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  #1  
Old 03-05-2005, 01:31 PM
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Compression fix

I've got a '78 300SD with 130,000 miles on it. I bought it a year ago. It hadn't run in 6 years. I replced the starter and retimed it. Someone had removed the injection pump and installed it WAY out of time. The compression on the #5 cly was a low (under 300 psi) and the compressor wheel showed signs of being run without proper air filtering. I assumed the engine had been dusted at some point but didn't investigate further. It ran well, with a miss on the #5 cylinder at cold idle. I drive it approx 1100 miles/week on a sustained high speed commute. Yesterday on thay way home my oil pressure started dropping in short bursts. I shut it off to find it had consumed all the oil in the pan in just 90 miles. I refilled the oil and started it. There was an impressive amount of blowby observable with the oil cap removed. I just rechecked my comression and there isn't a single cylinder over 200 psi. Oiling the cylinders brings it over 300 psi. So...it looks like it's time for an engine. I've found a few used ones, but was wondering how cost probihitive it is to rebuild them. I've got access to a boring bar and a hone tank where I work(I teach automotive). Will it cost me $500.00 in special tools and untold hours of aggravation, or are they a straight-forward rebuild? Any advice appreciated.
Thanks,
Joebiodiesel

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  #2  
Old 03-05-2005, 01:50 PM
boneheaddoctor's Avatar
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Odd.......thats low milage for those problems............incidently, when were the valve last adjusted. Won't account for the blowby...or the oil consumption however.
From what I understand if pistons are in good shape and the taper on the bore is not excessive you can get away with rings and maybe bearings..

New pistons are pricey if you bore it out.
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Old 03-05-2005, 02:02 PM
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I suppose it wouold depend on the engine shop's opinion, wouldn't it? I mean, you would have to bore ALL of them out and rehone it all and use oversized pistons and rings. Unless they feel that just a rehoning is necessary, in which case you can hone them all, use new rings and reuse pistons.
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Old 03-05-2005, 02:17 PM
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I thought you didn't bore these out. They are fitted with sleeves in the block, aren't they?
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  #5  
Old 03-05-2005, 02:25 PM
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Doh!! I was thinking about a gas engine as I am so used to dealing with them. Yes, if there is nothing wrong with the pistons, I would suppose you could disassemble the block, change all the bearings, new sleeves and rings.
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  #6  
Old 03-05-2005, 02:48 PM
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It's probably better to find a used engine somewhere instead of trying to just bandaid fix it. Look for a wrecked car or one with a bad tranny. I came across a wrecked SD about a year ago and it had a factory replacement engine that had less than 120K on it. The guy still had the receipt for the engine and it was $6K. I could have got the whole car for $700 but my wife didn't want to have a wreck sitting around.
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  #7  
Old 03-05-2005, 04:24 PM
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BHD, I adjusted the valves a couple of thousand miles ago. I'm sure the compression problem if from breathing unfiltered air for too long. Doesn't take long to sand the cylinders...especially in a diesel.

Thanks for the rest of the replies. I didn't know it was sleeved. I'll check on some prices for sleeve and piston kits. I just finished building an old Ford diesel tractor engine. Maybe I'll get to use the sleeve puller set again.
The rest of the engine should be in nice shape with the low miles on it. The camshaft looks nice and I bet the crank looks good too. I'll keep my eyes peeled for a good used motor too.
Joe
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Old 03-05-2005, 04:49 PM
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Find a strong used engine. A rebuilt one will run you about $6k, if you do it yourself figure $2k-$3k. Internal parts are expensive like pistons for example.

Pete B rebuilt one maybe he will chime in.

With a sleeved engine usually you replace the sleeves, new pistons, bearings, connecting rods, ect. Have the crank checked, new oil pump, have the head gone through, have the IP and injectors checked, ect, ect.
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Old 03-05-2005, 06:47 PM
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Joe,

Usually the only thing that wears on the pistons is the top ring groove. The top ring groove wears to a "V" shape instead of being square. This groove and others can be machined wider and a ring installed in the wider groove to bring it back to standard width.

