Rering/resleve, or not to bother? - PeachParts Mercedes-Benz Forum

MT_Merc · #1 03-25-2006, 05:00 PM

So, a couple months back we picked up a wrecked but running '85 300D-TD showing 215K miles on the odometer for an engine/transmission swap, and since then I've managed to get it pulled and partially disassembled. I ran it several times before pulling it, and it started and ran well except for some knocking noise that I suspect was injector nailing based on what I've read. I wouldn't say that it had a lot of blowby as far as I could tell; some, as I remember, but nothing terrible. I didn't get around to a compression check. Anyway, after getting the oil pan off, I got a look at the bearings and cylinder walls. The bearings looked pretty nice, just a few minimal scoring marks on the ones that I looked at (nothing like the ones I pulled out of my old 302 with who knows how many miles, they were original, said FoMoCo 68 on the bottom). The thrust checked out well on the rods (within normal tolerances according to the Haynes manual), the thrust on the crank was well out, so I suppose new bearings would be a good precaution no matter what. The cylinder walls, inspection-wise, were a mixed bag. On a couple cylinders I could still see the honing marks, but on others there was some scoring; the number one cylinder looked the most worn.

I would like to get this motor ready to go for the long haul before I throw it in. The motor seems to start, run, and rev out nice enough, but I'm seeing more wear on the cylinder walls than I'd like, and I'd hate to drop it in only to find that it burns oil. I'm leaning towards getting new rings and sleeves and maybe having the machine shop do the assembly on the short block in addition to the sleeves and honing. Rings, sleeves, and related machining will probably double the price of the engine work (I am replacing all the seals, it's had its share of leaks, and I'm sure I'll run into other little things), but I don't think the cost is too big a deal if I don't run into any serious issues. The pistons I'm planning on reusing, I do need to get the head off to look at the crowns, but the skirts look good. Top end work I plan on leaving for later; I'll pull the head apart and have it hot tanked to clear out all the accumulated sludge, but unless that looks pretty worn I'm not going to worry about it.

So, does all this sound reasonable? I know I need to find a good machine shop, I don't know how much good new rings and sleeves would do if I were doing it all myself. Also, I'm not expecting to come out with a like-new bottom end. As long as it's good to go for another 200K or so I'll be happy. I basically want to do as much as possible to ensure that we'll get good service out of it--it'll be a daily commuter--without blowing the whole wad on a rebuild that it's not really in need of.

t walgamuth · #2 03-25-2006, 05:25 PM

it is pretty hard to say anything from your description. i would have an experienced machinist look at it and take measurements to see how much taper there is in the bores. he will have books to see how much is allowed before work is needed.

it really would have been a good idea to take compression and leak down tests before tearing the engine apart.

the bottom end s are really robust and it is not uncommon for them to show vitrually no wear at 250k.

since it is apart i would do a valve job probably at least. and seals. and valves for those that are too worn.

the job of knocking out the sleeves and reinstalling new ones is a lot of time and work. the sleeves arent much but after installing the new ones you have to bore them to match your pistons and mill the tops off. it is also not a bad idea to deck the block to remove the twist it will have after 250k miles.

no idea of the cost until the needs are assessed.

tom w

MT_Merc · #3 04-01-2006, 08:57 PM

I'm afraid things just took an unexpected and unwelcome twist on the project. I finally got the pistons out, and the top ring land on number five piston is pretty badly busted up. Of course, I have no way of knowing what might have caused it, up to this point things have looked fairly good. The other pistons look ok, and actually the crown of the number five piston looks just fine as well. Sucks that this happened, but I am glad I didn't just put new seals in and drop it in the other car. Now I really wish I'd had a compression tester, I'm sure it would have shown way lower than the others as bad as it, and no way was it worth what was paid for it given this. Live and learn I guess, ya pays your money, ya takes yer chances.

Anyway, I'm going to be taking it down to the machine shop next week, and I'll see what they say, but are there any opinions as to what I'm looking at here? How often is a serious ring land failure an isolated thing? I'm hoping I can just replace the one piston, is that likely to work out if the other pistons check out ok? Does it affect the balance? I don't know if it's important, but one piston has 90.85 and the others (including the busted one) have 90.86 stamped on the crown.

engatwork · #4 04-01-2006, 09:20 PM

I've got a couple of good spare pistons if you need one. PM or email me.
The different numbered piston should have come out of the #1 cylinder.

mplafleur · #5 04-02-2006, 10:32 AM

You can find deals on sleeves if you look hard enough. I just bought a set for my SDL for $19 a piece. Now I need to make sure my machine shop can do diesels. Maybe I can drop off the block next Friday with the sleeves and new pistons.

t walgamuth · #6 04-02-2006, 10:47 AM

can measure the pistons including the ring lands and determine if they are good to reuse.

reusing them is no problem if they measure out.

sorry it isnt going the best.

tom w

MT_Merc · #7 04-02-2006, 06:59 PM

Yea, it's disappointing. I was hoping things would be good enough that I'd get away with a ring job, but I wasn't banking on it. I guess what I do now depends on how the cylinders and the other pistons check out. If the other pistons aren't too badly worn and the cylinders are close enough to do a hone and go I'll definitely be interested in picking up a piston. I am wondering what the best step will be if the cylinder walls are too far out. The piston set listed on the parts section are a 90.9mm, which I assume is means an overbore size. Is overboring a good way to go, ie, better than a resleve if the bores are out but the pistons are ok? I guess if the sleves and pistons are bad it's either bore and install oversize pistons or do the whole job with standard sizes; doesn't seem worth spending an extra $300 or so on the sleves if you can do basically the same thing with oversize pistons. Just thinking out loud, I guess.
Anyway, the machine shop I'm planning on taking it to was referred to me by a shop that does a lot of diesel work, and they seem somewhat familiar with Mercedes diesels. I'll be back if there are any new developments, thanks to all for the advice.

