Engine rebuild with no former experience........

Racediagnostics wrote:
Main bearing sizes, only four shown but there are five bearings?

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This are not the main bearing sizes. This are the size-index of the con-rod journals.

Ahh, thanks, that makes sense.

Some measurements today.



Micrometer set to 92mm.



Bore gauge set to zero in the micrometer.



These are the measured values at the top, middle and bottom of the bores in both the transverse and longitudinal directions. The measurements were taken at 13degC rather than the specifications which are probably taken at 20degC.

I have made an estimate of the for the likely values at 20degC but am not sure how accurate this is given the micrometre is also calibrated for 20degC.

Let me know if you think I should use a different value for cast iron.

The bore wear limit is 0.1mm just below the top ring, so it looks like I am well below this limit across all cylinders.



As for the pistons, the measurements are below. I was really surprised how much under the spec value they were, so I brought one into the house tonight to make a comparative measurement at 20degC and found the piston skirt on piston 1 was 0.025mm larger than at 13degC so used that value to adjust all the values. As the pistons are tapered, the bottom of the skirt measurements are the only ones that really make any sense.



So the bottom line of what I was wanting to check was the piston-bore clearance which has a spec limit of 0.08mm. From the table above you can see that piston 4 is the only one out of spec. However I am not really convinced that my measuring methodology is good enough.

It is also a PITA that the factory fitted the wrong pistons in positions 1 and 4, the marking on the block calls for piston code "2" and piston code "1" was actually fitted, that adds to the excess clearance.

Given standard size pistons in any group size are no longer available, fitting a larger group size piston is not an option.

Boring out the block to use the first repair stage pistons (92.5mm) would cost at least £1200 for the aftermarket pistons and machine work, for me I don't think it's worth it for one marginal cylinder.

What are your thoughts, please also offer any advice on my calculations.

Hi Jim,

how did you estimate the temperature correction value for the bore measurements?
Isn't it strange that piston 8 is bigger than it should be in the new condition? Taken the wear into account this piston should have (at least) fallen into group 2 when the engine was built together and I can hardly imagine that it was so much off size. That raises the question how accurate your measurements are. I am sure that you did your measurements thoroughly but there might be a cause of error that you (and me) didn't think about.
Would also be interesting to compare your measurements with somebody else who already did this job. But this is definitely not me .....

Regards,
Lutz

Jim, can be this an option. Sleeve a cylinder.
www.enginebuildermag.com/2018/09/not-sexy-but-necessary/

Rudiger

Hi Jim,

impressive work and documentation, thanks for all that!

Regarding your "Cyl.4"-problem: Because the space between the piston rings and the fire land area on piston No. 4 (and all others) are clean - no remains from burned oil, as well as on spark plug and combustion area in the cylinder head - the higher play not seem to lead to any problems. How it looks like If this cylinder would have burned oil, you can see on the parts of cylinder 1.

My opinion: No action required!

Even when the manual says, that 0,08mm is the spec limit, it's like in your refrigerator: If the "best before" date say's that your yoghurt is only best before today, normally it tastes perfect tomorrow as well.
Modern pistons has a Graphite coating on the piston shaft, that would be a perfect way to add some microns, but I don’t know how it’s applied. Above all, this material is extremely durable in this place.

Maybe you can contact this guys:
ftt-shop.franke-turbotechnik.com/Produkt...eitbeschichtung.html
They offer a recoating process with Polytetrafluorethylen (PTFE). I don’t know how it works, if it’s durable, what thickness or if these guy doing a good job, but maybe it’s a begging to ask them.
Alternative: www.kolbenbeschichtung.de/ Graphite coating up to 0,2mm, special offer to adjust play by coating.

Regards Martin

Chromix wrote: Hi Jim,

how did you estimate the temperature correction value for the bore measurements?

Regards,
Lutz

I used an online calculator which gave the thermal expansion for cast iron, however it is at best a rough estimate as it doesn't cater for iron with holes in it.

