Distributor chain drive

[Ricardo]

Just when I thought I had things running great and maybe we could make that east coast trip, disaster strikes arggg. Cruising along at 60, a sudden loud bzzzzz for a second and the engine dies. Upon inspection I find the hold down screw for the dist. adj. is loose. Retighten and try to start...the gas pedal tries to push my foot up with eng. cranking. Now I know this is serious. Towed home. Injector pump contol lever is stiff and won't return to idle position. Pull off valve cover...chain OK (only 1 year old) but distributor not turning with eng. Rotor is still firm and won't move beyond advance springs. Now I remember someone having the drive sprocket pin shear off, but I can't find the thread in the Yahoo archives. Has anyone saved this thread or can point me to it ? Who says grown men don't cry.
Richard V

[Cees Klumper]

I will have a guess at it - it sounds like your tach/distributor/FI pump/oil pump (!) gear assembly has seized up. You can start by taking the tachometer cable off, and taking out the assembly below that. There is a bushing in there that is supposed to keep everything together; in the engine Joe Alexander and I rebuilt two weeks ago, this busing (about an inch tall, bronze/copper end) was worn to the point where it seemed to be about to do what may have happened to you. Hopefully the engine did not lose oil pressure (for too long) in this ordeal.

[ja17]

Hello Recardo,
There is a spring under the distributor which will push the distributor up if left loose. If you simply retighten the distributor 5mm allen bolt the distributor will not engage. You must first re-time the distributor. Before tightening down the bolt push downward on the distributor, and turn the rotor to engage with the timing gear below. While holding the distributor down, now tighten the bolt.
It sounds like you may have two problems or somehow interconnected. Did you say the injection pump lever has become stiff? Disconnect the linkage to the pump and see if it is still stiff. Cees may be correct about the gears, but try these simple checks first.


Joe Alexander
Blacklick, Ohio

[Ricardo]

I disconnected the inj. pump linkage and the control lever moves somewhat but won't return to the idle position or full stop. I have an 051 dist. and it has a slotted set screw which seems to be for fine adjustment. It was this screw that was loose, not the main clamp. I'll hopefully get some time to dig deeper tomorrow
Richard

[ja17]

Ricardo,
Sounds like something may have happened in the injection pump. Siezure or binding in the pump could, (as Cees metioned), damage the timing gears. Removal of the injection pump may be needed.

Joe Alexander
Blacklick, Ohio

[Ben]

Could the pump have sheared teeth off its drive coupling ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

[Ricardo]

Well....I haven't got as far into this as I'd like, but here's what I have found. After hauling out the rad etc., I started into the dist. housing. When I got the cover off I noticed small metal shavings clinging to the dist. drive gear, hmmmm. I tried to roll the engine from the crank pulley and indeed the large sprocket was spinning on the idler shaft, so the key and the locating pin have sheared, at the very least. I wrapped a piece of cloth on the dist. drive gear(on the idler shaft) and tried to turn and pull it. The idler shaft did turn a partial turn before the gear came loose. So I'm now at the stage where I need to pull the inj. pump. One thing that is puzzling me is how to pull the tach drive. I have it loosened and was able to lift it up but it won't clear the head, unless it is meant to come apart, or else the head has to be removed first.
So has anyone heard of the inj. pump itself seizeing or failing in such a way as to cause the idler shaft to bind enough to shear the pin and key on the sprocket ? There is an idler shaft set on ebay right now that says it is for a 250sl, but my 250se eng. lists a slight variation in part no. which my local dealer says could just be a different manufacturer. The ebay part no. is 130 050 04 06, the BBB says for 250SL and SE 621 050 03 06. The 621 is the old style numbers, but my dealer says for 250SE the current number is 130 050 03 06. Is there any way to reference these numbers against actual eng. numbers ? When I get the inj. pump off I should have more to report.
Richard V

[ja17]

Hello Richard,
The top fitting for the tach drive must be unscrewed first. Next the 10mm set screw is removed and the aluminum/bronz bushing can be lifted out. It barely clears the head. After this the long tachometer/oil pump timing gear can be lifted out. I suspect the damage will be the worm gear part of this gear and the worm gear part of the chain sprocket/injection pump gear. The splined injection pump connection is not likely to fail. I will follow up with some photos and additional information. Stay tuned!


