Head gasket replacement on 300tdi - measurement confusion?

[julianf]

I think ive got to do a head gasket. Bubbles in the coolant. I cant see where else they would be coming from.


Anyway, the gaskets come in different thicknesses to adjust for tolerances.

The procedure for selecting the thickness always seems to involve measuring piston protrusion....
...but thats not going to change at all.


Noone (from my casual looking) seems to mention measuring the distance from the head face to the bottom of the valves.

Depending on how the head is skimmed (if its just the face, or if the valves are reground to match) it is surely this distance that is the one i need to be paying attention to?



Ive got a head in the garage, wrapped in oily cling, that i got re-faced and tested years ago, so it wont be the same head going back on.


Im guessing i need to take off the old head, measure that one, measure my replacement, and then adjust the gasket to suite (using the old gasket thickness as a starting point)?


And pay zero attention to the piston protrusion that everyone is telling me i need to measure?

 

[OJCar]

Just use the thickest gasket.

In the real world it make no perceivable difference to the output of the engine, the loss of the 0.0000000000001% of compression
and it guarantees that you wont get piston / head collision.

 

[Kayos]

I didn't think they were fussy?

@Tinbasherdan drove one with a blown head gasket and missing a piston for a few hundred miles, eventually fixing it at the side of the road with a rusty screwdriver and a baguette

(Some details may have been miss remembered)

 

[sako243]

Depending on how the head is skimmed (if its just the face, or if the valves are reground to match) it is surely this distance that is the one i need to be paying attention to?

The valve seats should be ground / relapped to seat them back in the same spot.

The head gaskets have a number of holes punched in them, near the air filter housing if I remember correctly. 1, 2, 3 or zero holes from thinnest to thickest.

I think almost all engines left the factory with 3 hole gaskets as it was too time consuming to measure and check. Far easier to slap the thickest on. Zero hole isn't officially listed I don't think but is commonly available and is thicker than the 3 hole.

As others have said you'll loose more power / compression from other things so I'd just slap a 3 hole back on and call it good.

 

[Nick DV]

........................ fixing it at the side of the road with a rusty screwdriver and a baguette

A real life case of "Improvise, adapt, overcome" I am intrigued however by the use of a baguette!

 

[Tinbasherdan]

As above, they really aren’t fussy. I melted a head between two bores and a hole in the crown of a piston due to over enthusiastic twiddling of the fuelling and it still got me back home albeit running very poorly, and a pig to start. It eventually expired 2 days later on the m61 on my way to pick up a new head.

Stick a 3 hole on and be done with it. Generally speaking, 300 gaskets tend to blow at the back of the head by the bulkhead

 

[julianf]

...yeah, this is an odd one.

No loss of power. No oil contamination. No coolant contamination.

But bubbles in the coolant which hinder the water pump.

I've not yet done a co2 test, as I'm waiting on bits to do one, but I can't think where else the air could be coming from.

It does not clear with driving, so it's not residual air. (not that there is any reason for there to be residual air either)

It doesn't really fit hgf, but I can't explain it any other way.

 

[julianf]

I wouldnt pay too much attention to the engine sound. It sounds no different to it always has.

I checked the "holes" - so far as i can see, its a 3 hole thats fitted.

 

[Nick DV]

Any loss of coolant, expansion tank empty?

 

[julianf]

nothing unusual. ive owned the engine for, maybe 14 years, and there has always been a minor loss of coolant over time, but my suspicion has always been on the header tank cap (which ive never replaced as it has been so minor as to not even be a concern)

there has not been a noticeable change.

 

[Bullet2012]

I didn't think they were fussy?

@Tinbasherdan drove one with a blown head gasket and missing a piston for a few hundred miles, eventually fixing it at the side of the road with a rusty screwdriver and a baguette

(Some details may have been miss remembered)

allegedly it was a cheese and onion bap.

 

[dave h 2]

Tie a vinyl glove over the water cap, if it blows up before the engine warms it's the gasket, if it doesn't maybe air is getting drawn in somewhere else.

 

[julianf]

Tie a vinyl glove over the water cap, if it blows up before the engine warms it's the gasket, if it doesn't maybe air is getting drawn in somewhere else.

Even if it's getting drawn in somewhere else, won't the glove still inflate?

 

[fizzy]

I have always been dubious of head skimming. Unless there is bad wear or pitting what is the point? I would have thought a warp of a few thou would soon vanish when the bolts are tightened down properly.
I remember on the Rover SD1 straight six engine the cure for a leaking headgasket was just to re tighten the 2 bolts closest to the bulkhead as they had a habit of working loose. A bit of threadlock problem solved. The head had a noticeable warp but that soon vanished when clamped down tight.

 

[harveyp6]

I remember on the Rover SD1 straight six engine

What did you have to go reminding about those for.......

 

[fizzy]

What did you have to go reminding about those for.......

I loved mine and it saved my life.
75mph off the M4 - swerved to avoid something. 30 foot embankment - no crash barrier. Nosedive into a concrete ditch. Stopped very quickly. Seatbelts took 95% of the impact. Actually stretched and snapped. Nice soft padded dashboard.
Straight 6 engine - big gearbox - solid propshaft to back axle. That isn't going to end up on your lap. Engine squashed down to 3 cylinders
Walked away from it - mind you bruising took 3 months to heal. Good job I was only 21 at the time.

 

[jo1010]

Do your glove/co2 test first,.....but are compressions all good? ( and leakdown test if your keen)...could be a slightly cracked head only showing when it's warm ( as you know they are prone to that)
....your minor coolant loss over time is the the red flag here

 

[dave h 2]

Even if it's getting drawn in somewhere else, won't the glove still inflate?

Maybe not, you said there was next to no water loss. The glove gives you an idea how much pressure there actually is for no money. If there's only bubbles when you have the cap off it's not the gasket.