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Cam Sprocket Wear
Here's the story. Changed the timing chain, tensioner, upper guides, oil tube fittings, rail, on a M116 85 380SL (double timing chain factory) at 94K. At approximately 105K, something (NOT the oil tube fittings popping off, more likely a blockage in the oil tube itself from a loose piece of RTV) the LH cam, cam bearings, and rockers had to be replaced, and that side oil tube was cleaned like a gun barrel and new fittings installed. Recently at 120K, I've heard "timing chain slap" occasionally when left overnight. I thought that maybe the tensioner was leaking down but it seems to be OK and may be near the limit of its travel. The cam sprockets seem to be awfully shiny and pointy. There are faint score/wear marks on the chain. I haven't checked stretch yet but what do you think of the following theory: The LH cam, being extremely difficult to turn while failing, put undue strain on the chain and stretched it, also putting a lot of pressure on the gears, wearing them at a fast rate, and also making the "chain stretch/tensioner limit" problem worse. Therefore, I'm going to:
1. Examine the guides and replace as needed (could be a hairline crack)
2. Replace the chain (AGAIN, GRRR)
3. Replace the cam sprockets (only) - I don't want to take the timing cover off.
4. Check the tensioner for proper operation and replace if needed (it couldn't possibly have failed at 25K?). It is a Febi.
Since that 94K, the oil has been changed at 3000 mile intervals. However, this engine and car were clearly not taken care of before I got it (I replaced the RH cam also at 95K due to oil tube fitting failure and lobe wearout).
I'm going to check the stretch during the week but I'm hoping someone will tell me that this theory sounds reasonable. I really don't want to get into replacing the crank gear, although that also probably took a beating (maybe less considering it's probably in an oil bath).
Last edited by Strife; 11-08-2008 at 07:21 PM.
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