Gutting pre-cats may not prevent engine failures

[SteveJ]

I have been awaiting confirmation of this theory from an independant source, and as they have now confirmed the original info, I thought I would share it with the rest of the membership.

There appears to be a problem with the crankshaft design in the 1ZZ engine that causes it to resonate at approx 4,000 rpm *THIS IS A KNOWN AND MEASURABLE FACT*

*Now the theory begins* - this vibration is then transmitted to the pistons which causes them to wear the cylinder bores unevenly. The theory is borne out in a number of non-roadster 1ZZ engine failures that have occured within Europe (all that do NOT use pre-cats) where oil consumption is extremely high due to uneven cylinder bore wear.

The one common factor is 4,000 rpm coincides with their local speed limits when in top gear and also helps to explain a drop in (although not complete abscence of)  failures of engines in post face-lift roadsters as they now have a 6th gear which shifts the engine rpm away from 4,000 at normal cruising speed.

If this is correct (and I have no reason to doubt either of my sources), then we can expect to see a lot more engine failures before Toyota finally admit to the problem. It also means that whilst gutting the pre-cats may help reduce the problem by removing the potential source of debris entering the engine (which it is fairly certain DOES occur although not proven), it is not guaranteed to save your engines life. Only time will tell.

[crankshaft]

Hi Steve;

Hmmm, sounds plausible, what speed does 4000 RPM equate to with the 5 Speed ??

PeterC

[Anonymous]

For my 1zz, 4000 rpm is about 75-77 mph.

[mrsmr2]

So what we should do is cruise around at under 4k revs and cane the nuts off it at any other time   s:twisted: :twisted: s:twisted:  

So anything under VVTi zone is OK then?   I sense a sudden increase in MPG if this is provem  s:D s:D

[Tem]

There appears to be a problem with the crankshaft design in the 1ZZ engine that causes it to resonate at approx 4,000 rpm

Do you have any knowledge about this matter in 3ZZ/4ZZ...?

[Anonymous]

4000 rpm is about 100mph in 6th on my car.  I reckon my engine might break soon   s:lol: :lol: s:lol:    s:roll: :roll: s:roll:

[markiii]

While I was present for the discussions with one of your sources and seeculated that the rest of your post was correct, are you now saying we have definative data to back up the fact that motorway speed limits for the appropriate gearing in different countries equates to 4000rpm.

please share.

I'm also curious as to your second confirmed source.

While I concure with teh speculative theory, I'd want a little more specific ref teh "proof" before confering it factual status.

[Anonymous]

The theory sounds plausible.  Is the center frequency of resonance precisely 4000RPM?  I imagine the bandwidth would be rather small, maybe +/- 100RPM.  If this were true, something might show up on a dyno of an well-worn engine that has bores getting out of spec.

Very interesting - thanks.

[Anonymous]

FWIW I find that 5th at 70mph is ~ 3200rpm

[Anonymous]

I am very interested! This may benifit my case as well.

[GSB]

I have a habit borne of several years of reading theoretical posts. Namely, I never believe anything until its been measured.

Toyota et al spend thousands of hours in design, analysis and development of new engines, and thousands more in NVH anlysis, eradicating any such resonance from their engines. If anything they engineer any resonant speeds into areas that the engine is unlikley to ever reach, not right in the middle of the rev range. Also, were such a fundamental design problem to exist, it would be a relatively straightforward fix to "re-tune" the resonant speed by altering some aspect of the cranks counterwieghts, or even the flywheel mass. Still, the idea is not without some merit, and is a fairly easy one to prove or disprove.

I have an SKF Microlog vibration analysis tool here at work, which, when plugged into a tachograph input will allow me to generate a vibration vs. engine speed graph. It'll also pinpoint any resonant speeds, the magnitudes of the vibrations, and the direction of movement. It'll also print out handy graphs which can then be published here. Let me finish the job I'm currently on, which believe it or not, involves balancing the rotating parts of internal combustion engines, and the avoidance of resonant frequencies in rotating equipment... Hence the suddenly very useful tool...

More data when the current job is over and done with. I'd anticipate having vibration analysis graphs here by the end of December.

[markiii]

Grant you have access to some very nice tools.
  s:D s:D

[Anonymous]

Interesting that this resonance problem occurs around the same rpm for the valve timing change.

