300TD engine rebuild - Page 2 - PeachParts Mercedes-Benz Forum

jake12tech · #1 12-27-2017, 01:23 PM

Quote:

Originally Posted by danielac

Oil pressure is normal as well. The mechanic hasn't diagnosed anything, all he told me was that it definitely wasn't coming from the top and that he'd have to dig deeper into the engine. The only reason I'm entertaining the idea of a rebuild is that for the expense of getting into the bottom end and diagnosing, not to mention repairing, I'd rather just put that money towards fixing everything and start with a like new engine. I've taken it to two very reputable Mercedes mechanics who have both told me that it's not something that they can tell simply by looking at it. I do appreciate everyone's help trying to diagnose, and I'll probably end up going that route, but for now I'd just like to know how realistic it is to do a diy rebuild if I'm patient and am willing to put the car out of commission for a few months. If it is realistic, I'd love some resources that would help guide me through it.

Rebuilding an engine isn't difficult and I think if you have common sense, a manual and torque wrench you'll be fine. If you have any doubts ask questions. You haven't acknowledged if it has been run low on oil. Then its highly unlikely it's a bottom end or rod issue, or anything bad.

Please start by checking chain stretch before you go wasting money and time. It is very much worth checking. You also really need a stethoscope to hear where the noise is from. It could be something as simple as a tensioner!

BillGrissom · #2 12-31-2017, 12:13 PM

Quote:

Originally Posted by jake12tech

Rebuilding an engine isn't difficult and I think if you have common sense, a manual and torque wrench you'll be fine. ...

A Chevy small-block V-8 yes. A set of 8 pistons costs <$100 and any auto machine shop knows them thoroughly, or just buy a complete "long block" for $1500. A M-B diesel, not so easy. The set of 5 new turbo pistons on ebay did drop price to $1300, so jump on that, but insure you can get other critical parts (bearings, sleeves, ...).

BillGrissom · #3 12-27-2017, 01:19 PM

Before considering a rebuild, measure compression pressure in each cylinder. If >350 psig, don't rebuild. Even if low, it could be due to valves (cheaper head job), and a leak-down test determines that. Once you tear it open, you can't test.

Main and rod bearings can be changed with the head on. In most old U.S. cars, you can do in the car, but the OM617 must be removed to take off the upper oil pan. That is the main thing that restores oil pressure. But, the low-end rarely wears and bad main bearings would give a low clunky sound.

Your symptoms sound like the oil pump chain tensioner failed, which would cause a loose chain and slapping sound. It did on my 1984 300D. I changed it thru the lower oil pan (engine in car). The part is <$10 here at P-P. Read my post w/ photos since tricky to remove the sprocket bolt but can be done. Others claim you must remove the upper oil pan (big job, engine out). You must remove the oil pump, so replace the O-rings on the outlet tube (Viton is best, and no you don't need a dealer for O-rings). You also must remove the #1 bearing cap, which lets you inspect bearing wear. Might combine w/ a front seal change if needed. I don't recall that I did, but might help (get more fingers in there).

When you do actually need a rebuilt, search for my post. I took my 1985 block to the "new sleeves" level, but haven't taken it to a shop to deck and hone to the pistons. Another guy posted many photos. People thought he was crazy, but he showed photos where he has a full machine shop in some remote ranch, and decked the block etc. I noticed that rebuilt OM617.952 engines appear to have dropped from $8500 to $6500 (ebay), but still out of my reach. There is also a set of new turbo pistons on ebay for ~$1200, which seems a deal since 1 new piston was $550 and you can't even find them. Someday, a custom piston maker like Egge might find the market, or someone here might front the NRE cost to get some made and hope they can resell them. Even cylinder sleeves are getting expensive and rare.

tdoublenastywitit · #4 12-27-2017, 09:49 PM

So your diesel engine is making a timid rattle and u wanna rebuild it???

If it wasn't making a rattle I'd be more worried!!

But by all means if you want to re build your engine for something fun to do then go for it. U could pull it of for sure. Just gonna cost u some bucks, time, and frustration.

vstech · #5 12-27-2017, 01:21 PM

Pull the lower oil pan off and strain the oil for debris...

If it is bottom end, you will have shards of metal there.

dkr · #6 01-01-2018, 02:28 AM

If you really, really need an engine, get a recently wrecked car or something that is rusting out. You'll get a bunch of extra parts or can sell the parts to pay for the engine. I bought an entire running car with an engine for $600 at 200K miles. As has been stated here, you're in for a ton of money on a rebuilt, so if you can get a good used one, you should.

These engines were extremely well built. Figure out exactly what is wrong with it before you conclude you need a rebuild. There are lots of stories on this forum about people buying good cars for super cheap because the last few mechanics couldn't figure it out.

Dkr.