1997 Mercedes Benz 280 Engine not firing & burning oil

We have timed the engine correctly; at TDC from what the manuals and some mercedes specialists said using the guides on the camshaft and setting the crankshaft to 0 as the crankshaft itself has the mark "0T".
Since the engine cranked with no problems I would not believe the work has been done incorrectly.

Now, I have no idea if the valve job has been done right because there were no tools to work the way intended.
I have read on the internet how worn engine heads burn oil and create the effect we have seen on the engine at cranking (throwing smoke up from the engine top intake).
I gues since we have got a rebuilt engine head for 45 dollars used the only way is to test again the one actually on the engine, confirm and then replace it.
I hope to be helpful and I will attach a picture.

We do not have any other methods to check the compression but to use the cork test on the spark pluginlet which had been done months ago.
I will not have any specific numbers though we had no experience with it, so what should we expect or what are other good ways to test the compression without any special tools?
Any help would be appreciated.
I will attaach another picture of the time when the problem had been discovered and the pistons were back submerged on cleaning liquid.

Since the compression tester we got fits the car we are currently working on, we do not know the difference between the compression of a working cylinder and a cranking cylinder.

The car we are trying to fix does not fire up, but the instructions indicate to fire it up for 15 to 10 minutes prior to testing compression.
Then it gives series of prepairing steps before the tester itself could b used.
We did not find some of the parts the instructions indicated and disregarded them.

Now, we did the compression test on the 1st cylinder by just trying to start up th engine.
The engine does seem to fire up for a while, but when the accelerator is not opening the intake manifold the engine dies instantly.

The compression tested 30, 60, 90, and 120 in the same cylinder at different stroking positions.
If you could help us with the usage of this tester on this type of cars we would greatly appreciate it.

Again, it is a C280 1997 Mercedes Benz which has been sitting for a while now.

Hope this helps

Hello,
We have recently changed the piston rings since while we were already at it, why not do the whole job ourselves?
So we ended up changing the whole piston head for all 6 cylinders from a C class almost brand new at a yunk yard.
In the end, the rings themselves had almost no miles left as we took them out.
Of course we first tried to only replace the rings so it could be an almost perfect transition, but the rings were stuck in the piston head and these did not expand at all.
Unlike the old ones, the new ones did expand and did move freely around the ring cavities.
That was one job done.

Now we are putting the engine back together, but since we could not fit both the torque convrter with the gearbox inside the car compartment, we had to take the transmission off as well.

Everything went well though the torque converter bled all 4 quarts out and more leaving the transmission which had already bled some liquid as well with virtually no oil, so we went on and bought one quart at our local mercedes dealership and 2 quarts at autozone along with the transmission gasket and filter.

Now we hope the job to be done right since we re-timed th engine at specs and got the pistons at TDC with the engine out.

Of course we let the engine and engine head spin a little after assembling and timing went with great success though it was a little hard doue to the lack of oil in the cylinder walls for a while until it rotated a little.

The timing rails have been bought and replaced and the engine seems to be ready to fire.

Please let us know if there is anything we could have missed.

Now, is it possible for us to completely drain the transmission ourselves or is it impossible due to probabilities of transmission malfunction.

We mean to change the oil since in several forums we have found that some transmission issues are due to the mercedes oil not being changed and we are only restoring the car after doing some framework on the rear end.

Is it fine to mix both mercedes dealership transmission oil and aftemarket transmission oils in this particular device or is it dangerous.
Also, is it possible to get any issues moving the transmission cylynder-like gears that go into the torque converter a little after pulling off the engine?

Thank you for your help

PS: normal psi for a cylinder on several mercedes is around 180 and our old pistons gave us around 120.