Chromix wrote: Hi Jim,

Isn't it strange that piston 8 is bigger than it should be in the new condition? Taken the wear into account this piston should have (at least) fallen into group 2 when the engine was built together and I can hardly imagine that it was so much off size. That raises the question how accurate your measurements are.

Regards,
Lutz

Yes, thats's odd, I will re-check the measurements on this piston when it is in the house at 20degC.
When taking the measurements I rounded up or down the thousandths to the nearest hundredth as I doubted that I was accurate enough to realistically record thousandths. That could account for an error of 0.005, lets add in another 0.01 for other errors and then my numbers could be +/- 0.015

Chromix wrote: Hi Jim,

Would also be interesting to compare your measurements with somebody else who already did this job. But this is definitely not me .....

Regards,
Lutz

There will not be many of these people around.

Hi Martin,

I tend to agree with you, as the piston and bore both look good visually. Probably no action necessary. I will take the block to be cleaned and honed then I will remeasure both the block and pistons at room temp as a final double check.

Hi Jim,

get it honed - why that? You may rethink, the bore diameter will not shrink by that!

Regards Martin

Jim, ask the machine shop to measure piston and sleeve. go from there.
Rudiger

Hi Martin,

Just a light home to recreate the cross hatch pattern where it has worn. I will discuss with the machine shop.

Hi Rudiger,

I will ask the machine shop if they think it is necessary.

Chromix wrote: Hi Jim,

Isn't it strange that piston 8 is bigger than it should be in the new condition?

Regards,
Lutz

I brought piston 8 into the house this evening the room temp is ~22 degC.

Here is the measurement, 91.993mm, it seems to correlate with my thermal expansion estimate which is good news for my methodology but doesn't explain why it is larger than marked.







Once the block has been cleaned and if my wife goes out, I may try to retake all the measurements with the block in the conservatory.

Well, then it is the way it is. Maybe somebody put the piston in the wrong box.

Regards, Lutz

Racediagnostics wrote: Hi Martin,

Just a light home to recreate the cross hatch pattern where it has worn. I will discuss with the machine shop.

Hi Jim,

please think twice, from a performance point of view: Is there anything that can or must be improved by doing this?
2 things will definitely happen:
• Bore diameter will increase (not good)
• Piston rings need to be renewed (expensive)

The machine shop of course sees a business case and probably will recommend this action.

Regards Martin

Hi Martin,

I actually managed to buy two full sets of piston rings cheaply from Autodoc (I can return the unused set) one set is iron, the other chrome plated. I think Autodoc had an error in their pricing , the full set of rings was only ~ £35.

Hello,

I would be not too concerned about the piston diameter measurement.
Unless liner, piston and rings show any unusual/ bad running pattern.
Your pictures show good running pattern obviously they lived very well with each other together.

Not convincing to see the mix of pistons, it's just telling us that not everybody at Mercedes was as focused about Quality as they could and should have been.

Piston can be "deformed" very easily and you just "hit" it hard on the table and you will measure something different.
Not to hit the piston, but we did this during school/ apprentice ship just to see how easy they can be deformed.

Anyhow, alloy like cast iron/ steel as well has internal forces that can/ will relax during operation. On small parts that's not dramatic but you are measuring 1/100 millimetre with the calliper and that's might be one more confusing factor after many 1000th miles time to relax internal forces.

Did you did a pressure loss check of each cylinder before you opened the engine? Would be interesting to see how pressure went away on Inlett/ Exhaust Valve and piston rings.
This should done each time before an engine is opened.
Presse loss test not a compression test only.
The test tells you where pressure is lost and thats what's to be avoided.
Replacing all parts will improve pressure loss for sure but why changing parts that are good/ keeping the pressure ?

To do a professional 3 angle valve seat job now is mandatory. Thats most likely a good job for a machine shop unless you got a Hunger or comparable valve seat machine available.

