Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: blue230sl on November 20, 2007, 16:55:36
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have tried to search for threads but my pc keeps timing out - so questions are:
what functions do the bearings perform;
what is the difference between 3 vs 7?
john
64 230sl
89 190e 2.6
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The bearings support the crankshaft. In essence, by spacing 7 bearings over the same span as 3, it's much stronger. Think of how easily a stick supported on both ends will bend. Now add a third support in the center, it takes a lot more force to bend it.
Democracy is two wolves and a lamb voting on what to have for lunch...
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thanks...wonder why they went from 3 to 7 and not 4 or 5...
john
64 230sl
89 190e 2.6
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Because of the spacing of the cylinders. I believe the 230 actually have four bearings. Two on the ends, one between cylinders 2 & 3, and one between cylinders 4 & 5. That gives you two pins betwen each main. When the displacement was bumped up, more support was required so they went to 1 cylinder between each set of mains.
Democracy is two wolves and a lamb voting on what to have for lunch...
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So in real historical evidence, have the 7-bearing engines lasted longer than the 4-bearing engines?
Craig
'70 280SL Euro, Manual, Leather
Silver/Black
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I'm not sure about historical data.
From a design perspective, the 4 bearing design is going to limit the amount of load the crankshaft can carry. So if you bore out and stroke a 4 bearing block, essentially turn it into a 280, it probably won't last very long at all if you actually use the added performance. (Assuming you could find a crankshaft that would allow you to stroke it.) Chances of a broken crank or spun bearing would be high.
If kept within its design limits, there's no reason that a 4 bearing I-6 engine can't last indefinitely.
Democracy is two wolves and a lamb voting on what to have for lunch...
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quote:
Originally posted by CraigD
So in real historical evidence, have the 7-bearing engines lasted longer than the 4-bearing engines?
Craig
'70 280SL Euro, Manual, Leather
Silver/Black
My experience is that the lower end of the 4 main bearing engine is as durable as durable as the 7 main.
One reason could be that the same volume of oil from the pump is distributed to fewer bearings resulting in less drop of pressure.
I prefer the 230 engines because the larger cylinder bores of the 280s leave thinner block walls, resulting in higher internal tempratures, especialy in cylinders 4 and 5. In 280 motors that I have taken apart these two cylinders always show significantly more wear than the others.
When I rebuilt my 230 motor at 100,000 miles I was able to use the standard size bearings, there was almost no wear and the oil pressure never comes down off the 45psi mark even when driven hard on hot days.
This motor was not the original to the car, When I bought (the car) the block and head were in the trunk. the original motor was damaged by a wrist pin failure that made the original crank and block unuseable.
Al Lieffring
66 230SL
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Hello,
My guess;
All Mercedes engines of the era are very robust. Non of them were prone to failure because of their design. The seven main bearing crankshaft looks like it is easier to balance and potentially had more capability to handle future power requirements.
It is a heavier engine with more internal "drag" (friction) due to additional bearings.
Download Attachment: (http://images/icon_paperclip.gif) 231.JPG (http://www.sl113.org/forums/uploaded/ja17/20071121175128_231.JPG)
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I would suspect that higher rpms as found in more modern engines greatly increases internal stresses. As I recal as rpms double internal stress increases to the third power! (cubed)
Joe Alexander
Blacklick, Ohio
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Here is a pic of my M180 which is being rebuilt. (I need some 80.5 mm pistons, 1st oversize, cheap.)
(http://i19.photobucket.com/albums/b177/wb300se/MB_220S/DSC_0131.jpg)
Thanks
Warren Bain 1965 220S, 1989 300SE, 1989 420SEL, 2002 Ford Crown Vic Police Interceptor
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Inline sixes balance naturally regardless of the number of bearings.
There is no easy method for calculating bulkhead stresses in cylinder blocks. Good thing, if it was easy I wouldn't be nearly as well compensated.
Democracy is two wolves and a lamb voting on what to have for lunch...
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Hello Paddy,
If you look at the massive counterweight in the middle of the four main crankshaft compared to the somewhat uniform balancing weights on the seven main, you will realize that designers had to be a little more radical when balnacing four main engines. In addition the flywheel and front balancers also had radical couterbalances to off set the spinning weight of two rods and two pistons between each
main bearing on the four main engine.
When you ever have a seven main crank assembly re-balanced they can simply balance each individual part or balance everything as a unit.
If you re-balance a four main engine the parts can only be balanced as a assembled unit.
