Valve seal questions... old 240D - PeachParts Mercedes-Benz Forum

#1 01-31-2004, 11:32 AM

Been searching but need more info, like how to establish valve guide wear to see if they should be changed also, installation tips, difficulty level for a mediocre mechanic, etc. Smoking heavily pulling out from stops and when letting off the fuel and slowing from say 75 to 60 in traffic, even when warmed up.

Fisherman · #2 01-31-2004, 12:15 PM

I just did the top end on my 75 240 and I can tell you that they can handle a fair amount of valve wiggle without causing any major problems.

Does the car smoke a lot under hard acceleration? Like a cloud behind you?

Does it look like oil smoke or diesel smoke, grey or black?

valve guides and seals will help but when running if the seals are leaking then you probably won't see that much smoke just from that.

resolution on mine was to adjust the max fuel delivery. I could not turn on my ac at a stop because the guy behind me would get fogged with smoke.

psfred · #3 01-31-2004, 03:09 PM

Valve guide seal change isn't bad on the 615/616, although a set of good valve adjustment wrenches won't hurt.

Basically, you set the piston at TDC on the affected cyinder, remove the rocker arms, then remove the adjusting and lock nuts, lift them and the valve spring off, pry the old seals off and press new ones down, using the little "hat" supplied with the seals to prevent cutting the sealing lip off on the threads.

YOu can check valve guide wear at the same time -- push the valve down off the seat and see it you can move the valve stem sideways. If you can, you need new guides. Engine will run OK, but you will have excessive blowby and oil consumption with bad guides, to the tune of a quart in 500 mile or so.

Note that on these cars some vac pumps have a vent to the intake manifold, and if you have a worn pump or busted rubber diaphram (only the older ones, pre 76, I think), you can pump large quantities of oil down the intake through the vac pump. Bad shutoff diaphram can cause problems to (W115 chassis).

Blue smoke at idle, or when you take off after extended (>1 min) or on deceleration is diganostic for valve guides or seals UNLESS you have a diaphram vac pump -- check that first. If you have oil in the line from the vac pump to the

Peter

#4 01-31-2004, 04:01 PM

Thanks for the quick responses! Definately smokes on acceleration, not black at all, greyish and lingering. Also on the deceleration from high speed using engine braking, sound like the seals Peter? One doesn't need to pull the cam towers to get the rocker arms out? And how do I decide which cylinders could need them, or is it a good bet on this old engine that they all need it? No oil in the vac outlet BTW, pulled the banjo at the intake. On the seals themselves I know they are color coded for intake/exhaust, but saw something about different lenghts for the extended valve lift in later engines?

psfred · #5 02-01-2004, 03:21 PM

The "rocker arms" (really cam followers) are on two tower mounts on the passenger side, just unbolt and slide out. At some point in engine rotation (and I don't remember it), you can remove at least one set with no tension, possibly both. May have to rotate engine to remove the second set.

Replacement guide seals are usually one size, although you might find some sets with small and large. Small goes on the intake, large on the exhaust. If you can't tell them apart by eye, it doesn't matter which one you use.

If one guide is worn, they all will be. If you decide to do a valve job, I recommend replacing the valves, as the exhausts will probably be worn to very close to the machining limit. They are a bit pricey ($45 each a few years back) because they are sodium filled. Using old ones is a false economy, as they will wear VERY quickly if the edges of the seat are too thin.

Install ONLY bronze exhaust guides, don't fall for the story that they are brass and will wear out too fast and substitute steel -- they are bronze (much harder than steel) and expand more with heat, both requirements for the sodium filled valves -- the stem gets MUCH hotter that solid stem valves, and this is by design -- the heat is transferred from the tulip to the head to make the valve last. Steel will wear oversized badly in about 10,000 miles, no matter what oil you use.

Clearance on new guides is essentially zero -- if you can get the oiled valve stem into the guide and push the valve closed, the clearance is fine. Many shops want to ream them to get several thousandsths clearance -- if they do, you have wornout oversize guides when you install the head, and the oil consumption will be just as bad as before.

You also need to check the injection timing and chain stretch -- late timing will result in grey smoke on accelerations, lots of injector knock, and low power. Black smoke hot at speed and load, too.

