OM606.910 cam timing enigma - PeachParts Mercedes-Benz Forum

spock505 · #1 05-16-2017, 02:24 PM

I don’t mind admitting this one has me completely stumped.

Brief history, low mileage car/engine with fully reconditioned head which I fitted sometime in April 16, since then the engine has never been 100% at tick-over with a slight wobble but not a miss.

At the time I had concerns when setting up the cam timing due to not being able to get exact TDC reported here, this I put down to chain stretch (as per thread) as I tried both tooth positions either side of TDC settling for the one shown.

Pic of final set-up showing 5 degrees or so ATDC

E300D timing chain stretch

After the rebuild compression figures looked like this with probably wet bores from assembly (please see follow-up post, as these figures may have been achieved using 14 BTDC configuration).

Cylinder bar

1 26
2 25
3 22
4 27
5 25
6 27

Since the rebuild I have carried out another compression (about six months ago) test followed by two this week

The figures from six months ago showed a significant drop but not as bad as the first set this week below, cylinder 3 and 4 have actually failed as per MB spec hence the decision to pull head.

Figures this week, timing still set as above

Cylinder bar

1 21
2 19
3 16
4 16
5 19
6 19

The compression tests this week showed a huge amount of oily carbon build up not only on the injector faces but also caking the heat shields across all six, oil was also seeping heavily out of breather pipes indicating blow by, smell of burnt oil was strong too.

As the compression test this week revealed a fail on cylinders 3 and 4, I immediately thought the timing is out clipping some of the inlet and exhaust valves, perhaps some worse than others due to variations on compression results, this was the only thing that seemed to make sense given the oily build up. So, out comes the parts list for a replacement head, parts ordered including dial gauge to make sure TDC is correct and the pointer hasn’t been moved during a water pump overhaul, however after reading another thread where the chap zip tied cam sprockets (same as my approach) but had an almost identical issue (loss of compression but resolved by moving cam timing),

Post 2

606 head removal

I thought give it a try, after all nothing to lose lose as swapping out head anyway, results are below.

Cylinder bar

1. 24
2. 27
3. 24
4. 22
5. 28
6. 22

Well there's a surprise similar to that experienced by the poster above, cylinders 3 and 4 are now well into spec but the problem is crank marker reads roughly 14 degrees BTC

So in summary, I have two settings, one ATDC and one BTDC both of which give different compression readings on different cylinders, returning duds to almost new pressure. Is there anything in-between, another adjustment perhaps, would moving the chain on crank sprocket as opposed to cam sprocket make any difference (clutching at straws here) ?

Not sure whether to pull head or not, over to you guys

spock505 · #2 05-16-2017, 03:10 PM

Thinking back, the first set of comp figures may have been done with the timing set at 14 BTDC, then on checking I may have moved it to the ATDC believing this was nearer TDC.

Can't be 100% sure but makes sense looking at like for like comp tests.

Frank Reiner · #3 05-16-2017, 05:38 PM

sp:

As to the difference in pressure, when the cams are advanced the inlet valves close earlier, hence there are more degrees of compression stroke after valve closing, resulting in increased pressure.

One tooth on the crank is a lot; example: if the crank gear has 18 teeth, one tooth = 360/18 = 20 degrees. One tooth on the cams would be 1/2 that amount; 10 degrees.

spock505 · #4 05-16-2017, 06:19 PM

Cheers Frank, on the first setting ADTC the engine is clearly consuming oil and lots of it, so i imagine the timing is leaving valves open when cylinders are under partial compression driving oil from rocker area directly into valve inlets.

Engine was running very bad when purchased due to carbon amongst other things, cam sprockets were zip tied on head removal with chain kept tight on pull side to avoid any jump of injector pump sprocket.

head returned from shop, replaced but may have changed to ATDC as mentioned above given how far out the other setting is.

Maxbumpo · #5 05-17-2017, 08:32 AM

Quote:

Originally Posted by spock505

Engine was running very bad when purchased due to carbon amongst other things, cam sprockets were zip tied on head removal with chain kept tight on pull side to avoid any jump of injector pump sprocket.

Don't worry about the timing chain moving on the injection pump timing sprocket, one of the pins through the timing cover prevents this, it is so close to the sprocket that it traps the chain to prevent exactly that.

Carbon: Caused by incomplete combustion. Have you fixed that?

Maxbumpo · #6 05-17-2017, 08:22 AM

I'd start by re-establishing TDC (if that is in doubt) to make sure your crank pointer is accurate. Remove the injector from #1, rig a clear tube of some sort (sticks up about six inches past the top of the valve cover) to make a good seal in the hole the injector screws into, and fill up that cylinder with oil about half way up the tube. Rotate engine, watching the oil level rise and fall with the piston. Find TDC by marking on the crankshaft balancer where the oil stops rising and then again where it starts failing, and TDC is exactly in the middle. Repeat this several times to make sure you get the same TDC each time, and then move the pointer so that you KNOW where TDC is.

