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#1
12-08-2008, 02:21 AM
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80 300SD valve problem
I'm kinda new to these cars and the engines, I have a 73 Mercedes 1113 truck and I've never had any problems with it so I got this 80 300SD. It was running great until I took it to do some shopping and on the freeway it all of a sudden started blowing black smoke and I lost 1 cylinder
 . I did some testing and I only have 150psi in #5 and 45% leak out the exhaust valve. I haven't torn the head off yet, but I was wondering if this is a common problem or if there is something I should be looking for specifically. I plan on getting the head off tomorrow to see if the valve is bent or burnt or what. And any advice on head removal would be appreciated.
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#3
12-08-2008, 02:36 AM
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head advice:
be very cautious when removing the pins. make good permanent marks for timing take pictures clean everything, most importantly the gasket surface area make sure to inspect head bolt length prior to install
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#5
12-08-2008, 06:40 PM
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I'm pretty sure it's the valve or the seat because when I do a cylinder leak test, it shows a 45% leak on #5 and I can hear it coming out of the muffler. And I have good compression on the other 4. I'm still waiting for the tool to take the head bolts out so I don't know for sure what it is.
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#6
12-08-2008, 07:09 PM
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As soon as you get this problem sorted, we're all going to want to learn more about the 1113.
I don't remember a case of losing a valve like that being posted on this forum in the 7 yrs I've been on here so maybe you should buy a lottery ticket.
__________________
1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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#7
12-08-2008, 07:13 PM
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I suspect you bought it and did not do a valve setting ?
A too tight exhaust valve will burn very fast... These engines need a valve setting every 20,000 miles to be safe.
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#8
12-08-2008, 09:35 PM
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Quote:
I still do not understand HOW this happens Leatherman.
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#9
12-09-2008, 06:59 PM
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Bump.. I'm interested in the correct answer too.
In the mean time, by reasoning it out, doesn't it go something like: A little too tight and they open early, close late. Closing late means we loose a little air out them on the compression stroke, probably not a big worry. Opening early means hotter exhaust gasses going by them at higher pressures. Not great, but would this really kill them all that fast until it got severe? Question is, at what clearance are things starting to get "severe"? There's not a lot to play with. A lot too tight (as in dragging on the cam all the time) and they never fully close. That'll for sure kill them in a hurry.. and the cam too probably.
__________________
'83 300DTurbo http://badges.fuelly.com/images/smallsig-us/318559.png Broadband: more lies faster.
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#10
12-09-2008, 07:48 PM
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Dumb question- Have you tried adjusting the valves? I had one tighten up and hang open one time, guess I did not get the lock nut tight enough. I re-adjusted it and the engine was fine.
__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver 1982 300SD - 232K miles - Wife's Daily Driver 1986 560SL - Wife's red speed machine
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#11
12-10-2008, 12:04 PM
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Well, it's the moment of truth. The head is off. I have two damaged precups, and a very burn exhaust valve. I was going to check the valve adjustment before this happened, but I did not. I did check it before I tore into it, and it was close. Anyone know where to find precups for any cheaper than $74ea.? Or is that a pretty good price?
 And as far as the 1113 truck goes, that is an amazing unit. It has a 6 cylinder naturally aspirated diesel with a 5 speed transmission. I recently hauled 20,000 lbs. of sod. Round trip was about 120 miles and I averaged 20 mpg! In a truck! I also have a 35 foot trailer I pull with it and I usually average 12-15 mpg. The only problem I ever had with it was the brakes didn't always work, but a couple of simple adjustments and now they'll about put you through the windshield. When I get a chance I'll post some pictures of it.
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#12
12-10-2008, 09:54 PM
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Why do the pre-chambers have to be new?
I think they would be real cheap at the pick your onw part type Junk Yard as the average person does not hav the tool to pull them (I have never seen any removed from engines at the Junk Yard so I assume the seldom sell any.) I could see using new ones I was replacing all of them.
__________________
84 300D, 82 Volvo 244Gl Diesel
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#13
12-10-2008, 09:57 PM
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You might want do delve into the cause of the damage to the pre-chambers.
Was it shot Injector Spray Nozzles, late timing (camshaft or IP),or ???
__________________
84 300D, 82 Volvo 244Gl Diesel
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#14
12-10-2008, 10:11 PM
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I've called around to the local junk yards, and no one here has a diesel mercedes. As for the injectors, I've tested all of them and they all have a good spray pattern and good pressure. I haven't checked timing yet, but plan to do so upon reassembly.
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#15
12-11-2008, 08:56 AM
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Ok.. the answer to why any valve... but especially exhaust valves burn if the clearance is not proper is this :
Convection of heat to the head by contact is a ( maybe the ) way the valves are kept cool ( or at least not hot enough to burn ). If they are set ...or the wear in the engine gets them to the place... where there is not FIRM contact with the head so that cooling can be accomplished then they burn.
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