Have you had a timing chain break!? - Page 6 - PeachParts Mercedes-Benz Forum

mplafleur · #76 10-01-2001, 11:01 PM

Well, the engine block is sitting upside down inside my garage, the head is at the machine shop and I've got a bunch of parts on my table.

The valves and seals go to the shop tomorrow.

Otherwise, I have:

Timing chain
Tensioner
Timing chain rail
Timing chain guide
Oil pump chain
Oil pump chain guide
Head gasket kit
Head bolts
Crank gear
Front crank seal
Rear crank seal
Oil pump
Oil pressure sender
Motor mounts
Main bearings
Rod bearings

Am I missing anything? Is there a need for the tensioner? It is just the insides (spring and pressure pin).

psfred · #77 10-01-2001, 11:27 PM

Michael:

I assume you have had the crank checked for journal diameter and condition -- if not, please have it done if you don't do it yourself! New bearings won't fix damaged crank journals.

If you took the pistons out, you will need new rings, too. If they looked OK, and you didn't remove them, you are probably OK, but if they have been removed, it is foolish at best to put old rings back in.

Check the piston pin bushings for wear -- there should be no play in them if you twist the rod -- any play means the bushing is bad and needs to be replaced.

If it were me, I'd have checked the bores for wear and re-sleeved them if necessary, and checked the rods to make sure they aren't bent -- not very common on these engines, but since it is apart already......

Peter

mplafleur · #78 10-01-2001, 11:49 PM

The bores shows no wear and have the original crosshatching. I don't want to touch those so I am being very careful not to move them around. I don't want the rings to move as I don't expect them to seat a second time.

The rod bearings look worn. The mains look ok but for some long scoring. The crank looks fine too. I will check for wrist pin/bushing wear (very carefully) when I take the crank out.

If I find problems with the piston pins, then I will have to rethink what I want to do. I've been told different things as to whether I can just put on new rings without reboring or honing and having it reseat properly. This means another trip to the machine shop. This was to be an inexpensive rebuild.

psfred · #79 10-03-2001, 08:58 PM

Michael:

Have the crank checked for taper and roundness as well as size of the journals, rod and mains. If there is anything out of tolerance, you will need to have it ground, polished, and balanced (which requires the pistons, alas).

Just don't spin the pistons in the bores -- up and down won't hurt anything as long as the rings stay in their usual range -- don't push them into or past the ridge at the top. They go up and down a lot when the engine is running.....!

If the the crank journals look nice and clean, with no scratches or wear marks, you are probably OK -- my brothers (and the one in the short block he bought) was OK, but the bearings weren't right, so were shot. Minor imperfections can be polished out without grinding, so long as the diameter isn't greatly changed (as in still within stated tolerance). If you don't know how to use a micrometer, have the measuring done by someone with a metric mic set, no SAE with "translation" -- it isn't accurate enough.

Scratches imply dirt, and that in turn implies crank damage. Sorry.

All you need to do if the pistons have to come out is put new rings in after cleaning the pistons. Check ring clearance (side to side), although if the crosshatching is fine, I cannot imagine the pistons are worn. The the wear is less the 0.002" (a ridge you can distintly feel, no more) at the top of the cylinder, you don't need to do anything except maybe "deglaze" with a ball hone (have a shop do this, specify no diameter change!)

You will still have oil pressure problems with new bearings if the crank is bad, so you will have to decide what to do. If it was run out of oil, there is enough babbit on MB bearings to save the crank at the cost of ruining the bearings, so you are probably still OK, and will have proper pressure.

If you don't want to re-do the crank, get some plastigage and check the bearing clearance with it -- the smaller the better above 0.0005" -- you may have some trouble getting the proper size, as most auto supply places hire help who think Chevy 0.005" is about right!

Good luck!

Peter

psfred · #80 10-03-2001, 09:23 PM

Oh, I forgot to say, it won't be cheaper to have to do it twice from saving money the first time!

