1.9 AFN. Resurfaced head, use same gasket?

Hi,

I've just had the head on my 98 Passat (AFN engine) resurfaced to remove a burn crater where the head gasket had failed. The machine shop said they removed 1/10mm. Now they (and the mechanic) want to use a 3 notch gasket to compensate for this. The gasket that was on was a 2 notch. No-one has yet gone to the effort of measuring the piston projection.

Just to be clear. Nothing has been done to the valves or seats (they will be ground with paste on reassembly) so theoretically the valves now protrude 0,1mm further out from the head surface.

I already have a 2 notch gasket which I bought, hoping the head would not need any work. Can and should I use this? Will I really notice any difference in performance / cold start / economy if I use the 3 notch gasket?

Looking at the gasket criteria:

If my piston projection is in the upper range for the 2 notch gasket it could be 1.10mm. The gasket is 1.53mm, leaving a gap of at least 0,42mm between the piston crown and the head.

How deep are the valve depressions in the piston? I read somewhere in here that Frank's TDIs developed some sort of rule of thumb that valve protrusion should not exceed 0.03" (0.762mm).

How fine can these clearances be? If my valves were already protruding 0.76mm (assuming this rule of thumb is developed to maintain factory clearance and that my valves are at the worst end of factory protrusion) they may now protrude 0.86mm after the skim. The necessary depth of the valve depressions in the pistons should then be about 0.6mm. (Well, that's a tiny clearance I think. Possibly problematic )

I also read in here that some guy measured these depression to 1mm deep. If that's the case I should be fine to use the 2 notch gasket. Or??

It's a little difficult for me to measure these things as the head is still with the machine shop and my only car is in bits at the mechanic's place. I get around by bus for now...

Any recommendations? The above values should be worst case numbers and so I assume the real case might be better. Is the 0.1mm skim really enough to justify the change to 3 notch gasket? Are the mechanics just staying firmly on the safe side?

I'm subscribing to this thread so I can learn something, but something that I know is that the head gasket is determined by the piston protrusion, but it's also assuming that the head was built to factory spec valve with regards to protrusion/recession. hopefully head experts will chime in soon.

I read somewhere that the VW diesel heads were not to be resurfaced or milled, although that may have been in reference to the old 1.6 IDI heads, due to the pre-chamber inserts. Does the Bentley service manual have any input on this?

I bet Franko6 would have the answer. You may want to send him a PM.

--Nate

Cylinder head gasket thickness is determined by piston potrusion from the block. However, this assumes the stack height of the valves are still in the original position. If the head has been machined, the valves will NOT be in the original position. This is why cylinder head rebuilders also machine the valve assemblies (seats, stems, etc.) to match whatever is machined off of the head surface. This way, the geometry (distance) of the valve face to piston remains the same.

It is true that VAG does not have a specification for machining cylinder heads... many manufacturers don't. However, in the aftermarket we have found over the years that so long as the head is true, both the surface and cam bore, and you do the above mentioned corrections to valve stack height, you CAN machine the heads down and put them back into service using the same head gasket your engine was originally equipped with.

And there's the word from a trusted source.

Thanks for the quick replies guys!

As you may be aware the cost of labour in Norway is ridiculous. So I'm already, with the skim and dismantling, paying close to the cost of a complete, factory new Mahle head from Germany. Doing the full valve jobs mentioned would likely bring the cost up to the retail price of a brand new head in Norway!

If I had more time on my hand I would definitely have ordered that complete head but at this stage I really need the car back on the road. I gambled that the head could be put back on again with no work needed... I lost.

But back to the gasket: From the replies so far I gather that 3 notch is the way to go. Unless someone can tell me that the clearances will be fine..

I agree with Oil Hammer.

As for a three-hole head gasket, that would mean a piston projection in excess of .044" (1.10mm) Most head gaskets are two-hole, which is 1mm-1.09mm. Measurement is done in line with the wrist pin and on both sides of the piston. The tallest measurement from all 4 pistons determines the head gasket thickness.

