Idle car vibrations

[unity]

Most people seem to agree that a 4 cylinder car is more prone to vibrations while idle than say a V6, V8 or V12.
When comparing 4 cylinder cars which car is likely to vibrate more at idle a 1.8L engine or a 2.4L engine?

[aaronng]

A long stroke engine should vibrate more at idle. If you were comparing your Civic and Euro, then the Euro should vibrate more. The balancer shafts only come into play at high RPM.

[bennjamin]

ill take a punch - the smaller capacity , the generally shorter stroke and less prone to vibration than a larger displacement engine. Thats just a thought.....so 1.8 will "vibrate" less than a 2.4l.

One thing to consider....have you compared the harmonic balancer / pulley on both engines to see which is bigger ?

[unity]

ill take a punch - the smaller capacity , the generally shorter stroke and less prone to vibration than a larger displacement engine. Thats just a thought.....so 1.8 will "vibrate" less than a 2.4l.

One thing to consider....have you compared the harmonic balancer / pulley on both engines to see which is bigger ?

Sorry but I am a complete nob. I wouldn't know how to.

[unity]

A long stroke engine should vibrate more at idle. If you were comparing your Civic and Euro, then the Euro should vibrate more. The balancer shafts only come into play at high RPM.

Thank you. Spot on. The Euro vibrations are noticeable. I don't notice anything on the Civic. I would have thought it would be the other way round considering I've paid 50% extra for the Euro over the Civic.
I must also add that the seat seems way more comfortable on the Civic than on the Euro. Just can't get comfortable in the Euro.
Are you saying that it wil be the opposite when both engines are reving at higher RPMs (ie Euro smoother at higher RPMs)?

[aaronng]

Are you saying that it wil be the opposite when both engines are reving at higher RPMs (ie Euro smoother at higher RPMs)?
Not at all. Just that the Euro's engine does have balance shafts which help at high RPM. When you compare both of them, your Civic should be smoother at both idle, low RPM and high RPM assuming that you are not lugging the engine.

[T-onedc2]

Most people seem to agree that a 4 cylinder car is more prone to vibrations while idle than say a V6, V8 or V12.
I've never found this to be true, the opposite instead, although I can't speak for V12.

[unity]

Not at all. Just that the Euro's engine does have balance shafts which help at high RPM. When you compare both of them, your Civic should be smoother at both idle, low RPM and high RPM assuming that you are not lugging the engine.

In these modern day Honda automatic cars is it possible to lug the engine or does the ECU intervene to prevent lugging (just as it prevents the car from over reving)?
I do find the Civic smoother across the board.

[T-onedc2]

Oh is your original question regarding auto gearboxes in particular while braking and sitting stationary in "D"?

[aaronng]

In these modern day Honda automatic cars is it possible to lug the engine or does the ECU intervene to prevent lugging (just as it prevents the car from over reving)?
I do find the Civic smoother across the board.

The autos are safe. I don't think it is possible to lug it unless you have it in M mode in a particular gear (say 4th) and suddenly have to go up a steep hill.

[unity]

Oh is your original question regarding auto gearboxes in particular while braking and sitting stationary in "D"?

Yes that's what I meant. Sorry, should have made that clearer.

[string]

The one with the more damaged engine mounts will vibrate more.

Yes a 4 cylinder is more prone to natural vibrations than a straight 6 for example, but drawing conclusions based on capacity or stroke alone will be purely speculation.

[aaronng]

Yes that's what I meant. Sorry, should have made that clearer.

If this is the case, then it is because the drivetrain is stopped, but the engine is still spinning and transmitting power through the torque convertor. EVERY auto car without a brake-activated declutch feature will have this vibration, some very bad depending on the torque convertor. Being a longer or shorter stroke engine is not the primary factor then, although that does affect it as well.

[JohnL]

A long stroke engine should vibrate more at idle. If you were comparing your Civic and Euro, then the Euro should vibrate more. The balancer shafts only come into play at high RPM.

I'm not sure about any correlation of stroke length to vibration caused by secondary imbalances (which are what we're talking about, not primary imbalance which should be at / near zero), my understanding being that the major factor is the engine capacity, i.e. bigger engine = greater vibration. Since straight 4 engines suffer from a lot of secondary imbalance, the larger they are the more their smoothness is going to benefit from balance shafts.

Secondary imbalance affects the engine at all rpm, so balance shafts will be "in play" at all rpm. However vibration at lower rpm is likely to be more noticable than at higher rpm because the frequency of vibration is more likely to coincide with the resonant frequency of the engine mounts and quite possibly the chassis itself.

Balance shafts do help smooth out vibration, but they only lessen some of the secondary imbalances, so balance shafts can only alleviate the problem not eliminate it. Without actually measuring it, it's hard to say if a smaller straight 4 without balance shafts will vibrate more than a larger unit with balance shafts.

[aaronng]

Without actually measuring it, it's hard to say if a smaller straight 4 without balance shafts will vibrate more than a larger unit with balance shafts.
Probably not, since the B-series and K20A don't have balance shafts and do feel smoother throughout the rev range compared to the K24A which has balance shafts.

