advice needed crank/cam timing

[flagstaff]

just changed the cyl head gasket on my 93 e280, and on reinstallation the car won't start. i double checked the crank/cam timing marks, and have found that when the cam marks align correctly, the crank is too far advanced to be in correct timing with the cams. my question is, does it matter whether the crank is 180 degrees out, relative to the cams, as long as it is positioned correctly and i then proceed to rotate the cams so that they control the valves as per no. 1 cyl on firing stroke?

i haven't explained that very well. what i mean is - the crankshaft doesn't know which is the firing stroke, does it? this is down to the cams .... or am i missing something?

i just need to be sure to get this timing thing right, before proceeding to any more serious possible cause for non-starting.

what i've got, then, is the crank positioned with the O|T (TDC) mark at the correct position relative to its marker on the timing chain cover. and i want to now unhook the timing chain and position the cams so that their alignment holes line up with the face of the cyl head.

is this ok? sorry to sound confusing ... i think it's because i'm confused.

 

[turnipsock]

I think it's going to make things confusing. If it's a distributor type setup, then you will have to mess around with the leads to change the firing order.

Is it one of these redundant spark setups? if so, it might work.

I haven't really thought this out yet, but I would just line it up correctly, otherwise the next person that plays around with it will have a load of sorting out to do.

 

[kth286]

flagstaff

You have to get the crankshaft firing on No 1 cylinder (front of engine) and the cams have to be in proper relationship with that situation.

The Crank Angle Sensor situated on the bell housing knows exactly where the crank is at anytime and which cylinder is on firing stroke etc. and the ECU computes everything from there.

The Crank Angle Sensor and everything in correct relationship to it, is the key to everything working properly.

Have you done what I suggested in your other post, and gotten a Merc specialist to visit and read the diagnostic codes.

Let us know your postcode and I might be able to suggest someone.

Regards

 

[paulcallender]

In addition to the crank and cam being correctly related to each other, you also need to make sure the distributor is correct too. For every 2 revolutions of the crank, the camshaft rotates once and the distributor rotates once. Once the crank, cam and distributor all sit in their correct place for TDC for No.1 cylinder, then you have timed it properly and it should fire.

If you have fuel, compression, timing and spark then your engine will run. If it helps, nobody gets cam timing wrong and everybody gets ignition timing wrong, when rebuilding a motor.

As a check, you should turn the engine through 2 complete (crank) revolutions, to make sure your cam timing doesn't result in the valves hitting the pistons.

 

[kth286]

flagstaff

As you should know, there is NO distributor.

paulcallender

wakey wakey - it has already been pointed out in his other posts about this problem, that this engine is all electronic, so no distributor.

Regards

 

[flagstaff]

thanks guys.

true: there is no distributor. i haven't done as suggested (and called a merc specialist to visit) cos i ain't got the money just now. i am hoping for a way out of this that doesn't involve paying someone else to do what may ... with a little logic ... and a lot of input from the members of this forum ;-) ... be possible to achieve in a DIY manner. if not, then so be it and i will call in the lone ranger.

until then ... well, gotta work tomorrow but back on the case on thurs.

my feeling is: no.1 cylinder comes to TDC (O|T mark on crank) once per revolution of crank. the crank sensor knows only that TDC has been reached - and not whether it is on the inlet or exhaust stroke. ergo, if TDC is achieved, then the cams can be rotated to the "TDC on firing stroke" profile independently of the crank. put the chain back on and presto! the job should be a good 'un.

...err, i think, anyway. crikey.

 

[paulcallender]

thanks guys.

true: there is no distributor. i haven't done as suggested (and called a merc specialist to visit) cos i ain't got the money just now. i am hoping for a way out of this that doesn't involve paying someone else to do what may ... with a little logic ... and a lot of input from the members of this forum ;-) ... be possible to achieve in a DIY manner. if not, then so be it and i will call in the lone ranger.

until then ... well, gotta work tomorrow but back on the case on thurs.

my feeling is: no.1 cylinder comes to TDC (O|T mark on crank) once per revolution of crank. the crank sensor knows only that TDC has been reached - and not whether it is on the inlet or exhaust stroke. ergo, if TDC is achieved, then the cams can be rotated to the "TDC on firing stroke" profile independently of the crank. put the chain back on and presto! the job should be a good 'un.

...err, i think, anyway. crikey.

I know why it doesn't start - simple - because it doesn't have a distributor! Only joking.....there are 2 models of ignition system used on the 280E, I thought it was the one with the 'pseudo-distributor'.

