MP4.2+6.0

Simple actually: You need to take one of the gears off to get the belt off without risk of damage. If you don't do that, then you end up going the half-@$! pry w/ the screwdriver way, which stresses the belt and often on only one side. Then in turn insidiously the brand new belt can have broken cords internally and/or be a bit stretched on one side an/or get small cuts or tears at the pry area. All been seen on the board(s) over time when people come back with belt problems. It can lead to off center belt on pulley tracking and/or premature belt failure. As in, worse than when you started... Explained another way, first you have to load up the tensioner by holding pressure against it to get the belt to loosen up. But even when you do and get the lock pin into it, it's not like the belt just flops around with a ton of slack. It is still somewhat tight, especially when you try to deflect it to the side and get it off the rollers and such. The belt is relatively wide and robust (unless abused during installs) so it very stiff when you try to get it off the driven parts, some of which have lips that are another challenge to freeing it up or getting it on. Again, the cam gear comes in there because it is essentially the biggest pulley like item which is removable and has no side lip. Thus you pull a cam gear and lots of slack is now available.

You also do it in theory to replace the cam oil seals, but I think few are doing those (or the crank seal). The sites that push it don't really make clear the cam ones aren't easy unless you are disassembling the head more.

Mister Bally

Great photos and write up.

mishar

That special tool holds camshafts in the exact position while crankshaft is in TDC. Rest of the mechanism (belt, sprockets, tensioners...) can't make any influence to that position when you loose sprockets. If not, a bit longer belt or different position of that eccentric roller tightening belt would move camshafts a bit spoiling timing.

Mister Bally

That's the reasons tool T3036, Cam gear adjustment tool was included. This is the red handled one in the photos. This allows you to easily move the camshaft as long as the locking bolts are tightened.

sbcrazy

What i found with loosening the cam bolts and pulling the cam gears loose (i did not remove them) it allows the gear to spin free without spinning the cam. This allows you to key the new timing belt as you install it.

As far as removing the old belt after securing the dampener with the pin i removed the eccentric tensioner pulley and the belt came right off. No prying or twisting.

If you follow the steps for installing the new belt you should be able to slip it right on. I did not have to force mine at all.

ltooz_a6_a8_q7

If I understand correctly, the cam bar is to hold the cams alignment and to hold the cams while your loosen the bolts only? The bolts are for the cam gears?
You have to put the cam bar in place before you put your new timing belt on, the gears can spin around until the bolts are tighten?
If I ever do mine, there will be a video. It's 109k miles now.

Thanks,

Louis

MP4.2+6.0

Trying again on why you do the cam pulley removal. Besides the belt install practicalities, you want/need to do it to sync the cams to the crank across the many feet of running belt length once the lock tools come off, and deal with EITHER any belt manufacturing or wear/stretch differences OR any prior half-@# jobs where they didn't get it synched right. I let all that slide in the prior response, which starts to get into the nitty gritty of valve timing, production and wear tolerances, plus potential clean up of prior unknown work.

From posts in the last year, it's becoming apparent to me at least some prior jobs seem to fall into the half-@$# category where it seems whoever did it likely didn't loosen the cam gears, pried belts on with screwdrivers and such. Knowing the job, it's how you can take some time out if it's about production and fast turns or arbitraging book labor hours for profit, but it gyps the owner with lower quality work than he expected and may well have paid for. Other times, maybe quasi shade tree mechanics without some or all of the necessary tools who dynamite it and maybe do it "for cheap." To me, either paint or felt pen marks--plus cut belts--are the usual clues. It is also now pretty apparent to me that in recent times the majority of posters don't have a precise understanding of prior maintenance, and sometimes no good info at all on prior belt maintenance. No faults here--just the nature of third and fourth hand vehicles, plus it now seems like shops and even dealers cutting corners in prior jobs in some cases. If you did the work yourself, saw it done, or know the shop's technique, then you can have more confidence in prior job quality.

