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1979 450SL UK spec
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Discussion Starter #101
Next I went on to measuring the rod bolts and basic bore with and without the old bearings.

The rod bolts all measure within spec which is 8.0mm minimum (original size is 8.4mm), they were all ~>8.3mm.



The rod measurements were taken with and without the bearing shells. Using the basic bore sizes and thickness of new bearing shells I can also predict the likely sized when new shells are fitted.



These are the crankshaft measurements for the main bearings and crankpin bearings. Again, using the basic bore sizes and thickness of new bearing shells I can also predict the likely sized when new shells are fitted.



Now using the measurements of the crankshaft main bearings and crankpin bearings I can calculate the clearance with the old bearings and what it will likely be with the new bearings.



As the crankpins measured up ok I went ahead and ordered new standard size big end bearings today, I already bought a set of main bearings some time ago.

Next I will start working on the heads.
 

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1983 380 SL
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Then finally heading off the the machine shop.

If ever there was a sure fire way to show the difference between an alloy block and a cast block... this picture says it all.
I picked my alloy block up in my two hands and carried it over to my truck. It was so light I was afraid it would roll around so I strapped it down. :)
 

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1983 380 SL
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@RaceDiagnostics what did the machine shop say? How long and what are they going to do? It took my machine shop 2 months or more to sleeve 1 cylinder. I would have thought they would have cleaned it but they didn't, so I had to take it back to them and they charged me another $100 bucks to clean it.
 

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1979 450SL UK spec
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Discussion Starter #104
I just asked them to give it a light hone and a wash, they didn't have a hot caustic bath, just a big parts washer so don't expect it to be too clean on return, I think I will have to do a bit more cleaning myself. I got a quote from another place that has a hot caustic bath, they wanted £190 to dip it!
 

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1979 450SL UK spec
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Discussion Starter #105
I started off today removing the old piston rings and checking the wrist pin clearances.





Good news, all the wrist pins were in spec.



As were the rod bush and piston bushes.





Next I started cleaning the cam shaft bearings and the pistons in a degreaser, they cleaned up fairly easily, despite being cleaned in a cold solution at about 6 decC, the weather turned colder today.







Next I measured all the cam towers....



...and the cam shaft journals.



Now the bad news.

The cam bearing clearance are out of spec, the left (from the front of car) bank just over, the right bank worse. New bearing sets are NLA from MB and ~600 a side at places that still have stock.



Well that is a pita, I will remeasure tomorrow but don't really expect them to be any different. I will search the web tonight to see what I can find.

To take my mind off this I moved on to stripping the heads, but this valve spring compressor wouldn't fit into the valve springs so will pick up a conventional one tomorrow.

 

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1983 380 SL
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Are you sure you're not being just a wee bit too picky? Take the first cam tower measurement for example. The max bearing size is 35.016 mm. Yours measured 35.02. That's .004 mm over, or 0.000157 in. In laymen terms that's 1.5 tenths. Are you quite certain your equipment is capable of measuring with that degree of accuracy... and even if you can measure down to tenths accurately, does it actually matter? These are cam towers holding a cam spinning on a film of oil. I'd increase the viscosity of my oil by a bit via oil additives before I'd start worrying about tenths of an inch in cam baring dimensions. But that's just me. :)
 

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Discussion Starter #108 (Edited)
Hey Jyuma, "too pickey" I just don't know as I've got zero engine building experience.

Do you remember a few months back I was saying that I had read the bearing above cylinder 8 was a weak point? It gave up first on my old 350 engine and had about 0.5mm of clearance and a loud clack. It seems like this engine is wearing there too, if you look at the table above, both the cam journal and bearing tower in this position have the worst wear.

Here are a couple of close ups of the worst bearing, nearly 0.1mm clearance, looks like there has been plenty of metal on metal contact.





I think I could live with the wear on the left side but would like to find an oversize set of bearings for the right side.
 

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1999 500SL, 1988 SEC
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Ya that tower needs replacing. I am afraid ebay is going to be your friend. A couple of suggestions, you might want to take the cam to an engine builder and have him polish the cam. Second, and I don’t know if they even do it to used pistons but maybe you could get the sides coated like the new replacement versions have.
 

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1983 380 SL
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You make a good point about #8 but even that one is only over by approx .003 inch. Are you concerned that the .003 inch is going to cause problems of a ticking sound nature? I would think that to be a valid concern but .003 inch clearance is not terrible. Of course optimum would be for the clearances all to be within spec but to bring everything into new spec range, even just for the valve train, would cost $thousands.

