A guy called me up about a VW LT35 2.5 5 cylinder turbo diesel TDi van, well pickup actually that had apparently been diagnosed with having the start of big end failure. He’s been hearing a bit of a rattling noise coming from the engine, more noticeable at tick over but he could hear it at other points while driving too.
It was like a metallic knocking very similar to what you get from big end bearing wear or failure, and as such it had been two the local garage who said they thought the noise was coming from the big end bearings but told him to go and see a guy at a commercial vehicle repair place that specialised in Mercedes Sprinters and VW LT35 van repairs. They too told him it’s the big end bearings and said this was going to be an expensive job requiring the engine to come out, a partial engine rebuild with a crank regrind probably coming to the best part of £2000 at a guess.
Well heart broken with all this potential wallet ache, and the thoughts of being off the road for a couple of weeks not earning money I got this phone call from him at 7pm on a Thursday night, asking me for my opinion. I drove over too him and had a look at this LT35, in the dark and rain – life is always like that.
On inspection, while the van was running I could see the harmonic balancer bottom crank pulley sort of wander back towards the block, like it had some kind of float going on, not being an expert with this engine type I probed into this some more. By turning all the electrical devices on like the main beams, heater fans, wipers etc, then also turning the power steering repeatedly and holding it on full lock – it would cause the maximum amount of load on the pulley and drive belt assemblies.
Under these load conditions you could really see the pulley float about heavily and this mysterious knocking noise from the engine was more obvious than ever before. You could hear the knocking noise every time the harmonic balancer crank pulley bounced off the timing belt covers. After about a couple of minutes of this loading, bits of rubber flew out from under the bonnet and the pulley finally gave up, and at the same time the knocking noise stopped.
So we ordered a new crank pulley, and I changed it over in about an hour without any major strip down work and the knocking noise has gone. No engine rebuild, no expensive repair bill, just a quiet engine. Inspecting the failed pulley the rubber had actually collapsed the held the inner to the outer so under load the outer would slip back towards the block.
You cannot see the rubber section while the pulley is on the vehicle as it has been designed and installed to “fail safe” so if the rubber collapses it will not fall off completely. As you can see from this picture, from the front it just looks like a large metal pulley.
I would state the most difficult job in changing the harmonic balancer pulley over is undoing the bottom crank pulley retaining bolt. It is tight, and I mean very very tight – it’t a typical crank pulley bolt problem, you need to lock the engine somehow so you can actually apply the force directly to the bolt. Just make sure when you put it back together, you use a high quality thread lock fluid to keep that bolt from releasing because if it does, then the cam belt wall ride off and it’ll be a very expensive learning exercise!