I had some free time and all the necessary pics, so I put this little DIY together. Hope it's useful to someone.
REPLACING TIMING CHAINS, TENSIONERS AND GUIDES ON A MKIV 12v VR6
The following DIY outlines the procedure for replacing timing chain parts on a MKIV 12v VR6 engine.
NOTE: If you are using this DIY to reinstall an upper chain and time the engine after a head rebuild or headgasket replacement (i.e., the head came off, but everything else was left in place), make sure to read the section pertinent to this topic in the DIY UPDATES at the end of the DIY!!!
Since timing chains are considered by VW to be a "lifetime" item, there is no recommended mileage for the replacement (or even inspection) of timing chain parts. However, while timing chains should realistically outlast the rest of the car, the design of the guides and tensioners used to keep the chains tight on a 12v VR6 is inadequate IMO. It is very common for guides and tensioners to fail (especially in older VR6 motors) as mileage approaches or passes 100k miles. Unfortunately, failed guides or tensioners may cause a chain to jump a tooth or more on a sprocket or may even cause a chain to snap. If either were to happen, serious damage to the engine would result as valves slam into pistons at high speed.
While there is no definitive indication that timing chain parts should be inspected and/or replaced, the most common sign of trouble is a rattling sound from the driver's side of the engine that occurs between 1000 and 1200 RPMs. This sound has been described most often as "marbles in a can" or like a sewing machine. Go to this thread to hear a sound clip of the timing chain noise that was present in my car, and eventually led to the writing of this DIY - Timing Chain Noise Thread. You can also download a video containing bad timing chain noise sent to me by dankvwguy HERE. Any noise similar to those in the clips in these threads should be considered suspect. When the timing chain parts are in good working order, the chains are under considerable tension and NOTHING should be loose enough to rattle. If you hear a rattling noise, and it's coming from one or more of the timing chain parts, it most likely indicates that these parts are either loose or broken and should be repaired ... or else!
The timing chain setup on a VR6 consists of an upper and lower chain. The upper chain connects the camshaft sprockets to an intermediate shaft sprocket (outer sprocket) and the lower chain connects a second intermediate shaft sprocket (inner sprocket) to the crankshaft sprocket. The camshaft sprockets have 27 teeth, the crankshaft sprocket has 24 teeth and the inner and outer intermediate shaft sprockets have 32 and 18 teeth, respectively. The ratio between the camshaft and outer intermediate sprockets is 3:2 (or 27:18) and the ratio of the inner intermediate shaft and crankshaft sprockets is 4:3 (or 32:24). This yields a ratio between the camshaft and crankshaft sprockets of 2:1 - i.e., the crankshaft rotates twice for every one rotation of the camshaft.
Each timing chain has a guide rail (curved on the upper chain, straight on the lower chain) and tensioner rail to keep them tight. The lower tensioner rail is a one-piece, spring-driven unit, while the upper tensioner is a two-piece design consisting of a tensioner rail and a separate tensioner bolt.
There are actually two versions of the upper timing chain setup. The early version used a double-row chain, a two-piece tensioner rail (phenolic plate(?) riveted to a metal backing) and a tensioner bolt that relies solely on oil pressure to apply force to the tensioner rail (the bolt has a bleed hole in the end to help regulate the amount of force applied). Because of an unusually high rate of wear of the upper tensioner rail (many are completely worn through the phenolic to the metal backing plate by 100k miles), the upper chain parts were replaced during the '97 model year with an "improved" setup consisting of a single-row chain, a single-piece, dense polymer tensioner rail and a tensioner bolt that uses both spring tension and oil pressure to apply force to the tensioner rail (spring tension extends the bolt to a minimum length, around 18mm, and then oil pressure extends the bolt to it's final position - this tensioner bolt does not have a bleed hole to regulate oil pressure). According to the ETKA CD, the switchover point between the older and newer upper chains setups is determined by engine production number and is as follows:
old setup - AAA engine #217000 and before
new setup - AAA engine #217001 and after
If you have an AAA VR6 and don't know where to look for the engine production number, then please read this THREAD.