I can't say, nor do I know, if .003 inch tolerance is OK in that area and should be let stand or not... but at what cost? When I did mine, I too noticed some variation in the cam tower clearances which prompted me to purchase not 1 but 2 #4 cam towers for the drivers side (Fleebay), neither of which made things any better. I opted not to spend several hundred dollars on "new" cam towers due primarily to the fact that they can be replaced, (with some difficulty), once the engine is placed back in the car and running. If at that time I observe an unacceptable level of ticking, then I'll make the decision... or not... to spend the roughly $600 bucks to replace one side (drivers) of the cam towers. I believe the cost to replace the cam itself would add an additional several hundred dollars. Perhaps it would be worth some effort to see if you can purchase just the one cam tower (perhaps Fleebay) and see if it is more inline with the written spec for that cam tower.

I sincerely wish only the best for you with your rebuild efforts but a slide down the rabbit hole of perfection can, at times, become an extremely costly trip. There are times when good enough has to be good enough... for any number of reasons... and don't think I don't see the irony in my suggesting that to you when I clearly don't follow my own advice in certain areas. :) :) :)
 

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Discussion Starter #111
Second, and I don’t know if they even do it to used pistons but maybe you could get the sides coated like the new replacement versions have.
I have found a place that does that and should bring the pistons back into tolerance.
 

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Discussion Starter #112
I have been searching for a set of oversized cam bearings so that I could grind the cam, however I don't seem to be able to find any in stock and they are NLA at MB, so it looks like I will need to buy both a standard bearing set and new CAM, ouch!

I got back into the garage this afternoon and started work on the first head.





It was easy to remove the collets as the tool locked in place.



Six months ago I glued this valve guide in place with high temp loctite, it held for most of the summer but I started getting a puff of smoke on start up again in September, it must have worked its way loose again then.



Into a bath of hot degreaser.



Once it had heated up I took the opportunity to remove the remainder of the valve guides.

Not as much comedy in my video on this compared to Jyuma's.



Washed and dried.



I will remove the broken bolt from this tomorrow....



....and clean up the valves.

 

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1983 380 SL
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It looks like the valve guide that had been glued in with loctite is an intake valve. I may have first repair size intake valve guides... ill look, but if you need them I can send them to you.

Update: Yup, I just looked and the bag says Intake 116-050-49-24. They measure 14.2 x 9 x 47.5 (mm).

They're yours if you want them.
 

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1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Do some research about rings before you use the chrome ones.
Those are only used in very dirty applications (like dirt track racers that don't run a breather).
I've been told by more than one engine builder to stay away from them as they're very difficult to seat and promote advanced cylinder wall wear.
I use plasma moly faced rings on all my builds, I bet they're higher than giraffe nookie for a MB though!
Don't belive everything you are told. Mercedes used the chrome moly rings. If that is true about dirty and excessive then why were my cylinder bores so clean after more than 100,000 miles. No ridge at the top and on one I could still see faint cross hatch of the original honing.
 

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Discussion Starter #115 (Edited)
Is there a difference between chrome moly and chrome plated? The ones I have are either grey iron or chrome plated grey iron. In fact it's just the top ring that's plated.
 

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Discussion Starter #116
It looks like the valve guide that had been glued in with loctite is an intake valve. I may have first repair size intake valve guides... ill look, but if you need them I can send them to you.
Thanks for the offer , however I already bought both the new standard size which is fractionally bigger than the original as well as the next oversize intake for this troublemaker.
 

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1999 500SL, 1988 SEC
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OK, I stongly suggest you read my head refurbishment on the W126 forum. The valve adjustments are very finicky with those puck adjusters. At a minimum you likely will have the valves ground, not just lapped. When you do you change the geometry some. So you should measure how far the valve stems stick out from the head and make sure your machine shop grinds the stems to the exact same length they came out. If not you will pay lots of money for those pucks to get right, and if they are not you will hear the tick of them. Trust me on this one
 

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1983 380 SL
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The following refers to my 380 (M116.962)... I don't know how much it applies to other engines but it's probably very similar if not exactly the same.

I agree that the testing procedure for getting the proper thrust washer thickness can be a bit daunting but it need not be expensive.
First we must understand fully what the thrust washer is intended to do. To that end we need to understand the following:

The length of the valve stems are held to very tight tolerances in the manufacturing process and as such the total length from the face of the valve seat to the tip of the stem is a well known and reliable value.

In like manner, the length of the hydraulic compensator from the flange that tightens against the surface of the head to the top of the ball is also a well know and reliable value.

And finally, all of the dimensions of the cam followers (rockers) are also well known and reliable values.

Therefore... the total of all these values when added together will indicate the nominal value of the thickness of the thrust washer which is somewhere between 4.75mm and 5.1mm.
Unfortunately we don't live in a perfect world, so some form or adjustment was provided by Mercedes in the form of trust washers in 8 sizes (thickness) ranging from 3.7mm and 6.15mm in .35mm increments.

