93 300E 2.8 Burned Valve??
 

Hi all,
My 93 300E 2.8 (M104) has 152k mi on it. It started running really roughly in the last 8-10 days -- hard starting, rough idle, coughing during acceleration. My mechanic, an independent who performed the 150k service several weeks ago, says there's no compression in No 4 and believes theres a burned valve. He estimates $1500 (minimum) to pull the head, have a look, replace the gasket and re-assemble and it could come up to $2600 for a full valve job.

Is this reasonable? Could the valve failure be legit? And what about the price? Everything I read in this forum indicates these engines never have valve problems. The car has been well cared for -- it has never used oil, except for when the head gasket was leaking (it was replaced by the dealer, as was the wiring harness at about 98k mi). Could this be the result of a bad tank of gas? My wife put a little Mobil in it, which we usually don't use -- but this sounds really far-fetched.

Comments?? Thanks in advance.

The prices are high.
I am in the east coast, but I hear a lot about a guy called Enrique in the west coast. Very good pricing and service.
Do search, you will find him (I do not know how far from you though)

Re: 93 300E 2.8 Burned Valve??
 

I Would have a Leak down test done to locate the problem..
It WILL tell you where the compression is leaking ..either a valve or rings...The Price is High!..I Have done several Valve Jobs on the 103/104 motors and I Have seen them burn valves!
Is The Shop MB only ?

Thanks.

Unfortunately, Enrique is over a 90 minute drive from here. But there are other shops.

Mark: thanks for the comment on the leak test. The shop is a Mercedes-only shop in Mission Viejo, named MB_Class Motors. The owner and main mechanic has worked on MBs for both the Fletcher Jones and Laguna Niguel dealers for many years and is very well trained. I've used this shop for about a year and been generally satisfied with his knowledge and skill, though his prices have been high. But when he said burned valve on a 104 engine, this makes me wonder. At a minimum, I will take it somewhere else for a second opinion. How did you deal with vavle jobs in a M104? Your own work? Have you a shop recommendation in Orange County?

Eric

I was a MB tech at Fletcher Jones..
Try Junior @MBworks @714 515 7592 He was a Tech at Fletcher Jones and has his own shop...Great Work and Great Prices!

Thanks, Mark. I'll look up Junior at MBWorks.

But I'll ask again, what could cause a valve to burn in a very short time and with no early indications? Could it have been related to gas? 104 engines are reputed to not suffer these problems.

same car , same problem , got nervous but compression check seemed fine , ended up being a set of plug wires , hope you have the same luck

Eric

Are you sure it is not one of the 3 coils that has blown ?

Regards

David

If you do not have a compression gage, I would just change the 3 plug connectors under coils and give it a try..
They are cheap, fit your common complaint, and they should be changed if they have to do a valve job anyway...
... or ,go get another compression test , just for ins....

If I were you, just for peace of mind, I would get a compression tester and confirm the poor compression on that cylinder. That can rule out all sorts of misfires. A compression tester is about $20 at Harbor Freight - I think there's actually one for even less than that. I don't really see a need for a leak down test - there's virtually no chance it's the bottom end. If it happened all of a sudden there's the possibility that a valve is stuck.

Hi all,
In my case, after getting some advice on this forum, I had two other mechanics do a leak down test. One of the mechanics was a name from the comments here, and one is someone I've known for many years who works on Porsches. I told both about the symptom (not requesting a leak down test), but both did that same test and both reported the same exhaust valve had failed.

So I went back to Oscar at MB Class Motors, who has been doing the work on my cars, and had him do the valve job. When the head was out, I looked it over. The one valve had a circular hole of about .25" in diameter that touched the outside circumfrence of the valve. Oscar sends the head to the same machine shop that's used by both local Mercedes dealers (Fletcher Jones and Liguna Niguel), so I felt confident in their ability. They recommended only replacing that one valve. While the other valves and the head showed a little carbon, there wasn't much and they were all within tolerance. The engine (the whole car) has run quite fine since then (just about 1 year, now). The engine is about as smooth as it ever was, and power is fine.

Why a valve job at "only" 152k miles? My (inexperienced) guess is that the hole in my exhaust valve was caused by some particle of foreign matter. Perhaps dirt in gasoline that made it through the filter, perhaps dirt that got in through the spark plug hole when the plugs were replaced at 150k miles. Others here may have better knowledge on that issue. While the head was out, we also plugged the hole that is known to lead to head gasket wear, and replaced the timing chain and tensioner. I didn't know about the 3 coils and the connector at the time. so I'd have to look at the invoice to see if Oscar replaced the connector by himself. Btw, gas mileage improved about 20% after all this work. Total cost ended up about $2400.

In the end, the car really did need the valve job, though the reason is a mystery. I was, and remain, very greatful to the members of this forum who gave me the recommendations that helped verify the problem and pointed me at a few good shops in my area. I will likely be using one or more of the shops given here for some work in the future.