Also for anyone without working experience with the typical modern Audi belt drive set up, the oblong thick washer/spacers at the ends of the cams which go directly under the geared pulley bolts themselves key to the cams so position those parts exactly, but the cam toothed gears are NOT keyed to the cam and can rotate a full 360 degrees under the bolts and eccentric washers. Those are a steel on steel taper dry fit across a large surface area, so once you torque them down, they really are on there unless you use the puller tool to get them off.

Anyway, with the lock bar you are synching the cams exactly to each other and in the assigned 0 TDC crank position, and meantime the crank is locked at the exact 0 position with the lock tool--again assuming it's not the crap job without the tools and the eyeball it to TDC and paint mark time. Cams rotate at only half the RPM's as cranks in 4 cycle motors, so the pinned holes in the eccentric washers that the lock bar uses are different sizes to avoid them getting 180 degrees of cam rotation out of phase. BUT, what it isn't doing is dealing with the specifics of belt wear and slight variability, over a very long belt circumference wise. Nor is it dealing with the possibility that even if done mostly or completely correctly in the past, either the belt was previously installed as a used one rather than back to new, or that the person didn't have the lock pin installed in the hydraulic tensioner and was kind of guessing. Yet more so from hands on experience if they didn't space it at the 5mm spec (or at all) with the tensioner pin in place. That all comes up if you don't change the tensioner and leave the crank pulley on, which makes access to the locking pin hole problematic. That is also a more likely scenario if the belt was only disconnected temporarily to do something else, like replace a thermostat or water pump in isolation. But, assuming it is the full job done per best practice with the pulleys loose, the lock bar, crank and tensioner pins in place, and the spacer for the tensioner in there, you let the cam gears find their natural resting place in sync with everything (properly done) with the belt drive. Then they get tightened the final time.

FWIW, having looked at it some and even counted the teeth on the gears to understand degrees of rotation, a guess is with the vagaries of belt wear and adjusting, the delta here if not dialed in could be several degrees of overall valve timing. That is material to power curves for a motor relative to to factory spec. More so when you figure the factory dialed it all in to maximize torque and HP curves and integrate it with the variable valve timing, multistage intake set up, etc. In plain eyeball English as another cut at it, when I haven't yet freed up one of the gears until late in the process, I can find it off up to about half a tooth when I go to line it all up, which should be about the maximum discrepancy unless it is just misinstalled and off a full tooth. I saw that discrepancy on my 2.8 V6 that used the same tool set but actually a meaningfully shorter belt; they used to put factory punch marks on the cam gears that went back to the yet older I5 motors so it all caught my eye as I sorted out the variability.

BTW, yes, you can pull other parts in freeing up belt too. I personally like to see the tensioner arm and pulley both free and and under load since it is the part probably most likely subject to distortion (and thus inducing belt mistracking and wear/abrasion issues) given the swing/pivot arm nature of it. I saw wear and tolerance issues on these where I made the mistake of buying an NTN (aka aftermarket crap sometimes shilled as OES) tensioner for my A6 4.2 and then later admitting to myself when I looked at it more that I had been conned and it really did not square to the motor as it should.

MP4.2+6.0

Loius, yes is the short answer to each of your questions. My parallel reply is the deep dive into the set up, the theory and the field realities.

03_AR_CO

This is a monumental thread, absolutely worth saving, MP thanks for your very thoughtful and detailed responses, and thanks to all for clearing things up for me on the cam gear dealio. I certainly do understand better now, just seemed counter intuitive to mess with the cam gear (bolts) at all. Last timing job I did was on my 4 cyl TT, before that my 5000S, pretty easy stuff, certainly miles less complicated, fewer moving parts, and fewer parts to align.

Shoot, what a great forum this is.

sbcrazy

for the visually challenged people. these pictures will give good reference and hopefully clear up the understanding of how audi designed the cam gear end and how you can re-set timing of cams with the keyed position washer (item labeled #2)