The newer setup lasts considerably longer. When I replaced my timing chain parts at nearly 150k miles, the upper tensioner rail had grooves in it from the chain that were only a fraction of a mm deep. IMO, the rail would have easily last to 500k to 1M (million) miles based on how slowly it was wearing.
The lower chain parts are the same on all 12v VR6s - AFAIK, no changes to them have been made during the production of this engine.
The procedure below was based on a '99.5 MKIV Jetta GLS 12v VR6, which has the newer-style upper timing chain parts. While the older and newer upper parts are slightly different in both form and function, the procedure for replacing them is the essentially the same on all 12v VR6s. Therefore, the procedure below should be generally valid for any vehicle with a 12v VR6 engine. For those older VRs with EGR systems, you will have to deal with the removal of some EGR components from the top, rear of the engine in order to access the timing chains. Newer VRs do not have to worry about this however. If your VR has an EGR system, make sure to see the section devoted to this in the DIY UPDATES section at the end of the DIY. (Note: Torque specs given in this DIY are from the MKIV Bentley manual - these torque values may be slightly different on earlier model 12v VR6 engines.)
The procedure assumes that the transmission, clutch, flywheel, upper intake manifold and other small parts (coilpack, TB, airbox ...) have been removed from the car and that other steps necessary to remove these have also been performed (front end of car raised, battery disconnected, etc). The removal of these parts on a MKIV VR6 has been expertly documented by FaelinGL here - http://forums.vwvortex.com/zerothread?id=2703042.
NOTE: If you are only replacing the upper tensioner bolt and/or upper guide rail, you do not need to remove the transmission, clutch, flywheel, etc. You can replace this part by only removing the upper intake manifold (and other associated parts) and then following steps 1 through 20 below. To replace the upper tensioner bolt, you do not need to remove anything. Simply follow steps 10, 48 and 52 to remove and install the bolt.
Please do the procedure at your own risk and be ready to make small adjustments while doing them. Also, please be observant while removing parts so that they go back together correctly. The procedure is fairly involved and extreme care should be taken while performing it. SEVERE engine damage WILL result if it is not performed correctly. Depending on how mechanically inclined you are, it should take somewhere between 2 and 8 hours to perform.
The tools needed to perform the procedures are:
1) 10mm, 13mm, 15mm and 27mm sockets or wrenches
2) 5mm and 6mm hex sockets or wrenches
3) spark plug socket
4) large flathead screwdriver
5) torque wrench(es) valid for the range of 89 in-lbs to 74 ft-lbs.
6) VW camshaft locking tool (#3268) or 1/8" metal or dense plastic plate
7) RTV sealant (ultra-grey, sensor-safe)
8) pieces of wood for removing and installing rear main oil seal
9) container and oil
The VW part #s for the parts replaced in this DIY are:
* 021 109 503 D - upper timing chain
* 071 109 513 - upper timing chain guide rail
* 021 109 509 E - upper timing chain tensioner rail
* 021 109 507 B - upper timing chain tensioner bolt (comes with copper crush washer N 013 827 1)
* 021 109 465 B - lower timing chain
* 021 109 469 - lower timing chain guide rail
* 021 109 467 - lower timing chain tensioner rail
* 068 198 171 - rear main oil seal
Note: The above part #s for the upper timing chain parts are for the newer style parts. For the part #s valid for engines with the older style upper timing chain parts, refer to James' 12V VR6 headgasket/timing chain/cooling system parts list.
All of the above parts were purchased from http://www.vwparts.com and http://www.germanautoparts.com. Some parts were cheaper from one source while others were cheaper from the other. All parts that I received from these two vendors were OEM.
Special thanks go to James (James 93SLC - luckily he had done this procedure before on his Corrado), Shashi (DJ-SBK) and Eric (BCDS2003T), for their help with the procedure.
Let me know if you have any questions.
As always, do this procedure at your own risk. I am not responsible for any mistakes in the below procedure or those that you make while performing it.
Modified by VgRt6 at 12:15 PM 10-13-2006