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

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.