bad camshafts- possible remedy

[carlover]

Originally Posted by RI_RS4

Some of the pictures I've seen show excessive wear on other cam lobes than just #3, and some people report a problem with #3 and #4. Then there are those people who had their cams replaced and do not report any specific cylinder. Has anyone put together a database of the codes and failures? Depending on the number of failures you've seen, there may not be a statistical significance.

Firstly, ALL the broken rocker arms were on the 3rd cylinder. It doesn't take a statistian to figure out the statistical significance.

Second, the wear or more accurately, grooves, on the 2nd intake cam of the 3rd cylinder are a result of the failed rocker arm.

And finally, if this problem is caused by valve float, wouldn't the valve be damaged and therefore be evidenced as a loss of compression?

[TimMullen]

Originally Posted by RI_RS4

First, for a rocker arm to break requires extreme force. The most probable cause of this force would be valve float, when the piston meets the valve and slaps it back against the rocker arm.

Two things...

Valve float is not when a piston hits a valve. A valve "floats" when the revs get high enough that as the valve opens, the inertia continues to open it, allowing the followers to "separate" from the cam. The valve is then open too far, and starts closing. The valve then "slams" down into the valve seat instead of being gently "lowered" by the cam. Valve float damages the valves and the seats.

In a non-hemispherical combustion chamber, and extreme conditions, the valve may hit the piston and damage the piston and/or valve.

But in a hemispherical combustion chamber (like the Elise's) the valve opens at an angle relative to the direction of the piston's travel. If the valve hits the piston, you get a hole in the piston, or more likely, bent valves that can no longer close (which then causes more damage to the piston).

[Dmbrown34]

Originally Posted by maz

the other thing is that this is a toyota engine and as such, it would be toyota, not lotus making the engineering change, wouldn't it?

+1

Why not just go after Yamaha? They caused the problem!

[Icedog_16]

Originally Posted by carlover

Firstly, ALL the broken rocker arms were on the 3rd cylinder. It doesn't take a statistian to figure out the statistical significance.

Second, the wear or more accurately, grooves, on the 2nd intake cam of the 3rd cylinder are a result of the failed rocker arm.

And finally, if this problem is caused by valve float, wouldn't the valve be damaged and therefore be evidenced as a loss of compression?

To dovetail with what you said, if valve float were indeed the culprit, wouldn't there be a relatively even distribution of rocker-arm failures amongst all cylinders?

FWIW, the compression test on my car showed number three to be a little low, but still within tolerance per Toyota specs at 210psi.

[ZTEC]

Lets not forget the spray bar that doesn't line up on #3 - We got a Tossed salad of potential problems.

[xtn]

We don't know if the follower wears first, allowing looseness which then wears the cam, or if the cam wears first, allowing looseness which then wears the follower.

It is possible that a weak valve spring allows float, which in turn begins to wear the cam lobe and weaken the rocker. One would think if this were true there would be a more even distribution of cylinders effected.

xtn

[JohnnyQuik]

Originally Posted by TimMullen

But in a hemispherical combustion chamber (like the Elise's) the valve opens at an angle relative to the direction of the piston's travel.

Not to Hijack an important thread, but I couldn't resist asking, "That thing got a Hemi?"

[RI_RS4]

Again, respectfully, I'm just offering different thoughts as an outside observer. No one has yet been able to say how many engines have been affected so far, which is why it may not be statistically significant. No one has come up with a failure mechanism, just some hypotheses that may or may not be true. And, as far as I've read, there does not seem to be any rash of broken cylinder 3 rockers on other cars using the same engine.

The oil spray theory might be reasonable if you can prove that oil does not get deposited on some part of the #3 cam lobe. Since the cam is running in the boundary and mixed lubrication regime a steady stream of oil will deposit a boundary antiwear layer.

Another theory would be a problem with the cam hardening process for a certain batch, where for some reason lobe 3 was not hardened properly. This can be measured in a lab.

I'm still not seeing how the follower can crack and fail as it does, unless some significant back-force is placed on it from the valve. The only other possibility I can think of is that there was a total lubrication failure on the cam, which causes the follower to overheat and become brittle. If you want to know the failure mechanism, find a private metallurgist, and a tribologist, or ones at a university that you can befriend and have a forensic analysis done.

Y'all would be much better served if you fully documented all instances of failures or near-failures in one place, and presented a coherent case. It may be here amongst the threads, but I just don't see it. I'm all for using forums like these to pressure manufacturers, but not until the case is solid.

[shay2nak]

I'm due for an oil change in 200 miles (07 Exige S) and I will be taking some of it back to be tested. I have almost 7000 miles and this will be my 2nd oil change. I switched to 5-40 mobil 1 Diesel truck oil at the 1st change and will be using it again for this upcoming oil change.

Maybe just to be safe it would be good to change the valve springs, but then the failure would occur on all/any of the valves if it were the springs.

It's wierd...


would it be possible to view cam wear without having to pull the cover? How about with a small camera, like a flexible Endoscopic camera?

[Icedog_16]

Originally Posted by RI_RS4

Again, respectfully, I'm just offering different thoughts as an outside observer. No one has yet been able to say how many engines have been affected so far, which is why it may not be statistically significant. No one has come up with a failure mechanism, just some hypotheses that may or may not be true. And, as far as I've read, there does not seem to be any rash of broken cylinder 3 rockers on other cars using the same engine.

The oil spray theory might be reasonable if you can prove that oil does not get deposited on some part of the #3 cam lobe. Since the cam is running in the boundary and mixed lubrication regime a steady stream of oil will deposit a boundary antiwear layer.

