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Burnt exhaust valve: intake cam timing offset a possible issue?
Stock Problems/IssuesDiscussions related to warranty related issues and repairs, or other problems with the OEM parts and software for MINI Clubman (R55), Cooper and Cooper S(R56), and Cabrio (R57).
Burnt exhaust valve: intake cam timing offset a possible issue?
Hi all,
I'm currently working on my new project, a fJCW with a burnt exhaust valve (bought in that condition), and I want to make sure it doesn't happen again right away:
While taking it apart I checked the timing (just wanted to see how the tools fit), and my intake cam was off (Crank position locked at the right spot with the pin, exhaust side of the tool slides in perfect):
It's off just a bit; valves didn't hit the pistons. Previous owner says the chain was done approx. 90k miles ago when doing the chain recall (at BMW).
Could this amount of timing offset (probably retarded valve actuation on the intake side) cause a lean condition?
When I did my valves and timing kit, I read there was a 2.5mm allowable space limit between the exhaust lock and the intake lock. Anymore and the VANOS could not account for the difference. I left mine when I got it around 1 mm.
If you've got a burnt valve to replace, you're destined to go back to that timing reset anyways. Should pay extra attention when putting it back. Back to your question, that timing offset is enough to cause enough issues with the entire ignition timing synchronization. I've serviced a client's 07MCS with the same issue, but instead, his is on the opposite end where it's advanced a whole tooth on the intake cam. That on a 40 tooth gear set yields about 9 degrees in advance angle. But his car didn't get as far down as having a bent valve nor burnt valve. He does, however, have limp mode and ECU spitting out 9 engine codes all related to knocking and misfire. When I took his valve cover off and check timing, the intake cam's angle was measured, I've got a rough estimate of 6.4mm rise and 46mm run, using arctan() function, it back calculates to 7.9 degrees offset. My haunch is that anything less than 4-5 degrees, the ECU should still be able to compensate that offset (normally on an aging engine with tensioner slack, you may start to see timing fluctuations with chain slap, but all this is still manageable, most appealing symptom is the timing chain rattle on the valvecover).
