Expensive balance belt change lesson
Discussion
Two years ago I had the timing belt / balance belt changed on my 968 engine. EMC in Birmingham built the car and I would have used them for this job but I live in North West London and used an independent Porsche specialist close to me. In September 2013, after 1,000 miles / six months I went back to have the belt retensioned per their recommendation.
After another 1,000 miles (most of which were on track), in September 2014 on the sighting lap at a track day the bolt securing the tensioner snapped, the tensioner fell onto the crankshaft, and the cambelt skipped, leading to 16 bent valves. Thankfully I was off throttle at the time and turned the engine off and put the car into neutral within seconds. The bill to remedy the damage was nearly £3,000. I got a nice shiny head back and the car is better than ever. It has cost me very little over the years so I wasn't terribly unhappy. I wrote an email to the garage that changed the balance belt but didn't get a reply. It's not worth pursuing further.
The point of this is that the garage that performed the remedial work suspects that when the balance belt was retensioned, the tensioner was merely crowbarred into position and retightened, rather than using the factory method of removing and retentisoning (I don't really know what I'm talking about here but a front-engined Porsche specialist will). It broke a year after retensioning (although only another 1,000 miles), so who knows what really happened.
The second point is that prior to the failure I did have a warning. When I started the car that morning it wasn't its usual almost turbine-like self. I could hear what sounded like the beginnings of bad bearings in the alternator, not bad enough to not drive the car though. I made a note to check it when I got back from the track day. If you hear such a noise and you suspect the alternator, remove the timing belt cover and see if the tensioner is loose, or if the noise is more noticeable.
Main lesson learned: I will only use a Porsche specialist that focuses on front engined cars in future. Hat tip to Kevin at EMC. I called him from Silverstone where the car broke. I'd removed the timing belt cover and saw what happened. He collected the car the next day, and it was ready to pick up two weeks later.
After another 1,000 miles (most of which were on track), in September 2014 on the sighting lap at a track day the bolt securing the tensioner snapped, the tensioner fell onto the crankshaft, and the cambelt skipped, leading to 16 bent valves. Thankfully I was off throttle at the time and turned the engine off and put the car into neutral within seconds. The bill to remedy the damage was nearly £3,000. I got a nice shiny head back and the car is better than ever. It has cost me very little over the years so I wasn't terribly unhappy. I wrote an email to the garage that changed the balance belt but didn't get a reply. It's not worth pursuing further.
The point of this is that the garage that performed the remedial work suspects that when the balance belt was retensioned, the tensioner was merely crowbarred into position and retightened, rather than using the factory method of removing and retentisoning (I don't really know what I'm talking about here but a front-engined Porsche specialist will). It broke a year after retensioning (although only another 1,000 miles), so who knows what really happened.
The second point is that prior to the failure I did have a warning. When I started the car that morning it wasn't its usual almost turbine-like self. I could hear what sounded like the beginnings of bad bearings in the alternator, not bad enough to not drive the car though. I made a note to check it when I got back from the track day. If you hear such a noise and you suspect the alternator, remove the timing belt cover and see if the tensioner is loose, or if the noise is more noticeable.
Main lesson learned: I will only use a Porsche specialist that focuses on front engined cars in future. Hat tip to Kevin at EMC. I called him from Silverstone where the car broke. I'd removed the timing belt cover and saw what happened. He collected the car the next day, and it was ready to pick up two weeks later.
Edited by nsa on Thursday 19th February 18:44
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