I have a 1991 190e 2.6. I've seen in a number of posts that it's relatively easy to resleeve the valve guides. What's the process? Particularly if there's a way to do it without removing the head. I seem to recall there's a way to do it by pressurizing the cylinders so the valves don't fall in.

Thanks

If you are replacing the valvestem seals, yes it can be done without removing the head.
You can not replace valveguides, without removing the head, as the valves have to come out.

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2007 C 230 Sport.

"Sleeving" integral machined cast iron valve guides such as those used on older engines with cast iron heads is a typical repair procedure, but aluminum heads always have separate valve guides, usually a bronze alloy, that are pressed into the valve guide bores with an interference fit.

Changing them is really quite easy for a properly equipped engine machine shop. The head is heated in an oven to about 400 degrees. Then the guides are tapped out and new guides are tapped in. The 400 degree temperature expands and softens the aluminum making it easy to remove the old and install the new guides.

IMO it's best to place the head back in the oven, turn off the heat, and let it slowly cool. This will minimize the chance of warpage.

New guides or sleeving old guides requires head removal and disassembly. Also, since the new guides may be slightly off center from the old, reseating the valves is mandatory, and if the valve stems are worn more that about half a thou or if the seat margins are thin they should be replaced. On an engine with fairly high mileage the inlet valves can often be reused, but exhaust valves are usually more worn and require replacement.

Duke

Duke:

What engine has cast in place valve guides?

Even Chevrolet used pressed in valve guides on their old (pre 1962) six with valve seats ground directly into the cast iron head!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

My '63 Corvette (I'm the original owner.) has - or I should say "had" because they have been rebuilt with sleeves - integral valve guides as do all cast iron head small and big block Chevrolet V-8s and all other domestic engines with iron heads. As far as I know all the I-6 Chevy engines also had OE integral iron valve guides, but it would be rare to find one today that hasn't had some kind of valve guide rebuild done.

Integral cast iron valve guides give reasonable wear and are obviously cheap, because it's just a machining operation on the transfer line, but they are more expensive to rebuild. Aluminum heads with bronze guides are more expensive to build by the OE, but they are probably cheaper to rebuild because very little labor is required to replace them. New bronze guides are no more expensive than sleeve kits for iron heads, but iron heads must be machined oversize first and then the repair kit installed and reamed.

Once an aluminum head comes out of the oven it only takes a couple of minutes to swap the guides and another couple of minutes to ream them after the head has cooled to room temperature.

A couple of years ago I watched the machinist replace the valve guides on my Cosworth Vega cylinder head. (He also owns a CV and had just rebuilt his head.) It was a piece of cake. The guy is a real pro. There's nothing like having the proper tools and lots of experience. A good part of his work is Merc and BMW heads, so if my 2.6 head ever need to be rebuilt, I know who's going to do it.

Duke

Duke:

You can tell we did mostly Ford and imports in our home garage....

Replacing guides if you have the press and pilots is easy. No way to do it safely without, although I have seen and heard of guides being replaced in situ when one came adrift in the head. Scary, as you can bugger the head if you screw up, and it's rather likely the valve won't seat properly. Better than with the guide floating around, though!

MB guides almost never need to be reamed -- factory clearance spec is 0.00 to 0.01mm -- essentially, if you can get an oiled valve stem in it by hand, it's fine. Any more clearance and they suck oil down the valve guides.

Haven't checked on the aluminum heads, but on the deisels with cast iron heads, the intake guide is steel and the exhaust guide is bronze.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

For my Cosworth head rebuild I measured all the valves (just a couple of tenths wear on the inlets, about five tenths on the exhausts) and selected sixteen guides from a big stock to achieve my target clearance range. Bob, the machinist, said the guides would need to to be reamed, but I wanted to trial fit the valves, first. I had already meaured and trial fit the loose guides to the valves and the fit was perfect.

Once installed in the head the valves didn't fit.
It appears that when everything cools down the interference fit creates a few tenths distortion here and a few there - enough to create some minor interference. One pass with a 9/32" reamer and the valves fit perfect!

The guide clearance spec you listed of 00-.01 mm works out to 0 to .0004". This doesn't sound right. Chevrolet's production spec for the CV guide clearance is .001" to .0027" with a service limit of high limit production plus .001". Their spec for cast iron heads with integral guides is about the same. My target range was .001"-.0015".