Next, with the engine at #1 TDC, look on the front right of the camshaft gear assembly. There is a hole on the driver's side camshaft gear which is supposed to line up with a hole in the support behind it at TDC. You should be able to stick one of the valve cover bolts through. There are also two index marks (dots) on the camshaft gears that should be lined up at the same time.

Maxbumpo · #7 05-17-2017, 08:29 AM

Here is a screen shot of the FSM procedure AR05.20-P-6010HA, that shows what I'm talking about above. "A" is the index hole, through which you should be able to insert a bolt from the valve cover with engine at #1 TDC, and "B" are the index marks on the gears to make sure the two camshafts are timed together.

spock505 · #8 05-17-2017, 09:43 AM

Max, that is probably one of the best solutions I have seen posted, very ingenious using oil to get past pre-chamber - brilliant!

Cams already locked with appropriate sized drill, thanks for the pdf though.

It's more oil than carbon, very soft and lots of it. I could smell burnt oil as soon as rocker cover removed.

The current setting of 4 degrees or so ATDC appears to be incorrect given oil burn and low compression, this changes quite dramatically as above, although not sure the BTDC is right also.

Maxbumpo · #9 05-18-2017, 12:29 PM

Quote:

Originally Posted by spock505

Max, that is probably one of the best solutions I have seen posted, very ingenious using oil to get past pre-chamber - brilliant!

I can't claim credit, just passing on an old trick. Dan Stokes has another good idea - remove pan and measure movement from below. That has it's own challenges though, when the engine is still in car.

Quote:

Originally Posted by spock505

Cams already locked with appropriate sized drill, thanks for the pdf though.

Do the round timing marks on the two cam gears line up when that drill bit is in place?

spock505 · #10 05-18-2017, 08:22 PM

Quote:

Originally Posted by Maxbumpo

I can't claim credit, just passing on an old trick. Dan Stokes has another good idea - remove pan and measure movement from below. That has it's own challenges though, when the engine is still in car.

Do the round timing marks on the two cam gears line up when that drill bit is in place?

That was a good shout though, overcoming something which at first glance looks insurmountable using a liquid.

yup, the two dimples are in horizontal pitch next to each other, two dimples on the cams match up with cam cap housing marks too.

barry12345 · #11 05-19-2017, 03:17 PM

Check that the engine has the injection pump on the right stroke. These cars can run much better than the old 123s with the injection pump on the wrong stroke. You mention a lot of carbon and that makes me suspicious.

Basically with cams in proper position. The tang in the injection pump should be about center when you move the crank to the right degrees for start of injection. The smallest distance as possible turned with the crank to get there. We had a member purchase a car and drive a long way home.

His engine not running right was exactly this. You may have also gotten he injection pump on the wrong stroke when you had the head off. You did make sure both the harmonic balancer marks and the cam marks where lined up when you pulled the head? If not there is a fifty fifty chance of it being wrong right there.

It does happen. Just by neglecting to check the cam marks are lined up when the bottom harmonic balancers are. Or else the injection pump was not on the right stroke when you purchased the car. You then duplicated it when you did the head job.

Anyways you have to stop playing around with the timing marks until you verify the injection pump is on the right stroke.

It only takes a few minutes to check and is absolutly required in your case.

spock505 · #12 05-19-2017, 06:27 PM

Cheers Barry, and agree, will re-check.

Current situation after my calculated experiment detailed here:

Re-etching timing marks

Engine is running a lot better with the appx 14 degree advanced settings, more responsive with more power, its also lost the 'wobble' on tick over with a much smoother idle. Starting is also more or less on first click of key, this I compare to my 210 with 962.

Its slightly noisier than before with one injector nailing although this has improved with each short journey, it could be there is a large carbon build up from before which might need shifting for complete smoothness. I also need to refit the plastic cover which may make a difference to the engine tone.

Apart from the nailing above, it now sounds like a 606 which is a refreshing having driven it on the other setting for so long.

The oil is probably pretty contaminated, so will change this out tomorrow, refit rocker cover. top up with new coolant and go from there.

I need to explore the crank vibration damper and exactly how that may have moved, as a general observation it looks like one solid lump of iron so not immediately obvious.

spock505 · #13 05-17-2017, 10:09 AM

Sorry, just re-read your last post on carbon.

Once the car was returned home after purchase, went straight into my garage for strip down due how bad it was running.

Everything topside is new or reconditioned including the head, EGR sorted too.

Let me see where we are at on TDC and go from there, having a known benchmark will give me a bit of reassurance as currently bewildered lol

spock505 · #14 05-18-2017, 10:46 AM

Max, in case your following my exploits, current thread here.

Re-etching timing marks

Maxbumpo · #15 05-18-2017, 12:26 PM

Quote:

Originally Posted by spock505

Max, in case your following my exploits, current thread here.

Re-etching timing marks

I read a little of that, I think the marks on the crank balancer are good.

What happened to this car??? It would seem that either the crank pointer is moved, or the crank balancer is off. Can you question the PO?