Lotus Elan

Valve train Noise

PostPost by: 1969Plus2 » Wed Jul 03, 2019 2:49 pm

A bit of a hard to answer question, but I'll ask anyway... How much valve train noise should one expect on a twin cam motor? This is my first twin cam (first overhead cam too) and I am not totally what is "normal."

I notice a mild ticking when I am at idle and next to a wall or another car. It gets louder after the car warms up. If I am just idling by myself with nothing else around I can't hear anything from behind the wheel. Running 20/50 weight oil.

I was inclined to think it might be a mild exhaust leak (since they also appear or get louder when the motor is hot) but also that some level of valve noise might just be expected.
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PostPost by: Mr.Gale » Wed Jul 03, 2019 5:28 pm

You shouldn't hear very much noise from the valves but you will here noise if the chain is not properly adjusted.

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PostPost by: Esprit2 » Wed Jul 03, 2019 8:55 pm

Stay with me... the paragraphs build on a common theme

The valve train uses mechanical tappets (aka, solid lifters). The valve lobes bang away on them, and they bang away on the valves. The valves do their thing, then slam shut against the seats in the head. There's going to be some clatter as a normal part of all that. The larger the valve clearances, the louder the clatter.

The valves slamming closed hammer away at the valve seats, gradually pounding their way deeper into the seats... that's called valve recession, and it's 'normal' wear. As the valve's head moves up into the seat, the stem moves up toward the cam lobe, closing up the clearances. As miles are piled on, the valve clearances get tighter and tighter. So it's not good to start with tight clearances... if yourself some room... some miles between times when it's necessary to re-shim the valve clearances.

The valves are cooled by contact with the water cooled head. When they are lifted out of contact, they live in a very hot environment, especially the exhaust valves. The valve clearance controls the dwell time when the valves are fully closed and being cooled. With larger clearances, the valves are in contact longer and run cooler. As the clearances close up, the valve's dwell time in contact with the cooler head get's shorter and they run hotter. If the clearances close up too much, you risk burning valves... mostly exhaust valves.

Valve clearances are given in a range, like 0.005"-0.007" for the intake, and (0.009"-0.011" for the exhaust. That's the operating range, not your allowance for sloppy work. The lower number in each range is the lower limit (time to re-shim), not the lowest acceptable starting point. Always target the top of the range in order to maximize the service life before you have to go in there again and re-shim. If you shim to the bottom of the range, you might technically be 'acceptably' correct; but with just the slightest valve recession wear you'll be out of range, too tight, and risking burned valves. So shim to the top of the range.

Shimming to the top of the range means that the valve clatter will be louder. Not "LOUD", but at the louder end of the normal range. As valve recession closes up the clearances, the valve train will become progressivelly quieter as it proceeds toward too tight and risk of burned valves. With the solid tappets, some clatter is normal and desireable. Your delicate sensibilities might prefer quiet, but quiet is a sign that something is going wrong, or that the next valve shimming maintenance is now due.

Most modern engines use hydraulic tappets, and that puts a 'soft' cushion between the cam lobes and valves. They run quietly, without clatter, and clatter is a sign that the valves need to be adjusted or a tappet is sticking and needs work... or replacement. If that 'hydraulic quiet' is what you're accustomed to, then a little clatter might seem worrisome, but it's not... with solid tappets, it's a good sign. At least as long as it doesn't get excessively loud.

Your description seems to down-play the clatter as being there but minimal. I can only go by what you write. Short of actually hearing the clatter in person, I interpret what you descibe as not being a problem... unless maybe it's too quiet.

As Mr.G pointed out, timing chain noise is a separate matter, and it's a whine, not a clatter.

Regards,
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PostPost by: 1969Plus2 » Wed Jul 03, 2019 9:05 pm

Tim, I for one appreciate the thought out perspective and I personally enjoy the way that you answer questions and contribute to the community here.

The noise doesn't particularly bother me and it certainly isn't as rackity as my old air cooled VW! As a question though, I would have thought that valve noise would come down as the engine heater up and expansion reduced the total clearance between the cam and the follower. Is this effect totally offset by the less viscous, hot, oil?
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PostPost by: englishmaninwales » Wed Jul 03, 2019 9:22 pm

Other causes of noise in the valve train include worn cam followers (becoming barrel shaped) or the follower sleeves (becoming hour glass shaped) or usually both.
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PostPost by: The Veg » Wed Jul 03, 2019 10:03 pm

1969Plus2 wrote:The noise doesn't particularly bother me and it certainly isn't as rackity as my old air cooled VW!


My first car was an air-cooled VW, and the advice I remember given given about valve clearances was that it was better to hear them than to smell them. :mrgreen:
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PostPost by: denicholls2 » Fri Jul 05, 2019 2:56 pm

Tim's excellent write-up leaves out that the design of the valvetrain determines the direction of wear. Direct-acting systems wear tight as Tim describes. Rocker systems usually wear loose instead as a result of the hammering on the additional parts, meaning the clearances need tightening up (and the starting point is at the opposite end of the operating range) as they wear.

Also not mentioned is that high clearances create additional impact on the valvetrain. The cam lobe "slaps" the shim (direct acting) or the follower (rocker) instead of it acting as a ramp as intended. In combination with tired springs, this results in the valve opening farther than intended, or "floating".

Too tight = burned valves
Too loose = faster wear, more concern about piston to valve clearance issues.

Get them just right. :)
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