The Mercedes tool for determining what size thrust washer is required does not measure anything other than the distance from the top of the ball on the hydraulic compensator to the surface of the head.
I don't know for certain but I assume that all things being equal, the thing the thrust washer is actually intended to compensate for, is the relative deflection of the ball on the top of the compensator when under pre-load. In other words... if you change the nominal dimension of the total of all the components by changing how far out of the head the valve stem protrudes (a result of grinding the valve and/or seat) then the ball on the top of the compensator will deflect further into the compensator body (due to increased pre-load) resulting in what's called a minus deviation. The Mercedes tool used for checking the proper valve preload would show this in the form of the indicator being below the line. Here's a picture of just such a deviation. The remedy in this case would be to replace the thrust washer with the next thinner size and test again. (more on that later).
MercTrustWasherMinusDeviation copy.jpg

On the other hand, if the pre-load is insufficient due to any reason (wear in the system) then the pre-load will not deflect the ball far enough into the body of the compensator resulting in a plus deviation as shown in the next picture. The remedy here would be to replace the thrust washer with the next size thicker and test again. (more on that later).
MercThrustWasher PlusDeviation copy.jpg

This last picture shows the result you're after by altering the thrust washer thickness. No remedy required, the thrust washer is the correct thickness.
MercThrustWasherNoDeviation copy.jpg

The instructions for testing the preload is to crank the engine for 30 seconds before testing. This can and will get extremely messy as the oil will be flowing freely through the oiler tubes and over the cam lobes as well as the cam and everything else up there. Use plenty of rags to catch the mess. Obviously you don't want the engine to start, you don't even want the plugs in the head so use a jumper switch to activate the starter without the ignition system receiving power. There are threads here on the forum that show how to do that.

After cranking for 30 seconds (that's a very long time while you pump oil all over the place) using the Mercedes pre-load gauge check the pre-load and replace the thrust washer if required according to the indications above.

Note: Other than those times where you have had the valves and/or valve seats ground, or you have replaced the rocker or the hydraulic compensator, if a change is required it will must likely be on the side of increasing the thickness of the thrust washer. Reason... wear. If the Mercedes pre-load gauge indicates the need for a thicker thrust washer the last thing you want to do is layout $22 bucks each for a variety Thrust Washer thicknesses and guess at the size. There are 16 of those little pucks of gold in your engine and at 8 different possible thicknesses each you could throw a significant amount of coin at this problem.

The solution is to be found at McMaster Carr. They sell hardened steel shims that are round and .010 inch thick that fit perfectly on the top of the thrust washers. Ten thousandths of an inch is .254mm which isn't exactly .35mm but it's close enough for you to estimate pretty accurately what size thrust washer to buy. If you find that the Mercedes pre-load gauge indicates that you need a thicker thrust washer just slide one of these .010 steel shims on top of the thrust washer (you need to remove the rocker to do so) and test again. If the gauge still indicates you need a thicker thrust washer, throw another .010 shim under the rocker as test again. Once you get real close to nominal, order the thrust washer that is closest to the total thickness of the existing thrust washer plus the thickness of the shims.

For engines that have been running fine and all you need to do is adjust the thickness of the thrust washer on a valve you've had work done on, this procedure should not take very long. However, if you're in a situation where you need to do this for all 16 valves, then you're in for quite the adventure.

Disclaimer: I wrote this from memory so I may have reversed the minuses and pluses, but a rose by any other name... :)
 

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1999 500SL, 1988 SEC
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Very nice write up and spot on. One thing though is there are different test tools. Seems like they changed them over time. We had quite a discussion on this and the end result is that we had to come up with an exact measurement to set up the correct reading for the go no go gauge. It is also inconceivable to me that the compensators have so little flexibility in them. Not like any chebby or Ford which has gobs of compensation.
 

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1985 280SL
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Don't belive everything you are told. Mercedes used the chrome moly rings. If that is true about dirty and excessive then why were my cylinder bores so clean after more than 100,000 miles. No ridge at the top and on one I could still see faint cross hatch of the original honing.
With all due respect, Rowdy, there's a HUGE difference between chromium and chrome-moly rings.


You're absolutely correct about effects of more modern rings, though. I tore down a lowly Chevy 5.7L throttle body engine with just over 400K on the ticker when the odometer quit. Hone marks in every bore with zero ridge at the top. This is as opposed to many that we've both torn down with a big enough ridge at the top of the bore to break rings on disassembly. My gurus say it's a combination of proper cylinder finish, ring face material, ring tension and very importantly, fuel injection (less cylinder wall wash-down, particularly at start-up when granny gave the accelerator a few good pumps to get 'er started. This is exactly why the newer GM aluminum engines can only be honed a few thousandths. They're counting on less wear.
 
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