Stop Start kills cam chains

[EmilysDad]

Very interesting read chaps.
My R class and

Ah! I'm not alone in driving one

 

[John Laidlaw]

Ah! I'm not alone in driving one

He’s the chosen one!!

 

[SL63 Mark]

We've got stop start in our new 320d Beemer, I have to disable it every time I start the car. Unfortunately this is a chore, and one more thing to think about. What I would like is a way of disabling it permanently. I will need to find a BMW forum (shudder).

Fortunately the SL55 does not have this system fitted.

 

[brandwooddixon]

I find that switching the gearbox to sport mode is the easiest way of disabling the stop/start

 

[ajlsl600]

Very interesting read chaps.
My R class and C class do not have this feature.
The company golf has covered 275K in 5 years without any issues, I wonder how much of thisnisndown to the fact that even in any type of traffic the first thing I do is switch stop/start off.

difficult to prove but i am convinced it makes a big difference, i believe there is a fair amount of load on the cam chain system at start up and a negligable amount once running. and i certain yr starter wont like it much either .long topic , seems majority view, its a waste of time. just another headache on the way, thinks, if i want it off i can manage to off the key myself.

 

[geraldrobins]

difficult to prove but i am convinced it makes a big difference, i believe there is a fair amount of load on the cam chain system at start up and a negligable amount once running. and i certain yr starter wont like it much either .long topic , seems majority view, its a waste of time. just another headache on the way, thinks, if i want it off i can manage to off the key myself.

I'm not that's right as when the engine is producing power and torque it gets passed through all the moving parts attached to the crankshaft. Although there may be a jerk at start up its from a low torgue starter not the engine at working power. I understand what you mean but unsure if its correct.
There also seem to be other engines with cam issues discussed here that don't have stop start, particularly the 1.8 petrols of a certain era.

Think of riding a bike it feels hard when you set off but going up an incline etc and there is just as much or more stress on the chain. A different type and function of chain of course.

 

[Botus]

Euro ncap did studies - lane assist its the most turned of safety aid... was something like 60% of cars have it disabled,
might be OK in Germany, certainly not in the UK if you know how to drive

 

[Botus]

the load to get a cam moving is massive - (without using tools or levers...) if I put a 4 pot 2 valve OHC cylinder head in front of you, with the std cam drive wheel in place, no matter how hard you try its highly unlikely you will be able to turn the cam even 1/4 of a revolution

once its running a 1000revs an average mum could maintain the load required to keep it turning without trying....

 

[stwat]

And what is the panels view on cylinder deactivation? Switching off one bank of cylinders leaving the other bank to do all that work?

Surely it must lead to all sorts of odd engine and timing year any chain wear?

 

[geraldrobins]

the load to get a cam moving is massive - (without using tools or levers...) if I put a 4 pot 2 valve OHC cylinder head in front of you, with the std cam drive wheel in place, no matter how hard you try its highly unlikely you will be able to turn the cam even 1/4 of a revolution

once its running a 1000revs an average mum could maintain the load required to keep it turning without trying....

How did we used to manage to start cars in the olden days with a starting handle when your battery failed, with say 50lbft of torque. It may be easier when its built up momentum but does starting torgue equal running torque or average running torgue.
I would expect the biggest forve to overcome in starting is the compression not turning the cam shaft anyway. But I am no expert just speculating.

 

[LostKiwi]

How did we used to manage to start cars in the olden days with a starting handle when your battery failed, with say 50lbft of torque. It may be easier when its built up momentum but does starting torgue equal running torque or average running torgue.
I would expect the biggest forve to overcome in starting is the compression not turning the cam shaft anyway. But I am no expert just speculating.

Compression forces don't go through a chain, turning the camshaft from stationary does.

 

[geraldrobins]

Agreed

Compression forces don't go through a chain, turning the camshaft from stationary does.

Agreed but I'm thinking the compression force exceeds that in turning the cam and turning the camshaft whilst the engine is under load also exerts forces on the chain.

 

[LostKiwi]

The higher the rpm the less force on the chain. Two reasons for this. The force is only on the tension side of the chain and the higher the rpm the less time any given link is under stress before having stress removed (hence less lubricant forced out between the links) and secondly the camshaft and cam sprockets have momentum thus take away the peaks of load making the peak stresses lower.

In terms of overcall effort at start up the valve train probably accounts for 20-30% of the total effort of turning the engine over (compression and piston to bore friction accounts for the rest).
The point is that starting from rest is the highest load on the chain so stop start will aggravate any weakness in the valve train and specifically the timing chain, especially given there is no oil pressure at this time either so minimal lubrication.

 

[geraldrobins]

The higher the rpm the less force on the chain. Two reasons for this. The force is only on the tension side of the chain and the higher the rpm the less time any given link is under stress before having stress removed (hence less lubricant forced out between the links) and secondly the camshaft and cam sprockets have momentum thus take away the peaks of load making the peak stresses lower.

In terms of overcall effort at start up the valve train probably accounts for 20-30% of the total effort of turning the engine over (compression and piston to bore friction accounts for the rest).
The point is that starting from rest is the highest load on the chain so stop start will aggravate any weakness in the valve train and specifically the timing chain, especially given there is no oil pressure at this time either so minimal lubrication.

Thanks for your explanation and I understand the point but i'm still not convinced but will give it some thought.

 

[Botus]

Thanks for your explanation and I understand the point but i'm still not convinced but will give it some thought.

look at the gearing.... the crank gear or toothed sprocket is half the size of the cam gear.. its like a bicycle, use the small one on the front (the crank the pedals are attached too) and run a big gear on the rear wheel its easier to turn... whilst that doesn't help the debate about wear, it does help explain why the starter can turn things over - when I doubt you can turn a cam by hand

 

[ajlsl600]

I'm not that's right as when the engine is producing power and torque it gets passed through all the moving parts attached to the crankshaft. Although there may be a jerk at start up its from a low torgue starter not the engine at working power. I understand what you mean but unsure if its correct.
There also seem to be other engines with cam issues discussed here that don't have stop start, particularly the 1.8 petrols of a certain era.

Think of riding a bike it feels hard when you set off but going up an incline etc and there is just as much or more stress on the chain. A different type and function of chain of course.

get you, but thats like a steady load, for which if we are lucky the maker has allowed for in the design. there does seem to be a question as to how the design takes stop start loads into account..over the cars design life how many more times will stop,start be activated, compared with the cars not having it,and was that taken into account, beyond any warranty issues, i am not convinced. i think a bike being pedaled up a hill is a constant regular design load and ,as it were ,jumping up and down on the pedals induces a shock load under which the chain is more likely to be subjected to loads that will cause it to fail.

 

[Robuk22]

I thought I would resurrect this thread as I feel it is important.

I have been banging on about this on different forums trying to get the message across. To start an engine you have to overcome the moment of inertia, as mentioned by an earlier poster, this is when the chain comes under maximum stress. With auto stop/start technology active the estimated lifetime starts are in the region of 600,000 as against 60,000 without the system. I presume when the engine stops the oil pressure drops and the chain tensioner then relies on its internal spring and ratchet system to keep tension on the chain therefor more starts would probably put more wear on the ratchet. Hence the problem with worn ratchet teeth causing loose chain at startup leading to lost timing.
It appears timing chain failure is occurring earlier in an engines life from around 2011 when the stop/start tech was first used by the majority of manufactures.
To save on frictional losses and reduce that dreaded CO2 duplex chains have been replaced with single row chains, we now have weaker chains and possibly hundreds of thousands of extra starts putting extra stress on those weaker chains and extra wear on the chain tensioner.

I have disconnect this tech from both my cars, a Mercedes Coupe and a Porsche Cayman, with my method you loose brake hold on the Merc with everything else running as normal, on the Porsche everything works as normal. The other advantages of this method are (1) You now have a standard continuous charge from the alternator which always attempts to fully charge the battery even on short journeys this did not happen previously. (2) You don`t need to code the battery (3) You can use a cheaper enhanced wet lead acid battery or any lead acid battery with the same amp hours in place of the expensive AGM (that`s only needed for stop/start), in fact you can disconnect the aux battery as that again is only used by the stop/start system. The Merc`s been running for over 11 months with stop/start disconnected.

 

[AMGeed]

^ At some point in time, disconnecting the Stop/Start function will probably be an MOT fail.
OK, you can circumvent this by reconnecting the lead to the battery, but why bother?
Isn't it just as easy to simply press the ECO button on the dash whenever you start the car.
It's become a habit in my W212 and I've only had the car 6 weeks.

 

[Jim2]

I think its a combination of both introduction of single row timing chains, and stop start systems at the same time.

I would bet money that double row chains with stop start systems have fewer issues.

I'd say that double row chains are more reliable and trouble free in any case, regardless of stop/start or make of engine they are fitted in.

 

[Tony Dyson]

Yes but manufacturers will nip currants in two today in order to save money and a duplex chain is an easy target for the bean counters.