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Interference Engine Damage

Q. Hi, I replace a lot of timing belts that have broken. As you know some engines are interference type. Is there a way of telling if the engine has been damaged before replacing the belt without removing the head for inspection? The way I do it now is just replace the belt and hope for the best.

Interference Engine Damage

However I just replaced the timing belt on a 1999 Neon single cam and had no compression on two cylinders. I am assuming it has damaged the valves. If this has occurred would it just be valve damage or could it also have damaged the pistons?


A. This is a good question, and I wish there was an answer that would work for all engines and all situations. But there just isn't. You can't do a compression test before you replace the timing belt, for obvious reasons.

Sometimes if you take the valve cover off and remove the rockers, you may be able to see a valve stem that is lower than the rest. This indicates the valve is bent and is not seating properly. Now this is not a sure fire way to confirm a bent valve.

Interference Engine Damage

If you have a boroscope, you can look inside the cylinder and see if there is a bent valve or a damaged piston, or any other type of damage.

It is rare for a valve to actually damage a piston. They may get nicked or marked somehow, but I never had to replace one because of it.

Interference Engine Damage

But the best and only sure fire way is to take the head off and visually inspect for damage. It is a 99% certainty that you will have to pull the head off anyway.

I have replaced a lot of timing belts on interference engines, and only once did I, or I should say the vehicles owner, got lucky and not bend any valves. But 999 times out of 1,000, the valves will bend.

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