I am planning to do the timing chain on my R56 soon and wondered if anybody had a definitive opinion on this - How necessary is it to change the intake and exhaust camshaft sprockets while doing this job, assuming there is no damage to the existing ones? The thing is, the one with the VANOS adjustment hub is very expensive (like $295) and if so I would like to get away with just getting a timing chain kit and changing all bolts, guides, seal and crankshaft sprocket and not bothering with camshaft sprockets if I can avoid it.

Any caveats or advice?

 

You probably don't have access to it but the factory service manual can offer guidance on questions like this.

Over the years with chain drives from bicycles to motorcycles it was if the chain needs to be replaced so too do the sprockets. Sure no way a bicycle sprocket costs $295, well, back then. But back when I was riding bicycles and my money came from cutting grass, a paper route, even a few dollars for new bicycle sprockets was a *lot* of money.

I have never had an automobile engine chain need changing but I would if faced with this replace the chain and sprockets. A worn sprocket can accelerate the wear of a new chain (or vice versa). Replacing a cam chain, or chains, is not a job I would want to do twice, the 2nd time replacing the prematurely worn chain and the should have been replaced with the chain sprockets. If the chain fails prematurely then you face dealing with (possibly) valve/piston contact. That would make the cost of a new sprocket pale in comparison to what you will spend to address the collateral damage from a failed cam chain drive.

 

Fair Enough. Yes the $194.95 (updated price from another vendor) for the sprocket is definitely worth it, given what you mention about catastrophic engine damage from a failed timing chain.

 

I just completed this job a few weeks back on my wife's R56 and I reused both sprockets, they looked to be in great condition. I did the chain as it was time at 160,000 km but had no problems before the job. Comparing the old and new chains the old one may have been slightly elongated. I had done the updated main tensioner at 80,000 km and found the original was weak. All the plastic guides were in fine condition too. Be sure to replace the TTY stretch bolts for both sprockets and crank hub. I did the chain, tensioners, plastic cassette/guides, bolts, new VC gasket, did the plugs and serpentine belt while i was in there. I had the camshaft locking tool, made my own crank holder out of 3/16" steel and just kept a jack under the engine to move it up and down as needed. Everything working great so far no codes.

 

That's good that so far things are working ok. But the real test is if the cam drive hardware lasts another 160,000 km and it does so without failing catastrophically.

 

Really? The sprockets just fail on their own? Everything I read about failures had to do with the faulty tensioner, running low on oil and the plastic guides.

 

Worn sprocket contributes to premature chain wear. One failure mode has the chain getting loose and getting out of time. A loose chain can beat the guides up. They are plastic and durable as far as it goes but they do not like a loose chain. And if a chain can jump one or more teeth the chain can break from the shock.

Just seems like false economy to replace the chain and yet not the sprockets. But with a DIY chain R&R of course it is up to the individual.

 

I'll have to keep an eye on it I guess, too late now haha, it is after all a 13 yr old daily commuter car and grocery getter. The whole design is poor when you have a timing chain that needs maintenance as frequently as a timing belt, especially on an interference engine.

 

Also - since I am now convinced to buy the sprockets as well - How difficult is it to do this job with the car NOT in service mode? i.e. with the front end intact? Should I take off the front end or try it with everything in place? Also the Haynes manual mentions rotating the engine 4 or 5 times after the assembly to check that nothing is binding up. Which end of the crankshaft do you turn to do this? The water pump end or the other? I am just to visualize how much space I will have to do this if I don't take the front end off. Thanks.

 

Check out FCP Euros timing chain guide on youtube, no need to do service mode. It gives you like an extra inch or two thats it.

 

So that's the video I referenced when working on our Mini, I also did not bother with Service mode, I also didn't use a serpentine tool, once everything is removed and out of the way a big adjustable wrench will work fine to release the belt tension. I forgot to mention previously that I also did replace the crank seal and hub, as well as the three hub bolts. I did this on a base hatch N12 engine so dual vanos which is different than the one in the video meaning the cam bolts are both the same length/part number. The new OEM crank bolt I got from the dealer was different, the original was longer and had a loose captured washer on it, the new bolt was shorter and had a bigger flange head like it took the place of the loose washer, so being a slightly shorter bolt makes sense. Double checked the part numbers with the dealer, the VIN was used to order the bolts. Also follow all of the torque specs I watched another video where the mechanic did not torque everything as it should be and stuff came loose after and the valves met the pistons, at least he owned it after and admitted his mistake. Also, in the FCP Euro video he reused the cam sprockets, but my wife is now probably driving a ticking time bomb lol.

 

So I have everything back together but haven’t put the valve cover back on yet. But something is stressing me out. I torqued everything correctly except the exhaust cam sprocket which I overtorqued by 90 degrees. I don’t know what the hell I was thinking - it said +90 degrees and I did a full 180. So should I remove that bolt and use another one? Or should I just go with it since it didn’t break? I know about bolt stretching to yield point and then going into plastic expansion. What are the potential ramifications of the over tightened bolt? another question is if I was just going to remove that exhaust camshaft bolt - how would I do it? Put the locking tool back on, crank locking pin, loosen tensioner, take out bolt and go again with pre-tensioner tool and then real tensioner? I can’t think through how to do it. Any advice would be appreciated.

 

So, I decided to put in a new exhaust cam bolt. But now I am doubting everything I've done. I put the crank pin in and cam lock tool on (I had to push hard towards the front of the engine to get it bolted on where the middle bolt hold the two pieces of the tool together (!!) ) I loosened the exhaust cam bolt, then slacked off the tensioner a bit, replaced exhaust cam bolt and torqued it and the tensioner back to spec, this time only doing +90 degrees on the cam bolt.

NOW the chain has a tiny bit of slack in it. I think that I may have screwed this up entirely and will have to buy new intake and exhaust cam bolts and start over using the pretensioner tool. The strange thing is that the cam locking tool didn't fit the second time like it did the first, it was almost as if the intake cam had rotated +/- 5 or so degrees towards the back of the engine after I finished the job the first time (where I over-torqued the bolt).

I am assuming that the tension on the chain is NOT taken up at all when the motor runs. The first time i did the job when I over-torqued the bolt, the chain was super tight and now I can rattle it a bit on the sprockets. I don't want to rotate the engine by hand at all for fear of getting the cams and crank out of phase. Any advice?

 

All good 1000 miles later FYI

 

I'm going to be doing this on my R56 Base in the winter. 132k on the odo (new to me). No rattles but I'm doing it as a preemptive strike. If my sprockets don't show any wear, then I'm planning on reusing. The primary reason for changing is chain stretch and guide degradation rather than chain wear. If signs of significant wear are seen then it makes sense to change the sprockets out. Old school American V8s always had the chain and sprockets changed at the same time but chain stretch was rarely a problem.