Joe Alexander
Blacklick, Ohio

[ja17]

Hello Richard,
Here is an illustrated removal sequence for the verticle timing gear which drives the tachometer and oil pump;

First unscrew the tachometer cable.


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Next you must remove the 22mm fitting (cap), try using a box end wrench or crows foot. 7/8" is virtually the same size.


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Next remove the 10mm set screw.

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Now the aluminum/bronze bushing (sleeve) can be removed. It just bearely clears the head. This part wears allowing too much gear lash, eventually wearing the timing gears. Rerwsulting gear failure can cause sudden loss of oil pressure, since this gear drives the oil pump!
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Remove the verticle timing gear and inspect for wear or damage.

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The old bushing is worn over four millimeters or nearly a quarter inch.

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This is the entire timing gear train. In your case Richard, if your injection pump has locked up, you may have to remove the horizontal timing gears and sprockets also. This is a lot more work. Let us know what you find. You probably will begin by removing the injection pump after removing the verticle timing gear.

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Joe Alexander
Blacklick, Ohio

[Ricardo]

Joe
Thank you for the excellent breakdown of the parts and the dissassembly sequence....aren't digital cameras wonderful!
I have the tach drive shaft out now and I don't really see any damage except possibly a bit of scoring on the top of the shaft where it sits in the alum. bush/housing. I will post a picture when my camera's batteries are recharged. Would the expected damage to the worm gear be obvious or needs to be somehow measured? Looking down the hole to the idler shaft worm gear, again nothing obvious to my eye. I suspect the large alum. bushing may be worn as you showed in the photos; where are you measuring the 1/4" of play that you refer to?
I plan on pulling the inj. pump today; should I be able to turn it over by hand to determine if there are internal problems with it?
I guess there is no point in waiting to pull the idler gear as the sprocket has certainly sheared the pins. This causes me some trepidation, though the BBB seems to explain the steps fairly well, still the thought of dropping the chain or other bits into the crankcase has me on edge. I'll report back later.
Richard

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[Ricardo]

I have another question regarding the tach drive shaft. My engine has been transplanted from a 250SE, and the part numbers for the idler shaft and tach drive set are different than for a 250SL. Is it possible that when the engine was put into my car that the tach drive from the old engine would have been used? The BBB shows a shorter tach shaft for some SE's than what is shown for SL's, this has me wondering if some SE's came without a tach and the shaft would have to be changed to the longer shaft in order to drive the SL's tach. Does this make sense ? Would they be interchangeable? The idler shaft shown in the BBB is the same for all three variations only the tach shaft is shown as different.
Richard

[ja17]

Hello Recardo,
The sedans do not have a tachometer. The verticle timing gear has no top stage to drive the tachometer. A special fitting is used on the SL for the tach drive also. Tom Collit unscrewed the top stage of his worn out SL gear an screwed it onto a good sedan gear making a SL gear! I never tried this, but everything looks identical except for the top stage and the special SL fitting for the tach.

