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Timing Chain Snag - Solved? Posted by DnstrDan [Email]  (#1361) [Profile/Gallery]
(more from DnstrDan) on Mon, 9 Jun 2014 08:03:43
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Nearing the end of a three-month DIY campaign on my 1999 Saab 9-5 SE / B235E with nearly 160,000 miles (installed PCV kit #6, replaced the water pump and seals, pulled the valve cover for inspection, dropped the sump, re-screened the oil intake tube, and replaced the stock oil sump with the "Bobby Bright" modified accumulator pan), I pulled the timing chain tensioner on a "while I'm in there" whim -- even though there was no appreciable noise when the engine last ran several months ago -- and measured 15.4 mm extension. As a visual inspection of the plastic chain guides indicated that wear was within allowable limits, I decided on a plan to roll in a new timing chain. Since the sludge (IMO) was low to moderate (<10% screen obstruction - primarily just sublimated, rough hard brown deposits on the crankcase walls and inner timing chain cover), oil starvation never seems to have been an issue with this engine.
I had no problems with turning the crankshaft clockwise (from the frame of reference of an observer looking into the crankshaft pulley) through several complete rotations (with the spark plugs removed), and got the timing marks to match up on the crankshaft pulley and camshaft gears. There were some disconcerting loud metallic snaps that occurred in a periodic fashion; I concluded that these were sticking valve lifters popping open as the camshaft rotated. After leaving things alone for several days, I tried to recheck the timing alignments before intending to break the old chain. Here's where things went south. After a few turns of my socket wrench on the crankshaft pulley bolt, the crankshaft came to a dead stop and would not budge! I backed off the tension a bit and tried again several times: same result. Horrified, I now contemplated having to either dropping the engine to pull the timing cover or calling a flatbed truck to haul the vehicle away to my best Saab mechanic in L.A. to finish the job. With those two options in mind (neither desirable) and with "nothing to lose", I decided to rotate the crankshaft counterclockwise as far as I could. Eventually, the crankshaft timing chain "freewheeled" (not unlike a bicycle derailleur) such that the chain stopped moving even though the crankshaft continued to rotate CCW. I immediately stopped and then tried going CW once more. To my wonderment, the timing chain re-engaged the crankshaft gear and now the entire works - crankshaft and camshafts - rotated through an entire revolution without snagging or stoppage.
I now suspect that some of the chain links had doubled over when slack, and that this was the cause of the earlier mechanical stoppage for movement in the CW direction - since the stoppage always occurred at a precise location and not irregularly. Moreover, turning the crankshaft CCW eventually caused the chain to drop off the crankshaft gear because of excessive slack - but this perhaps also caused the chain to unfold where it had doubled over. At any rate, once I began rotating CW again the chain re-engaged and I was fortunate that the misalignment between the crankshaft and the camshafts was not misaligned so much that there is any apparent interference between the valves and the pistons (although I'm going to have to triple-check everything before I proceed).
I would appreciate any advice / pointers before cautiously proceeding further with breaking the old chain and rolling in the new one. (Yes, I know that pulling the timing chain cover and replacing all of the plastic guides and both timing and balance chains is the best way to go -- I just don't want to do that. The sole reason for undertaking this effort was to eliminate a coolant leak -- talk about "scope of work creep"!).
_______________________________________ '04 9⁵ Aero Sedan (m/t) '04 9⁵ Aero Wagon (a/t) --- '99 9⁵ SE (LPT) - donated in '20
, Mon, 9 Jun 2014 08:03:43 <-- Viewing This Message, Sat, 14 Jun 2014 23:41:25, Sat, 13 Sep 2014 08:32:40
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