Counterweighted replacent flywheels and front counterweights on four main engines must be matched to the old parts so counterbalancing forces are the same when replacing theseparts.
On seven main engines, since all the parts are symetrical and balanced individually and as an assembly, you are able to switch and relplace flywheels and front weights without any balancing.
Think of a crankshaft like a bridge, one with four supports (bearings) the other with seven.
Joe Alexander
Blacklick, Ohio
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I'm speaking from an engineer's perspective (having spent the past 25 years designing engines). Balancing an inline six cylinder engine is not difficult compared to other configurations. V-6 is notoriously difficult to balance, for example. With the I-6, the primary and secondary forces and couples naturally cancel without requiring a balance shaft.
This is not to say it can't be done wrong. It sounds like you're saying the seven main engine is internally balanced and the four main is externally balanced, which is certainly an advantage to the guy working on them in the field.
Democracy is two wolves and a lamb voting on what to have for lunch...
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Hello Paddy,
It's nice to have another "motor head" on board, I am sure we will have some additional questions you can help us with soon!
Joe Alexander
Blacklick, Ohio
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Hello Paddy,
What's your thoughts on the Mercedes 5 cylinder engines. Sounds like a nightmare to design, but I suspect with a crank throw every 72 degrees it is smoother than the v8 with two crank throws every 90 degrees?
Joe Alexander
Blacklick, Ohio
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Here is a pic of my crank being polished, in my class.
(http://i19.photobucket.com/albums/b177/wb300se/MB_220S/DSC_0082.jpg)
Thanks
Warren Bain 1965 220S, 1989 300SE, 1989 420SEL, 2002 Ford Crown Vic Police Interceptor
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While we are on the subject, is it true that the early 250 engines had main bearing lubrication problems?
Apparently some regrinding of the cranks was required to solve the problem...
naj
68 280SL
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Another answer to the questions. The bearings keep the axis of the shaft rotating in a 3 dimensional straight line. The piston forces make the shaft flex and bend. Bearings are designed big(wide) enough to contain these forces. 7 bearings place a containing counter force on both sides of each piston. 3 or 4 bearings leave 2 or 3 pistons between bearings. Bigger engines and turbines have bearing oil pumps that lift the load off the bearing before the shaft turns, thereby lubricating the shaft at all times. Supposely 90% of gasoline engine wear is on the first few strokes before oil pressure gives lubrication. Happy motoring.
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The engine wear on start up is kind of a myth started by big oil companies trying to sell some new additive. Some wear can happen on start up but there is no load on the engine until it fires and then oil pressure should be there quickly. Lighter or synthetic oils solved a lot of these problems.
The real culprit is dirt. Even pices as small as 2 or 3 microns can scratch engine bearings. Most oil filters only filter down to about 10 microns so a lot of wear can happen when oil gets dirty.
Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061
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Hello Naj,
The 250 Series engines had two different version crankshafts and bearings. I believe that by the time the 250SL came along, they all had the later version. The 280 SL engine also had two differnt style bearings but used the same crankshaft on both.
Joe Alexander
Blacklick, Ohio
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quote:
Originally posted by ja17
Hello Paddy,
What's your thoughts on the Mercedes 5 cylinder engines. Sounds like a nightmare to design, but I suspect with a crank throw every 72 degrees it is smoother than the v8 with two crank throws every 90 degrees?
Joe Alexander
Blacklick, Ohio
I have to confess that I'm not very familiar with MB's line of engines. 5 cylinder engines aren't very common (although there seem to be more of them these days), but inline engines are generally even firing and not difficult to balance, so they do tend to be smooth running. V-8 engines with 90 degree vee and shared pins will also be even firing and balance easily, so they also run very smoothly.
Democracy is two wolves and a lamb voting on what to have for lunch...
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Are you all now talking about the durable OM617 5 cylinder diesel engines?
Were there 5 cylinder gasoline engines from this marque?
1967 230SL
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Peugot and/or Reaunalt 'featured 5s, not so?
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Yes Chad, these were the Mercedes diesel engines. I think Audi also used a five cylinder gasoline engine also.
Joe Alexander
Blacklick, Ohio
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I know GM and VW both sell an I5 gasoline engine. Ford/Mazda/Volvo have announced one, but I don't know if it's actually in production yet.
Democracy is two wolves and a lamb voting on what to have for lunch...
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I talked to my machinist over the weekend and asked him to give me his take on extra friction from three more bearings. He looked at me like I was from a another planet which only confirms what I already know.