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(Sorry for the bad picture)
I know the other timing gears are the same as the injected sedans. Some of these gears originated in diesel Mercedes engines back in the fifties. That explains some of the diesel part numbers. Mercedes made improvements over the years. Later gear sets were nitride hardened (case hardended) for better wear resistance. This gear set with the horizontal and verticle timing gear is expensive. About $500.00 us dollars with both gears and a bushing. Mercedes suggests that these be replaced as a pair. I know of many instances where only single gears were replaced with no consequence.
Gear failure can result in sudden loss of oil pressure or the engine loosing all injection and/or ignition timing. Gear wear is usually a result of poor lubrication causing the aluminum/bronze bushing (sleeve) to wear and allowing excessive lash or movement of the verticle timing gear. This allows misalignment of the two gears and contributes to gear wear and possibly failure. Checking the gear "lash" is fairly simple. Unscrew the tachometer cable, with fingers gently twist a screw into the top of the verticle gear and check the up and down movement of the gear.
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I have found some reference to the amount of play allowed in the August 1959 Workshop Manual (BBB). Beginning on section 18-6/1, a good description is given of the origins, variations, and improvements in the gearing. Some part numbers are given but may not be current. The amount of "play" should be checked to be (0.1 to 0.25mm). Shimming is allowed if the play is excessive. The manual suggests that the bronze end piece of the aluminum/Bronze bushing be be pressed off and shim washers installed between the two parts. I have found that a bronze shim washer between the gear and bronze/aluminum bushing works very well also.

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 Of coarse replacing a worn aluminum/bronze  bushing  #126-180-00-44 will eliminate a lot of play.

Joe Alexander
Blacklick, Ohio

[Ricardo]

Thats great Joe!
This confirms my suspicions about the tach drive shaft used on the SE's and SL's.
I got the inj. pump out this evening, glad no one warned me about the bottom mounting nut or I might not have attempted....sheeeesh, also the BBB doesn't tell you that the oil/water cooler line has to come off and that there is still a half gallon of coolant waiting to dump on the floor when you least expect it....still can't see much obvious damage to the gears or spline drive for the pump. The collar that sits between the drive sprocket and the dist. worm gear has some telltale evidence though....

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I guess thats a bit of the locating key that sheared off and stuck on there....
Now what do I do with the pump? It won't turn over by hand....should it? If there is internal damage would this be part of a normal rebuild or should I start looking for a rebuildable core? This is an 018 pump, will an 018y or z work? Are there core exchange type rebuilders out there? So much to do.....so little time, top down season is half over around here.
Richard

[ja17]

Hello Recardardo,
Revome the six slotted screws on the rear cover of the pump. Removal of the cover will expose the internal rear half of the pump. It sounds like you may find the centrifical mechanism in the rear of the pump damaged.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Joe,
Should everybody here be checking the end play on this tacho shaft.
Is there something to check on the distributor drive while one is at it??
 

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[Benz Dr.]

OH BOY......(sigh)
 All these people with screwed up engines.

  The coupe version of the 129 and 127 engine has the same distributor drive in most cases. Some Coupes have an electronic tach. - at least mine did.
 There was a thread about IP's and how they're lubricated. I was going to comment about this but never did - now I have to. The three pumps ( or more ) all work on the same basic principal in that they all need lubrication from the engine oil. On the early pumps there's a cavity at the back which is filled to a certain level set by the dip stick. Engine oil should NOT enter this area or the seals inside the pump are leaking.
All pumps have an oil line running to the pump from engine oil pressure. The early cars have an oil lock or check valve which will let oil in at all oil pressures, except when the pressure drops below a set amount at idle. This is to prevent gasoline from backing up into the engine oil. On the newer pumps ( mid 250 and on ) the oil just runs through the pump and drains back into the oil pan. If the seals go in thes pumps you can very quickly gas down an engine.
 You can run any car with an oil lock but the early ones MUST have one. These oil locks can get stuck or sieze from moisture and then they won't open. Rapid pump failure or seizure will result.
 There is no way that you can sheare off a distributor drive pin under normal operating conditions. These pins are VERY hard as are the shafts that run the helical drive gears. The very small wodruff keys could sheare off but all these pieces are bathed in engine oil at all times so failure is somewhat rare.
 Pull the oil lock apart. It should move back with only slight pressure. If it's stuck... better give me a call.
regards,
Dan c

Daniel G Caron

[ja17]

