300 TDi Head Gaskets

[Bush65]

MLS gaskets usually fail as a result of not haveing perfectly smooth/flat surfaces to seal against. they are much less tolerant to imperfections in the block/head face.

...

Those are my thoughts as well. Which is why I would like to see more information given in posts about failures rather than simply giving MLS gaskets a bad reputation.

IMHO they have the potential to solve the blown head gasket issue I have seen on 300Tdi's running high boost pressure.

My Isuzu engine has dry sleeves that protrude a specified amount above the deck of the engine block, but the stock MLS gasket has bonded rubber around the coolant and oil passages.

I note that some MLS gaskets have a thin bonded rubber layer over the entire surface (both sides), and these would not tolerate surface imperfections as you say.

[piper109]

Those are my thoughts as well. Which is why I would like to see more information given in posts about failures rather than simply giving MLS gaskets a bad reputation.

IMHO they have the potential to solve the blown head gasket issue I have seen on 300Tdi's running high boost pressure.

My Isuzu engine has dry sleeves that protrude a specified amount above the deck of the engine block, but the stock MLS gasket has bonded rubber around the coolant and oil passages.

I note that some MLS gaskets have a thin bonded rubber layer over the entire surface (both sides), and these would not tolerate surface imperfections as you say.

I have heard of MLS steel gaskets being used on the D24T Volvo/VW 6 cylinder diesels though I have not used one myself as they are extremely hard to find. People swear by them. You can adjust the thickness to suit the requirement by peeling off layers and they can reputedly be re-used.

If I am to change my head gasket, I would like to be well informed on this type. I have not yet found a price on the BGA head gasket and I am not sure that the thickness on my engine is completely right as it is not the original head. I suppose I will have to remove the head before buying the gasket.

Its my understanding that the head bolts are "torque to yield" so tightening them beyond the book angles will not result in any higher clamping forces, just stretch the bolts.

Steve

[Bush65]

I have heard of MLS steel gaskets being used on the D24T Volvo/VW 6 cylinder diesels though I have not used one myself as they are extremely hard to find. People swear by them. You can adjust the thickness to suit the requirement by peeling off layers and they can reputedly be re-used.

If I am to change my head gasket, I would like to be well informed on this type. I have not yet found a price on the BGA head gasket and I am not sure that the thickness on my engine is completely right as it is not the original head. I suppose I will have to remove the head before buying the gasket.

Its my understanding that the head bolts are "torque to yield" so tightening them beyond the book angles will not result in any higher clamping forces, just stretch the bolts.

Steve

I'm not sure if your saying that you have a Volvo engine that you want to change the head gasket on or if it is a Land Rover.

If it is a 300Tdi, not having the original head has no bearing in the gasket thickness - the thickness depends on how far the pistons protrude above the block at TDC. Assuming the correct thickness gasket was used before, then it would be the right thickness to use again. However if it was possible that it was not correct ....

As I have said before, I'm not convinced by the common suggestion/belief that the tightening procedure for 300Tdi head bolts takes them to yield. Having said that I have not conducted any tests to prove it either way - I am happy to accept any good evidence or proof, but not unfounded conjecture.

However your assumption/statement that clamping force will not increase if the head bolts are tightened beyond yield is completely false.

While mild steel will exhibit a yield point during a tension test, the high strength steels (such as used for head bolts) do not have a definite yield point. For conventional design procedures, 0.2% offset strain is used in place of actual yielding.

If the head bolts are tensioned to beyond 0.2% strain, they will suffer permanent elongation/stretch, but the tension (and hence clamping force) will continue to increase considerably, though at a reduced rate.

[disco_al]

the gasket pictured (which was supplied by our Bearmach dealer) was about £5 more than the standard composite fibre gasket, so a small price to pay for the reassurance of having a MLS gasket fitted

[piper109]

I'm not sure if your saying that you have a Volvo engine that you want to change the head gasket on or if it is a Land Rover.

If it is a 300Tdi, not having the original head has no bearing in the gasket thickness - the thickness depends on how far the pistons protrude above the block at TDC. Assuming the correct thickness gasket was used before, then it would be the right thickness to use again. However if it was possible that it was not correct ....

As I have said before, I'm not convinced by the common suggestion/belief that the tightening procedure for 300Tdi head bolts takes them to yield. Having said that I have not conducted any tests to prove it either way - I am happy to accept any good evidence or proof, but not unfounded conjecture.

However your assumption/statement that clamping force will not increase if the head bolts are tightened beyond yield is completely false.

While mild steel will exhibit a yield point during a tension test, the high strength steels (such as used for head bolts) do not have a definite yield point. For conventional design procedures, 0.2% offset strain is used in place of actual yielding.

If the head bolts are tensioned to beyond 0.2% strain, they will suffer permanent elongation/stretch, but the tension (and hence clamping force) will continue to increase considerably, though at a reduced rate.

Dear bush65,

Whilst its true that I have Volvo diesels, I was talking about a 300tdi gasket of the same type because I would like to change mine. I do not know for sure either if the angles for specifically 300tdi tightening will take the bolts to yield but I do know it is common practice to do so and it would not surprise me if this was the case.

In fact quite often the old bolts need to be measured for length to see if they have yielded past the point of being re-used.

The fact that they are longer is proof of them having yielded.

All steels, mild or otherwise will yield. On the better steels the yield point will be much closer to the ultimate. To clarify, the yield point is just above the elastic limit to where there remains a plastic deformation if this value is exceeded.

regards, Steve

[Aragorn]

Angle tightening is usually used to give a specific amount of stretch on the bolts, meaning a very accurate clamping force.

If you were to simply tighten it to 200lbft (for instance) the exact clamping force will depend on how clean the threads are, how clean the head surface is, wether theres any oil around etc etc etc.

By tightening them to a small lbft setting, then angle tightening by 360 degrees, you know exactly how much tension is on the bolts (because you know the bolts pitch, and you know its tensile strength etc) and therefore you can be sure its correct and even across the head.

I suspect that yes while fitted the bolts may be stretched slightly, they should return to their original length afterwards.

[FLR100]

I have changed dozens of head gaskets all with no problems whatsoever until i used the mls, the head and block face were checked thoroughly and in perfect condition, the mls i used was a bearmach and was pure steel, it leaked imediatley by presurising the water system in a big way, changed it for a normal type and the job was sorted and there has been no other issues,

when you are bieng paid to do a job the customer is not likley to pay you twice because of a faulty gasket so i stick to what i know works everytime

[mayur]

hi iv been reading this thread did anyone come up with an answer for the tighting toqure on a MLS gasket thanks

[western]

if there's no torque tighten info with the gasket, go with the info in the workshop manual for that engine.