Please help me with a diagnosis and mechanical advice!
Discussion
My Mercedes 560SEC is feeling a bit poorly and I was hoping the PH mechanical gurus could provide their opinions about what the problem might be and where to go next with it.
The symptons:
The symptons:
- The engine is making a tappety/clattering/clicking/knocking noise. It seems to be coming equally from both cylinder banks and is constant.
- There is white smoke coming from the exhaust which does not go away when warm. This seems to only be noticeable at idle and has been getting worse, when I set off it seems to disappear. The smoke smells of petrol and combustion, but seemingly not of antifreeze.
- The idle speed which was fine at about 800-900rpm has started to drop to around 600rpm and when it does there are occasional jolts from the engine.
- The engine still drives beautifully once on the move (apart from the clattering) and definitely seems to be making its full quota of horses when boot is applied to carpet.
- As the clattering sound seems to be coming equally from both cylinder banks, a timing chain issue seems most likely? Could be camshaft related but then would both sides sound the same?
- White petrolly exhaust fumes are a sympton of incomplete combustion if I recall correctly? If so, then perhaps a problem with timing or ignition? Would them only appearing at idle be due to the engine not firing on all cylinders at idle? If so, why might this be?
Well rich petrol smell, low idle speed and uneven idle suggest it isn't firing on one or more cylinders. I would disconnect each HT lead one at a time, in turn, to identify which cylinder isn't firing (i.e. which HT lead you can disconnect without it making any difference to the engine's running). Sounds like an ignition issue to me.
HustleRussell said:
Well rich petrol smell, low idle speed and uneven idle suggest it isn't firing on one or more cylinders. I would disconnect each HT lead one at a time, in turn, to identify which cylinder isn't firing (i.e. which HT lead you can disconnect without it making any difference to the engine's running). Sounds like an ignition issue to me.
I thought as much. I might try that then, and possibly invest in a complete new set of HT leads as they could probably do with replacement and aren't too expensive.redgriff500 said:
Impossible to say from your description but I'd suggest you pop in to the nearest sympathetic garage as they will give a quick guesstimate for free.
That's the thing, I don't know any sympathetic garages. As this is my classic second car it doesn't hugely matter if it's off the road for a while whilst I play with it. Half the reason I bought it was as a mechanical project. I would like to know what the issues are and sort any I can myself before asking a garage to do any work.redgriff500 said:
Because without meaning to be rude, from what you're written it's clear you don't know much about fixing cars.
Well maybe not by the standards of some on here, but there's only one way to learn. I've replaced all sorts of parts before and done pretty much all the servicing on family cars for years so I know which end of spanner is which and how pretty much every part of a car works, but I've never done anything like changing a timing chain or similar before, and would be somewhat dubious of attempting such a task due to the consequences of getting it wrong. Goole the problem for example, finds this ; http://www.benzworld.org/forums/w126-s-se-sec-sel-...
Those links have some interesting things worth looking at, cheers for them.
I've had a look at the spark plugs and leads and they look rather tired so new plugs and leads have been ordered.
The pictures of the HT lead connections didn't really work but they are rather corroded and fouled up (one of them particularly so) and the leads look generally rather old.
New rocker cover gaskets are also on their way, so the cam covers will be coming off later this week to see if the source of the tapping can be found.
It is a lovely engine to work on, so simple and nicely laid out so you can get to everything.
I've had a look at the spark plugs and leads and they look rather tired so new plugs and leads have been ordered.
The pictures of the HT lead connections didn't really work but they are rather corroded and fouled up (one of them particularly so) and the leads look generally rather old.
New rocker cover gaskets are also on their way, so the cam covers will be coming off later this week to see if the source of the tapping can be found.
It is a lovely engine to work on, so simple and nicely laid out so you can get to everything.
I had the smaller 3.5 litre version of this engine (m116) in my old 280SE 3.5, I think yours has the m117 in it. Mine was running rough with low idle when I first got it, new ignition components- leads, plugs, cap and engine fuel lines seemed to sort it out -also check all your vacuum lines and linkages, these can cause all sorts of odd running problems on merc engines. The clatter sounds like the timing chain, if I remember rightly it has plastic guides which can break with age.
Have you tried adjusting the idle control screw to bring it up a bit? If it's the same as the m116, it'll be a fairly big slot-head screw near the aux air valve at the front centre of the engine.
Have you tried adjusting the idle control screw to bring it up a bit? If it's the same as the m116, it'll be a fairly big slot-head screw near the aux air valve at the front centre of the engine.
Edited by chazola on Wednesday 21st March 14:11
chazola said:
I had the smaller 3.5 litre version of this engine (m116) in my old 280SE 3.5, I think yours has the m117 in it. Mine was running rough with low idle when I first got it, new ignition components- leads, plugs, cap and engine fuel lines seemed to sort it out -also check all your vacuum lines and linkages, these can cause all sorts of odd running problems on merc engines. The clatter sounds like the timing chain, if I remember rightly it has plastic guides which can break with age.
Yep, it's an M117. I am hoping that the rough idle is ignition related, but I'll have a look at vacuum lines and things if it turns out not to be. I'm told the timing chain and guides were done about 30k ago but with no documentation to prove it I have to assume it's never been done. It does indeed have plastic guides which wear out. I'll take a look at them when I get the rocker covers off.
chris182 said:
I'm told the timing chain and guides were done about 30k ago but with no documentation to prove it I have to assume it's never been done. It does indeed have plastic guides which wear out. I'll take a look at them when I get the rocker covers off.
yea, should be pretty obvious once you get the covers off- theses are easy to take off at least 
Almost all merc engines I've had with high miles made some kind of tappet noise/clatter on start up but it should go away after a few seconds/when warm.Gassing Station | General Gassing | Top of Page | What's New | My Stuff