[JohnL]

I've never found this to be true, the opposite instead, although I can't speak for V12.

All engine configurations suffer from secondary imbalances, and straight 4 engines are inherantly among the worst offenders (as are 'flat' 4s). Straight sixes and V12s are among the best, i.e. have the least secondary imbalance and are thus inherantly smoother engines.

If your experience differs then I'd suggest some other issues with the cars you've been in, such as good vs bad engine mounts, good vs bad engine tune, not firing on all cylinders etc.

Fitting a lightweight flywheel to a 4 cylinder engine is likely to result in a greater increase in vibration than doing the same thing to say a 6 or 12. For reasonably smooth operation, 4 cylinder engines typically need a much heavier flywheel than say a straight six of the same capacity, and even then are unlikely to be as smooth.

[aaronng]

A 4-cyl boxer engine is perfectly balanced though. There isn't any vibrations to be had other than those generated by the exhaust gases.

[JohnL]

Probably not, since the B-series and K20A don't have balance shafts and do feel smoother throughout the rev range compared to the K24A which has balance shafts.

If I understand my Honda engine nomenclature correctly, then the engine with balance shafts is 400cc bigger than the engine without balance shafts. I'd suggest that this suggests that balance shafts have some beneficial affect but not huge.

It seems to be the general rule of thumb that engines above 2L will need balance shafts more so than engines below 2L. It's interesting to note that pre WW1 racing cars often had straight 4 engines well over 10L, and though the max rpm was rather low I'm sure they weren't very pleasant engines to sit behind...

[JohnL]

A 4-cyl boxer engine is perfectly balanced though. There isn't any vibrations to be had other than those generated by the exhaust gases.

No engines are perfectly balanced (well maybe electric motors and turbines), not even rotaries. Flat 4s have significant secondary imbalance that causes the engine to vibrate in a 'yawing' manner, i.e. if you draw a vertical line that passed through the middle of the crank shaft then the engine will 'wobble' around this axis (engine mounts permitting).

Straight 4s will (I think) tend 'wobble' around a horizontal axis that passes through the middle of the crank, a well as up and down and side to side. Flat 4s have fewer secondary imbalances than straight 4s, but are still not particularly good in this regard, certainly not comparable with straight 6s, flat 6s and V12s.

[aaronng]

A boxer 6 will have that same rotational yaw as the boxer 4 too. The movement will be more consistent (and perceived as having less "vibration") as there are 6 instead of 4 cylinders though.

[unity]

EVERY auto car without a brake-activated declutch feature will have this vibration, some very bad depending on the torque convertor.

So with a car having a bad vibration are you saying that it's an inherent characteristic of the torque convertor, or is it a problem with the torque convertor itself that is fixable?

[aaronng]

So with a car having a bad vibration are you saying that it's an inherent characteristic of the torque convertor, or is it a problem with the torque convertor itself that is fixable?

That's how it works. In a manual car, try putting it into 1st gear and releasing the clutch while holding the brakes down. That is what the auto's torque convertor is trying to do if you are stationary and in "D" with the brakes on, while trying to prevent your engine from stalling. Live with it.

[unity]

That's how it works. In a manual car, try putting it into 1st gear and releasing the clutch while holding the brakes down. That is what the auto's torque convertor is trying to do if you are stationary and in "D" with the brakes on, while trying to prevent your engine from stalling. Live with it.

How would you know if your torque convertor was faulty or damaged?

[aaronng]

How would you know if your torque convertor was faulty or damaged?

Your car wouldn't accelerate at all or would jerk non-stop while accelerating.

[JohnL]

A boxer 6 will have that same rotational yaw as the boxer 4 too. The movement will be more consistent (and perceived as having less "vibration") as there are 6 instead of 4 cylinders though.

Yes, the vibration will tend to be less because there are more firing strokes per crank revolution (e.g V12s are smoother than straight 6s even though a V12 is very much like two straight 6s joined at the crankshaft, which is probably a simplistic analogy...).

However I think it's also to do with the way the firing strokes can be distributed in what order through all the cylinders in the engine (i.e. flat 4 vs flat 6 making flat 6 smoother), not just because there are more firing strokes per crank revolution. I could be wrong, I'm not an expert on this...

[T-onedc2]

Now that we're talking auto gearboxes in "D" at a standstill I can confirm that comparing a boxer 4 (Liberty GT 2.0) to a Boxer 6 (Liberty 3.0R Spec B), the 4 has noticable vibrations as mentioned in the first post, the 6 has barely any.

[MWAKU]

i don't mean to hijack but um, is it normal, for first start in the morning my h22z 99 prelude idles at 1200 then, when its warmed up, idles normal at around 700 +- 50?

i don't know, as i've only owned carby b4, so yeah, which always had hi revs at idle (gronked carby)

[migoreng]

that's right..
a cold engine idles higher like around 1500rpm to warm up quicker...
after a few mins it should drop down to 1000rpm idle..once warm it should be around 750rpm for our cars..

[MWAKU]

oh ok thanks man, just making sure