Tight Valves

[mygreenbus]

Someone asked me the other day what it meant when their mechanic said their Bus had "tight Valves". I told him I thought it meant that over a period of time, the valves were not opening as far as they should be. I could not tell him why this happened, i.e. what makes them tight. Anyone shed some light? Thanks, I just thought I'd find a solid answer instead of my assumptions. BTW he runs a pancake 1700 not an upright if that makes any difference.
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'72 Bus

[white74westy]

[Abscate]

The valve can stretch, which lets the spring pull the valve stem farther up into the rocker cover, reducing the valve clearance (thats the 'tight' part the mechanic refers to)

The head bolts can loosen up -same thing - that usually loosens stuff though - and makes a lot of noise.

the valve seats can pound into the cylinder head - tight valves

and a couple more estoteric things can happen that make me ill so I won't post here.

All of this points to why YOU - the driver/owner/operator has to maintain an old car - to keep it in tune and to keep you in tune with its aging process.
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[Wildthings]

A well built head on a well tuned engine will show very little change from one valve adjustment to another. I have noticed that my valves typically loosen over time as the valve stems, adjusting screws, and lifters faces all wear. If you don't account for this wear, then as the mileage goes up the valves will not open as far and the adjustment will be too loose even though it checks out okay with a feeler gauge. Using lash caps on the valve stem ends or using a Dremel to flatten the stem ends every 40-80K miles is a good idea, as is refacing the lifters somewhere around 80K miles.

A too loose adjustment means the valve pound the head harder as they close and the combination of valve stem wear and concave lifter wear means the valves do not open as far as they should, leading to poor performance and hotter running heads. Either of these things will mean the valves will begin to recess, starting the death spiral.

[SGKent]

the first couple valve adjustments the cylinders seat into the heads and the clearances tighten up. After that the engine should open up a little as parts wear like Mike indicated. If an engine has 5,000 - 10,000 miles+ on it and the clearances keep getting tighter, something isn't right. My T1 engines would open up about .001" every 7,000 - 10,000 miles as the screws wore.
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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin