M278 (4.7L) Timing chain tensioners

[Will Barber]

Hi all.

Typical weak point on most MB's, bank 1 timing chain tensioner is weak on start-up so I intend to have both changed. Only done 76k with FMBSH and oil & filter changed every 8k miles.

A couple of questions first...
1. Are these tensioners hydrauliclly operated or are they spring tension?
2. Are they located on the engine externally (like most motorcycle engines) or are they internal beneath the timing chain case?
I'm just trying to see if it's possible to do with the engine in situ as it's damn tight down the back.

Thanks in advance.

 

[S500 Pete]

Hi all.

Typical weak point on most MB's, bank 1 timing chain tensioner is weak on start-up so I intend to have both changed. Only done 76k with FMBSH and oil & filter changed every 8k miles.

A couple of questions first...
1. Are these tensioners hydrauliclly operated or are they spring tension?
2. Are they located on the engine externally (like most motorcycle engines) or are they internal beneath the timing chain case?
I'm just trying to see if it's possible to do with the engine in situ as it's damn tight down the back.

Thanks in advance.

I've got a 4.7 with 88000 miles on it. It is noisy for a couple of minutes on start up then quietens down.
Is this what you are getting with the chain tensioner problem?

 

[Will Barber]

Yes but only for about 3 seconds. The seals within the tensioner are failing by the sounds of it.
I'm used to doing these on Bentleys but not MB. I am a technical authorat the main Bentley factory and work on them all day, so I know they definitely need changing.

 

[star]

Tensioners are internal and might need a modified oil valve pressed into head under tensioner, the noise might be a gear problem??

 

[Will Barber]

It certainly doesn't sound like gear noise, definitely chain tension only.
Are we talking approx 6 - 8 hours ??

 

[mattkh]

2. Are they located on the engine externally (like most motorcycle engines)

I thought a critical chain like a timing chain would be always covered to stop any flying debris interfere in its operation.

 

[bembo449]

I've got a 4.7 with 88000 miles on it. It is noisy for a couple of minutes on start up then quietens down.
Is this what you are getting with the chain tensioner problem?

Im.alarmed you are ignoring such a noise pal

 

[star]

It certainly doesn't sound like gear noise, definitely chain tension only.
Are we talking approx 6 - 8 hours ??

Not your engine but same.

 

[Will Barber]

There's a MB Indy near me in Warrington, Cheshire so I'll give them a call tomorrow and see what they quote me.
As my DTC code is 001177, it leads to a problem with the inlet cam only, which in turn suggests the cam phaser. However after 3 seconds the noise disappears and the engine runs as sweet as a nut, suggesting that is is oil pressure within the chain tensioner which is low on start-up?
It's a difficult call without removing bank 1 timing cover. It's also a worry that the same problem may occur on bank 2 so it might mean a very large bill to get this sorted!

 

[ajlsl600]

Seems oil seal in tensioner may be passing warm oil on shutdown, hence rattle on start up till tensioner refills.. My view tensioner change early not later better than damage if chain breaks or skips. Also slack chain may damage other stuff. It ain't supposed to be loose or rattle..

 

[Will Barber]

Yes thanks for your input, appreciated.
I'd do the job myself as I've replaced phasers, tensioners, cams, pistons, cranks, everything there is to know on Bentley's as that's what I do for a living. I write all the service information for the worldwide dealer network, so I know what I'm doing.
However, not being familiar with the M278 engine, and not having any cam and crank lock tools, it's probably a wise decision to let MB tecs do the job instead.

 

[ajlsl600]

Most likely right. Tho personally I would hate missing the chance to learn exactly what's going on there. But then, fortunately I can work under cover and without hurry. And I have the facilities to make up the tooling if need be.

 

[star]

There's a MB Indy near me in Warrington, Cheshire so I'll give them a call tomorrow and see what they quote me.
As my DTC code is 001177, it leads to a problem with the inlet cam only, which in turn suggests the cam phaser. However after 3 seconds the noise disappears and the engine runs as sweet as a nut, suggesting that is is oil pressure within the chain tensioner which is low on start-up?
It's a difficult call without removing bank 1 timing cover. It's also a worry that the same problem may occur on bank 2 so it might mean a very large bill to get this sorted!

The cam adjusters are oil fed, they were on back order for months.

 

[Will Barber]

Well my local Indy won't do it.
Unfortunately Reading is too far away.... can anyone reccommend an Indy in the Shropshire/Cheshire area?

 

[John Laidlaw]

Well my local Indy won't do it.
Unfortunately Reading is too far away.... can anyone reccommend an Indy in the Shropshire/Cheshire area?

Try Dave at MD Motorcare, Ellesmere Port 0151 357 3111
If he has the capacity he loves these kind of jobs!

 

[star]

Well my local Indy won't do it.
Unfortunately Reading is too far away.... can anyone reccommend an Indy in the Shropshire/Cheshire area?

the thing is that you need all the parts ready and waiting when you start the job. We waited 10 weeks for a gear, then do you do one or four, they all can fail.

 

[Will Barber]

Star - Thanks for the advice, but I honestly don't think it's the cam phasers, having worked on similar W12 and V8 Bentley's for 25+ years, I'd say I'm 99% sure it's bank 1 hydraulic chain tensioner.

John Laidlaw - Thanks for the heads-up on MD Motorcare, I'll see what he says.

 

[star]

Star - Thanks for the advice, but I honestly don't think it's the cam phasers, having worked on similar W12 and V8 Bentley's for 25+ years, I'd say I'm 99% sure it's bank 1 hydraulic chain tensioner.

John Laidlaw - Thanks for the heads-up on MD Motorcare, I'll see what he says.

I’ve been working on mercs for over 30yrs and it could be either but you know which way I’m leaning to. I look forward to the update/result of the strip down. This one we’re in the middle of, sounded like chain bank 1. If you strip the engine for the chain and tensioner/check valve and it turns out to be cam gear, do you wait for parts or build it back up? I’d make sure all bases are covered, so you won’t be stranded waiting for parts.

 

[Will Barber]

Hmm.. see what you mean now.
Are all 4 cams equipped with phasers?

 

[star]

Yes there four, we’re replacing chains, tensioners and fitting check valves as well as cam gears. Only one failed but it’s so much work to get to it, I’d rather replace them all and not have it come back and not have to do the job again.