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.