Touche-shady craftsmanship M117 Head

[txstinger]

Touche… I’ve been pierced by the shady craftsmanship of the used car mechanic. It started with my desire to own a R107. I spotted an 83’ 500SL euro selling below market with some rough idle. The mechanical seemed in good repair so I rolled the dice and purchased the car. I drove the 500SL from New Jersey to Dallas/Ft. Worth Texas in 21 hours.

Back home, I started to work on the rough idle. 1) I checked the compression on each cylinder and logged on my history work sheet (#2 was 15% lower than average of others). 2) I solved many vacuum leeks and idle is now 50% better. 3) Found bad Idle Speed Controller (causing high and surging idle) – replaced burnt transistor – idle now consistent at 800 rpm. 4) 500SL barely passed emissions test. 5) Idle starts getting rougher over the next few months causing me to change all spark related items – miss gets better, however something is not right. 6) Replace all fuel injectors and rubber above intake manifold, engine is strong, however something is not right. 7) miss continues to get worse, so recheck compression and #2 fails terribly. 8) Identify exhaust leak and suspect burnt valve….

I phone David Poole in Dallas to line up a machine shop. He gave some solid advice and cautions with breaking the cylinder head seat from engine.

David Poole’s tip: Valve failure with these engines are rare and can be caused by carbon build-up stuck between the valve and port seat. Remedy – remove rocker assembly from top of failed valve, place 3/8 drive extension on top of valve spring retainer, and smack with rubber mallet many times. This should free loose any carbon build-up.

GREAT TIP – however, did not solve my exhaust valve leak and I decided it was time to pull the head. A substitute for the Impact Puller 116 589 20 33 00, is to used a ¼ drive deep well 3/8 inch socket and one of the valve cover bolts. (See photo: car work 018).

My daughter and I pull the head and found even worse failure than a burnt valve. I could have replaced a burnt valve, but what are my options regarding bad workmanship. My guess is a used car shop made quick/cheep repair by replacing the valve and reaming the head port by an enormous amount. The exhaust valve closes almost flush with the head. This repair lasted long enough to sell the car and continued to get worse until total failure. The compression test went from 15% less than average to 85% less than average within 3500 miles of driving. (See photos: car work 020 - daughter 15 years old aspires to be an engineer , car work 028 – good exhaust valve right protrudes high on head, car work 029 – bad exhaust valve right protrudes low or flat on head, car work 030 – exhaust valve port)

Guys, I need some encouragement and advice with options/opinions on remedies to this ghastly problem. My Specs are as follows:
Euro M117.962 engine, Cylinder Head 117 016 33 01, and Cam # 60.

[t walgamuth]

can't you just have a new seat put in by a competent machine shop?

am i missing something?

tom w

[Rob Pruijt]

First, it is very unlikely that your problem is caused by a recent bad repair job.
Valve seats are very hard and replacing them is much easier and cheaper than grinding them much down. If your head struck to the cylinder block it was not recently removed and the person that sold you the car was probably not aware of the worn valve/seat.
Most likely the valve has been to hot (lean mixture) or the valve adjuster failed. The valve then hammers into the head, this may be a very slow process.
Any good machine shop can replace the valve seat, since this is done by warming the entire head it is best to replace all seats that look worn. After that you will have to grind in the valves. If you have no experience it may be advisable to have the shop do it.
Also replace the chain, tensioner and guides, it will be disappointing if you have to do a head job again.
You can not expect to buy a 83 car below market value without some wear. If you feel this is a ghastly problem you may be better of with a new car. Old cars can be fun if you have a relaxed view towards mechanical problems.
Hammering on the valve to release carbon deposits sounds like a strange advice. The carbon deposit ring on an old valve helps to seal the valve. If you remove this carbon you will have to grind the valve to make it seal again.

Rob

[txstinger]

Thanks for the input of options and this is what makes car repair forums great. I lack the knowledge of what can be done to the M117 aluminum head and know there are guys here with the needed answer. I believe in taking time to make a plan of action, asking other for their valuable input, and then work the plan.

The head seems to have been removed before my take-off; bolts and gasket differences. The head was not stuck to the engine. I was only warned about the many problems these M117 engines can give when one removes or breaks the factory seal of engine to head.

My background with major engine repair/machine work is only with US pushrod engines. Around 1980, I moved to the Datsun 240/260/280/300 overhead cam engines. Then in 1985, I bought an Alfa Romeo spider and loved their design/simplicity. I never needed to perform deep engine maintenance to either of those two engine families. Due to the Datsun’s cost, horsepower, handling, and available high performance part selection, I chose them as my primary projects. I not scared of the M117 and look forward to learning them with my daughter (who must work on the 500SL to drive it ).

