The cylinders must be bored and honed to size (maybe a bit under, I'm not sure), and then the aluminum is etched out of the bore with acid on leather hones to expose the porous silicon. There was a machine shop here that did one for my friend with the Mercedes shop, but they are out of business.

It's only machine work, although a bit different than most. The finish on the bores isn't the same as the factory one, since I seem to remember that they are etched differently, but it works.

Not all of us are wealthy, Peter, nor necessarily worried about whether we can recover the money we spend on our cars by selling it next week (or, actually, are most of us in the business of repairing cars for a living!). I would presonally prefer to rebuild an engine I know than buy a used one of dubious quality, and I believe a new short block under these conditions is somewhat unrealistic.

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!

Having spent a lot of time investigating and developing fixes for Chevy Vega engines, owning 3- 500 series cars, etc.

Wear surface on both is silicon.

Vega failures all due to coolant leakage through cheap fiber head gasket (differential expansion between alloy block and CI head tore it up). Glycol displaced oil off the cylinder wall leading to severe scuffing, coolant loss, overheating, meltdown. Engine had been 'bullet proof' as developed by Olds Toranado Div. with alloy head and jacketed head gasket.

Proper method of field repair/clean up of al-si cylinders: final step is lapping with the silicon etch paste on felt pads. The paste etches the aluminum out leaving a pure silicon surface exposed.

Conventional high precision boring/honing is done(with torque plates attached to the block to preload the bores properly) to desired diameter -- before final etch process.

Use OEM or similar cast pistons for proper surface metallurgy to ensure long life. Forged aluminum pistons will work OK if fit to 0.004" instead of OEM 0.001".They will rattle on start-up but quiet down when heated up. Best to polish dry moly into the forged aluminum piston skirts for scuff resistance and use assembly lube on the bores.

After A LOT of research, here is a condensed version of my findings...
The paragraph below is from a good article re honing in general from the following website. http://www.babcox.com/editorial/ar/ar90058.htm

"Aluminum honing
Though we're not yet seeing many all-aluminum engines in the aftermarket, a growing number of engines with all-aluminum blocks (no liners) are being built by the OEMs. Tim Meara of Sunnen says both Mercedes and Porsche have aluminum blocks that use an alloy similar to that used by Chevrolet in the Vega engine years ago. The 390 alloy has a high silicone content that provides wear resistance.

Honing this type of alloy requires a four-step process. First the bores are honed with a #220 vitrified abrasive, followed by #400 stones and finally #600 stones. The cylinders are then finished by lapping with cork and a special lapping compound that removes just enough aluminum to expose the harder silicon particles."


Subject: [racing] Re: 944 1st overbore source, 12/6/02
From: George Roffe geo3@earthlink.net

However, looking at the FSM it says:
"If it is necessary to machine cylinder bores, they can be restored with a
SUNNEN CK - 10/CV - 616 cylinder repairing machine for installation of
oversize pistons."

The final process listed in the FSM says:
"Lapping with Sunnen silicium mixture."

This mixture even has a P/N: AN-30

Folks would have you believe that it takes some German wizard and a pinch of eye of newt to prepare the bores. I've read so many different and conflicting things about bore prep for these engines it isn't funny. The FSM makes it seem like it's no big deal, just follow the procedures they outline. Am I missing something?

Re: honing 944 cylinder walls, 10/30/01
From: Blaszak Precision mblaszak@kos.net

Well JD, partly right and partly wrong. Yes the basic silicon is part of the cylinder/block material but after that you are misguided. Take some time and read the PORSCHE Workshop manual. You will find on pages 13-53 to 13-57 the process and materials explained in great detail.

The process goes like this:

1) Rough turn the cylinder to desired size (boring)
2) Dress the cylinder to 0.02mm of finished desired size
3) Polish cylinder to finished desired size (silicon is now exposed in the cylinder walls) And Voila...
4) Lapping with Sunned silicium mixture to treat cylinder walls

Yes you polish or lap the cylinders to expose the silicon in the block material, but the final step consists of cleaning out the bores and applying a thin coating of silicium paste. You now use a hone that has felt pads on it and no abrasives, and hone the silicium material into the walls of the cylinder. It takes from 1-2 minutes per cylinder to complete.

