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Matt, Engineer
Category: Car
Satisfied Customers: 20389
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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if you replace a cam belt, and have the timing out by 180 degrees

Customer Question

if you replace a cam belt, and have the timing out by 180 degrees and turn the engine over by hand and the engine becomes tight and you continue to try and turn can you fracture a cam follower and would the cam follower be on number 2 cylinder?
Submitted: 6 years ago.
Category: Car
Expert:  Matt replied 6 years ago.

Sadly the answer is yes to all of these, although the damage may not be on no.2 as it depends where the crank was when you had it all timed up.

Also you're more likely to have bent a valve rather than cracked a follower, I'd set the timing correctly and then try a compression test to see if the engine is sealing OK.

If it is sealing OK its worth a look under the cam cover to inspect the valve gear for any damage
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Customer: replied 6 years ago.
The problem is the mechanic who replaced the cam belt said the engine became tight and then realising the timing was out by 180 degrees but not admitting this, I believe he had slightly fractured the cam follower by having the cam belt in the wrong position whilst turning over by hand and exerting a little too much pressure, when I received the van back I ran it for 2 miles and the cam follower snapped on the intake valve and jammed the valve slightly open so the engine started to backfire through the intake, after taking the engine apart again we found one snapped cam follower and one slightly twisted, this indicates to me someone had stressed this component before the engine was fired up, the unique thing about the citron diesel engine is the intake valve hits the top of the piston flat on so the stress would transfer to the weakest point being the cam follower so to my original question and your answer I cannot see the valve would bend before the cam follower would stress? I have taken this up with our structural engineer and he confirms that this would be the case and I have also been informed that the citron cam followers are designed to shatter if a cam belt breaks? what is your opinion , as the mechanic now claims that the cause of the problem is that a bit of carbon from the intake manifold was sucked into the combustion chamber and caused the cam follower to snap? as through not servicing regularly?, the van has done 125k and has always run perfectly.
Expert:  Matt replied 6 years ago.

I'd take a look inside the inlet manifold for carbon deposits but unless its a big lump of debris this sounds like an unlikely scenario to me.

I'd tend to agree with your diagnosis that the cam follower had been pre-stressed - if you remove the follower entirely you may be able to see a witness mark from the valve stem and if you can borrow the use of a borescope and look into the cylinder you should see a round mark in the carbon on the piston if the valve has touched it
Customer: replied 6 years ago.
we found no marks as there was no carbon on the top of the piston because i insisted that they took the head off to make sure the valves had not damaged the piston this is why I am questioning the mechanics claim carbon entered the combustion chamber and as the value sits completely flat on the piston face you cannot tell if there was any stress between the 2 components, many thanks
Expert:  Matt replied 6 years ago.
The only thing to test would be to have the remaining cam followers crack checked. any engine rebuild shop should be able to do this and this would give strength to your argument if its on more than one cylinder
Customer: replied 6 years ago.
I do not see this having any relevance on my argument as the mechanic would have only stressed the one cam follower before realising his mistake as you would not be able to rotate the engine any further as it would deadlock? many thanks
Expert:  Matt replied 6 years ago.

Its possible that hes pushed past No.2 and onto the other cylinders is what I was thinking.

the other thing to check would be for any signs of contact on the valve seat to see if the 'big lump' of carbon could have left any witness marks here - I suspect you won't see anything

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