Help! - Can a Volvo XC70 w/ a misaligned timing belt run?

My mechanic says that he did not cause the engine problem i.e. my valve #2 burning out because if the timing belt was put on incorrectly that the car would not run. I have a picture with the timing belt misaligned by one tooth. Is he not telling the truth? The folks that did the repair said that it could take a while before the misalignment caught up and created the problem.

One of the regular responders was a Volvo mechanic for a number of years. He says they will run with timing on the camshaft off one, or two, teeth. Three teeth off, not so good.
I don’t think the timing being off one tooth caused one burned valve. If one, why not all the valves?

I have owned Volvo’s in the past and did some work on many different models of them. One thing that was common yet not that frequent was burnt valves. Again, saw it many times but it is not really a serious problem with the make of car.

How many miles on the car?
It is possible to have a belt off a tooth or two and the car still run.

In theory, if one valve (assuming exhaust valve here) burns then all of th exh. valves should have a degree of burning.
However, if a valve was marginal with even a microscopic flaw it’s possible that a valve on one particular cylinder could give up before the others.

Many years ago I bought a Subaru with an engine problem. Someone had advanced the ignition timing too much. (distributor equipped)
The pistons were being burnt right out of the cylinders due to this.
In one cylinder, the piston was half disentegrated, the next cylinder in the firing order was less damaged, and so on through the last 2 cylinders.
The damage on all 4 piston varied greatly with the last piston barely touched.
One would think all 4 would have been affected the same but they were not.

The mechanic who did the repair said that he could see the damage from the misaligned timing belt. He mentioned that there was repeated damage in the same location to that one valve from something hitting it. Forgive me, I am not a mechanic, so I cannot remember what was hitting it - a piston perhaps. That would be the reason that it only affected one valve and not all.


I just spoke to a volvo dealership service center, and they say that the misalignment would cause the piston to miss and hit the engine. If it was only missing in one spot that would be the reason it affected only one valve and not all.

I am just trying to cover my bases and get as much information as possible in order to go to the original mechanic to discuss options since the damage was caused by their error.

I am not sure it is reasonable for me to ask them to reimburse me for the entire cost of the repair to the head and valve. But there are other repairs that are now required due to this, i.e. my oxygen sensor was damaged due to oil leakage. I am not asking for a full refund of the more than $2,500 that I spent to get the car running again. I believe that the original mechanic should make subsequent repairs to my vehicle at no charge in order to make up for their error. Does that seem reasonable? Any advice on how to handle this is kindly welcomed.

Many cars (even interference ones with interference engines) will run if the belt (or chain) is off by one tooth. Not too sure about your Volvo though. If it is able to run being 1 tooth off…first off you would probably notice a performance problem or a lot of knocking. And over a period of time it could cause a burnt valve.

What do service departments know of such questions as this? What does the average mechanic know the valve to piston clearance? Very little. The specialist who might know, or could quickly find out, would be at an automotive machine shop, or an automotive performance shop.
It’s not difficult to tell how many camshaft teeth off will cause the piston to contact a valve. One tooth off on the camshaft sprocket is about 8 degrees of camshaft rotation. Here is how to actually measure the amount needed for contact: set a piston at top dead center, carefully turn the camshaft(s) away from their index marks until a valve contacts a piston. How many camshaft teeth did that require? I think it would be several teeth; but, hey! do the actual test. It would only take a couple of minuets if camshaft alignments marks are viewable.
Here is a picture of a camshaft sprockets to give you and idea of the lay-out.

Common but not frequent? burnt valves not serious?. One tooth off on any BMW means collision (it is dangerous to say any but I can’t think of one that would survive). Performance suffers tremendously being one tooth off. How did you not notice it? The one tooth off mis-diagnosis can happen when people dont take into account for flex in the belt. Haven’t you ever rocked the cam back and forth with the belt attached? there is movement. Most likely the engine was in time (not off by a tooth) and you were just looking at the cam position affected by belt flex. One tooth off will not burn valves, much less just one valve.

If you put the belt on wrong and conditions are the worst possible, it would take about ten days to burn a valve. Worst possible is at 200,000 miles and having questionable valves in the first place. Intake or exhaust? The exhaust is the most likely to burn with retarded valve timing.