1996 SL500 with 112k, starting bogging down badly and then stalled out. I had it towed. It came up with PO300, PO305, PO306, PO307, PO308, no more codes. It has a clacking that seems to be coming from the bottom end.

It barely starts, then stalls out pretty quickly. My indie checked the compression and the entire bank is in the 60's. He is telling me it is a bad connecting rod and I need to replace the entire engine.

Where do I start with this!??!?

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

I'm not a 500 series specialist, but loosing compression on one bank sounds like maybe a cam timing problem on that bank. Like the chain skipped a tooth or two, or maybe a broken cam shaft on that bank. Sounds serious.

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)

If it were towed to my shop, and wound up in my bay, with those results...

I'd be pulling valve covers and checking timing chain, timing chain guides, and camshaft timing. Once we established that those things were bad (the guides and camshaft timing, the chain you just replace due to age and the stresses of jumping time), I'd recommend looking for any valvetrain damage on the affected side, and if there was any, recommend removing the head to see what the pistons look like.

I've never had to go that route, as on all the ones we've seen had no valve train damage, but it's the next step if damage is suspected. If you do go that route, it is strongly recommended to pull both heads and plan on doing a valve job on them while they're off.

Once this was all done, my service advisor would put together an estimate to replace the timing chain, guides, and anything else you might need that would be related/in the area. And there's always something else. Usually lots of other things. Little things, and medium things, but they all add up to a couple of extra thousand dollars, so it makes a difference in your final decision on whether to fix things, replace the engine, or just never return our calls and abandon your car on our lot.

That's where I'd start. Oh, and for god's sake, stop turning the thing over (especially with the starter or letting it try to run, if you must turn it, do it by hand). If it still turns, begin repairs now. Once it finishes breaking and locks up, things only get worse.

MV

If the timing belt jumped would it cause the bottom end noise?

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

Just for laughs, why don't you dis-connect the catalytic converter from the left bank and see what happens.

I spoke to my tech today and he clarified what he thought the problem was. I am not mechanically inclined so half of it probably went over my head.

It has a bottom end noise that's been there for quite some time, they speculate that it's either a connecting rod, or a journal bearing. That is separate and preexisting from my new issues.

In relation to the compression, they do in fact suspect a timing chain jump. They did pull the cats and they verified they are ok. Their next step is to measure the backpressure or something, once again over my head. They are pretty confident that this will point to the timing chain.

They did mention that there is a new updated tensioner, and that the old tensioners caused a lot of problems with jumped timing chains.

I will know more Monday. My question is by running it the way I did with the timing chain jumped, is there a possibility I might have bent some valves as well?

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

Read above. My fault for misinterpreting what he said.

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

Got you .
That sounds better.

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2007 C 230 Sport.

If indeed it had a pre-existing lower end noise, and the rest of this is new, that changes things a bit.

If the noise appeared at the same time, I'd say proceed with the timing chain repair and then see about the noise, it may well be related.

If the noise is in fact an older seperate noise, one that indicates other problems aside from the timing chain, cut your losses and buy an engine. Either a MBZ one, or a junkyard one that you will rebuild completely before putting in. Don't get a wrecking yard engine and put it in as-is, it will probably have the same timing chain guide issues in short order.

This will be expensive, probably more than the actual retail value of the car. Decide very carefully how you want to proceed, nothing is as bad as throwing several thousand dollars into a project, then realizing it will take several thousand more that you either don't have or don't want to spend. Then you end up selling the whole thing for a big loss and kicking yourself all the while.

Choose wisely...

MV

Engine is back up and running, but the faint knock I had before has gotten worse. My indie says it's a connecting rod/bearing and doesn't have confidence in the engine.

Anyone know if a connecting rod/bearing can be replaced from the top end? At this point I'm going to bring it for a 2nd opinion before trashing the car.

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

If it was a connecting rod bearing the engine would knock worse real fast. Rods bearings once going out won't last long at all. A faint knock however maybe just a bit of a colapsed piston skirt. This could also be a ready to blow condition. If the piston skirt falls off the piston could wedged in the cylinder and lock up, taking the block crank and rod with it. Tell me this does the knock go way once the engine is fully warmed up? Is the engine warming up fully? Some motors have alot of clearance between the cylinder and pistin. When cold they will chatter a bit. Once warmed up fully and everything has expanded they're quiet.

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)

Well it's odd, before I brought it in it had an engine knock sometimes only, and it was faint. But after he got it running, he told me over the phone that the engine knock was very loud and gave it weeks, not months if I drove it.

I haven't heard it yet with my own ears, I'll be looking at it tommorrow. I'll see if it goes away when warmed up.

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2007 Corvette Convertible Torch Red
1996 MBz SL500
2008 Harley Davidson Night Rod Special

I would still recommend a second opinion.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The valve train in an engine has to stay in proper timing. If not the pistons continue to up and down in the cylinders and if a valve is opening at the same time the will collide. Sounds like you may be headed for a replacement motor. Take your time one will come along. A nice low mile motor out of a well taken care of car will come along at the right price.

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)