Flying rockers. - PeachParts Mercedes-Benz Forum

milterino · #1 10-09-2009, 11:17 AM

76, 450 sel. While driving at 60 mph I heard a rattling noise at rpm frequency from the ds front of the car. This continued for about a half miile, then a bang and then a dead engine. Towed home. Found normal compression on the ps but no compression pressue at any of the cylinders on the ds. Valve cover off and each rocker arm from each of the 4 exhaust valves on the ds had left thier valve and was lying in the valve cover bed. In addition the "thrust piece" from valve 8 had been knocked off and was lying next to its rocker. Somehow they had been swept off thier respective valves. Oil delivery checked and under starter rotation oil was found to dribble down from each of the 8 holes in the oil delivery tube onto the cams on the ds and equivelently on the ps.
Timing. On the ps, when the mark on the rotating washer lined up with the mark on the cam tower the "o" on the crankshaft was at the pointer. So that's how it should be, right? However, at this instant the ds rotating washer mark was ahead of the tower mark by a about 40 degrees.
Any ideas on what happened and what to do next? Milt.

Tomguy · #2 10-09-2009, 12:48 PM

Timing chain guide rail broke on that side, and you skipped a tooth. And then you jumped a few teeth causing catastrophic failure. The initial jump of 1 tooth caused some small interference between valves and pistons, which then caused a bigger jump, and you had several (maybe all) valves literally smash into the pistons with detrimental results. Expect many broken valves, damaged piston crowns, a damaged head, perhaps a bent camshaft and scored cylinder walls. A stretched timing chain and weak rails - $200 in parts at MOST and a 4 hour DIY job - is the death of many m116 and m117 engines

milterino · #3 10-09-2009, 01:30 PM

Tomguy, thanks for your answer. I have since discovered that the 4 exhaust valves springs have not extended. So what you say sounds correct. The valve heads may be bent down there. So, next step is to take off the head and see what's going on.
I do have a 1975 engine from a parts car. It has the same camshafts (00/01)as the 1976 so I wonder if I could switch camshafts or even motors.
As for taking off and reassemblying the camshaft. I don't have a valve spring depressor. Is it possible to just sequentially loosen the bolts perhaps a turn of so at a time to get it off and reassemble it the same way. Milt.

Tomguy · #4 10-09-2009, 02:45 PM

No spring compressor needed for cam removal/reinstallation. You could make your life easier & get one, and wait 'till the cam's on to reinstall the rockers, but if you can't the easiest thing to do is keep the cam installed on the head from the donor engine, pull the whole head & cam off the donor engine installed (5 bolts, 1 on each cam tower; there's a head bolt and a cam retaining bolt on each tower. The angled one is the head bolt, the straight one is the cam bolt).

Swap the whole head, new guides & chain all around, and as long as there's no piston or cylinder damage, you'll be back on the road!

milterino · #5 10-09-2009, 04:13 PM

Tom: Thanks for your help. Taking off the head seems to be the easiest way out if the pistons and crank are ok on the present engine. I will call Mercedes on Monday and see if the 2 heads are equal or what the difference in the engines are. Milt.

Tomguy · #6 10-09-2009, 05:00 PM

Milt: Depends if it's actually a '75... if your cam is the same, 00/01, those are for hydraulic studs not mechanical. If your replacement head really is a '75 it would have mechanical studs and a 40-some or 50-some series. There will be a p/n on the head - a 117 xxx yy zz number - as long as it's the same you're 100% ok. If not, it will still fit, it just may be different and you will want to swap both heads if so.

GGR · #7 10-09-2009, 08:16 PM

Sorry to read that. If you run both your engine numbers into EPC you may be able to determine if they have the same heads. If you do not have access to EPC post your engine numbers here and I could try to check for you. While you have the head off, measure the position of your pistons relative to the block at TDC with a comparator. That may tell you if there is any damage on the rods or the krank journals (though damage down there may not necessarily translate into the piston going lower).

milterino · #8 10-09-2009, 08:54 PM

My plan is to get the head off next week and see what things look like and proceed based on the circumstances that present. Thanks for your imput. Milterino.

PanzerSD · #9 10-09-2009, 09:07 PM

Quote:

Originally Posted by Tomguy

Timing chain guide rail broke on that side, and you skipped a tooth. And then you jumped a few teeth causing catastrophic failure. The initial jump of 1 tooth caused some small interference between valves and pistons, which then caused a bigger jump, and you had several (maybe all) valves literally smash into the pistons with detrimental results. Expect many broken valves, damaged piston crowns, a damaged head, perhaps a bent camshaft and scored cylinder walls. A stretched timing chain and weak rails - $200 in parts at MOST and a 4 hour DIY job - is the death of many m116 and m117 engines

Holy sh** I know what I'm doing soon...changing my timing chain!
do the M117's mess around with woodruff keys like the 617 Diesel engines?