Peter

samiam4 · #6 02-02-2004, 01:04 PM

Peter,

I agree with you on 99%- BUT the factory replacment guides are STEEL!!! I've seen bad aftermarket parts where the hole was not concentric with the OD. But, in general shops want to ream or hone to fit-and their reference is a Chevy 350!
Why are you saying they are Bronze ??????? They were never brass on a diesel. I think you might be confusing them with a 300E???

When I did mine- I made a go-nogo gauge per the manual. Then it was easy to check of the new guides.

Generally, in my cases I've noticed hard cold weather starting in the engines needing valve/seat/guide work. They test 400 psi warm, but still start hard. Check around on valve prices... they can vary greatly. I put new intakes in mine because I found a supplier whom sold me a set for $5/valve. All my exhausts fell within spec. Valve in set dimension was within spec too=)

Michael

psfred · #7 02-02-2004, 08:58 PM

No, Michael, I'm sure the factory replacements for the 617 are BRONZE, not steel or brass. No such thing as brass valve guides in MB diesels -- maybe on a gas engine circa 1910, but certainly NOT on a diesel. The ones we put in my brother's car were, anyway.

Bronze is a copper/tin base alloy, brass is copper/zinc (or the other way around). Brass is a very ductile, work hardening fairly soft material. Bronze is a somewhat less ductile, very hard material with a somewhat abrasive character that work hardens like crazy (you can sharpen a bronze sword just by hammering out the edge, no grinding needed), somewhat harder than most unhardened steel alloys. It's used in a number of applications, but the reason for it's presence in MB diesel exhaust guides is it's hardness and thermal expansion coefficient. Steel won't expand enough for sodium filled guides -- if they fit tight at room temp, the valve stem will "ream" them oversized pretty fast.

You're right, loose valve guides can make a diesel hard to start -- the valve won't seat properly at low speed. They will also wear a "slot" around the seating surface from rocking back and forth slightly. My brother's 617 had vavles like this -- terrible condition.

The replacement short block was worse (he broke the crank in his) -- loose pistons, something like 0.020" ring ridge, crank the first even SAE dimension UNDER the first regrind, bearings pounded out (duh!).

Peter

samiam4 · #8 02-04-2004, 01:13 PM

Peter-

I Purchased factory guides for my 617 engine and they were steel- definately not bronze!

Your whole rational on expansion rates is flawed. The guide is press fit into the steel head. The guide will not expand freely with a higher expansion rate. It is limited by the steel... If you want I can send you an excel spreadsheet that will compute max, mins interferace fit, min/max removal force etc etc.. It's designed for pressed in pushings or I can send you a mathcad which handles thick walled cylinders.

I design to this stuff all the time. Actually, I can think of lots of cars with steel guides-I can name many many beyond 1910!!! Granted that most current aluminum head cars use bronze.

All this is a moot point. If you use the factory guides and factory valves with factory clearances- it will work the way they designed it. IF you chane one part or tolerances, then we'll see if you are better than the german design heritage.

Michael

psfred · #9 02-04-2004, 02:24 PM

Michael:

Bronze has a higher expansion coefficent that steel, so the hole in the guide grows faster -- remember, the exhaust valve stem is sodium filled and MUCH hotter than a solid steel valve -- the purpose is to transfer the heat to the head and keep the tulip much cooler at high load. This has nothing to do with insertion pressure, size of the hole in the head, or anything else. Most of the guide, and the portion that actually seals and controls the location of the valve stem, is outside the head. The point is to keep the guide clearance positive under heavy load, otherwise the guide will wear (the valve stem is MUCH harder). Intake guides are steel.

TAke a look at the exhaust valve guides on FastLane -- sure look like bronze to me!

I believe BRASS (not bronze) guides were used in some early engines for machining purposes, but certainly not for long -- wears too fast. All the early ones had poured Babbitt bearings, too (up to the 1950s, anyway).

Peter

McRoth · #10 02-04-2004, 04:17 PM

One quidk question for you guys: Do you have to remove the cam & therefore the timing chain & all, to replace the valve seals and/or guides? I need to replace mine soon & I keep putting it off because I really don't want to mess with the timing chain.

Thanks!

leathermang · #11 02-04-2004, 04:45 PM

Peter, is there a possibility that with the bronze wanting to expand and kept from expanding by the strength of the steel.... that its expansion would be towards the hole... making it smaller ?

