Questions and Answers

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.

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?

Thanks,
Ray

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.

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.

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.