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View Full Version : Does cam belt breakage always cause damage?



driver2008
14-02-2010, 12:42 PM
Does this automatically result in damage? I was doing about 10mph in my 1.4 petrol when the engine died. Didn't hear any clanks or bangs, possibly a brief tinkling noise. Recovery garage say head has to come off to inspect for bent/broken valves/piston damage in at least 2 cylinders, cost up to £1k. Would it not be possible to fit new belt and try to start it up, before removing head?. For those interested, new belt was fitted at 55k miles and had done 40k miles, but was within a few days of being 4 years old.

zollaf
14-02-2010, 12:54 PM
if you remove the rocker cover and see if any tappets are sitting low, then this is a sure sign of bent valves. the problem is that regardless of what speed your doing, when the belt goes, the piston hits the valve at incredible speed. this will nearly always bend the valves. fitting a new cambelt is an option, but is very rarely succesful. far quicker and easier to pull the camshaft out and spin it over, or compression test it.

STEWY L
14-02-2010, 12:58 PM
some engines are designed in such a way that the pistons will not hit the valves should the timing go "amiss", (i've worked on many in forklift trucks) ,and because of this, no time limit is placed on belt renewal as the only consequence of a snapped belt is the inconvenience
of a breakdown.
however,if a time limit is quoted,then it's done so for a reason, to prevent damage
should it fail. the damage however,could be simply broken lifters/rocker levers,(acting as a fuse if you like) rather than bent valves.
in such a case the valve stem hieght could be checked with a straight edge( a bent valve would be lower than the rest) and a decision taken from there,however,the head would still need to come off to ensure that all debris from followers/lifters were retrieved,
regards,
stewy.

driver2008
14-02-2010, 01:12 PM
if you remove the rocker cover and see if any tappets are sitting low, then this is a sure sign of bent valves. the problem is that regardless of what speed your doing, when the belt goes, the piston hits the valve at incredible speed. this will nearly always bend the valves. fitting a new cambelt is an option, but is very rarely succesful. far quicker and easier to pull the camshaft out and spin it over, or compression test it.


Thanks zollaf, enjoy your bike ride, maybe I'll do the sme today.

driver2008
14-02-2010, 01:21 PM
some engines are designed in such a way that the pistons will not hit the valves should the timing go "amiss", (i've worked on many in forklift trucks) ,and because of this, no time limit is placed on belt renewal as the only consequence of a snapped belt is the inconvenience
of a breakdown.
however,if a time limit is quoted,then it's done so for a reason, to prevent damage
should it fail. the damage however,could be simply broken lifters/rocker levers,(acting as a fuse if you like) rather than bent valves.
in such a case the valve stem hieght could be checked with a straight edge( a bent valve would be lower than the rest) and a decision taken from there,however,the head would still need to come off to ensure that all debris from followers/lifters were retrieved,
regards,
stewy.
Thanks Stewy, guess I'll just leave them to it. Am frustrated that these problems are inadvertently designed in for the sake of extra performance. Bring back 'no contact space' for valves/pistons, and chains or gears instead of toothed rubber belts.

zollaf
14-02-2010, 02:50 PM
brief tinlkling noise, that would be the valves being destroyed i would say. i must say i do prefer belts as they are a lot easier to change than a chain, and chains do have problems as well. gears are good, but more expensive to make, especially for an overhead cam engine, since the cams are a long way from the crank. you just have to put this breakage down to bad luck im afraid.