1991 500SEL timing "slippage"

marc

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Hello - first post.

I have a 1991 500SEL that refused to start last week (had run as quiet as you could wish and flawlessly up until then - barring every now and then the engine would fail to turn upon start up- suggestion was "missing teeth on starter motor" as a possibility - this was due to be inspected).

Garage took car in to service and get running, said it was the starter motor and set about replacing it - changed that, no start. It was assumed it could be electrics and a seperate electrical engineer was due to look at the car.

Next call I get "the timing has slipped and smashed your valves".

I am told £250 to remove the head and to diagnose the extent of the damage (and warned to expect a bill up to £2000 to replace valves etc - worst case scenario).

Here is my dilemma - the car was turning but not firing before being taken away - sounded like fuel/electrics - ie turned OK but failed to fire. It did try to start now and again but wouldn't.

The garage seem to be saying that the slipped timing was the problem all along - HOWEVER - there was no burning oil/noises etc. when the car was taken. I suggest any damage was done whilst in the care of the garage.

Is this possible? (ie is it possible, with no warning, that the "timing has jumped" and "smashed the valves" could be true?) How likely a scenario is that?

Is it safe to say that the damage was almost certainly caused by the garage? Am I fair in suggesting they should have realised the timing may have slipped BEFORE the valves were damaged?

IF the timing had slipped and damaged the valves would that have been blatantly obvious? (ie remember first a new starter motor was installed so the timing issue seemingly didn't exist at that point in the inspection/diagnosis).

Can timing slip with no warning and damage valves?

Whose fault would you say this is?

I appreciate the difficulty in helping me reach a conclusion, but all opinions and info will help. I can't afford £2000 but without the repair my otherwise perfect 500SEL is dead... Many thanks.
 
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andy_k

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to answer your questions,

yes it's quite posible for the timing to jump especially if the chain has become stretched or the tensioner was worn - on the v*s that chain is very long and it's failure about the most common killer of the engine

"it was turning OK but failing to fire" could be the damage was already done then - a car with bent valves won't start you won't hear any noise aside from the initial contact.

No you are not fair in saying they should have realised the timing had slipped before they tried to start the engine - you had told them the starter motor needed replacing not the timing chain.

I'm sorry to be the bearer of bad news but my guess is that the damage was done before the car went in for repair which was one of the reasons it wouldn't start.

Andy
 
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marc

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I didn't say it was the starter motor. The mechanic came to try to start the car and concluded it was the starter motor - then took the car and worked on it.

Should he have known the valves were damaged already?

Would there have been any clues about the chains slipping? ie the car was running perfect and silent - do these chains just slip with no warning?

Would the damage have been done once or would continued starting without realising the valves were damaged have damaged things even worse?

And lastly - thoughts on the viability of a repair/rebuild... worth it? and what work (worst case scenario) will be needed?

Many thanks for the advice, it's the only thing keeping me from ringing the Samaritans!
 
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andy_k

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I didn't say it was the starter motor. The mechanic came to try to start the car and concluded it was the starter motor - then took the car and worked on it.

Sorry my fault fot not reading your original post

Should he have known the valves were damaged already?

Not really - he would depend on your information to build his diagnosis, if you told him it was failing to start sometimes he would naturally assume a starter problem (or a bad earth)

Would there have been any clues about the chains slipping? ie the car was running perfect and silent - do these chains just slip with no warning?

yes they can do just as a timing belt can snap without warning. More usual would be the sound of chain slap for a couple of seconds when you first start the car - the only aside here is that by the time the chain is slack enough to make a noise it's slack enough to jump a sprocket

Would the damage have been done once or would continued starting without realising the valves were damaged have damaged things even worse?

the damage would be done within one full revolution of the engine, further starting would do nomore harm, all the bits that are going to hit each other would have done so already

And lastly - thoughts on the viability of a repair/rebuild... worth it? and what work (worst case scenario) will be needed?

I'd say a rebuild was worth it but if cash is tight have you considered doing the work yourself? You could put a second hand engine in but that would be an unknown quantity and no guarantees that it won't do exactly the same thing. Rebuilding will give the car a whole new lease of life and as long as you plan to keep it would make sound economic sense.

Many thanks for the advice, it's the only thing keeping me from ringing the Samaritans!

You are not alone, we looked at about 4 or 5 cars similar to yours last year, all of which had suffered a similar fate and were being offered for scrap value. It seems to be a common fault on the big V engines, the chain is long and follows a convoluted route - sooner or later it's going to fail. I guess the dealers/specialists have a scheduled service interval for it's replacement, something the home/independent garages neglect. As a small bit of good news, you got off quite lightly, two of the cars we looked at had the whole top half of the engine destroyed where the chain came out the side and top of the covers - very messy and even more expensive

HTH

Andy
 
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marc

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Andy - MANY thanks for the reply.

Here's where I am at...

The car had one problem - now and then it would fail to turn. The starter motor was very worn when replaced and I expect that was the reason the engine failed to turn now and then (had been a problem for some time).

One morning the car failed to start - it seemed to be out of petrol - ie it wasn't firing - this was possible as I had a slightly unreliable petrol gauge.

Said mechanic looked at it and then took it away. He changed the starter motor and still couldn't start it. Then yesterday (more info!) he said HE damaged the valves trying again to start it. I'm thinking that he ought to have considered slipped timing and checked the timing chains before continuing to crank the engine. The damage was done by him - he has admitted this. (There is also a possibility - I'm guessing - that he over used eazy start and got a bad backfire).

I'm quoted £250 to remove the head and check for the extent of the damage from a different mechanic (I'm not exactly trusting mechanic number one!).