Having looked at the parts diagram, in addition to the crank sensor, there is a camshaft position sensor too. I also notice your ignition system would have a lead for cylinders 1, 3 and 5, so you could clip an inductive timing light onto this and see what you get. And mark the appropriate place on the crank pulley, with Tipp-Ex?

Am I the only one here with a Mercedes which has a coil, distributor, points, a bunch of leads and spark plugs and no electronic gubbins???? I set up my timing today, and then gave it a final tweak after a road test and some tinkering. Don't you feel you're missing out here?

 

[LAMAR]

One revolution of the crank is 380 dergrees. No 1 piston will move from TDC to BDC Back TO TDC . If the timing is 180 degress out the piston could be at BDC when it should be on its compression stroke so I would suggest that you time it correcty. Crank AT TDC in relation to the cam timing.
Any way if it wont start and you can see this is not correct you need to eliminate it from the list of possibles :!: :!:

 

[Richard Moakes]

I discussed this no-start after cylinder head gasket change with an engine minded friend today, and one of the absolutely outside possibilities we discussed was the crank being 180 degrees out of phase.

What I don't know is how you get out of this situation without having contact between valves and pistons? Is the M104 a zero clearance engine?

Good Luck,

Richard

 

[flagstaff]

jeez; zero clearance. this is getting worse by the hour. and i'm not even working on the damn thing

 

[LAMAR]

prehaps a compression check would be in order ;-) ;-)

 

[paulcallender]

Have you spun it on the starter motor yet? Or did you do the "2 turns by hand" check before you tried starting it?

If you've spun it with the crank-cam mistimed, you might have (not definitely have) bent a valve or two and lifted the head. At least you know how it all comes apart LOL.

 

[Richard Moakes]

If the crank was 180 deg out of phase, I reckon no contact will have been made between valves and pistons.

No doubt the ECU compared the cam sensor and crank sensor and said no-way this engine is running.

Brute force method would be lift head, and then reset timing. However I suspect this would not be a popular option.

Only other way that I can think would be safe would be remove camshaft and re-insert in the correct position.

My worry would be that if you remove chain and try to spin either crank or camshaft to put it back in sync, then at some point a valve and piston would touch if this is a zero clearance engine.

Someone must know? Certain engines have clearance and can survive a belt/chain failure.

Cheers,

Richard

 

[190surgen]

You should have set the engine up to No 1 TDC and marked all the timming marks, then when you rebuilt it you wouldn't have this problem

 

[flagstaff]

i did. but the reference i was using for the crank wasn't correct - the haynes manual wasn't too clear on the point.

you're definitely someone to look out for, when constructive comments are at a premium.

 

[Richard Moakes]

Good info to be had here....

http://www.continentalimports.com/ser_ic100345.html

 

[Richard Moakes]

Bad news, it looks like M104 is an interference (Zero clearance) engine...

http://www.mercedesshop.com/shopforum/showthread.php3?t=87958&highlight=m104+interference

As I see it you have a number of options.

1). Take it to an independant and grin and bear it
2). Take the head off again, new gasket etc... and reset everything and hope nothing made contact.
3). Cry into your beer if valves and pistons made contact.

Good Luck,

Richard

 

[996jimbo]

Just a word of encouragement - I suspect that if the piston and valves had hit whilst turning the engine over you would have known about it.

If you've got all the timing marks correctly lined up, one way of checking which cycle the cyliner is on is to take out the spark plugs and look inside to see which valves are open (sorry but I know nothing about the M104 engine and assume that this is possible). A long probe (lets say screwdriver for the avoidance of doubt) poked in the spark plug hole should give you the relative piston positions. That at least should tell you if you are 180 (or 360) degrees out.

 

[flagstaff]

UPDATE:

thanks for all the input, guys. took the covers off today and checked the timing marks and lo and behold ... the timing was spot on. the thing i thought was the wrong point for the crank alignment actually turned out to be the right one.

holes in cam sprockets lined up correctly when #1 is on firing stroke (you can see this by looking at the cam lobes, no need to poke into the cylinder); healthy spark. plenty of fuel pressure.

but still only fires for a few seconds, and then dies. no untoward noises from valve train, such as would be made by bits of metal striking each other.

the mystery is still a mystery. looks like the loom theory is gaining credence.

but like i say, thanks very much to everyone for helping out.

 

[paulcallender]

Yep, at this stage I'd go for getting a readout of the fault codes. Its a shame (perhaps a crime?) there is no DIY-affordable Mercedes fault code reader out there for these models. So you're stuck with going to an indy, or making a big investment. But it will put you on the path to a working engine again...