Pistons and rings are now out, so it's a good time to change piston rings.
As somebody mentioned before the machine shop is might be a little hesitant to just hon/ prepare your liners for new piston rings.
They want to make money without the danger to receive a claim later and honing used liners owns more risk then honing fresh machined liners.

I would look for a honing brush and prep my liners myself. Just a slight brush to prep the honing pattern for the cast iron rings.
Chromed rings are harder and might be better suited for fresh machined/ oversized liners with out any previous wear pattern.

If you want be 100% safe, pistons need to be renewed and liner need to be machined.

Just my 0.02$

Kind regards

JP

Jim, get a set of extractor sockets, I found them to be very handy on stripped inhex bolts. www.ebay.de/itm/Schrauben-Muttern-Ausdre...er-Set-/273530222942
BTW, great work and even better documentation! this will help a lot of people.

Racediagnostics wrote: Hi Martin,

I actually managed to buy two full sets of piston rings cheaply from Autodoc (I can return the unused set) one set is iron, the other chrome plated. I think Autodoc had an error in their pricing , the full set of rings was only ~ £35.

Wow!

Catch up for the last couple of days.

I gently cleaned up the decks.



Checking the decks for flatness with a straight edge.



The thinnest feeler gauge I have is 0.04mm and that would not fit under anywhere.



The same for the main bearings with the old shells.....



.... and without the shells.



Moving on to measure the crank pins and main bearings.



Then finally heading off the the machine shop.

Hi JP, I did a compression test and had a go at a leakdown test but got inconsistent results, seemed perfect and when repeated seemed to be leaking, I guess you need some experience to get good consistent results.

A set of new pistons and liners would be nice but not really worth it for me and the car.

I am going to investigate the three angle valve job.

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.

Hello Jim,

yes I agree doing the same measurement/ check twice and receiving inconsistent results does not make it easier to decide on next steps.

Please find attached a link in respect of flex honing in case your machine shop is hesitant to prep the current liner for the new rings.

blog.brushresearch.com/how-flexible-honi...for-cylinder-sleeves

Liner surface needs to be prepared for the new rings, then the cast iron rings should work good after some running in time.


Usually the Mercedes head should have already a 3 angle valve design.
Just „grinding“ the seats with compound can be ok, you could check with a leak down/ vacuum tester if the seat and valve are leak free.

johnmaherracing.com/tech-talk/3-angle-valve-job/

But I would go for a valve seat cut in the head/ 3 angle design and recut the sealing surface of the valve.
Then the valve and seat are matched with a little use of grinding compound and function is tested with leak down/ vacuum test.
You can use your vacuum device for brake bleeding. Just check if the vacuum remains.

Finally I would check if manifold and head are matching. If not this is an easy way to gain some cheap hp just by matching manifold/ head and gasket with out restrictions.
Nothing to do wrong just check for sufficient wall thickness upfront before you start grinding.

Porting goes deeper into the head , but this is different story and opens another can full of worms.


Kind regards


JP

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.

Does anyone know if undersized cam tower bearings are available at any suppliers in Germany?

Hi Jim,

removing the valve springs is perfect by this way:
www.youtube.com/watch?v=6GjQVGpBmvs
That's how I'm doing that since decades.

Regarding the "bearing-problem": Is the calculated play too high or do you see some wear/damage? Instead of measuring all parts separate, sometime it's more useful to evaluate the play of the assembly and/or compare with the assembly of the other parts which seems to be better/good. Unless you didn't noticed any functional problem or noise up to today and all bearing surfaces are OK it may be still good for doing what it was designed for.

Regards Martin

Hi Martin, I should make more progress today with this.



Here are a couple of close ups of the worst bearing above cylinder 8, 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.

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.





Washed and dried.



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



....and clean up the valves.

Hi Jim,

your progress is breathtaking!
Did you pounded out the old guides with the hammer? This can be done much softer...
Before you plan to insert the new guides, take a look to the pictures. Getting those parts fitted well needs some prepartion to meet the best fit alignement to the bore. The better the alignement is, the less work on the valve seat is necessary later on.

Cheers Martin