McRoth, the seals do not require taking the cam off... but the guides require taking the head off the engine.

samiam4 · #12 02-04-2004, 09:48 PM

PsFred,

I'm not aware of ppl using brass. I know that there have been several different alloys used. Some wear much better than others. I know Porsche tried some alloys for "better heat transfer" but they died an early death. I'm not remembering if it was 2.2? 2.4? or 2.7 liter engines.

I believe it was Thompson (the "T" in TRW) whom invented replaceable shell crankshaft bearings. I don't know the patent date, but it was either before or during WWII. I know the germans paid fees for some of the design- aka I've been told. My father actually sat next to him on a flight shortly after he had retired from TRW.

So that's a babbit crankshaft bearing.

Humm- how to be more convincing?? I installed the guides in my head. Ie I drilled out the old ones until they were shell thin(loses press fit) and then pressed the new ones in!@ WHEN I DRILLED them, the shavings were definately steel, not bronze.

the p/n's are 616 053 03 29 and 30 for exhaust.

I do not care what fastlane shows in their picture-they are aftermarket parts. I agree the fastlane picture is a yellow colored metal and heck.. from the pci I'd say it's brass, not bronze .
Go back to their website and look at OM603 guides and notice that ONLY the oversized INTAKE is bronze. Doesn't go with what you are saying in the least.. just say aftermarket ppl do what they want=)

I installed guides purchased at a mercedes dealership and they were STEEL. But maybe things have changed in 2 years

The fast lane price is about $6 and the current dealership wholesale(attainable mailorder) is $7.50. So, I guess you saved $7 on a 5 cylinder? Is that cost effective given how long the orginal steel guide lasted?

To be a devil's advocate to your thinking: The bronze must expand faster so no siezure will occure(excess wear)?? Well, every mercedes diesel and for many years gas engines came with Aluminum pistons and cast iron blocks with cast-in sleeves( or replaceable)......"The point is to keep the guide clearance positive under heavy load, otherwise the guide will wear"

So my point: Doesn't matter on expansion rates- it matters on how it was designed.

How can you say the bronze ones are "harder than steel". All bronze alloys are tested on the Rockwell "B" hardness scale while almost all steels exceed the "B" scale and are done with a "C" scale. Granted, I have no specific idea on what alloy Mercedes used...

Oh on a different note: From my experience, I had a vehicle where the valve guide to stem clearance was a little large and put the Isuzu truck together. The valves ends pitted! Not enough heat transfer due to exceess clearance=0)

Michael

:p

psfred · #13 02-04-2004, 10:44 PM

Hardnes depends on the exact composition of the material and the treatment thereof.

Most of the valve guide is outside the head -- sticks up what, an inch? The top part is what is going to hold the valve straight, it doesn't matter what the bottom is -- in fact, the guides on the Volvo are tapered. You measure guide wear on that engine by lifting the valve a specified amount check the distance the valve will more sideways.

Brass and bronze look quite a bit alike, although bronze isn't as gold colored.

Steel guides are available, but I've been warned not to use them.

Bearings before steel shell bearings plated with babbit were physically cast into the block or rod, then machined (often by hand with a scraper) to fit. The bearing material (babbit) is the same, just in a big chunk when cast in place instead of a thin layer on a steel backing.

So long as the babbit is thick enough, the steel shell system is much superior -- babbit is so soft a precision fit cannot be maintanted, even with the harder versions. Some shells only have 5-10 thousandths of babbit -- MB bearings look like there is a couple mm of babbit there.

Babbit (named after the inventor) is an alloy of lead, copper, tin, and zinc in various amounts, depending on the use and desired charactersitics. One of the things you have to watch when pouring them is that you don't get the molten metal too hot -- the lead vaporizes. Not only seriously hazardous to the health, but it changes the babbit mix considerably, and the lead is the "dry start" lubricant.

Peter

Lycoming-8 · #14 02-04-2004, 11:49 PM

Relative to the Babbit crankshaft bearing part of the thread.... All '29 to '31 Model 'A' Fords, and most of the US manufactured cars of the era had poured babbit rods and main bearings. Most of the stock 'A' engines are still being restored using that same process. Once poured the mains are line bored for the finished crank journal size.