The car has covered 130000 miles with no recent Mercedes service (but servicing carried out as and when needed).

I have owned it a year. It's fully loaded and very clean. I paid £2800 for it a year ago (on an H reg) from a relative that is a car dealer and took it part exchange). I can't see the point in doing the work and selling it and before this had not considered getting rid of the car the entire family are happy with (especially my son who enjoys the massive space in the back with heated electrically adjusted seats!).

I can't do the work, my time is my money (I am self employed) so I'm looking at about £2000. I agree that a rebuilt 500SEL would be worth keeping!

What would need changing? ie would all valves need replacing or just the damaged ones? etc.

My only problem is now working out liability!
 

Mark300SL

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Marc

Here is a possibility

The timing slipped as you went to start it - and the piston was lodged against a valve. - Now the engine cant turn over - as it is basically siezed.

Mechanic diagnoses a possibly knackered starter motor - not a totally perfect diagnosis, - but probably just about acceptable.

He fitted the starter and the new high power starter gets the piston to go past the valve and the damage is completed. note I said COMPLETED - it is very likely a decent portion of the damage had already occured before the starter was fitted.

I will always help someone if a garage is at fault - but in this particular case I really do think there wasnt a lot the mechanic could have done other than remove the plugs and attempt to turn the engine over by hand. However non of the symptoms would have led me to to assume the timing had slipped - and therefore I would also have felt no need to check it.

Only damaged valves will need replacing , and hopefully there wont be too many. The probelm with the timing system on thge V engines - is that timing chain slippage does more damage than a "normal" cambelt snap.
With a cambelt, once the cam has stopped there are only a few valves open - so the cars tend to do about 10-25% of the valves. With a chain driven timing system that slips - the engine keeps opening all the valves and subjecting them to contact.

Normally I would fit a new belt and then compression test to determine which cylinders are low - but I think this may be too much work with the location of the chain in the V8 engines

HTH - however painful :(

Mark
 
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marc

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What's odd is the fact the car just wouldn't start. Now and then it would seemingly fire and give up.

A new battery was fitted, a new starter and still no start (although the engine turned).

The mechanic then suggested the alarm was tested and then an electrical engineer was next in line.

In the interim the mechanic continued trying to turn the engine. I guess I need to speak to him and get his account of when the damage either occured or was merely discovered.

I'm guessing a rebuild is on the cards and hope for the best.

IF I have just damaged valves, would that mean new valves fitted and ground in, a new head gasket and seals and new timing chains and tensioners?

(I'm guessing - only ever worked on straight six XK Jaguars - my first love!).

Likelihood of piston damage? (and terminal rebuild costs)

PS - so happy to have stumbled on this forum, many thanks for the assistance.
 
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marc

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state of play

Rockers removed showed damage to one side of the engines valves...

Cylinder head being removed as I type.
 

scotth_uk

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Marc,

Sorry to hear about the bad news. Keep us posted with the developments.
 
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marc

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OK - head off... One side valves damaged (said to be usual in such situations). A £20 tensioner is missing - causing the damage. Unbelievable a £50k+ car (when new) can be smashed like this but there you go...

Parts £1000 labour - 35 hours £800. BUT - here's the pain. Can't tell if the oil rings are scored/cracked. So I could spend £1800-£2000 and it blow smoke and need more work (massively expensive of course).

I paid £3200 for the car and had no other issues - all the family love it, it's ideal. But surely there comes a point when I'm throwing too much money at the car?

My options appear to be:

a) sell the car as it stands (no idea if I could or what I'd get) and add the available money I have to that and buy a different car (would want a Benz or at a push a Jag or BMW TBH).

b) seek a price for a recon engine to be dropped in.

c) Spend £2000 and hope for the best (a rather insane idea IMO - given no assurances re the future potential costs).

The car is 12 years old and I could end up spending £2000-£5000 on it only to see the gearbox fail, steering etc etc.

Opinions VERY welcome on this awkward decision. Nice to be amongst people that understand why I wanted to own this car in the first place (a £1 for every "if you'd bought a ford" and I'd be having the work done by Mercedes!)
 

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Marc, given your situation re do I or dont I. I would be tempted to do a complete engine rebuild yourself over the winter. Doing that would give you peace of mind that everything was in order. The cost? well as you take it apart you can juggle the books so to say and if you feel at any stage that the cost of lets say an engine re bore is prohibitive then you could always just stop there and all it has cost you is time.
 
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marc

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Great as a project, not great when the missus and little 'un need a lift in the rain to school :(

Besides which, the car is too big for the garage!

My options only involve paying someone else to do the work ASAP.

Been offered a BMW 5 series a friend has for sale - so far I am in a whirl. I loved the car but haven't got funds to do it just for the hell of it. I guess this is the pitfall when someone owns a £50k limo and is being a bit of a dreamer - I can afford to buy and run it but when it goes bang I'm in a world of pain! I assume many here share that status?

(I went form a 190e to the 500SEL after owning Jags since I was 18 - 18 years ago!).
 

scotth_uk

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Call up crewe engines and see what they'll charge to swap out the engine.

For my M103 2.6, they wanted about 1350+vat for the engine and about 300+vat for fitting. One year warranty included.
 
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marc

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They did my 190e - not great it has to be said. Nothing really "wrong" but they didn't tune it properly IMO.

Will give them a ring anyway...
 
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marc

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OK.

Crewe engines say...


Unlikely to have caused piston problems unless timing was out for a long time.

But of course peace of mind is what made me considered an exchange unit.

Prices...

Engine exchanged = £2295 +vat
Fitting = £455 +vat
Collect vehicle from London = £180 +vat.

Gulp. As because of that £20 guide :(
 

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