Please note, that is not a spelling error. The mixture is a Silicium material and not a silicon or silicone. I'm not going to argue these points. For those interested in the procedure more, please refer to the shop manuals as it is completely outlined there in the pages that I referred to in Manual 1A 8 Valve Engines.

Hopefully this FINALLY clears up any confusion on the subject.

Subject: Re: Silicium coating in cylinders, 10/30/01
From: "JD Binford" jdbinford@home.com

Contrary to Mr. Blaszak's claim above....please refer to the two sites below which discuss silicium carbide. http://www.agp-abrasifs.com/index_uk.html and http://www.lapport.de/e/spez_1.htm and the reason is......."Silicium" is French for "Silicon"....so where ever you see the word Silicium in your Porsche repair manual, just subsitute the word Silicon................NOW you know the rest of the story;-))

__________________
"There are a number of mechanical devices which increase sexual arousal, particularly in women.
Chief among these is the Mercedes-Benz 450SL convertible." --P.J. O'Rourke

French!!??!! In a Porche manual?? Ewwww.

__________________
Norm in NJ
Next oil change at 230,000miles

There were a number of problems with the Vega engine, none of which had much to do with the silicon/aluminum process.

First, it had a cast iron head (huh?????) because Chevy couldn't get an aluminum one to stay together soon enough for production (and production was on an "emergency" basis becuase the Wankel rotary didn't work). Differential expansion was a serious problem, exacerbated by the cheap head gasket.

Second, the block design itself was defective -- no coolant between the cylinders, so if it got hot, the bore went serious out of round because the walls grew between the cylinders too much. Instant bore/cylinder abrasion, followed by copious oil burning. Just sitting it traffic was enough, and even a small amount of coolant loss would do the engine in. This was fixed after the first year of production, I think, but re-designing the block to fix the "shrinking bore" problem. Buick (who pioneered aluminum blocks in the early 60s) didn't have this problem due ot the steel sleeves (dry ones) they used. When the steel sleeve was removed, the bores changed shape.

Third, the head gasket problem, compounded by using a cast iron head. Coolant leakage into the cylinder is bad news, as noted above.

Last, even if the engine survived -- and the later ones did, forever -- the body was junk. Ed Cole's reply to people who wanted inexpensive cars (he called them "cheap") -- sloppily designed, lousy materials, poorly built. I suspose he thought he was "teaching them a lesson" by building a travesty of a car and telling people "but you wanted a cheap car!". Deliberate misunderstanding -- I believe he was the guy who took the camber limiter off the Corvair to save $1.50 per car and killed several thousand people, too.

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!

You guys should stick to Mercedes when it comes to history. Having owned a '72 Vega GT that I sold to buy a Cosworth Vega (and still own), a former GM engineer, and a researcher/historian who has published a quarter million words on the history and technology of the Cosworth Vega here's the deal:

The rotary engine development project was after the original Vega development and was intended to power the H-special coupe derivatives of the Vega platform, which turned out to be the Monza. The rotary project was suspended at the eleventh hour in 1974 due to insoluble emissions and fuel economy issues, so the H-specials got the Vega four, Buick V-6, and Chevrolet small block V-8s. The biggest fallout from this was that the RH small block motor mount had to be disconnected and the engine lifted several inches to change the #7 spark plug.

There was a planned L-10 engine option with a SOHC 8-valve semi-hemi aluminum head (much like the M103 head) on the Vega block that was designed and built, but suspended when Chevrolet finalized the development contract with Cosworth for a DFV-architecture DOHC 16-valve head in 1970.

The cylinder wall scoring problem had multiple causes - inconsistent etching, head gasket leaks, and overheating were all factors. The causes were found and cured as time passed. Better etching, better gaskets, and coolant slots in the top quarter inch of the block's siamized bores all contributed to vastly improved durabililty by 1976. GM included a 5yr/50K powertrain warranty beginning in '76, which was the longest OE warranty in the industry at the time, but the damage to the car's reputation was done and sale continued to fall.

