JW in Texas

Curt went ahead & posted his hypothesis over on our forum where Jake, the guy in the "excellence" article, hangs out some. You guys can go over & read what he had to say about it here:

http://www.boxsterspec.com/index.php?showtopic=1258

He has a wealth of knowledge on these motors.

Macster

and under marginal lubrication. AT low engine RPMs oil pressure is low and if engine operated at too low an RPM for the load it is subjected too the bearings will see high loads with perhaps low oil pressure and flow.

The way the car is driven appears to have no bearing (no pun) in the IMS failure's frequency.

My best advice is to just drive the car normally. I would however, advise more frequent oil/filter services (and do not overfill!).

Long ago -- when I bought my '02 - I decided to forego the 15,000 mile oil change intervals in favor of 5000 mile oil change (and filter change) intervals.

That was over 200,000 miles ago... still on orignal IMS. And engine -- after warmed up, sees the whole spectrum of RPMs, though I avoid engine lugging and do not track car. Still the rev limiters comes close to the red line on occasion...

Sincerely,

Macster.

blue2000s

There's another issue to consider. The variable valve timing system operates by adding or relieving tension on the timing chain. Suppose one of the cams were to receive a change in timing before the other, causing a severe imbalance in the load on the IMS. Or suppose the chain guides somehow catch the chain enough while the engine is spinning at a low speed to create a severe load on the bearing.

There's another failure over on 986forum and again, it occured when the car and engine were moving slowly.

First986NJ

I read Jake's comments over at that link with interest. One thing I am not clear on, by suggesting that the oil change interval be shortened and that Mobil 1 NOT be used, is he suggesting that you move away from synthetic oils altogether, or just Mobil 1 ? What about Castrol Syntech ?


Jake, if your reading through...I know you can't reccommend an oil, but can you at least say if you would suggest that a synthetic oil still be used or no and why?

Macster

camshaft timing adjustment mechanism thus is not even operational and AFAIK this has not resulted in a failed engine. A bit of rough idle (with maybe a CEL) is the symptom.

Thus based on the above, even if the two cam shaft timing adjustment mechanisms were triggered at different times this doesn't seem to be sufficient to cause IMS bearing failure or even some other mechanical failure centered around bearing but not directly related to the bearing and its function.

Another factor is the IMS only drives one exhaust cam shaft at the IMS bearing end. The other exhaust cam shaft is driven from the opposite end of the IMS.

An arqument could be put forth that at low engine speed -- IIRC around 1400 rpms -- when the timing is advanced that if this adjustment is in the right (or wrong depending upon one's point of view) direction, causing additional load to the IMS by way of the exhaust cam chain, that this could over time wear down, so to speak, the IMS bearing.

I do not know in which direction the tension is when timing advanced at 1400 rpms or allowed back to normal at under 1400 rpms or when the timing is again changed at something over 5000 rpms (word is it is retarded slightly to improve gas mileage) or when rpms drop below 5000 and the timing change is undone.

Given the possibility for frequent cam shaft timing adjustments though and the rather infrequent IMS bearing failure event I don't think the cam shaft timing adjustment has anything to do with IMS bearing failures.

If a cam shaft chain tensioner broke or a guide failed, that could at least initially masquerade as an IMS bearing failure, but my input is any cam chain tensioner/guide failure is an after effect of the IMS bearing failure, not the cause of it.

Sincerely,

Macster.

blue2000s

Unfortunately, it's all speculation on all our parts. The point is that the IMS is part of a much more complicated system than it would appear on the surface and it would take some true, organized failure analysis to understand the cause of the failures.