I'm facing the same dilema with my 300DT -- do I just put a head on it and ignore the low compression, or do I re-do the entire motor? Head is $1200 plus gasket, etc, motor is $3500 more, (pistons are $2500 from my usualy supplier) plus 12 hrs R%R and 50 hrs rebuild by the time book -- and since I've not done one of these before, many more hours, I'm sure. The damned thing had better run forever after I rebuild it!

Peter

mplafleur · #81 10-03-2001, 10:06 PM

Peter,

Thanks for the tips. I certainly will be extremely careful in making sure I don't rotate the pistons. I don't want those rings to unseat. Since they look fine with absolutely no ridge, I don't want to do anything with them.

I'll plastigage the crank when I get the new parts in and let you know what I find. I'm only going to hold onto this car for no more than another year.

When I rebuilt the head on my '75 300D, I think I paid $100 each for the pistons and those were Mercedes parts. This was in the late 80's. My brother gave them to me at cost, but I don't think the mark-up is THAT much. The turbo parts must be extra special.

Kebowers · #82 10-03-2001, 10:41 PM

the picture you provide shows a missing roller. In all probability the missing roller (in peices) is in the oil pan. It (and it's next door neighbor?) probably cracked and fell off. It may have jamed in the sprocket when it came loose and that is what pulled the chain in two.

What caused it to crack? It got hit sometime after manufacture (dropped, hit on ?) or it was slapping around , or the sprockets are worn.

However, I noticed the adjacent roller to way too short!! There should not be a lot a end play on the rollers!

mplafleur · #83 10-03-2001, 11:19 PM

I did find the rest of the roller in the pan. I first found a full length section that was about 1/3 the circumference. Then two days ago I found the rest. The remaining 2/3 was split in two, not down the length, but across the roller, at about 60/40 in length.

psfred · #84 10-04-2001, 08:20 PM

Michael:

The pistons for the turbos have a wonderful oil channel precision cast to route the oil spray around the crowm and back down the sides for cooling. They also have the steel ring for the top compression ring, and holes from the oil cooling channel into the oil control ring. About $425 each, I think, as opposed to $110 for my brother's 75 330D. Fortunately, if the ring lands aren't worn, they can be reused with new rings as long as the cylinder walls weren't too bad -- I've seen them with an extruded lip where the ring was banging up and down on the land due to execessive piston to sylinder clearance.

If the 87 wasn't such a blast to drive, bad engine and all, I'd never have bought it, but in good shape will be very nice transportation for a long time -- I tend to keep my cars forever.

MB puts a ton of babbit on their bearings, unlike GM (0.010", plated), so unless you got something in there that ate up the mains, you will be all right. MB cranks are HARD! My brother broke his, but that was because the PO had it rebuilt, nasty job, used oragne silicon sealant on everything, and a chunk seems to have shot down off the oil filter housing (in front on the old 617) and cut off the oil suppply to the thrust bearing (#2 main) -- starved the #2 crankpin, so it failed, too, classic sharp radius crank failure, cracked from the inside edge of the journal to the outside of the crank. It had been broken for some time -- one side was black from oil dirt -- before it blew. Block seems to be OK, but we got a short block just in case, and used that. Pistons, except #2, in the old block were fine, didn't discover that until we had bought new ones. The #2 main was spinning in the block, bearing was welded to the crank, and the motor ran!

Peter

mplafleur · #85 10-06-2001, 08:14 PM

I used some plastigage on the rod and mains with the original parts. The clearances on the mains are .004 and the rods are .003. Good for a Chevy.

I don't know what they are for the replacement bearings. I am hesitant to use the stretch bolts again.

The mains are not stretch. So I put a new bearing in and the clearance went to .003. Only down .001. Is that enough? Keep in mind that I did not replace the bearing on the opposite side.

#86 10-07-2001, 08:14 AM

Michael,

Sounds like you're still moving right along with your engine.

I have a Haynes manual that was written in England, so terminology is sometimes a problem.

It says "Radial play of crankshaft in bearings" is .030mm to .050mm. I believe that this is main bearing clearance tolerance.

It also says "Radial play of big end bearings on crankshaft" is .030mm to .060mm. I believe this is rod bearing clearance.