Other than the pistons, other overhaul parts aren't to expensive from FastLane or other online suppliers.

P E H
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  #10  
Old 03-05-2005, 07:31 PM
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Cool!, lots of good advice in this thread. I'm glad I asked. I'm not sure what I'm going to do yet but I know what I'm looking at now.
I checked FastLane and see that pistons are $1100.00 or so....YIKES!!
I don't like this car that much.... it hasn't been that faithful.
There are a couple of local used engines in the $700.00 price range.
I'll most likely tear this engine down to see what's up before deciding what to do.
Joe
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  #11  
Old 03-05-2005, 07:36 PM
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All MB engines are extremly expensive when you get involved in internal parts. These engines are the cheaper ones to rebuild too! An M119 runs about $20k, a rebuild on a 6.3 I was reading can run $20k-$40k.
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  #12  
Old 03-05-2005, 09:32 PM
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I agree with PEH.... These are expensive but strong pistons... and since there are very exact specifications available in the Factory Shop Manual it is perfectly reasonable to take the engine apart and measure stuff before making a decision..
Often , since these pistons are so expensive, one can check out normal machining procedures combined with specialized parts.... I am thinking about products from such specialists like Deves rings... which can advise you from the getgo about what would be reasonable to minimize unnecessary expense while providing reliable parts for your engine.

http://www.deves.com/about.html

I am including the search url because it looks like many third party endorsements of them..

http://www.google.com/search?hl=en&lr=&q=deves+rings&btnG=Search

http://www.peachparts.com/shopforum/search.php?searchid=226739
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  #13  
Old 03-05-2005, 09:45 PM
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If you consider looking for a used engine, this site may help you and also give some kind of idea what you may expect to pay.

I used this site http://Car-parts.com to find an engine once and found one. My experience buying the engine and having it shipped was a good one. But with used, you can only go by what they tell you!
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  #14  
Old 03-05-2005, 10:27 PM
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I'll bet the pistons are shot if the engine got dust in it.

Check the ring groove side clearance with a new set of rings -- if there is excessive clearance, replace the pistons. If there is any visible damage, replace also. They are expensive due to the cooling passages machined and/or die cast in them -- there is an oil jet spraying on the bottom side.

Sleeves are about $35 each at the current moment, press in nicely with no hassles.

Please remember that MB piston to bore clearance is SMALL -- 0.001". You will need to hone each bore to fit the intended piston. If you do not do this, the engine will expire shortly, the cylinders wear horribly if you have excess piston clearance (I have an example in my garage).

Crank will likely look new -- MB uses an HUGE amount of babbit on the main and rod bearings, even running them completely out of oil doesn't usually damage the crank. If scored, there are two repair grind sizes.

Aim for a bit less than 0.001" oil clearance on the crank bearings if you have to grind it.

Valve guide clearance is essentially zero -- if the valve stems can be inserted into the guides when oiled by hand, and the spring will close the valve, they are fine. Do not ream them for "clearance" or you will be doing a valve job soon, plus have terrible oil consumption. Use ONLY bronze exhaust guides. Steel ones are available, but fail in service, usually within 10,000 miles -- the exhaust valves are sodium filled and will broach out the steel guides, causing excess clearance, worn valves, and excess oil consumption.

Watch for the presence of aluminum or copper seals under closing plugs -- if you leave them out on reassembly, you get nasty oil leaks. Don't loose the spacer on the front of the crank, either -- it is the seal surface for the front crank seal, and while the engine will go back together just fine without it, the will throw oil all over the place (another not quite bright experience.....).

As far as rebuilds go, this one isn't bad at all. Pay attention to factory clearance specs and it should run another 500,000 miles!

Peter
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  #15  
Old 03-05-2005, 11:07 PM
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Hatterasguy,

Geez, I'll sell you my complete 6.3 with 53,000 actual miles for $20,000.

P E H

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