starter motor keeps burning out

[BlackC55]

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[BlackC55]

What thickness head gasket have you got. There are a few different kinds depending on amount skimmed. 1.4mm or 1.2mm

You have to get this absolutly correct otherwise pistons WILL hit valves.

 

[Dieselman]

^ Isn't the gasket thickness determined by the amount of piston upstand, rather than the head thickness?

 

[mafya]

What thickness head gasket have you got. There are a few different kinds depending on amount skimmed. 1.4mm or 1.2mm

You have to get this absolutly correct otherwise pistons WILL hit valves.

I bought a genuine MB one and don't know what thickness it is. The mechanic I am using has done a few head gasket jobs on diesel mercs, its on his head if he messes it up.

 

[mafya]

Update

Popped in to the garage this morning just as he got the final injector out. I picked up the 4 that are ok and have dropped them off at John Hoggs diesel specialist here in Sheffield to check if they are ok and give them a clean.
I have been busy with work so havn't been in touch with the garage but as I left he did say the head will be off and going to get tested at the place they use.
Going to speak to him in the morning to see whats happening.

Billy

 

[Danny DeVito]

^ Isn't the gasket thickness determined by the amount of piston upstand, rather than the head thickness?

Piston upstand ?

 

[Dieselman]

Piston upstand ?

The amount he piston projects above the surface of the block.

 

[Danny DeVito]

I bought a genuine MB one and don't know what thickness it is. The mechanic I am using has done a few head gasket jobs on diesel mercs, its on his head if he messes it up.

I would imagine that MB supply different thickness gaskets ? I do know that my R5 Turbo had a thicker gasket but dunno if it was Renault original, i suspect not. But best to check first

 

[Danny DeVito]

Just a note too about the inj removal. Won't he need new bolts and inj seals ? A further note.. i saw ebay had an inj seal .7 instead of .6 to compensate for recutting the inj sealing face

 

[Danny DeVito]

The amount he piston projects above the surface of the block.

That seems appropriate then. The gasket need only be thicker if the block were skimmed. I don't know why they make engines that bend valves if something goes wrong. Seems a bit silly really for a problem thats obviously about for a such a long time. Why not do away with interference engs ?

 

[Number_Cruncher]

>>Why not do away with interference engs ?

It's just about impossible on a diesel engine, as the piston comes so close to the head at TDC.

We're lucky though, our well designed chain driven cams are very reliable when compared with belt driven engines.

 

[bolide]

Why not do away with interference engs?

High compression ratios and lots of carefully-engineered squish mean very tight clearances

I did some reading up & measuring on a BMW E12 M535i engine a few years ago. IIRC I got a rule-of-thumb piston-valve clearance of 80 thou from someone. Again, from memory the BMW engine worked out at less than half that - 30 thou. (Experts please correct me if I'm wrong!)

Not much clearance and no room for modification. Just shows you how much confidence they have in their engineering

Nick Froome
the independent Mercedes Estate specialists

 

[Danny DeVito]

So why not recess the valves then ? The chains are clearly a lot less likely to break thats why they have such a long life span. A new question is why don't they all use chains ??

 

[Number_Cruncher]

So why not recess the valves then ? The chains are clearly a lot less likely to break thats why they have such a long life span. A new question is why don't they all use chains ??

If you recess the valves, you will reduce the comression ratio, and compression is vital for disel engines.

Why don't they all use chains?

Noise, cost, and weight.

However, more and more modern engines are being fitted with chains. The buying public are now becoming more aware of the troubles caused by snapping cam belts.

 

[Danny DeVito]

Can they not compensate by reducing the cylinder size ?

 

[Dieselman]

Can they not compensate by reducing the cylinder size ?

That would reduce the engine output and direct injection diesels in particular don't work work below 500cc per cylinder due to insufficient mixing volume.

I recently had a head skimmed and could have measured the clearance, but didn't. The block and the head are both flat, so the only clearance is the gasket and very slight recessing of the valve seats.
This causes the valves to come very close to the pistons when opening.
Due to the head having a more heavy skim the gasket thickness was increased by one step, but the last one I did was left at the standard thickness as it was only a light skim.

 

[mafya]

update

Well today the mechanic phoned up and told me that the pressure test people have told him the head is cracked.
I'm off to pick a replacement tommorow which has been pressure tested and skimmed and comes with a garantee.
I'm also going back to Mercedes where i bought the head gasket kit from and i'm going to ask them if they come in different thickneses.
The head gasket kit comes with all gaskets required and also new injector seals. I have also bought new injector stretch bolts and a set of stretch head bolts aswell.
The head i'm getting comes complete with valves, shouldn't this enable a standard gasket to be used regardless of the head being skimmed?
Sorry i couldn't answer posts individually as i have been up 15 hours and my bed is calling.
Will keep you updated.

Billy

 

[jonnyboy]

Mystery solved, well done

 

[Dichtung]

Wonder what`s cracked the head?

 

[BlackC55]

Overheating probably.