With modern viton seals replacing the junky OE nitrile seals oil consumption went from a quart every 200 to a quart maybe every 5000. I drive so few miles between annual oil changes I can hardly measure it. The old guides were SEVERELY worn. Don't know why as the design should not yield much side force, but the car does have over 4000 miles (out of about 74K total) of race track hot laps.
No measureable wear on the aluminum/silicon bores, but the guides were shot. As long as the bores don't score, they seem to last forever. Mercedes licensed the Reynolds/GM cylinder bore technology (as did Porsche and BMW) used on the Vega 140 and Cosworth Vega engines and developed it from there.

Duke

Duke:

No, that is the spec. Essentially no clearance cold. If the valve spring will close the valve on assembly, it's fine. No way the VALVE is going to wear, after all! Way too hard.

The exhausts on diesels are sodium filled, too -- hence the bronze guides -- steel doesn't expand enough and they wear oversize.

A valve guide with 0.0027" clearance on an MB diesel could get replaced as out of spec. When checking, if you can feel movement sideways with the valve off the seat, the guide is shot. Very much less clearance than American practice, and if you ream them to that clearance, the engines almost always sucks oil down the guides. I know, my brother's engine had been rebuilt (badly, as some crap from the oil filter housing gasket -- excess silicone sealant, we think) plugged the oil passage to the #2 crank main bearing and caused the crank to fracture) -- not many miles on it, I don't believe, and oil ran down the valves. Very little play in the guides (steel on the exhausts), but man was there oil in the combustion chamber!

GM had fits with that Vega engine. Weird design in the first place (cast iron head on an aluminum block!), and they died at an amazing rate -- I know a number of people who got the engine replaced UNDER WARRENTY (12 month/12,000 miles in those days) due to oil consumption. The casting was a very poor design, so that piston clearance vanished on slight overheating (I think the problem was mainly no or too small a coolant passage between pairs of cylinders, but no longer remember). Get hot sitting in traffic, loose a bit of coolant, and the cylinder walls got eaten up. Certainly, the first two years or so of production all died by 30,000 miles or so. If you got a good one, they ran fine, but that was a crapshoot.

GM eventually fixed the problem, as I'm sure you noticed in the Cosworth, but abandoned the technology about the same time. Rover bought the Buick V8 version and still make it.

Typical GM -- always going rotten just about the time it should be getting ripe. There is a reason GM didn't make money building cars from about 1976 to somewhere in the 90s, if they indeed do.

Kinda silly to just give up, since the siliconized blocks are fantastic if done right.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I'll say it again-

Mercedes NEVER put bronze exhaust guides in diesel engines. They are a steel/iron alloy. Period! Some machinist's opinion that aftermarket bronze guides are superior to the factory stuff. I've always had the best luck with internal engine parts from the factory! Don't get me started on Lemforder!!!

You can do valve seals or if the car has sufficent mileage- a valve job. I would use factory parts here- gasket, and valve guides. I've seen bad aftermarket parts where the ID and OD were not concentric. Not worth the problems over saving 5-10 bucks total.

Gasket is similarly an issue. In addition the factory has a great warrentee policy, so it's definately worth it.

For a engine example with cast in guides, valve rotators and sodium filled exhaust guides: GMC V6 engines- 305, 351, 401, 478 gas and diesels(351d?) from 1960-1979.


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

The problem with the early Vega blocks was the etching process. It was inconsistent. The process was supposed to be etch away about half of thou of aluminum, leaving a pure silicon wear surface, but it was inconsistent - some areas weren't etched and some were over etched. If there was surface aluminum the rings would tear it off and score the cylinders. Overheating exacerbated the problem. On my '72 Vega GT a piston/wall scored and broke a piston skirt on a cross country trip at about 40K miles when it was two years old. I was close enough to have a friend flat tow me home. I bought a new fitted block and rebuilt the engine. Two years later I got my parts expense refunded under GM's "secret warranty" that got them in trouble with the FTC.

The Buick 215 had iron sleeves, so was a totally different design.

Porsche was the first to pick up the GM/Reynolds 390 alloy block for the 928. They improved on the process that GM had mostly perfected, but the bad publicity from the early Vegas caused GM to abandon the technology. Mercedes picked up the technology in the early eithies and BMW followed not long after.

Interestingly, the current Mercedes V6 and V8 engines use cast in ALUMINUM liners in a cast aluminum block. All I can figure is that they decided the block would be better with a different alloy than what is best for the bore wear surface, and I assume it's still Reynolds 390 or something similar.

Duke

Might come in handy for visualization...Best of luck. It is not too bad of a job.
Take the opportunity to check for cam and rocker wear if you have an 89 or earlier model before the material changeover.
http://w124-zone.com/?p=122

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