But lets say the labor to properly set-up the head is beyond the reach of the owner at this point. What would be the results of using the three hole gasket? Are there problems?

Just got the car back from the mechanic. I tried to talk to him several times about the clearances and using the 2-notch gasket. He would hear none of that!

So it's back together with a 3-notch gasket.

My first impression: It feels a little down on power and it seems to churn a tiny bit longer when starting. I will have to use it a bit more to tell for sure. The first cold start should tell me if there is a real difference there. The trip meter has been reset so guess I'll just top up the tank so I can start monitoring the consumption.
With the leaky head gasket I was getting just over 5L/100 on a tank. Hope it hasn't moved too far from there!

All in all: If I'm ever in a similar situation I will buy a complete new head - no doubt. It has ended up costing the same and time will tell if I'm left with a sub-optimal car. Plus, the peace of mind of a new head would almost be worth it alone!

I'll try to come back with an update when I've measured the consumption!

Just thought I'd post an update:

I've done some 15000kms since the new gasket and the consumption per tank seems to have settled on around 5.5 - 5.7L/100 for the same mixed driving I was doing before. The power is probably similar, maybe it's lacking a little bit on steep climbs? And it starts just fine.

It's ok for an old car, fuel is really not where the money goes anyway...

K, thanks for the update. Now if only I could translate the mileage into mpg's.
Found it; almost forgot about the conversion table that we have here and I'm called a veteran.
http://www.tdiclub.com/misc/conversions.html

kfet said:

Just got the car back from the mechanic. I tried to talk to him several times about the clearances and using the 2-notch gasket. He would hear none of that!

So it's back together with a 3-notch gasket.

My first impression: It feels a little down on power and it seems to churn a tiny bit longer when starting. I will have to use it a bit more to tell for sure. The first cold start should tell me if there is a real difference there. The trip meter has been reset so guess I'll just top up the tank so I can start monitoring the consumption.
With the leaky head gasket I was getting just over 5L/100 on a tank. Hope it hasn't moved too far from there!

All in all: If I'm ever in a similar situation I will buy a complete new head - no doubt. It has ended up costing the same and time will tell if I'm left with a sub-optimal car. Plus, the peace of mind of a new head would almost be worth it alone!

I'll try to come back with an update when I've measured the consumption!

Click to expand...

That is why you should make absurdly sure you understand the details before talking to a mechanic and then if they try to sell you something you know is wrong, you won't have to argue. You will be able to say, "No, you are wrong, X not Y is the part you need to sell me".

At a very respected European repair shop I almost got in a fist fight with one of the mechanics. He sold me spark plugs for an ABA engine, my Jetta had an AEG engine.

When I tried to exchange them for the correct plugs he went through the roof claiming only New Beetles had AEG engines. We went round and round on this and he finally stomps off and looks at the application chart like he should have done in the first place.

kfet,

stumbled across this thread that revived... The mechanic is answering a question that has to do with gasoline engines. When they are surfaced, you reduce the volume of the combustion chamber in the HEAD. Most often, you cc the cylinder head to match combustion chambers and keep the compression ratio (CR) for each cylinder the same.

The TDI has the combustion chamber in the PISTON. The cylinder head is still flat, just like before. So, what he has done is lowered your CR and worse, caused a portion of your combustion to occur outside of the intended place. That will cause partial burn and usually reduced efficiency, along with the total reduced CR. It's only .01mm, but it does NOT help!

As for rebuilding or replacing, there are issues with aftermarket heads for the PD's. First, there is some real TRASH out there. If it's not total junk, then what we have seen are valve seats that are not the same hardness as those in the OEM cylinder heads. They are soft enough that they will not have the same life-expectancy as the OEM heads. We think the valve and seat quality is the difference in hundreds of thousands of miles compared to thousands of miles of life-expectancy.

Also, the cams are going to be the same mistake that is in every PD head...Wrong profile for the cam lobes and early failure rates.