Is it worth putting an engine in a 96 R129 with 100k? - PeachParts Mercedes-Benz Forum

spinedoc · #1 11-02-2007, 08:47 PM

I cannot believe how unreliable this car has been. I just put in a rebuilt transmission at 75k miles (actually 2nd SL500 that needed a trans).

Just the other day I had a connecting rod failure at 112k. Misfiring in an entire bank of cylinders. Indie pulled the plugs and checked the compression, severely low in all of the cylinders. Has a very loud clacking coming from the bottom end. He called over a friend who has an engine shop to get a second opinion and they both agreed it was most probably a connecting rod.

So..... I can get a used engine installed for 5k or so. But is it really worth it anymore? This is my wife's car, and sometimes my daily beater when I don't want to scratch up my vette at work. It's a 96 with 112k on it and a fairly new tranny.

What do you guys think? I know I can get a 2000 in good shape at the auction for 15k, but after having 2 SL500's that had tranny problems and now this one with a bad engine I don't think I would go SL again.

If I do get rid of it I will put it up as a parts car, in case anyone wants to offer before it goes on ebay. Its in great shape with a newer soft top, good body/paint, etc.

So, what would you do?

waybomb · #2 11-02-2007, 08:59 PM

Fix it and drive it. Or fix it and sell it. But I don't think you'll get much with a blown engine.

ctaylor738 · #3 11-02-2007, 09:25 PM

Something has obviously gone south in the engine, but wouldn't a rod mess up just a single cylinder? I would suspect a timing chain problem if it blew the compression on all cylinders on one side. Still an expensive problem, but not (as) catastrophic.

How does the mechanic explain a conn rod failure affecting all compression on one side?

TheV12pwr · #4 11-02-2007, 10:49 PM

There is no connecting rods in this engine...

waybomb · #5 11-02-2007, 10:53 PM

Quote:

Originally Posted by TheV12pwr

There is no connecting rods in this engine...

Huh? You must mean push rods, dude.

What connects the pistons to the crank? Connecting rods.

TheV12pwr · #6 11-03-2007, 12:36 AM

Quote:

Originally Posted by waybomb

Huh? You must mean push rods, dude.

What connects the pistons to the crank? Connecting rods.

The connecting rods ...

t walgamuth · #7 11-03-2007, 05:11 AM

Quote:

Originally Posted by ctaylor738

Something has obviously gone south in the engine, but wouldn't a rod mess up just a single cylinder? I would suspect a timing chain problem if it blew the compression on all cylinders on one side. Still an expensive problem, but not (as) catastrophic.

How does the mechanic explain a conn rod failure affecting all compression on one side?

I agree the diagnosis of a connecting rod makes no sense.

Tom W

spinedoc · #8 11-03-2007, 06:59 AM

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

t walgamuth · #9 11-03-2007, 08:42 AM

The timing chain slipping could cause some pretty bad noises including pistons hitting valves.

It could also account for consistent low compression if the intake valve is not open for a full breath of air on the intake stroke.

I would take it someplace else for a second opinion. The diagnosis sounds a bit off to me.

The bottom ends on any Mb engine is the least likely source of trouble. They are very very bulletproof.

Whatever it is it sounds serious.

Good luck

Tom W

spinedoc · #10 11-03-2007, 10:42 AM

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?

lynns · #11 11-05-2007, 04:27 AM

Quote:

Originally Posted by spinedoc

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.

Please read http://forums.mbworld.org/forums/showpost.php?p=2471617&postcount=2 and http://www.benzworld.org/forums/2027392-post10.html

t walgamuth · #12 11-05-2007, 06:27 AM

Again, it is very unlikely to have trouble with the bottom end in a benz motor. The exception is if it was run without or low on oil or if a head gasket failed and put water in the oil in sufficient quantities to ruin the bearings.

I would recommend getting a second opinion.

Tom W

spinedoc · #13 11-12-2007, 03:34 PM

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.