Engine knock.....I think

[haroonz7]

Guys

Ive got a C250TD auto - with 140k on it. today morning a started her up and am sure i heard a knock not the usual TD sound a slight "ping" so to speak. difficult to discribe....and as i rev the engine the sound went so its just on idle..... Any ideas??

Can it be timing or some kind of missfire??

 

[television]

Timing chains rattle when worn, and the sound comes from the front of the engine, How many miles has it been

 

[haroonz7]

the mileage now is 141k ive only just noticed the sound.....is it worth changing the timing chain?? and is it a big job?

 

[television]

the mileage now is 141k ive only just noticed the sound.....is it worth changing the timing chain?? and is it a big job?

You can feed the timing chain through by cutting the old one and joining it onto the new one, and use a joining link.
You are coming up to the max life, the only rattles from cold on the start up and usually stop rattling after a few sec, but I cannot guarantee that this is you problem

 

[Number_Cruncher]

>>and use a joining link.

Just to clarify here. If a timing chain is rolled in, the joining link is a temporary fitment only. The ends of the new timing chain need to have the ends of the pins rivetted over to provide a permanent joint.

However, if the engine continues to make a knock on startup, it's probably best to listen with a stethoscope to pinpoint the noise before spending any serious money on timing chains.

EDIT: One part I would pay close attention to is the vacuum pump.

 

[television]

Yes correct, I thought that it would be standard practice to do that. We do have some post where folk are running on the joining link

 

[haroonz7]

I think i'd better find exactly wherer the knock is coming from and then gain some opinions

 

[television]

I think i'd better find exactly wherer the knock is coming from and then gain some opinions

Good thinking,and the first move

 

[haroonz7]

Just had a though - if it was the chain the rattle would be more noticable....??? Where is the vac pump located??

 

[roofless]

it might just be the belt tensioner bush.. best to rule it out first by pressing down on the damper with a hammer shaft ect 71 in this link http://www.detali.ru/cat/oem_mb2.as...GM=717.460&CT=M&cat=19S&SID=20&SGR=045&SGN=03

 

[Number_Cruncher]

>>Where is the vac pump located??

Towards the front / right of the engine. Follow the large diameter vac pipe back from the brake servo.

 

[haroonz7]

Just had a look and found the damper. Will try it in the morning.

 

[haroonz7]

Update - Ive managed to borrow my friends stethascope thing, so i cheked at the front of the engine where the chain is and that sounded ok no tapping sound moved to the left hand side and again nothing, still on the left hand side moved to the lower part of the block and there was a tapping sound.......bit worried its something major, any ideas?
Also should mention when i first started her up today she was parked on the level road and there was no knock, but then (within 3 min) i moved the car on the drive facing down (a slight decline) and once there the knock appeared.

I switched the engine off after i used the stethascope thing, then started it after my cup of tea and no knock for say 30sec then heard a slight knock. I have to say after 5 min or so once the engine is warm the engine is spot on. There is no loss of power at all.

Not sure if the fuel economy would cause this but the last tank full i got approx 33 mpg and this is a combination of around 40% short trips under 5 miles and the rest motorway of around 20 mile trips.

 

[turbopete]

i was led to believe that a MAJOR service wasnt required untill 250k miles by a guy who worked at a merc stealers at the time. he said thats the first time any maintenance is scheduled for the timing chain. is this information incorrect? i was given that info for both my w202's. cant ask him about my 210 as he's not with us anymore

 

[Number_Cruncher]

Tapping on the lower left of the block?

Check all of the alternator brackets for security. Likewise the exhaust to gearbox clamp.

Also, remove the inspection plate, and check the flex plate between the crank and torque convertor - you'll need to turn the crank over - look for cracks and damage near the flex plate / torque convertor securing bolts.

Check to make sure the engine mounting hasn't collapsed - there should be about 13mm gap between the shell of the mounting and the cross member.

As you've seen, what I'm advocating is to check all the easy, simple, cheap things to check from the outside before spending any money inside the engine, and I'm sure there are other things which can knock which I've missed off the list.

 

[haroonz7]

I think i might get my mechanic to have a look at these points as I have no idea as to what I am looking for.....would the knock actually go away once the engine is warm??

 

[Number_Cruncher]

As the engine will run smoother when warm, it will move around on its mountings less, and so anything loose will be less likely to knock.

It's all easy checking, and should be done before you move on to condemning anything iexpensive nside the engine.

Did you rule out the belt damper - they can make a real racket!

 

[haroonz7]

I'll checking the damper today after work - I agree need to check the all external parts which can move. I dont know where the torque convertor is? I would like to do all these checks my self but as its my first merc i have no diagrams or anyway of knowing where these points are - thats where you guys come in i suppose........

 

[Number_Cruncher]

>>I dont know where the torque convertor is?

Underneath the back of the engine, you should find a black plastic cover. Inside the cover, you can see the front face of the torque convertor. As you turn the crankshaft, you will see parts of the flex plate and bolts pass this inspection hole, and you'll be able to inspect the flex plate through it.

 

[haroonz7]

I think i should be able to give that go - will i need to put the car in N or leave it in park?