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Hi,

Recently my Land Rover Discovery went into the main dealership to get, what appeared to be, a simple fault with a HT cable or a faulty spark plug.

When I rang the garage to confirm if it was ready to be picked up, I fell off my chair when they quoted $2,000 for the work. It transpires that they had stripped the thread of the spark plug when attempting to diagnose the fault and the Helicoil also failed. The cylinder head has now to come off and a threaded sleeve machined in!

They claim that the spark plug had been over tightened but the plugs, as far as I am aware, have never been removed or replaced as they are supposed to be those life time plugs.

This smacks of a ham-fisted mechanic being over-exuberant with his tools and I'm having to pay the price.

Any advice out there?

Cheers,

Mark

Sorry Mark, I think you are being very harsh on the garage/mechanic concerned without knowing a lot more detail as to what actually happened.

Firstly, there is no such thing as a life-time spark plug, if there was, you wouldn’t be in the position you are currently in. You can buy a long-life plug which can last up to 100,000km’s but there still comes a time when they will need to be replaced or checked.

You don’t give the age or mileage of your Discovery and you seem unsure whether the engine is fitted with long life plugs or not so it is very likely the plugs have been removed from the engine in the past.

Presuming the old plugs were fitted correctly it is almost impossible to strip a thread on removal. If a plug is fitted initially with hand pressure only and then tightened correctly with a plug socket then it should in theory be easy to remove.

Threads can get damaged because they are not cleaned properly and if the plug is almost forced into the cylinder head it will only become a problem when it is removed. The mechanic removing the plug can often be the innocent victim of somebody else’s poor workshop practice.

Or the cylinder head thread itself may not be that flash full stop which will obviously cause a problem when removing the spark plug.

I have also seen the wrong heat range of plugs fitted where the threaded portion of the plug extends too far into the combustion chamber. This can cause a number of problems one of which is a heavy build up of carbon on the exposed threaded portion of the plug.

Damage to the cylinder head thread can happen on removal of the plug because of this heavy build up of unwanted carbon.

Where the garage may have gone a little astray is not altering you immediately to the fact they had encountered difficulty in trying to remove the plug. At that stage it would have been your call to continue or not.

I’m not trying to defend the workshop concerned but I believe you need to try and find out a little more information before you start painting them in such bad light.

A meeting with the service manager or workshop foreman may help you make that decision.

Thanks for the response, I guess its just one of those unfortunate things. Following your explanation I have a better understanding of what can cause such problems and the harsh tone of the initial query was perhaps a little unjustified. It was a big shock to the system though. I shall take your advise and have a chat with the foreman.

I wasn't sure what your reaction would be to my reply to be honest, so thanks for accepting it in the spirit in which it was written.

After over 40 years in the industry, you get to see the good and the bad side of what happens in workshops.

The guy on the tools is not always in the wrong.

I have said it before and I will continue to repeat it; if workshops were to improve their communication skills there would be far less unhappy or confused customers.

Cheers

Hi. I was a mechanic for a 12 years and over that time had a couple of spark plugs that for some reason bound up on the threads while trying to remove them, no matter how carefull you are it can happen and there is not a lot you can do once its bound up. It seemed to happen on cars who had not had regular servicing. Cheers.