Timing Chain System Life

[gusgriff]

I am new to and learning the 318Ti and M42 engines and have questions about the ruggedness and life expectancy of the timing chain system components. What components tend to wear out first and what is the mileage expectancy of the chain mainly but also the guides/rails, tensioner piston and sprockets. If this was a timing belt system I would not be asking.

I am trying to determine whether I need to do some preventive maintenence on an engine. I am replacing the M42 with a cracked head with another engine because the condition of the block is unknown. I plan to rebuild the block of the removed engine if still viable and I can find a viable head at a decent price.

[mohaughn]

I would replace the tensioner if you are going to be in there. As long as there are no missing teeth or any obvious metal to metal wear on the sprocket or any obvious stress on the chain you shouldn't have to replace it. The same for the guide rails. They will show obvious signs of wear and fatique. If the motor has been kept up with and was never oil starved or had any other major issues, the chain and guides will last for a very long time. There are examples with well over 250k miles and no issues. My car has 160k miles, 50k of which are almost totally on track, high rev miles, and i'm on the original timing chain equipment and never think twice about it.

Although, I would have to question why was the head cracked, and could that damage have caused any other issues. The guides cost significantly more than the chain itself. So that extra 60$ for the chain might be good insurance to make sure you don't have to go back in again. Since you said you really don't know the condition, I would just factor in another 300$ to replace the tensioner, guide rails, and chain all together and know it is done right.

[gusgriff]

Thanks for the reply. Wish I knew what caused the head to crack. Overheating is the suspected cause. Got the car at good price with knowledge it would need a rebuild. I believe the owner used it for loan collateral did not have the money to fix the engine and let it get repossessed. If I knew a head was all it needed, I would have already pulled it for rebuilding. The replacement engine I bought came out of a 318is in good but wreaked condition with 102K miles on the odometer. I got a 90 day guarantee and saw them pull the engine and have the VIN so I am pretty sure it is legitimate.