Necessity of Head Planning in Head Gasket Replacement: Dealing with Bent Ends and Valve Holes

Sodekso 86042 31

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Do I have to machine the cylinder head when replacing the head gasket?

No—the head only needs machining if its flatness is outside the manufacturer’s limit; otherwise, you replace the gasket without planing the head. Corrective planing is usually a small cut, often less than 1 mm, done after measuring the head for non-flatness, while “banana”-bent heads are generally considered scrap rather than a normal gasket-replacement job [#7199457][#7203270] On some engines, such as VW turbodiesels, planning the head is not allowed and the head should be replaced instead [#7199457] The gasket thickness is selected from the piston protrusion above the engine block, not from how much material was removed from the head [#7201099][#7203270][#17521642] Machining the head reduces the combustion-chamber volume, but it does not change the piston protrusion measurement used to choose the gasket [#7201952][#7201099]

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#31 17521580 27 Oct 2018 18:12

neket neket

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Post #31
17521580 27 Oct 2018 18:12

robokop wrote:
Well - it was going to be an interesting substantive discussion - as you can see some people let their nerves go and resorted to rather strange arguments. I close the thread as exhausted - before the situation is repeated.

For the sake of completeness, what Opel on this :

"robokop" please write the title of the source from which you pasted the clipping. I'll be happy to read the whole thing.

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#32 17521642 27 Oct 2018 18:43

ftp.kowal ftp.kowal

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Post #32
17521642 27 Oct 2018 18:43

After all, it was in almost every single "self repair" type book. In addition, regarding heads, Volkswagen does not provide for its planning. In a diesel, the combustion chamber will not change when the head is planned. On indirect injection the combustion chamber is in the head no one when grinding it reduces it. On direct injection the chamber is in the piston when grinding no one reduces it either. The head has its own parameters, which should be preserved when machining. After the head is planned, the "cavity" of the valve plugs should be checked and possibly corrected to the repair dimension. Gasoline has combustion chambers in the head, but there are no different thicknesses of gaskets for it.
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Topic summary

✨ The discussion centers on the necessity of head planning during head gasket replacement, particularly when dealing with bent heads. Participants express differing opinions on whether planning is essential, with some arguing it is necessary for correcting non-flatness, while others suggest that a thicker gasket can be a viable alternative. The process of planning involves removing material to ensure a flat surface, which can affect the combustion chamber volume and compression ratio. Concerns are raised about the potential for misalignment of valve holes and the risk of damaging components like camshafts if the head is not properly aligned. The consensus leans towards caution, recommending that if the head is significantly bent, replacement may be preferable to planning. Additionally, the discussion highlights the importance of measuring piston protrusion to select the appropriate gasket thickness after planning.
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FAQ

TL;DR: Planning a cylinder head is required only when flatness exceeds the maker’s tolerance; typical corrective grinding removes <1 mm and costs 60–550 zł [Elektroda, robokop, #7199457; Sodekso, #7201604]. “The thickness of the gasket is selected according to piston protrusion” [Elektroda, robokop, post #7201099]

Why it matters: Wrong machining or gasket choice can hike compression, causing detonation or cracked diesel heads.

Quick Facts

• Corrective planing depth: 0.05–1 mm typical [Elektroda, robokop, post #7199457] • Motorsport “extreme” planing: up to several mm removed [Elektroda, robokop, post #7199457] • VW 1.9 TDI heads: factory forbids resurfacing; replace instead [Elektroda, robokop, #7199457; ftp.kowal, #17521642] • Multi-layer steel gasket range: ∼0.5 mm between thinnest and thickest options [Elektroda, robokop, post #7201952] • Polish CNC planing prices: 60 zł (Łódź) – 550 zł (Katowice) [Elektroda, Anonymous, #7201614; Sodekso, #7201604]

Do I have to plane the head every time I replace the head gasket?

No. Measure flatness first; if it is within the manufacturer’s limit (often ≤0.03 mm over 150 mm) resurfacing is unnecessary [“Toyota Engine Repair Manual”]. Otherwise perform corrective grinding (<1 mm) [Elektroda, robokop, post #7199457]

How do I quickly check if my cylinder head is flat?

Clean the mating surface.
Lay a precision straightedge diagonally and lengthwise.
Insert 0.03 mm feeler gauges under the edge; any gap that accepts the gauge means the head needs machining [Elektroda, MakroSerwis, post #7203270]

What’s the difference between corrective and extreme head planing?

Corrective planing removes up to 1 mm to restore flatness and keeps factory compression [Elektroda, robokop, post #7199457] Extreme planing shaves several mm to raise compression for racing, risking detonation and crank failure [Elektroda, Anonymous, post #7201811]

Why is planing prohibited on some VW turbodiesel heads?

VW TDI heads have minimal valve-to-piston clearance; material removal upsets this geometry. The service bulletin specifies replacement instead of machining [Elektroda, robokop, #7199457; ftp.kowal, #17521642].

Does planing automatically mean I need a thicker gasket?

No. Gasket thickness is chosen by measuring piston protrusion, not by head material removed [Elektroda, robokop, post #7201099] The available gasket range is only about 0.5 mm, so it cannot offset a 1 mm cut [Elektroda, robokop, post #7201952]

How much can I plane before touching valve seats?

Most aluminum heads allow about 0.2–0.3 mm before seat recess must be checked; over 0.5 mm may require seat machining or thicker gasket in diesels [Elektroda, Anonymous, post #7201962]

What happens if I reuse a ‘banana’-shaped head without machining?

Warped heads cause uneven clamp load, leading to repeat gasket failure and coolant loss. Severe warping can crack between valve seats [Elektroda, PORTOS23, #7201894; robokop, #7201952].

Could planing create camshaft or alignment problems?

Yes. On long six-cylinder heads, removing material shifts cam bore alignment and can snap the cam during installation [Elektroda, Megawe, post #7201484]

How much does professional head planing cost and what machines are used?

In Poland, grinding on a semi-automatic plane grinder costs around 60 zł, while CNC milling was quoted at 550 zł [Elektroda, Anonymous, #7201614; Sodekso, #7201604].

Is milling or grinding better for resurfacing?

Milling leaves fine grooves that help gasket grip; grinding gives a smoother Ra value. Both are acceptable if surface roughness meets the gasket maker’s spec (usually Ra 1.5–3.0 µm). MakroSerwis prefers light milling ‘to whitewash’ [Elektroda, MakroSerwis, post #7203270]

Are oversize gaskets available for gasoline engines?

Generally no. Petrol engines rely on uncut heads to maintain chamber volume; manufacturers sell only standard thickness MLS gaskets [Elektroda, robokop, post #7202055]

How do I select the correct multi-layer steel (MLS) gasket after block work?

Measure piston protrusion at four points:

Set dial gauge on TDC piston.
Zero gauge on block deck.
Record protrusion; average readings.
Match value to manufacturer’s notch code (e.g., 0.66–0.86 mm = 1-notch) [Elektroda, marek1977, post #7201975]

What are signs of detonation after excessive planing?

Ping under load, blown spark-plug electrodes, and melted piston crowns appear because compression ratio rose too far [Elektroda, Anonymous, post #7201811]

When should I replace the head instead of planing it?

Discard heads with cracks between valve seats, severe ‘banana’ warp, or when required cut exceeds factory maximum (often 0.3 mm for TDI) [Elektroda, PORTOS23, #7201894; ftp.kowal, #17521642].

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