So far, it seems the best course of action is the machine shop repairing the valve seat. My fear is it may be beyond machine shops efforts.

The manual states to test the valve adjuster with the butt end of hammer for recoil. Is there any other test? Is the original valve seat of the same cast material as the head or is it’s origin of different material/part that is pressed into place? My plan is to clean-up the head tomorrow and really inspect/assist the situation. I may have jumped to the conclusion of bad craftsmanship. Due to the budge of aluminum mushroomed material on the outer rim of valve seat, I assumed that the seat was reamed with tool as a patch. That would be a ghastly remedy to a head that cost as much as entire engines of other makes.

Man, these engines are costly!!!

[Rob Pruijt]

Valve seats are made of very hard metal and are pressed into the head. There are different quality seats. In my cars, since running on GPL, I always used extra hard seats. Normal seats are less durable for engines running on GLP. But even the “softest” seats are much to hard to ream easily, you will need a special machine and very hard (expensive) chisels.
I would take some time to find a machine shop with the necessary expertise, maybe the dealer can help you finding a shop. I live in the Netherlands, all machine shops over here have experience with European engines. But even over here some shops are much better than others. Some shops go for the quick repair/low price, others for high quality. The shop I go to also repairs vintage cars. Last time I was there the were working on a pre-war Rolls engine, that was a nice engine!!

One of the problems with old cars is that over the years a lot of people may have worked on them. Repairs, especially before a sale are not always very good. You just cannot expect the previous owner to have the engine repaired at a price that may exceed the estimated resale value.

[page62]

Originally Posted by Rob Pruijt

...maybe the dealer can help you finding a shop.

I'm fairly certain you can find a machine shop in the DFW area that has expertise with these engines. After all, Texas is simply crawling with old MB's!!!

But instead of asking the dealer for a referral, I'd ask some of the local independent mechanics who specialize in MB's. You'll find the right machine shop real quick!

[txstinger]

I took the head to a machine shop today and the prognosis was not good. He wanted $700.00 to repair the head and that was only if he did both sides = $1400.00. I’m really not wanting to go that route.

I will look at more shops or options during this week.

I scanned Potomac German Parts and found some hits. I blasted them an e-mail and will probable hear from them tomorrow. So far, this looks the most promissing.

[Strife]

The valve seat can also be damaged by pounding from a bad cam lobe and/or cam follower. Hopefully I got to mine before this happened. I think that this is at least as likely a problem as a bad hydraulic compensator. Of course, nothing "happens" without a cause; in my case, the whole calamity was caused by shrunken oil tube fittings (NOT clogged), not delivering oil to the cam bearings and cam, wearing the cam and follower, banging the valve(s)...and so on.

[Chas H]

Given the machine shop's price, a salvage head will (should) be much cheaper. I don't understand why all the seats need replacing. I've had one seat replaced on many heads and the repair in total was perfect. And the price to replace one seat was far less than buying a salvage head.

[txstinger]

Originally Posted by Chas H

Given the machine shop's price, a salvage head will (should) be much cheaper. I don't understand why all the seats need replacing. I've had one seat replaced on many heads and the repair in total was perfect. And the price to replace one seat was far less than buying a salvage head.

That is exactly what I'm wanting to do. I'm scheduled with another shop tomorrow.

[txstinger]

Strife, enlighten me with the home brew first grear start...

[Hatterasguy]

What would a new bare head cost? Why not give Phil a call, you would be surprised what he can get.

Metric Motor's is awsome when it comes to the diesels, they seem to really know how to do good machine work on these engines. I'd give them a call.

[Chas H]

Y'know, since you're into the engine this far, you should consider pulling the other head and inspecting it.

[txstinger]

Well, I got the head cleaned up a little and I think you guys where spot on. My initial thought was the valve looked to good to have caused that much damage. The exhaust valve must be one hard bugger. It does not have a mark on it. However, found a lot of play in the valve guide and the rocker is worn with a small flat spot. I’ll spend some more time cleaning and testing other components tomorrow. Thanks to all for making me focus.

[jhodg5ck]

The last Metric diesel engine (240D) ate itself in about 12,000 miles :-/ Also had one of their 'full euro' 5.6L M117's in.. Had full custom headers, extrude honed intake, MSD ignition.. Made 235RWHP

My advise be Very careful in which machine shop you use....Only deal with one that handles Mercedes heads w/ utter regularity. Not the "yea, we dun a few"....

I go through the trouble of sending all my machining to New York from Atlanta just because I know the fellow does the job Right.

Jonathan