engatwork · #8 04-02-2006, 07:05 PM

You don't want to have to replace piston$ unless you absolutely have to. Try to resleeve/bore to your existing pistons if they are in good condition.

t walgamuth · #9 04-02-2006, 07:11 PM

if the other four pistons are good you will prob be better to sleeve and hone back to stock and use exist pistons. if there are other pistons bad then the boring and using oversize pistons may be more economical.

tom w

MT_Merc · #10 04-10-2006, 10:44 PM

Bad news and good news from the machine shop. The bad news is that the other pistons have worn out ring lands, so the total failure on number five piston probably wasn't just a fluke. They're also saying the cylinder walls are beyond service limits, so they need to be redone. Given that, I'm leaning towards a set of oversize pistons and overboring it. I didn't want to bite that bullet, but at this point it seems like the best overall solution. So, does the rotating assembly need to be balanced when replacing the pistons? I've gathered from reading around here that Mercedes matched pistons to the rotating assembly, and so switching pistons affects the balance. Is there a specific process to balancing a 617, or can any experienced shop do it?

As for the good news, they said the valves and seats had plenty of material left, so they went ahead and ground them. They are recommending that I replace the valve guides on the exhaust only, the guy I talked to said he thought the intakes were tight enough, but that all his book told him was to use a Mercedes go/no-go tool for checking it, which he obviously doesn't have. I didn't have any way to measure anything when I disassembled the head, but I did notice an appreciable amount of play in all the valves, some worse than others. Can anyone point me to the proper measurement process and/or give some general advice? Would I want original sizes on the guides, or oversize? All I really have to go on is the Haynes manual, which is hardly comprehensive, and I don't know how accurate their instructions and measurements are.

t walgamuth · #11 04-10-2006, 11:31 PM

the first benz diesel i had rebuilt we had balanced. the balancer said that there was very little to balance as the factory had done a very thourogh job of balancing.

we have on more than one of my engines replaced pistons and not balanced and the results were very good. so unless you get a bad batch of pistons probably you dont need to balance it.

to be safe i might weigh the existing pistons and if they are all equal i would then make the new ones equal them.

i have balanced my own pistons before with a drill press and a paint scale. on my 52 caddie motor. worked fine.

tom w

#12 04-11-2006, 01:37 AM

http://cgi.ebay.com/ebaymotors/5-Mercedes-Benz-Diesel-Cylinder-Liners-MAHLE-300D-300SD_W0QQitemZ8054178321QQcategoryZ33613QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

$180 BIN price, good deal.

barry123400 · #13 04-11-2006, 02:15 AM

Best of luck with the rebuild. The only comment I have is the valve to valve guide clearance should be in the mercedes intended ballpark. The oil flow up on that head is quite heavy compared to a lot of other engines. Plus it keeps your valve rubbers functional longer. I think mercedes clearance requirements are tighter than most. Plus of course on average valve grinding machine gives a better job without sloppy guides. I do not have the recommended clearances on the valve stems to guide figures. One of the on site manuals should have them. Skinner?

the tenor man · #14 04-11-2006, 01:33 PM

I went through all of this on a 240D...my advice is that unless this car is a real beauty...(no rust anywhere, great interior...you really love the car more than a few thousand bucks), stop now and cut your losses....I'm sure that you can find a better example out there for $3000-$4000.

When my car was finished (I did all of the grunt work) it ran a bit better. It's hard to tell on a 240D...there are already SLOOOOW!.

I don't think it was all worth it....just my opinion.

Jim Schaffner

MT_Merc · #15 04-11-2006, 04:02 PM

So, I'm wondering where the best place to get pistons is. All the places I've looked list 90.9mm pistons, which they claim is standard. I can't really figure that one out becuase the original pistons are 90.85 or 90.86mm; .04mm is not standard size, but neither is it big enough to be an overbore size. Another thing I'm wondering is how important it is to get the OEM Mahle brand. I've found Kolbenschmidt brand pistons (again "std.") for about $200 cheaper, but I've never heard anything either way about non-OEM pistons. Any recommendations on what to get and where to get it for a decent price?

By the way, the car is a solid, rust-free car, but a fixer. We've had it since 1986, and I don't think I would be bothering with any Mercedes (face it, you do get shafted on MB parts and repair matter what you do, unless your usual practice is to buy beaters for cheap and drive them into the ground), except that this is the first car I remember and the whole family is somewhat attached to it. It hasn't been wrapped around a tree, the only appreciable rust on it is a fender that got a bunch of debris from a missing liner, and it's going to be fixed. I will admit to being less than mercenary when it comes to cars and money spent on them. Logical though it may be, I'm just not interested in treating cars as appliances. If I were starting from scratch, I wouldn't be taking this path, but considering the attachment to this car that's not an option. Also, the donor car, had it not received a horrendous smack to the side, started and ran well enough that it might have been a $4000 dollar car if the buyer hadn't done a compression and/or leakdown test. The money's there to rebuild it, it's going to get rebuilt, and our '78 will see the road again.

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