putting the head on the engine and I seem to have an extra nut. It's large and looks like a suspension or pully type nut. It's very clean and no signs of road grime, dirt or rust...any ideas? I hope it's not something that goes inside under the valve cover. I don't really see where I am missing a large nut on the engine anywhere.

I'm kinda outta big parts to put back on. I bagged all the small nuts and bolts and labeled them as to what they were for. But anything big and obvious I did not label...I guess this one was not too obvious. It was in the big tray of head job parts so it came off in the process.

I am clueless...anyone ever do a 603 head job and have any ideas?

it's pictured with a glow plug and quarter for size reference.

Attached Thumbnails

 

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

Thanks for the good pic. Do you know the thread size? Wrench size? Assuming that the nut is original, similar nuts are used for:

Oil filter housing lid (2 nuts)
Trap cat factory replacement pipe to turbo inlet (4 nuts)
Turbo mounting brackets to exhaust manifold (4 nuts)

The above is all from my picture collection when I replaced the head on a 1987 300D Turbo with OM603 engine. There could be others. I don't see anything inside the head with that nut. All of this assumes someone in the past didn't have the right nut and used that one as a substitute.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

oil filter not touched. no cat trap.

maybe a turbo mounting nut underneath...

turbo-to-head stuff was not touched that I recall.

can't find any pulleys missing a big center nut.

the fact that the nut is clean leaves me really scratching my head....almost like it's internal??????

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

I highly doubt that nut came from the 603. it's a thrust face equipped nut, and likely came from a body mount.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Exhaust manifold? Those are usually copper or copper colored a bit distorted.

Sixto
87 300D

Maybe it's the nut for the long bolt that holds the spring arm for the belt tensioner.

__________________

85 190E 2.3(SOLD)
86 230E (-->300D) sold
87 300D (-->300TD) sold
68 250S w/ a 615 and manual tranny (RIP)
87 300TD (SOLD)
95 S280 "The KRAKEN" (Turbo 2.9 602 transplant) traded
86 190E 2.3... current project

I took the head off the 603 not so long ago. It is still in pieces and I do not recall seeing a nut that size and shape. I can not find one similar in the collection bins also. Exhaust nuts usually are made of copper for easy removal. Is it possible that it is one of the nuts you used to extract the timing chain guide rod?

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Good call! Takes a 13mm wrench.

Sixto
87 300D

not the tensioner...this is a pretty big nut. maybe 19 or 21mm I think. I had a big plastic bin that I put every nut, bolt and part into while doing the head...this nut was in that bin so it must go somewhere...

I guess I'll be crawling under the car again and look around some more. Maybe I pulled or removed something for working clearance?

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

Methinks something that big ("maybe 19 or 21mm I think") would have to be from the suspension or chassis.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Can you get the thread diameter and pitch? Go to a hardware store and see what bolt it threads onto. Maybe it's not even metric and didn't come from that car. Maybe you used it as a spacer while extracting the chain guide pins.

Sixto
87 300D

No, it's off the car for sure. I've been working on two cars so haven't crawled under the benz yet...I suspect I'll find my answer underneath...I think I kinda recall a bracket or something underneath for the turbo....

__________________
1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5