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

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

No eBay APP ID and/or Cert ID defined in Kunena configurationJim, get a set of extractor sockets, I found them to be very handy on stripped inhex bolts.
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?