There were some poor decisions early on to save a little money like deletion fo the originanlly planned front plastic inner fender liners, which were later added along with inside zinc coated, "zincrometal" front fender panels. GM also found that they were using reversed polarity for the Elpo primer process for the first couple of years, which compromised corrosion resistance.

Keep in mind that the Vega was meant to be a low priced car to compete with inexpensive imports that were built with much cheaper labor, so GM either had to innovate to get more labor productivity or reduce build labor or material content. Few seem to remember that most cars of that era were rust buckets. Early Vegas were worse than average, but when was the last time you saw an Audi 100LS. Its engine rivaled the Vega for roughness and noise. They rusted almost as fast. The inboard front brakes were lucky to go 12K miles, and they cost twice as much!

Duke

About the Cosworth Vega -

This factory oversight is pretty shocking, because I recall that these engines were practically handmade and that GM lost money on every one that they sold, even installed in a POS like a Vega.

GM had some serious managment problems in the 60s and 70s, some of which they appear to never have cured (my brother quit them for this reason -- idiots making life miserable for the actual engineers), and the Vega was a typical result.

The body design, also typical of GM in those days, was simply inadequate, corrosion problems aside. Much too light, not enough strength (and when the stuffed a V8 in there, worse, almost as bad and the "crosseyed" 66 Mustang!), compounded by sloppy manufacture. NOTHING GM made in that era was well designed or well built except Buicks -- for some reason, Buick could make decent cars (less warrenty problems, longer life, etc) even if the basic design was bad. Who knows why...

Also typical was the fact that GM didn't do proper testing of the design (I do know that the cast iron head wasn't the original specification) and rushed the whole car into production. The engine eventually turned out to be a pretty reliable one -- I've even seen a couple still running -- and the Cosworth was a gem. GM did lose a bundle on the Vega and engine, and typically, again, dropped the whole thing, engine included, just about the time the engineers got it working properly. This is not an engineering problem, it's much more a problem of non-engineering management screwing things up (like deciding on a cast iron head at the last moment, or cheapening something, or changing interior design details weeks before production starts -- Ed Cole was famous for that).

All around, a waste, as the engine, when finally working, was rather nice. Funny firing order (hence the vibration, as I remember), but could have had a long production run.

They replaced it with the "Iron Duke" pushrod engine that at least had longevity to recommend it -- this was the "backup" design that Cole rejected in favor of the aluminum engine.

Everyone had corrosion problems in those days, too -- Ford replaced many rear fenders on station wagons under "secret warrenty" programs as they rusted away terribly, often in a couple years. I'm not sure what he root cause was, probably the production methods for making the sheet steel. MB's of that vintage, particularly the W116, have horrible corrosion problems.

Thankfully, Reynolds didn't give up on the silicon impregnaged block program.

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!

So psfred (and others),
would you be as kind enough as to detail the procedure as given in the mercedes service manual?

__________________
"There are a number of mechanical devices which increase sexual arousal, particularly in women.
Chief among these is the Mercedes-Benz 450SL convertible." --P.J. O'Rourke

No, the Vega and Cosworth Vega had the conventional 1-3-4-2 four cylinder firing order, and the Iron Duke wasn't any smoother than the 140 Vega engine. The roughness is due to the large displacement long/stroke architecture and simple rubber mounts. Those were BIG four cylinder engines for that era. Better engine mounting and the twin counterotating shafts that balance the four-cylinder's second order unbalanced vertical shaking force have considerably improved modern fours, but they will never be as smooth as a good I-6. That's why I rejected a 190E 2.3 16V in favor of the 2.6, even though "on paper" the 16V had better performance.

Duke

Gawd, the "Iron Puke". What an overweight, under powered gas hog. That was a resurrection of the 1963 Chevy II engine. Nobody wanted it then, and we found out why when it came back, not in the Vega, but in the Pontiac Astre. A Vega with Pontiac badges.

