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

http://www.peachparts.com/shopforum/diesel-discussion/300145-e300d-timing-chain-stretch-2.html

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

http://www.peachparts.com/shopforum/diesel-discussion/208998-606-head-removal.html

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, 08:22 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 · #6 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.

Maxbumpo · #7 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?

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.

spock505 · #9 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 · #10 05-18-2017, 10:46 AM

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

http://www.peachparts.com/shopforum/diesel-discussion/386034-re-etching-timing-marks-2.html#post3710622

Maxbumpo · #11 05-18-2017, 12:26 PM

Quote:

Originally Posted by spock505

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

http://www.peachparts.com/shopforum/diesel-discussion/386034-re-etching-timing-marks-2.html#post3710622

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?

Maxbumpo · #12 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 · #13 05-18-2017, 08:09 PM

Quote:

Originally Posted by Maxbumpo

I
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?

Max, this is a very good question and one that I have asked myself many times whilst carrying out work.

I read a post by Moth some years back on the 124 picture thread (think it was MB org web site) where he posted pictures of his beautiful S124 in DB189 - Smaragdschwarz. It's a really unusual colour probably best described as blue/black with an undertone of Emerald green, I think at the time he also mentioned how rare it was especially in UK diesels - imagine my surprise to read one of the free ads with an S124 300TD advertised which had more than a passing similarity to the colour, above, I rang the owner thinking this couldn't possibly be the colour but sure enough the owner came back after lifting the hood and said, "the three numbers are 189, letters DB"

After getting back off the floor due to the sheer coincidence if nothing else, asked if he would take an offer subject to a few checks, (yes the picture were all taken in the rain from about 20 feet away, -

).

The cars mileage checked out at around 123k or thereabouts, it was also being sold from an affluent part of the world so I took a chance, offer accepted !

A week later we tentatively pulled up at the address in my partners jeep only to be very disappointed, it had been used as a work horse and not maintained properly since the last owner.

The chap was probably looking out of the window sensing my disappointment popped out to say hello. There was a moment when the hand reached for the 'R' position in the Jeep to make good our escape, but that's not me, a deal is a deal.

He informs me there's no fuel in the car making it 50/50 if we will make it to the service station, we did though on five cylinders.

Eventually we get the car home for a proper inspection, two front tyers were bald and should never have been on the road, engine has two stuck glow plugs along with a manifold half blocked in soot carbon.

Here's the puzzling part, the overall body is in good shape, very good shape with only cosmetic rust on a few bits, structurally around suspension mounts, jacking points it's all good prompting me to restore the car as a daily driver.

What I do not understand and cannot get my head around is how from the time of his ownership, in miles around 40k so many parts ended up worn to the absolute point of failure, especially as prior to this it had MB service history up to 80k ish.

Mileage is held electronically here in the UK, prior to this I have paper with the exception of one of the earlier years, however it was under different ownership at the time.

The car has spent several years in my garage, plus my impression of PO he wasn't mechanically minded, maybe he thought cars don't need maintenance!

So, basically I am not surprised with this timing mystery and in a way, a little relieved as finally getting to the bottom of why the engine has never run properly despite reconditioned head, new nozzles, glow plugs, DV's and other ancillaries.

spock505 · #14 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 · #15 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.