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2.7 Alternator Replacement - Some thoughts having done it

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Author Post
Mon Jul 29 2019, 03:24pm
Joined: Jan 03 2018
Member No: #3382
Location: South

I'm not a professional mechanic and this isn't a full write-up so please treat accordingly, but I recently changed the alternator on my 2.7HDi C6 and wanted to share a few thoughts for anyone contemplating the same job.

This stemmed from receiving the “Battery Charge Faulty” message on the central display, following which I confirmed it was the alternator by testing the battery output. I was actually about 2 1/4 hours from home when this happened and whilst I have breakdown cover, I only ever consider this a last resort. The reason I mention this is that the C6 actually got me home - doubly impressive considering I had to use the lights for the last hour or so of the journey. Clearly, I was lucky and the alternator was not totally stuffed; but given the car’s relative electrical complexity, I’m still impressed.

Initially I simply tested this using a multimeter and with the system under load, following which I ran a Lexia diagnostic. I also changed the battery, but that’s another story… Prior to this I had the tell-tale ‘canary’ sound at tick over, which can be indicative of a failing / failed alternator clutch. In my case the bearing was in relatively poor shape when I got it out - it was very noisy, even when just turning it on the bench.

Changing the alternator at home is entirely possible if you take your time. First off, I would strongly recommend reading the engineering docs available on this forum. They help to plan the job by giving you the basic steps involved. However it is a little fiddly and whilst some tasks are easiest from above, most of the work is done underneath on the driver’s side (for right hand drive cars). I’m not going to repeat the steps in the docs, but just want to share some points I discovered that might be useful to others.

The alternator is static-mounted and the serpentine belt is held in tension by a self-adjusting (sprung) idler pulley. The assembly needs to be rotated clockwise (towards the front of the car) to slacken the belt and then carefully ‘locked’. Space is tight between the tensioner and the inner wing, so getting a breaker bar in there is difficult - a tommy bar with a suitable socket worked for me. There is a small hole in the housing that allows it to be secured in the ‘relaxed’ position at which point is can be left to rest - whatever is used must be strong enough not to bend or break under the forces of the tensioner. I used a small steel rod, but I imagine most would use a screwdriver (just make sure it’s strong enough). DO NOT let the tensioner ‘snap’ back without either belt-tension or a peg in place.

The wheel arch liner needs to be entirely removed, which includes the forward-facing section that runs under the front bumper. My car has the lane departure warning system unit built into this, so simply disconnected the loom at the multiplug and cable tied this to stop it from getting damaged. The under tray / sound deadening panel will also need to be removed. I didn’t replace the belt so simply slid it off the crankshaft pulley from underneath. Obviously, if I was also replacing the belt I would have removed it all together at this point. In either case, this part of the process is likely easiest with two people - one to hold the tensioner and one to carefully slide the belt off the crank pulley. Had I have planned things better I would also have changed the crank pulley, but I hadn’t and so I didn’t. I suspect that will become a job for another day. With the liner removed, access isn’t too bad but it’s a constant battle between the front of the engine, the cross member extension and the inner wing.

Viewing from underneath, the alternator is above the A/C compressor and this needs to be extracted to provide the necessary access. This has been discussed elsewhere on this forum and it is quite tricky. The principal difficulty is caused by the two hoses connecting to the compressor - I was paranoid about damaging them (and / or anything else) and one has a hard metal section limiting its movement. The docs are a little vague at this point - think how Haynes used to opportunistically describe a task as ‘manoeuvre the part to remove it’… Once I’d slackened the retaining bolts for the compressor, I used them to hold it in place whilst I determined the run of the hoses. Using the additional degree of movement afforded by loosening the compressor, I could re-direct the run of the hoses towards the outside of the car - effectively, into the void between the bottom edge of the radiator and the subframe. I then carefully lowered the compressor body and rotated it around 90 degrees such that it was near parallel with the subframe extension. This is really all done by feel and I suspect different techniques will work for different people.

The alternator is secured to a casting on the block using two bolts. They are fairly accessible, but there is an idler pulley that must be removed beforehand. With this in place you’re not able to extract the alternator, but it can be removed by slackening the bold that runs through its centre. The main problem with the alternator is its weight - unless you’re working with a lift, most of this job is done laying under the car which is uncomfortable and fatigue is a problem. The body of the alternator has webs through which the bolts secure it to the block. There are tangs within these webs with a small degree float (effectively like a small sleeve) and if they’re not correctly aligned the alternator will not go into the mounting points correctly. If the new unit fouls on these points and these webs won’t align with the holes on the block casting, check these sleeves are not proud of the mating face - they can stop everything from lining up. I used a wooden drift and a rubber mallet to give me a little leverage when needed, without fear that this would cause any damage.

With the wheel arch liner removed it’s not difficult to access the alternator bolts, but there is limited space between the alternator and inner wing. It’s worth thinking about this when deciding how to torque it all up, since there’s likely not enough room for a torque wrench to get on the bolt head. I used a spanner and a spring balance. The fixed idler and A/C compressor should go back on quite easily - though I was similarly careful about re-running the A/C hoses back into their original location. Releasing the belt tensioner is straightforward (I hadn’t removed the tommy bar and socket), but obviously you need to ensure the belt is correctly routed and on seated on each of the pulleys correctly.

Once all was said and done, this fixed the battery charge problem and I was getting good voltage under load. I appreciate this is a little long-winded, but I hope it’s encouraging, if not helpful, for anyone looking into this job.

I remain hugely impressed that the car got me all the way home.
8 User said Thank You to mixolydian for this Post :
 C6Dave (29 July 2019) , Eric (29 July 2019) , MarkBevan (29 July 2019) , FraserG (29 July 2019) , cruiserphil (30 July 2019) , MGmike (30 July 2019) , Tjensen (30 July 2019) , Candide (07 August 2019)

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