Crankshaft bolt
Six months ago, I changed the cambelt, water pump and tensioners on my 2005 Zafira A 1.6 with the Z16 XE engine. Upon undoing the crankshaft bolt holding the crankshaft pulley in place, I found the bolt was coated thickly with a white compound that I believe was threadlock. The threads on the bolt were very badly damaged, being almost non-existent in one place.
I carefully cleaned the threads with an oil spray and sourced a new bolt from Vauxhall, but upon tightening first by hand, then with a socket set, the bolt refused to tighten. My local garage tried re-tapping the thread and thread-locking the bolt into it. This worked for a few months until the bolt came loose and destroyed the crankshaft pulley. I bought a secondhand pulley from ebay, which was fitted with a stronger threadlock. Six weeks later, the bolt came loose again and destroyed the pulley again.
My local garage asked an engineering specialist firm that skim heads for advice. I suggested using helicoils, but the engine specialist was of the opinion that the crankshaft is too brittle for helicoils and that a new thread that is cut will not hold. They say they have seen this before on Vauxhall/opel cars with crankshaft bolts. Instead, they have suggested using a metal putty to hold the bolt in place, which we are trying next.
Should this fail, is a helicoil likely to be successful? I assume I would need two to hold the crankshaft bolt or would one suffice? Given the car’s age, a replacement engine would be uneconomical. John Whittington
Metal putty can provide a firm locking action, but it will not be possible to torque up the bolt to the required tension. This means that the crankshaft pulley will not be clamped efficiently and will begin to move and wear. As it wears, the movement will increase, putting you back in the position of having a damaged crankshaft pulley.
The placing of a helicoil depends on a new larger thread being cut into the receiving aperture. The torque setting for the crankshaft bolt on your Zafira is 95Nm +45° +15°, which means the thread will be under quite a load.
There is a thread insert which is designed for a heavier load and one of the companies that sell this insert can be found here: http://bit.ly/2h6cnpa. Hopefully this could be fitted, returning the engine to service without too much expense.