Nothing to add to this, I just thought it coincidental  s:) s:)

[GSB]

Grant you have access to some very nice tools.
  s:D s:D

When you work with engines this big, you need them...  s:wink: :wink: s:wink:  

[Anonymous]

 s:o s:o   How cool is to have GSB onboard?  s:D s:D

Side note: I work on a US Navy base where they do depot level maintenance of aircraft, among many other things.  It is one of the few remaining Naval Air Depot facilities to survive several rounds of facilty closings.  I'm right across the street from the main hangar and hear jet engine noise all day.  A common bumper sticker is "Jet Blast: The Sound of Freedom"

[Tem]

Interesting that this resonance problem occurs around the same rpm for the valve timing change.

Valve timing change occurs from idle to rev limit  s;) s;)
(that's why it's called variable)

[mrsmr2]

Yes, but there is a definite difference around 4.2k revs, which almost coincides just before the peak torque arrives - according to the scientific diagram in my brochure.


Oh, and can one of those engines fit in an MR2?

[Anonymous]

I have always noticed an extra kick of power at 4k so assumed there was a profile change or something.

[GSB]

Oh, and can one of those engines fit in an MR2?

  s:D s:D  Not liklely I'm afraid... The rotor alone weighs someting like 160tonnes, and its about 60ft long, ao you're MR2 would be a bit back heavy...  As for fuel? Phenomenaly thirsty, but then it does knock out the equivalent of about 340 thousand bhp

[aaronjb]

s:D s:D  Not liklely I'm afraid... The rotor alone weighs someting like 160tonnes, and its about 60ft long, ao you're MR2 would be a bit back heavy...  As for fuel? Phenomenaly thirsty, but then it does knock out the equivalent of about 340 thousand bhp

The question is, in that picture.. which one's you? Because I can't see anyone with big spiky red hair and a big pink nose  s:lol: :lol: s:lol:

Anyway, vaguely back on topic - if the theory turns out to be correct then it would be very worrying - essentially all our engines are doomed to fail sooner or later (depending how long we spend cruising on the motorway, basically).  s:( s:(  (My glass is half empty, sorry  s;) s;) )

But then if it is true, as Grant says, we could move the point of resonance by switching flywheels (never a bad idea anyway  s;) s;) ) potentially to somewhere less damaging.

I seem to recall one of the big Japanese tuners also sells special crank pulleys with liquid harmonic dampeners that can be 'tuned' - but that's getting a tad expensive then  s:) s:)

[Anonymous]

Anybody want to buy a never used lightweight crank pulley?   s:lol: :lol: s:lol:    I actually bought one from someone on SC because it was a good deal.

[Tem]

Yes, but there is a definite difference around 4.2k revs, which almost coincides just before the peak torque arrives - according to the scientific diagram in my brochure.

There's a difference in power, but there's not difference in VVT-i behaviour  s;) s;)

(someone who knows something about engines once tried to explain to me that every engine has a bump in power at certain rpm, which is related to bore and stroke and tons of other stuff, but I really didn't get half of it  s:oops: :oops: s:oops:  )

[SteveJ]

Interesting that this resonance problem occurs around the same rpm for the valve timing change.

Valve timing change occurs from idle to rev limit  s;) s;)
(that's why it's called variable)

I dont know where this mis-conception comes from, but VVT-i is an on-off switch - the only reason it is called 'variable' is because there is a change in the valve timing. The 'i' bit is because the timing change occurs at different points in the rev range depending on the current demands on the engine.

Take a look at the workshop manual for the engine - the valve control mechanism is controlled by an on/off solonoid - there are absolutely NO analogue devices present in the control system.

Now if it were called :-

C onstantly
V ariable
V alve
T iming with
I nteligence

we would be talking a whole different ball game.

[Tem]

Take a look at the workshop manual for the engine - the valve control mechanism is controlled by an on/off solonoid - there are absolutely NO analogue devices present in the control system.

Yes, it's an on/off switch, but it's controlled by a PWM output  s;) s;)

More about PWM, first hit from Google:
 m http://www.embedded.com/story/OEG20010821S0096 m

[so.simple]

There appears to be a problem with the crankshaft design in the 1ZZ engine that causes it to resonate at approx 4,000 rpm *THIS IS A KNOWN AND MEASURABLE FACT*

*Now the theory begins* - this vibration is then transmitted to the pistons which causes them to wear the cylinder bores unevenly. The theory is borne out in a number of non-roadster 1ZZ engine failures that have occured within Europe (all that do NOT use pre-cats) where oil consumption is extremely high due to uneven cylinder bore wear.

It makes sense and coincides with the explanation I got when my engine blew... Could this be the "unknown reason" for the "sudden oil starvation" which caused a rod to break, opening a hole in the cylinder wall? As I said on my first post, "I was cruising at about 100Mph"...

http://www.mr2roc.org/forum/viewtopic.php?p=65630#65630