Quote:
Originally Posted by TheCrispyNoodle
Yesterday I discovered the root cause was a sheared key on the lower crank timing pulley that mates with the crank pulley bolt. This has disintegrated causing the timing pulley to spin on the crankshaft. Ouch.
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This is a VERY common problem.
I ran into this for the first time about 20 years ago on my 1983 100 Avant. I didn't have time to do a t-belt change myself, so I put it in to a local specialist garage (that I don't use any more). Everything was fine until about a year later when the engine lost all power. It would start and run, but wouldn't rev under any kind of load - could just about get 5 mph out of it!
I discovered that the timing was out and presumed that the t-belt had jumped a tooth. I retimed it, retensioned the belt and after a day or two, it lost power again. I realised that something was seriously wrong and took it all to bits. I was quite surprised to find that I could undo the crank bolt with my standard ratchet with virtually no effort, as I normally need a 6-foot extension to break it loose. I was even more surprised to find that the locating key (it's not a separate key - it's part of the casting) on the crank gear was nowhere to be seen - just a little bit of metallic powder.
The garage had either not torqued it properly, or had not used loctite, or both. That's the last time I used a garage for this kind of work.
As I've had six I5 engines over the years, I now keep a spare crank gear (got it for GBP30 about 10 years ago), and always inspect the removed one for any wear or cracking near the key.
There is some confusion over the torque required for the crank gear bolt. The manual says 350 Nm. But that's using the 2079 special tool, which has a torque multiplying effect. Using a standard torque wrench (with no multiplier), it works out to be about 450Nm. Without a torque wrench, that seems ridiculously large which is why I reckon many garages (whose mechanics often do things by feel), consistently under-torque it. My method in the past used to involve me wedging a huge screwdriver in the teeth of the flywheel, while a calibrated wife would stand exactly 2 feet along the handle of the breaker bar. She's a bit out of calibration at the moment, and refuses to be recalibrated, so I've bought a big torque wrench!
Scott Mockry's website (essential reading for any 10VT/20VT owner) has a detailed page on t-belt changing:
http://www.sjmautotechnik.com/troubl...g/S4timing.htm
Keep us informed on the engine rebuild. As you can see from my signature, I've got one of these to do - haven't got around to starting it yet. I'm optimistic that it's just a few bent inlet valves, so it might just be a couple of hundred to fix it.
Paul