Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Effects of error in Camshaft/Crankshaft sprocket sizes (theoretical)

Assuming it’s impossible to get perfectly sized camshaft and cranskshaft sprockets for driving timing chains, how does an engine adjust if one (or both ) of these sprockets is undersize, due to wear (or production tolerance? Would the valve timing be off after many miles of use? For example, if the camshaft sprocket is undersize, the cam would turn too quickly compared to the crank. Or is there a means of compensating?

They have teeth and it is the ratio of the number of teeth on one sprocket to the number of teeth on the other that determines the timing, not small differences in circumference. Emphasis on small differences.

My vue worth 3L motor has idler sprockets that are on shafts that have offset mounting bolts. U set initial cam/crank timing and than tweak idler position to make very small pos/neg cam timing adjustments. So as the belt stretches over time, u could theoretically adjust cam timing due. But who does?

No worse than a timing chain gradually stretching and loosening over time. It does affect engine performance, but it’s so gradual that the driver rarely notices it unless it gets really bad or the belt or chain ‘jumps’

Mercedes has an offset key to makeup for timing chain ‘stretch.’ I thought it was a joke when first told about it.

Cog wear and chain stretch both affect timing, but not the ratio. (for the OP), the ratio is just like that on a bike; it’s solely a function of the number of teeth.

And realize that it’s the same in all engines…2:1. Since one turn of the camshaft opens both the intake and exhaust valves, and those actions take place in cycles 1 and 4 of the piston’s four strokes, the cam shaft MUST turn at half the speed of the crankshaft. The engine simply will not continue running any iother way.

Agree with all the above. The ratio of the sprockets on the cam shaft and crankshaft are set by the number of teeth, not circumference. On long chains, they use tensioners to take up the slack to prevent the chain from jumping a tooth as the chain stretches. And I can tell you from experience, the tensioners work. I had a Toyota Pick-up that I replaced the timing chain on at the 250,000 mile mark. The chain was stretched to max, according to the shop manual, and the tensioner had very little room left to go. A new chain and tensioner fixed it right up.

I did not notice any change in engine performance after installing the new chain, so any variation of timing due to chain stretch didn’t mean much. I doubt it accounts for more than a degree at best. The distributor runs off the camshaft and didn’t show any major difference.

Agree with above…it’s 2 to 1, controlled by teeth…As parts wear, cam timing can slowly change a little, becoming retarded, which actually gives a SLIGHT boost to high RPM performance…Cam timing is just not THAT critical…