It might take a tenth of a horse power, maybe....
Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061
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quote:
Originally posted by Benz Dr.
I talked to my machinist over the weekend and asked him to give me his take on extra friction from three more bearings. He looked at me like I was from a another planet which only confirms what I already know.
It might take a tenth of a horse power, maybe....
Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061
I agree, although above 4500 RPM it will probably be a little over 1 hP (I could probably calculate it...). But there is so much friction elsewhere in the engine, the difference in a few extra hydrodynamic bearings isn't going to be significant. Besides, the added support will allow you to produce so much more power that it will more than make up for the friction.
Democracy is two wolves and a lamb voting on what to have for lunch...
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How about this- additional bearings might decrease the friction. They eliminate the vibrations, amplitude, and the shaft rotates on a straight axis. Harmonics, etc, you know??
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quote:
Originally posted by glennard
How about this- additional bearings might decrease the friction. They eliminate the vibrations, amplitude, and the shaft rotates on a straight axis. Harmonics, etc, you know??
No. In order for a hydrodynamic bearing to work, the oil film must be maintained at all times. Once you get metal to metal contact, the bearing is toast. So bearing friction is primarily a function of the relative speed of the two surfaces and the viscosity of the oil in the film.
When the oil film breaks down and asperity contact takes place, friction increases exponentially. The heat from this friction causes metal transfer between the bearings and the crankshaft. Eventually the bearing shells stick to the crankshaft and spin. Catastrophic engine failure is imminent at that point. This all happens in the blink of an eye.
Democracy is two wolves and a lamb voting on what to have for lunch...
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3 bearings = 1/3 distortion and 1/3 load on each. 7 bearings = 1/7 distortion and 1/7 load on each. 7 is better than 3. The 7 bearing engine with lubrication will last a lot longer than a 3 bearing engine at 7000 rpm! Turbines have more uniform radial loading than 8, 6, and 4 piston engines. 90, 120, and 180 degree bangs.
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quote:
Originally posted by glennard
3 bearings = 1/3 distortion and 1/3 load on each. 7 bearings = 1/7 distortion and 1/7 load on each. 7 is better than 3. The 7 bearing engine with lubrication will last a lot longer than a 3 bearing engine at 7000 rpm! Turbines have more uniform radial loading than 8, 6, and 4 piston engines. 90, 120, and 180 degree bangs.
If crankshaft distortion is great enough to affect bearing friction, it will cause metal to metal contact and bearing life will be extremely short. Friction in a hydrodynamic bearing does not significanly vary with unit loading. The concept most of us have of dry or sliding friction is not applicable. More unit loading simply increases the pressure in the film. It will have a slight effect in that film thickness will be slightly reduced, but other variables are more significant in determining film thickness. Hydrodynamic bearing friction is completely determined by the shear stress in the oil film.
Parameters that will affect hydrodynamic bearing friction are the bearing diameter, length, etc.
Bearing life indeed can be affected, as the greater oil film pressure can lead to fatigue failure of the bearing shell.
Democracy is two wolves and a lamb voting on what to have for lunch...
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I realize this is an old string but it appeared to be the most appropriate one to add my question to...
My 230SL is being restored by Bud's and I plan to have a new AC system installed. The car has the original M127 four-main engine. Has anyone had any bad experiences or know of problems with excessive main bearing wear (or broken crankshafts) resulting from added strain on the crankshaft?
thanks all, Charles
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You'll no doubt be getting what most of us think of as a "rotary" compressor with your new rig from Buds; it's what is commonly used these days. Our cars originally had piston-type compressors which were a much greater load on the engine than the rotary type will be on yours, and I'm not aware of any reputation for failure associated with even the old style. Not a direct or definitive answer but of some comfort, I hope.
[And the modern compressors are not actually/literally rotary-type, but something involving a rotating "swash-plate", a sort of cam that drives multiple small pistons that do the compressing, but the nice result is that the whole thing is much smaller and lighter, has little rotating and (especially) reciprocating mass, and all of that is along the longitudinal axis of the car. Uhunh. Anyhow, it's a lot smaller, smoother, lighter and tidier -- and easier to power -- than the old style. And everyone just usually thinks of it as a rotary compressor, 'for short' you know. ] :)
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got it, thanks for the quick response Dennis,,
The head had a recent rebuild w/valve job but I'm not sure when (if ever) the lower end was rebuilt. Since the original main bearings could likely still be in play, I was concerned. thanks again.
