Question 0n 08 S5 4.2 & Timing Chain Issues

[Chumpy95]

New here and I read somewhere that apparently there were 2 different 4.2 motors in the 2008 and one has the dreaded timing chain guide issue and one does not......ANYONE know how I can tell the difference in which motor might be in the vehicle I am about to purchase?....Any help in being able to see if this is true and if so, how to identify this would be appreciated. Maintained buy Audi dealers til around 85k and the car currently has 95k on it. She's real pretty and 6 speed manual gear box.

[hahnmgh63]

I think the CAUA was the only 4.2 available in the S5 in 2008, first year of it in N. America. Being that you're talking about a first year model year there may have been improvements/revisions to some of the parts up through the 2012 model year. The B8 4.2's are known to have less issues than the B7 4.2's but being that 2008 was 16yrs ago, more like 17yrs from production there is bound to be degredation to the plastic guides due to age and heat cycles.

[Smac770]

B7 S4 4.2L - BHF
B7 RS4 4.2L - BNS
B8 S5 4.2L - CAUA
B8 RS5 4.2L - CFSA

So maybe you're thinking the BHF or the BNS in the MY08 B7 vehicles? The B8.0 S5 4.2L was only the CAUA engine.

https://www.ilcats.ru/audi/?function...65&language=en

[Chumpy95]

Thank you very much for the intel , I am now reading that they also had a 40 valve 4.2 and apparently that is way more problematic than the 32 valve, which happens to be the one I am looking at and it looks like about 85,000 of this car's life was striclty serviced by Audi dealerships and oil changed on a regular basis. That is making feel a drop more confident in pulling the trigger on this weekend warrior.

[hahnmgh63]

The 40 valve motors were before 2008, they did have the advantage/disadvantage depending on how you look at it of a front mounted timing belt instead of a rear mounted timing change. I've got the BCY version in my '03 RS6, a great motor and a very reliable 500bhp output. There's been a lot of engineering talk about what Audi did with their V8 motors with the timing chains. They have improved the system somewhat since 2008 but it is still a very complicated arrangement with lots of guides, rollers, and 4 chains. On the other hand the Porsche Cayenne 4.5 or 4.8 V8 motors with the same 'V' layout and double overhead cams per bank have just one timing chain and the guides tend to last longer. And if you do need to change it the parts are half the price of Audi's and much easier to work on. I hope i never have to do the timing chain on my RS5, they due tend to last longer than the older S5's setup though.

[Smac770]

The 5-valve engines were the old turn of the century MPI (multi-port injection) designs. All the FSI (direct injection) engines are 4-valve engines. In MY08, the B7 S4 BHF and C6 A6 and D3 A8 BVJ were the old MPI 5V V8s. These are the notorious ones, in regards to that chain stuff, apparently. The BNS, CAUA, and CFSA are all FSI engines.

[Chumpy95]

The 40 valve motors were before 2008, they did have the advantage/disadvantage depending on how you look at it of a front mounted timing belt instead of a rear mounted timing change. I've got the BCY version in my '03 RS6, a great motor and a very reliable 500bhp output. There's been a lot of engineering talk about what Audi did with their V8 motors with the timing chains. They have improved the system somewhat since 2008 but it is still a very complicated arrangement with lots of guides, rollers, and 4 chains. On the other hand the Porsche Cayenne 4.5 or 4.8 V8 motors with the same 'V' layout and double overhead cams per bank have just one timing chain and the guides tend to last longer. And if you do need to change it the parts are half the price of Audi's and much easier to work on. I hope i never have to do the timing chain on my RS5, they due tend to last longer than the older S5's setup though.

Thank you for the education, as I have had a ton of cars and this would be my first Audi.....Just didnt wanna drop 14k and then another 10k for a timing chain job. I have heard with proper maintenance , they can last quite a while.

- - - Updated - - -

The 5-valve engines were the old turn of the century MPI (multi-port injection) designs. All the FSI (direct injection) engines are 4-valve engines. In MY08, the B7 S4 BHF and C6 A6 and D3 A8 BVJ were the old MPI 5V V8s. These are the notorious ones, in regards to that chain stuff, apparently. The BNS, CAUA, and CFSA are all FSI engines.

I am a novice to Audis, so I appreciated the education and response.

[hahnmgh63]

As an example since yours is a 2008, the main crankshaft guide (aluminum with a Phenolic plastic guide plate) is now part # 079-109-507-AF, there were two previous revisions dating back to 2008, 079109507Q & 079109507R. With many manufacturers, unless there is a tech service bulleting requiring or recommending a change to a new part you really don't know what the new part revisions are for. Is the part improved or possibly a new supplier so they gave it a new part suffix? But being a 2008 the guides are old, the Phenolic plastic does get brittle with age & heat cycles. It isn't a fun job to do as the engine has to come out and there are a couple of special cam holding tools that need to be used to hold the cams in place while you get everything tightened down properly at TDC. The chain/guide setup is an engineering marvel to look at but as I mentioned, Porsche went a more conventional/practical route of simplicity compared to Audi.

[Chumpy95]

The 5-valve engines were the old turn of the century MPI (multi-port injection) designs. All the FSI (direct injection) engines are 4-valve engines. In MY08, the B7 S4 BHF and C6 A6 and D3 A8 BVJ were the old MPI 5V V8s. These are the notorious ones, in regards to that chain stuff, apparently. The BNS, CAUA, and CFSA are all FSI engines.

Thanks for that info....From what I can see, if these 4.2 32 valve engines are properly maintained, they are far less problematic. The Carbon build up is what it is.....I was just worried about a 10k chain replacement and it seems like I might not have to worry so much, based on the previous owners and records of maintenance .

[Chumpy95]

As an example since yours is a 2008, the main crankshaft guide (aluminum with a Phenolic plastic guide plate) is now part # 079-109-507-AF, there were two previous revisions dating back to 2008, 079109507Q & 079109507R. With many manufacturers, unless there is a tech service bulleting requiring or recommending a change to a new part you really don't know what the new part revisions are for. Is the part improved or possibly a new supplier so they gave it a new part suffix? But being a 2008 the guides are old, the Phenolic plastic does get brittle with age & heat cycles. It isn't a fun job to do as the engine has to come out and there are a couple of special cam holding tools that need to be used to hold the cams in place while you get everything tightened down properly at TDC. The chain/guide setup is an engineering marvel to look at but as I mentioned, Porsche went a more conventional/practical route of simplicity compared to Audi.

Thanks again for the education, great motors apparently but like most things German engineered, they tend over engineer them!