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Car Forum / Mercedes-Benz Cars / June 2005Old 300D / Possible broken timing chain
A friend's old '79 300TD quit and he thinks the timing chain may have broken. Is this an "interference" engine in which the pistons will hit the (now) untimed valves? Or a "free" engine in which there's sufficient clearance between valves and pistons to avoid disaster? > A friend's old '79 300TD quit and he thinks the timing chain may have > broken. [quoted text clipped - 4 lines] > Or a "free" engine in which there's sufficient clearance between valves > and pistons to avoid disaster? It's an interference engine. Usually a bunch of parts are scrap. It's simple enough to remove the valve cover and check the chain. >> A friend's old '79 300TD quit and he thinks the timing chain may have >> broken. [quoted text clipped - 7 lines] > It's an interference engine. Usually a bunch of parts are scrap. It's simple > enough to remove the valve cover and check the chain. Yuck. I just bought a 84 'Euro' (some cool stuff, like rear headrests, cloth seats, small bumpers, and power front, crank rear windows) 300D with a locked-up engine that stopped "suddenly". I haven't had time pop the valve cover, but this sounds real likely. So when you say "A bunch of parts", what typically get's lunched? I would assume some bent valves, and one or two pistons with valve prints on them - but then the nightmares start - are the connecting rods robust enough to stand up to this kind of abuse - and, worse yet, how stout is the crankshaft - that flywheel is pretty heavy, and I would imagine it's trying real hard to twist the crankshaft during the split second when the pistons are introducing themselves to the valves. And one further question - I understand that there are different timing chain/sprocket options for these engines - specifically single vs. double row. Anyone know about this, how interchangable the two are and how desirable any such change would be? Thanks, Conrad > >> A friend's old '79 300TD quit and he thinks the timing chain may have > >> broken. [quoted text clipped - 28 lines] > > Conrad All the diesels have 2 row chains. The last engine I repaired that suffered a broken timing chain had a broken camshaft, a coupla broken cam bearing stands, a few bent valves, a broken chain of course, cam sprocket ruined, injection pump sprocket or as Benz calls it "timing device"- ruined, this is an expensive item, and a crankshaft sprocket ruined. Plus new gaskets and seals, timing chain tensioner and rails. This adds up to big bucks for parts, plus about 20 hours in labor. It's conceivable that more damage could occur. The customer really liked the car-a 1980 300SD- and spent more money than the car was worth to repair it. HTH Chas Hurst >> >> A friend's old '79 300TD quit and he thinks the timing chain may have >> >> broken. [quoted text clipped - 44 lines] > > Chas Hurst Many thanks. I'm surprised pistons weren't on the list- they must be pretty tough. If this can be done in 20 hours, I'm guessing that either you're pretty fast, or that one doesn't have to pull the engine to replace the timing chain goodies. I don't know how to determine what these cars are worth. By one measure, it's worth what you can get one for on eBay. Or what you find in one of the Bluebooks. But I think you could put $10k into restoring one of these beauties, and have much more car for a much longer time than you could get with by just buying a $10,000 chevy. No? Thanks again, Conrad Yes, if you are willing and able to fix the things that will break. If you need to have a shop fix everything then it's simply too expensive. The other consideration is parts cost. Parts for say a 300D are reasonable because of the model's relatively large population, but that's not so for low volume models like a 6.9 V-8 or V-12 for example. And buy and "expensive" car - that's one that's in premium condition and has a complete maintenance record for it will be cheaper to own that some old dog that really should be in the bone yard. > > All the diesels have 2 row chains. The last engine I repaired that suffered > > a broken timing chain had a broken camshaft, a coupla broken cam bearing [quoted text clipped - 24 lines] > > Conrad As I said, it's conceivable more damage could occur. In the example I posted it was unneccesary to pull the engine, so the major portion of the labor is removing the head which is not a big deal especially when the timing chain is already broken. What a car is worth is purely a personal matter. If I had $10k to spend, I would by a Benz I can drive away. Check Kelly's BB, you'll be surprised how much of a Benz $10k will buy. Chas Hurst |
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