Timing is out but deviation is steady: set timing or major overhaul
 

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Quick question (I hope!).

Vehicle: 2000 Boxster S, standard transmission, 140k kms. IMS bearing has NOT been changed and the clutch is original with plenty of clutch remaining.

Just checked the camshaft position deviation via shiny new Durametric and found the timing on both banks is a fair amount out of spec (-7 and -10 respectively - see screen cap).

The deviations stay rock steady at all RPMs and there aren't any other symptoms of loose timing chains / failing IMS bearing (rattling at startup, chain slap, bit of plastic or metal in the oil, etc.), at least none that I can detect. Engine runs smoothly and there are no error codes.

Question:
Does this call for a major overhaul now (cam chain tensioners, guides, etc.) or, since there are no other indicators, should I first just try resetting the timing without pulling everything apart?

(If this is just a normal timing thing, would prefer to put off major overhaul until the clutch goes at which point I'll do the IMSB, clutch, and timing overhaul all at once.)


Appreciate any insights you can share!

Make sure the engine is nice and hot or else you mat get false readings that show higher deviation than actual. That said, -10 and -7 are quite a lot, and I am surprised you don't have a check engine light from the -10 reading, as I think the threshold is either -8 or -9. The spec is +-6 degrees. I personally am at -5.xx (very close to -6) and holding steady so I am just watching and waiting, if it ever makes a significant jump or over time gets much higher I plan to have the chain guides (or whichever the name of it is, the pieces that wear that cause the deviations)

I don't know if timing being off can cause readings like this - it seems like timing off would cause bad running.

Steve

You are not going to see codes until you get beyond 12 degrees or so. You are also not going to be able to correct this issue by resetting anything; it is a wear issue.

As this is a five chain engine, you most likely problem is the small chain tensioning paddles that sit between the cams (a common problem on the five chain). Without leak down data, the actual condition of the rest of the engine is speculation, but more than likely the engine is fine other wise.

This is a good plan of (non) action ^^^.

Thanks for the feedback, very helpful!

Engine had been running at idle for maybe 5 or 10 min when I took the readings, but given the balmy Canadian climate (sub freezing at time of test), it's possible it hadn't reached full operating temperature. Will re-run after a serious warm up and see if the deviations drop.

For future reference, anyone have any sense for how much adjustment CAN be done via fine tuning (i.e. via the camshaft sprocket)? Are we talking a degree or two only or several degrees?

Take the car out and drive it for 20-30 min., then check the deviation values. Letting it idle for 10 min. ain't going to do it.

Again, you are not going to adjust your way out of being 10 degrees out; one tooth on the gear is about 12 degrees, and you can only adjust the cam timing slightly with the adjustment system. You have a tensioner wear pad wear issue, and if the values repeat after driving the car, you need to replace some parts.

Thanks JFP, will retest after good 20min drive. Regardless of results, I will definitely be replacing the internal chain ramps / whatever else shows signs of ware.

Assuming the re-test under hot engine condition yields the same or slightly better results, am I risking any damage continuing to run the car until the clutch starts to show some signs of ware (current clutch drives like new - prior owner did almost all highway miles)?

I would prefer to do the clutch, IMSB and timing rebuild all at once, but of course if I'm hurting anything having the timing this far out, not the end of the world to write-off the current clutch and do it all now.

Thanks again

The situation is not going to get any better, and could get appreciably worse. You are nearly at the point the engine is going to code now (if the numbers check out the same). I would plan on doing a major winter project this winter.

The first year I had my car, I tackled the deviation problem in my cold garage during the winter down-time. (OP is Canadian, he'll know what I mean). I decided to drop the engine out of the car which makes the replacement of the plastic guides soo much easier! While it is out you can easily check other things like the coolant tank (replacement sans motor is sooo much easier), oil filler tube condition, AOS, etc.