Since .1mm = .004inches, these "radial plays" are quite tight compared to the Chevy's I've built. .05mm(the max main bearing clearance) would be .002 inch.

I hate to say it, but it appears that this may be where your oil pressure was going. Good news is that you should be able to find a good crankshaft shop that could grind the crank and get everything tight again. Since it sounds like you now have the engine out, maybe this wouldn't be too much more trouble.

These are just some thoughts for you. I'm sure you'll want to consult an official MB manual for clearance spec's before taking such a step.

After rereading your successive posts, maybe by replacing the upper half of the main bearing, you will get your clearance where it needs to be on the mains. Remember, using plastigage will not allow you to check for a flat crank. But maybe you're close enough with new bearings. Keep checking and good luck.

Best of luck,

psfred · #87 10-07-2001, 08:18 PM

Michael:

Bearing oil clearance for the 617 (the latest I have handy) is 0.002" to 0.003". At 0.004" I'd expect oil pressure loss. If you come down 0.001" by putting in a new half, you may be OK, but you won't know until you put in both halfs.

Also, make sure the bearing shell is CLEAN, and the cap and recess are, also, or you can end up with NO clearance (bad, bad, bad!). I don't use shop cloths when putting an engine together, only the high quality blue towels -- they shed much less lint. Make sure the shells, caps, and recesses are oil free when using the plastigage, too!

You can check for flat spots on the crankpins with platigage, but you have to turn the crank 90 degrees between each check, a huge pain. Get a micrometer and have someone show you how to use it -- you will be good enough in a couple measurements to see if the cranpins are tapered or out of round, anyway.

Having the crank ground will require new, undersized bearing shells and balancing, in which case new rings as the pistons have to come out (they have to be on the crank to balance it.....)

As you don't plan to keep the car, if the crank is nice and shiny, with no obvious wear spots where the babbit on the bearing rides and no scratches, and you can get 0.003" or less clearance on all journals, you can get away with just new bearings. Any visible damage to the crank, and the new bearings will look like the old ones very quickly. Your call!

Peter

mplafleur · #88 10-07-2001, 10:14 PM

Peter,

Thanks. Again, I don't want to take the pistons out.

The crank is shiny, no scratches, and no wear spots. I don't plan on keeping the car for more than another year. Replacing 1/2 did get it to within spec.

I'll take the whole thing out and put both halves in and see what I get.

I just bought an engine stand and got the thing off the floor. Now it almost gives the impression that I know what I'm doing. But it's all you guys that get the credit!

Just for background: I'm an electrical engineer working for Visteon. I test powertrain control modules that we sell to Ford, Jaguar, Astin Martin, etc. so I know a bit about the control side of the engine. I grew up on a farm where my dad did all our own wrenching. He was a mechanical engineer for Chrysler (Mercedes now). I don't like to pay anyone to do something that I can do. I'm 40 and going back to college for my masters in Electronics and Computer Control Systems (whatever that means). I just learned to fly last year and I'm a year or so away from my black belt in Koei-kan.

If I can help anyone out with anything, I'm more than glad to do so.

psfred · #89 10-07-2001, 10:36 PM

Michael:

You are really a true he-man if you are wrestling that block around on the floor! An engine stand is the ONLY way to go! Unless MB really lightened them up, they weigh almost as much as an american V8 bigblock!

If the crank is unmarked, and that includes no visible tracks from the bearings, put new ones in and go. Not the purist approach, but if you aren't going to drive it forever, let the next owner worry about it (My brother says you need to have the rods reconditioned to, buy he never takes a motor apart without a complete rebuild!). The worst that will happen is that the oil pressure will drop again. MB nitrides the crank 0.030" deep, so it is hard to hurt them.

Check the clearances again with the new bearings, and if you are near 0.002" go for it.

Peter

#90 10-08-2001, 07:12 AM

Michael,

I'm glad you are getting help here, but you're the one working through everything. You get the credit for keeping another MB on the road.

I'm a doubleE myself and have done all sorts of control systems over the years for various different systems varying from oil production to automatic conveyor control. Doing engine management control would be a real kick for me.

Keep up the good work,

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