Charles
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Hello Charles,
The main issues with the AC on the M127 engine is the fastening of the vibration dampner and front crankshaft pulley. Many crankshafts have been damaged when the vibration, dampner/pulley assembly have come loose and ruined the front of the crankshaft. Later engines had an improved fastening arrangement for the dampner/pulley assemblies. A repair procedure was explained in a Feb. 1968 suppliment to the early BBB. A special crankshaft "stretch bolt", special spring washers and larger dowel pins are used to repair and improve the attachment of the crankshaft counterweight/pulley assembly.
Dealer workshop manuals (BBB) were "loose leaf" so that suppliments could be added as problems and procedures evolve on new models. The final print editions of these manuals should have these suppliments added to them and are bound. If you have the latest edition of the BBB, this information should be found on pages 03-10/3 and 03-10/4 of the early BBB.
When the M127 engine is equiped with AC it increases the stress on this dampner/pulley assembly. At the vary least I would make sure that the new style stretch bolt and special spring washers are used to hold your dampner/pulley assembly in place. The original dowel pins should be adequate as long as the crankshaft is not damaged. Using a "rotary style" compressor also reduces the strain on this assembly.
The M129 and M130 engines in the 250SL and 280SL had the improved crankshaft bolt and spring washers. In additon these engines had six bolts holding the pulleys to the vibration dampner. The 230SLs had three.
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thanks Joe, I forwarded your response regarding the stretch bolts/washers to David at Bud's.
take care, Charles
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In regards to analysis of the 4 main and 7 main bearings earlier in this thread, it is not a simple comparison. The actual bearing design and the distribution system for the oil would also have a major impact on bearing life. In other words, a poorly designed bearing configuaration and lubrication system on a 7 main engine, may not last as long as a well designed 4 main bearing system.
In general, the 7 main bearing engine, is considered stronger from the added support. Longevity is more a function of how well the engine bearings, and lubrication systems were designed. Mercedes has re-designed the bearings and oil distribution systems on the same series engines from time to time to improve durability. There is a multitued of different styles of crankshafts, bearings and oil pumps for the basic in line 6 cyl. Mercedes engine of the era. We can only assume that this was evolution of improvement in the design.
Major improvements in metal alloys have contributed to extreme longevity of many new modern engines. Silicone enriched aluminum engine blocks, hardened camshaft and crankshaft journals etc.
Does anybody remember the GM Vega? ...............an example of one of the early failures of the aluminum engine block.
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You're welcome, Charles, for what I had to offer. And true, as far as it went; the new compressors are a lot less strain all around. Fine. But there are people here -- and Joe is a prime example: present case in point -- who bring the breadth and depth of decades of working with these cars. When I speak up to answer someone who's even newer at this than I am, I often mention that someone with a lot more knowledge will likely be along soon with more on the topic. Sure wish I'd taken the time and space to do so this time. But that's how it works around here; the power and value of the information available is just really neat, is what it is. Best wishes.
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The only time I've seen broken crank ends were always on a 127 engine. The design simply isn't strong enough to take the added strain of a AC compressor. The newer rotary style pumps would be much better but I'm not a fan of AC in a 113 for any reason. You may stay cool while your engine deals with all of that extra heat; trying to get it out of an engine compartment blocked with all sorts of extra hardware.
If you ever need to replace the short hose between the thermostat housing and the water pump then you'll rue the day you ever thought about having AC. What should take an hour to change will likely take most of the day - at least 4- 5 hours more.
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Hello Dan,
I have never run into the broken crank senerio but I agree with you on these overly complicated AC Brackets. It turns simple maintenance into real misery. Your advice, being a Canadian in cool climate, may fall of deaf ears to our Florida members.
I like the Sanden Compressor on the sedan AC bracket.
Take care,
Joe Alexander
Blacklick, Ohio
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So do I, and thank you, Joe, for setting me on that path, but still 'tis not as simple as it looks. The final fight fought was to slice the mounting ears off the space-squandering and overly thick -- $65.00! -- adapter plate, then shorten and weld them directly to the sedan bracket. This eliminated contact with the air cleaner housing sheet metal and actually resulted in a generous clearance there. Finally.
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Attached is a photo of the kit that will be installed. I presume that's a rotary compressor in the picture.
I noticed that the air cleaner housing sheet metal on my car has been cut (butchered) to accommodate the previous compressor. Not sure what can be done at this point to cosmeticallly 'clean up' the hatchet-job.