Why Don't They Do This?

[thornebt]

There's something I've wondered about for a time and I know someone on here will know the answer! There are often problems with car cambelts and camchains, tensioners etc. Why do the engine designers not come up with a couple of gears linking the crankshaft and camshaft instead of using a chain / belt? So there would be a gear on the crankshaft and camshaft and whatever number of linking gears (maybe two would suffice) inbetween to make up the distance between the two and ensure the correct rotation.

I'm sure someone on this forum probably knows knows why it isn't done that way. Or perhaps it is? It would be extremely reliable I think.

Cheers. Bruce.

 

[Anonymous]

Cost/Noise/Weight pick any combination or all of them.

As an example when manufacturers make inlet manifolds out of plastics, why then add a few pounds
back by installing gear driven cams?

It's all about Co2 savings and mpg figures I suspect.

 

[Anonymous]

Good question, I believe some old F1 cosworth engines used gears instead of a chain for increased reliability but it's probably not used in road car applications because of the cost, complexity and noise.

There is a subtle advantage of chain (or belt) over gears in four stroke engines. As there is a 2:1 ratio required, gears will always have one tooth on the crank gear meeting the same two teeth on the cam gear. That will result in uneven wear. When dismantled and reassembled the timing marks on the gears will line up again and return the teeth to their old mates. That system may become very noisy.
A chain or belt will be designed to have a number of links that shares no common factor with either gear. That is a system that will spread wear evenly to all teeth on both gears, through their contact with all links on the chain, (or steps on the belt). That system will continue to run quietly as it wears evenly. A gear train between the crank and cam must cross the cylinder head gasket at some point where there may be a gear tooth clearance problem.

Having said that a chain or belt requires a tensioner which sometimes gives trouble, but it crosses the engine block to head gap without problems.........

Gears can be done but very complex........

 

[tianorth]

I think Bentley use gears instead of chains/belts.

 

[drdino]

Weight, noise, cost, need for lubrication (the latter tends to not be applicable any more as timing chains and new belt applications are of the wet type as well).