The real travesty was putting that pig of an engine in the Fiero. I had one in '83. I know the first "year" for them was '84, but mine rolled off the assembly line in November '83 and was my Christmas present that year. With several other 4-cyl engines to choose from, they picked that pig. Blecch!. Several recalls that didn't fix fundamental problems. Neat car, dog engine and the six wasn't much better.


Peter, I can't help but wonder why you give Buick such credit when they're the same thing as Olds & Pontiac. IIRC, the plants that made them were called BOP plants for Buick, Olds, Pontiac. Trim & stickers were the only significant differences among them.

__________________
Norm in NJ
Next oil change at 230,000miles

Follow the procedures as listed exactly as in the manual; it's not complicated, just exacting -- American machine shops get these two things mixed up regularly.

I have done several engines with not a problem, but like I said, it is exacting; you can do it with around $1200 in equipment, and use a Lisle pro shop hone w/ several sets of stones (you will be constantly re-sizing these stones depending on cylinder taper) and a heavy-duty variable-speed low RPM drill (I use Bosch). The boring process is very precise, and extremely slow with this process, and there is indeed an art to it, but I have yet to ruin a cylinder (and thus an engine) -- although the standard accepted repair method now includes an aluminum silicate insert you can install and bore if you ruin your cylinder(s).

These specs are units American machine shops do not even measure for the most part-- mainly because a great majority of domestic engines are nowhere near this precise. You will need a bore gauge that measures down to 1 micron, keep the boring steps within 10 microns, limit top-to-bottom taper to 5 microns max, and keep piston-to-bore clearance ~13-18 mics.

Just about as important is the block-to-cylinder head thread inserts -- I like Timeserts (as opposed to Helicoil), because they hold the thread profile better (they are one-piece) instead of potentially deforming and pushing out the cylinder walls. You can pre-load the cylinder walls by making a steel plate w/ a hole in it slightly larger than the cylinder diameter and torquing it down as you bore each hole. The #'s on the pistons and above each cylinder (w/ head removed) correspond to sizes, and they were used by Mercedes to fit pistons to the appropriate bore when block was final-honed and measured (most of this info is in the book; just read it thoroughly and have a blast -- you can order the liners through Mercedes if you need them). You can also reuse a larger piston on a smaller bore by using the last 2-3 engine boring steps as listed in the manual, depending on the size difference, and you'll definitely want to re-balance the crankshaft assembly. Anyway, when I can break free again, I will try to explain in greater detail those boring questions you probably have.

__________________
Don't ask me, I'm a shop-owner by default

Benzrepair... What can I say, thank you oh so very much. Excellent info there. There is one niggling problem though. I DO NOT own a copy of the mercedes engine repair manual and I am therefore unaware of the procedures you speak of. I live abroad, and ordering it would take longer than I can/am willing to wait. So if you could please outline the necessary procedures, or scan the page in question, you would be doing me a world of good
Thanks again

__________________
"There are a number of mechanical devices which increase sexual arousal, particularly in women.
Chief among these is the Mercedes-Benz 450SL convertible." --P.J. O'Rourke

Keep in mind you cannot change the bore size without having a larger piston to fit it to -- make sure you have an oversized piston available, or a good used piston which is a larger size. I do not have the capacity to look that up for you right now. If I get some extra time, I'll locate it for you (it is like 12 pages long, just for the boring process...).

__________________
Don't ask me, I'm a shop-owner by default

Thank you Benzrepair,
As for oversized pistons, I don't see why one couldn't use custom JE/Ross/etc units as long as the max overbore doesn't exceed 0.5mm... The stock pistons have a pretty disappointing design, with 4 cutouts per cylinder instead of 2, would have thought Mercedes would be more meticulous than that

__________________
"There are a number of mechanical devices which increase sexual arousal, particularly in women.
Chief among these is the Mercedes-Benz 450SL convertible." --P.J. O'Rourke