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This photo shows a customer shaft with the damage to the keyway. This damage is caused by the keydrive wearing, then it rounding the internal surface of the keyway. Once the key starts spinning, the oil pump will not be functioning, causing oil starvation which will rapidly inflict damage throughout the engine.
We receive a lot of questions as to why our repair is more expensive than other solutions advertised. We charge £295 +VAT for this repair and each repaired shaft comes with a new OE 77mm drive key. As engineers with over 40 years experience, we developed our repair to be the best possible solution to this common problem. This page will explain our repair and show you that our solution is the only one you should consider.
We start by machining out the original keyway, ready for our custom made insert. We have these manufactured for ourselves and hardened to 55 Rockwell. This creates a much harder environment for the keydrive to be housed in. The original keyway is created using the broaching method, which isn’t ideal for a prceise keyway and the slightest misalignment can cause chatter. We use spark erosion to create the keyway as it more precise and allows for perfect alignment. This is essential for the high speeds the balance shaft will be rotating. You can see, in the photo below the insert with the darker end showing the hardening treatment. We have these made overlong and with a larger diameter than required so we can machine each one individually to suit the shaft it is being used in. The manufacture of this keydrive is the main reason our repair is more expensive.
We then place the insert in our cylindrical grinder and machine it to just oversize of the keyway we have machined in the shaft. Once the grinding is complete, we shrink the insert with liquid nitrogen and use a hydraulic press to place it in the shaft. The left hand photo below shows the insert being ground to size. Once the insert is in place, we then grind the outside of the shaft as the keyway insert will have swollen the shaft in this area. If this wasn’t carried out, the shaft journal would not be an exact fit back into the bearings in the balance unit. The right hand photo shows the journal size being ground on the balance shaft.
The photos below show the finished repair. You will see other repairs where the end has been highly polished. This is done to hide the process being used but we prefer to show the work we have carried out. These photos plainly show our insert in the end of the balance shaft. So its really down to personal choice at the end of the day...... You can do it the cheaper way or the right way! Contact us today to make the right choice.