Hello Naj,
It would not hurt to check the up and down movement of that verticle gear. It is a good indication of the condition of the aluminum/bronze bushing which will affect  the gears. If you find that the up and down movement of the verticle gear is 3/16" or greater, I would remove the bushing and inspect the gears. Shim or replace the worn bushing. Hopefully the gears are still OK. We checked three W113's at the tech session. One had excessive play and required inspection. A worn bushing was found and a shim washer was added to bring things into specs.
As far as the distributor, a small spring controls "lash" up and down movement of the distributor gear. The spring is located between the distributor and the distributor timing gear. (see previous photo). This spring is often missing. This condition can contribute to gear wear or cause minor variations in timing. The distributor can be removed and check to see if the spring is in place.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Thanks for that Joe,
I checked last nite and I would say I have 3/16 inch lift!
Another long nite ahead!!

Thanks


naj
'Kloines Scheisserle'
65 230SL
68 280SL

[ja17]

Hello Naj,
 After the bushing is removed the verticle timing gear can be removed and checked for damage. If the bushing is worn badly, you may want to replace it. I measured Cees' new bushing #126-180-00-44 and it was approximately 62.7mm in length. If you are shimming it, a brass injector seals just happen to be the exact diameter to use for a shim. Be sure to align the hole in the aluminum/bronze bushing carefully before tightening down the 10mm set screw during re-assembly.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Are you a mind reader as well Joe??
Was just wondering what I could use to shim up the bush!
Will let you know how I get on.
Thanks again
 

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[Ricardo]

Got the pump open today and found some bits and pieces floating around in there; a small arm, short small shaft and a spring. See photo.... There are some impact marks on the inside of the casing and it appears as though this short arm came off of it's pivot/mounting and probably jammed the pump. It's hard for me to tell the extent of damage, nothing very obvious.....man these things are well made..... but I guess it needs to be sent out to a rebuild shop.
Dan, I'm not sure where the oil lock is located. I can't find it in any of the pictures or diagrams in the BBB and there doesn't appear to be anything like that on the pump where the oil line connects. I don't think you are referring to the eng. pressure relief valve, but I can't find the check valve on the pump.
Should I send out this pump or look for another?
Richard



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[Cees Klumper]

The aluminum/bronze bushing below the tach drive (#126-180-00-44) costs around $60 new here in Europe. I suppose I will check its condition every 40K miles or so, to avoid "sudden failure" or premature wear of the tach/oil pump/distributor/FI pump gears - very expensive gears indeed (from memory a set costs something like $500 not to mention the damage that will result from a disengaged oil pump). But maybe these bushings are designed to wear evenly with the wear of the engine, and MB was going on the assumption that, with a major engine overhaul, this bushing will always be checked/replaced.

[Cees Klumper]

Richard - on the pump, I would check to see whether you can find another one at e.g. a salvage yard or off Ebay, and see if it (1) is fine to work with or (2) you can use the parts off of it to fix your existing one. After that, I suppose you can always take it to a shop to have it tested/calibrated?

p.s. I just noticed that this post put me in the "silver level" category. Who would have thought I had it in me  

[ja17]

Hello Recardo,
The oil lock Dan is reffering to is the check valve on the small metal oil line, between the block and the injection pump. This check valve was deleted on the later versions. In addition a larger diameter metal oil line replaces the smaller diameter line on the earlier versions. Certainly check to make sure this line is clear.
I agree that an inexpensive sedan parts pump could be a good investment. You may get lucky and find a good working used unit.


Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Hi all, some good info here.
 Only problem is that the 230SL IP is unique to this car. Some parts will interchange but I'm far from an expert on what will or won't. The place that does all my pumps has what's left of a 230SL IP that we've been using to fix other pumps.
 I do know that the injection pressure valves are different as is the camshaft. Somehow the size of the rollers inside of the pump determines how much fuel is injected. The pump is checked for ouput at each element and they all have to be the same and at exactly 60 degrees apart.
 We can look at it for you if you want.
Dan c

Daniel G Caron