Another theory would be a problem with the cam hardening process for a certain batch, where for some reason lobe 3 was not hardened properly. This can be measured in a lab.

I'm still not seeing how the follower can crack and fail as it does, unless some significant back-force is placed on it from the valve. The only other possibility I can think of is that there was a total lubrication failure on the cam, which causes the follower to overheat and become brittle. If you want to know the failure mechanism, find a private metallurgist, and a tribologist, or ones at a university that you can befriend and have a forensic analysis done.

Y'all would be much better served if you fully documented all instances of failures or near-failures in one place, and presented a coherent case. It may be here amongst the threads, but I just don't see it. I'm all for using forums like these to pressure manufacturers, but not until the case is solid.

I know there are in excess of 20 of these - and those are only the ones who've posted here - and I really cannot think of an exception to at least the number-three cylinder being involved. I can go back and count if you'd like. But you may want to check these threads and see if you still think that it may not be statistically significant.

http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302
http://www.elisetalk.com/forums/show...ighlight=p1302

So that's seven threads on LT (not including this one or other ones I didn't think merit being included) with a total of 757 posts and 29982 views. Sounds like a statistically significant problem to me.

Hadn't seen this one before, so add another two cars to the list:
http://www.elisetalk.com/forums/show...ighlight=p1302

Here's an extra one thrown in from elsewhere: http://www.exiges.com/ubbthreads/sho...=&fpart=1&vc=1

[xtn]

Originally Posted by RI_RS4

I'm still not seeing how the follower can crack and fail as it does, unless some significant back-force is placed on it from the valve.

Well, if there is too much lash and the follower doesn't "follow" any more - that is to say that it floats a bit - the forces it sees will become much more concentrated as it slams itself back home instead of riding around the lobe smoothly.

So such lash might be caused by:

1. valve floating due weak spring (seems unlikely without more even cylinder distribution)
2. follower wearing first
3. cam lobe wearing first

If we toss out #1, we are left wondering: regardless of whether the follower or the lobe wears first, what it the underlying cause of the excessive wear? I lean towards suspecting a faulty cam lobe hardening process as the reason that makes the most logical sense given the reports that we have.

xtn

[mp3moose]

Just FYI, My engine had broken rocker arms for cyclinders #2 and #3.

[MattG]

I'd like to see some data addressing the concerns about potential oil starvation in these engines, to see if there's a link there. The apparent consistency with cylinder #3 could potentially be explained by the oil passages from the pump to it...I have no idea how it's laid out, but if it for example had the longest oil passage run of any of the cylinders for whatever odd reason, and if the engine suffered oil starvation in corners, might it be possible that this is a contributing factor (or even primary cause)? So far though, I haven't seen anyone data logging oil pressure in a controlled environment to really test how much of a problem that'd be.

[Icedog_16]

Oil starvation in corners probably doesn't play a part as a good number of us who have been affected have spent little, if any, time tracking the car.

[AlanS]

Originally Posted by carlover

Firstly, ALL the broken rocker arms were on the 3rd cylinder. It doesn't take a statistian to figure out the statistical significance.

Second, the wear or more accurately, grooves, on the 2nd intake cam of the 3rd cylinder are a result of the failed rocker arm.

And finally, if this problem is caused by valve float, wouldn't the valve be damaged and therefore be evidenced as a loss of compression?

Judging by my car, the wear is not a result of the failed rocker arm. My car was probably one of the first to experience the problem, before the cylinder #3-specific issue came to light, but I had one broken rocker arm (which I think might have been #3, but I'm not 100% certain). However, I had significant wear on three of the four high-lift cam lobes. The #3 cylinder was one of the worn ones because the unworn cam lobe was on the end, so it had to be #1 or #4.

[Icedog_16]

Whereas I had relatively little wear. Again, I believe that to be a function of how little time I actually spent on the 2nd cam. Out of 336.3 hours, my car spent less than 2 hours at 80-100% throttle and 5.3 hours on 2nd cam, which is paltry considering it had 18293 miles on it. Yeah, I really drove it hard.

[adamant]

On my second now.
Replaced first last year after 8 months of complaints to lotus that there was
insufficient power from the engine. Eventually replaced showing severe wear on cam #1 and #4. 14 months later a valve breaks (engine has been well cared for and never overevved). Open ing cover reveals all 4 cams severely worn again (about the depth of a penny!). lotus only pay for the camshaft and I have $4000 repair bill Thanks Lotus!. This time I am taking the cover off every 6 months any wear and it goes back under warranty.

[Icedog_16]

Originally Posted by adamant

On my second now.
Replaced first last year after 8 months of complaints to lotus that there was
insufficient power from the engine. Eventually replaced showing severe wear on cam #1 and #4. 14 months later a valve breaks (engine has been well cared for and never overevved). Open ing cover reveals all 4 cams severely worn again (about the depth of a penny!). lotus only pay for the camshaft and I have $4000 repair bill Thanks Lotus!. This time I am taking the cover off every 6 months any wear and it goes back under warranty.

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[ulmpharmd]

Does this problem relate to the 2007 and 2008 models at all?

[Boosted2.0]

Originally Posted by adamant

On my second now.
Replaced first last year after 8 months of complaints to lotus that there was
insufficient power from the engine. Eventually replaced showing severe wear on cam #1 and #4. 14 months later a valve breaks (engine has been well cared for and never overevved). Open ing cover reveals all 4 cams severely worn again (about the depth of a penny!). lotus only pay for the camshaft and I have $4000 repair bill Thanks Lotus!. This time I am taking the cover off every 6 months any wear and it goes back under warranty.

'

check your exhaust valve clearance regularly. Might want to think abotu upgrading to MWR valves & springs too