder? The day will come when I will do this experiment. I'll wager that differences will be found and more than folks will think. The tolerance stack up of the fully assembly will prove that it's not as accurate as folks like to think
Well FBB, got some news for you. The earth isn't flat nor the center of the solar system. Theorists figured that out. Practical experience verified it. Let me be quick and to the point about the 308 example. If you lock the cams and when you try to install the new belt it's like 1/2 a tooth off which would be 6*, the correct way to turn the cam is easy. Of course, you have to have the foresight of an engineer. To start, before you remove the old belt you must mark a gap on each sprocket, and the corresponding tooth on the old belt. Then count the number of teeth between the marks on the old belt and mark the new belt similarly. Then you do what you need to do to place the marked teeth on the new belt in the marked gaps on the sprockets and everything will be just fine. 308 guys have been doing that for years. No need to unpin the sprockets. So it's very easy to figure out which way to rotate the cams if they need to be moved to get the belts on. It's simple math, integer math in this case. All those guys moving the dowel pins were actually messing up the timing on there 308s. I wonder how many bothered to set the lash as required before setting the timing???
I'm gonna start a "Cam timing argument" thread for you guys. You're all wrong. Everybody knows you don't have to change them.
Depends on the job. Not interested in doing a major. Annual maintenance, stuff like brakes, CV boots... I all in. Basically, if I can do it in a day.
I am going to stop this mental masterbation. I know what I have to do, and I will do that. Your mileage will vary.
If you hang around here long enough you will start believing that a 2.99" diameter pipe won't fit in a 3.01" diameter hole, ...... unless you measure it.
Nope I think I am done, following Mitchell's lead. The answer is we cannot have a more advanced discussion if you cannot get past the basics as I have proposed. I will end by saying "just do it the ferrari way"
FBB when you start grasping a straws it's had to have a meaning full discussion. For example talking about folds in the new belt when doing a 308. The belt is noting more than a flexible gear. It has a pitch and teeth and all that matters is having the correct number of teeth between any two gaps chosen as reference on ant two sprockets. I'm sure you will see it differently but for those who care to bother, he is a link to Birdman's 308 belt change write up. You will see it is exactly as I stated. Replacing Ferrari 308 Mondial timing belts And for those who care to, take a look at the 360 WSM under the maintenance section for belt changes. They do a lock and swap with rudimentary check of the factory timing marks. Now perhaps you might explain how a 355 is so much different that a 308 or a 360? As I stated, a belt is just a flexible gear. It has tolerances. You interchange one gear with another and the most things can change is what the differences in tolerances allow, baring other mechanical issues (which would indicate problems elsewhere). Now, I'd also like to point out that while you may choose to worry about a belt swap changing the timing from the last time a belt was changed by +/- 1 degree max I would have to press the point that most of us are driving these cars 3 to 5 years, or more, or 15k miles between belt changes. If you believe in belt stretch then you would also have to accept that by the time you are up for a belt change the timing of the engine will be significantly off compared to when the belt was new. So what's the big deal about a max of 1 degree in cam timing when you are going to see 2 , 3, 4 maybe more degrees of drift in timing over the life of a belt? And further more, you have to accept on the 308 that to have the correct timing the valve lash has to be correct as well. You can set the timing perfectly by the book but if the lash is too tight the effect is to advance the timing. Too loose and the timing is retarded. But all of these adjustment have tolerances so what is the actually timing of each valve? On a 355 it's even more complicated because it has hydrolytic lifters. Setting the timing on a 355 is based on when one specific tappet moves x.xxx mm. That only relates to the valve opening if the tapes are all functioning correctly, if all the install heights of the valve stems are correct, etc. You have 40 valves with 40 tappets with 40 cam lobes, all of which have tolerances, and then there is the tolerance on timing itself. So setting the timing based on a single cam lobe says nothing about the timing of the other 12 intake vales on that bank other than if every thing is within tolerance they will be within some tolerance (+/- x degrees) of the timing of that based on lobe 1. All I know, and this is not theory, it fact, is that going back to my original figure in post 98, https://www.ferrarichat.com/forum/144716640-post98.html, is that if there are X belt teeth along segment A and Y belt teeth along segment B for both the old and new belts then changing the belt can only change the timing from the last belt change at most by the proportionate fraction of the belt length tolerance along that segment as I indicated in that post. That's where the hole/pipe comment comes in. If you have a hole 3" hole with tolerance +.01", -0.0" and a pipe with outer diameter of 2.99" +0.0", -0.01" then you know the worse fit will have a gap of 0.03" and the best 0.01" You don't have to measure to know that. And if you want to throw belt tension into it, under the assumption that the belts are just rubber bands, then also consider that the tension on the belts is dynamic. The cams have mass and angular momentum. That means that there will be greater tension in the belts when the engine is increasing RPM than when running at constant RPM because of the change in angular momentum (i.e. angular acceleration). And that tension will also be a function of how fast the RPM is changing. So if the belts stretch the timing would be dynamic and change based on operation conditions. Finally, for what it's worth, I have a pair of belts that were on a 308 for 25 years/ 27k miles (not a typo) and when I laid them out and measured their the lengths one was 0.8 mm over the exact design length and the other was 1.00 mm over. Both were barely over the manufacture's as new tolerance of 0.75 mm. What that means is that even if both belts were at the tolerance limit for minimum length belt stretch would only amount to 1.75 mm in the worst case. That is for a belt with a design length of 914.4 mm. For reference a new belt measured 914.5 mm or 0.1 mm over design length, much less than the 0.75 mm tolerance. That 1.75 mm, proportioned along the belt drive segment, would result is a change in timing due to belt stretch, over 25 years, of about 1 degree. So much for belt stretch.
Take a back flap off a matchbook cover, Remove one of the camshaft retainers, cut the small piece of cardboard trimmed to size on the camshaft bearing and replace the retainer the cam won't move on its own. Now you still need to secure the camshaft when loosening or tightening the cam sprocket bolt this method will not hold it secure. This is also a procedure another manufacturer says to do when performing camshaft timing on their Overhead 4 cam 32 valve engine.
That's an old procedure I don't here much about anymore because it can, and has, resulted in cracking the cam retainer and if that should happen you are in a world of hurt.
John, as you and I both know, the tolerance stack up of the components along with the fact that the timing cannot be individually adjusted per each cylinder (or each valve), the harsh reality is the system is just not as accurate as many like to believe. The connecting rod wrist pin bore to crank shaft main bore has a .002" total tolerance alone. I don't see the dimension in the WSM from piston top to wrist pin bore but most certainly it has a tolerance. The angular relationship of the crank shaft connecting rod journals will also have some tolerance along with the camshaft lobe angular relationship. So, it becomes very obvious to folks that understand geometry and tolerances that if timing the motor using cylinder #1, it's a pretty sure bet that the same values won't be measured at #2, #3, and #4. That alone makes the case that splitting hairs is overkill.
in my engine outs I did not need the cam lock for timing the motor however if you are going to remove the bolt to realign the cam pulleys.....Dave's cam lock is a great tool for the job.
